Table of Contents
- Plate Tectonic Theory
- Plate boundaries
- Anomalies
- Earthquakes
- Foci
- Induced seismicity
- MEDC case studies
- LEDC case studies
- Volcanoes
- Types and eruption types
- MEDC case studies
- LEDC case studies
- Example Essay
Plate tectonic theory and plate margins
The earth dates back around 4.6 billion years, in which time it has been ever changing. Starting off as a gaseous ball of fire and rock, the earth has cooled tremendously, enough so that it’s formed a ‘crust’ which we now live on. A simplified time scale of the history of the earth can be taken from Nigel Calder’s book The Restless Earth.
‘We can depict Mother earth as a lady of 46, if her “years” are mega centuries... the deeds of her later childhood are to be seen in old rocks in Greenland and south Africa . Like human memory, the surface of our planet distorts the record, emphasising more recent events and letting the rest pass into vagueness - or at least into unimpressive joints in worn down mountain chains. Most of what we recognise on Earth, including all substantial animal life, is the product of the past six years of the lady’s life...flowering plants did not appear until she was 45 - just one year ago. At that time the great reptiles, including the dinosaurs, were her pets and the break-up of the last supercontinent was in progress.
It was as early as 1620 that theory of plate tectonics began to emerge, (just over a minute in Calder’s timescale). It was Francis Bacon who introduced the idea that the plates fit together much like a jigsaw and that they must once have been joined together. He saw the likeness between the east coast of South America and the west coast of Africa (Fig 1). However, it was only in the early 20th century that the theory was developed, when in 1912 a German meteorologist Alfred Wegener published his theory that all the continents were joined in one supercontinent he named Pangaea (Fig 2). Wegener’s theory develops the ideas of continental drift, but was only fully accepted by the geoscientific community after the concepts of seafloor spreading were developed in the late 1950s and early 1960s.
Since the initial ideas were introduced a great mass of evidence has emerged to support the theory, however, Wegener was restricted to what was available at the time. Despite this he collated strong supporting evidence from several different scientific areas. Wegener studied the fossil records that had been found on the eastern coast of Africa and Western coast of South America, which showed the Mesosaurus, a small reptile that lived in Permian times (about 280 million years before the present, at the time Pangaea formed). The fossil was found only in South Africa and Brazil. As well as a plant that existed when coal was being formed around 345 million years before present day, which was found only in India and Antarctica. The geology of the Eastern coast of America and Western coast of South Africa also corresponds with the theory as rocks of similar age, structure and formation occur in both places. The Appalachian Mountains in eastern USA also match geologically with those in North West Europe. Lastly Wegener looked for evidence left by the climatology that would have been around 280 million years ago. He did this by looking at coal formed in areas that may once have been joined together. Coal found beneath the Antarctic ice cap was formed under the same warm and wet conditions as coal found in tropical Brazil and central India, and evidence of glaciations has also been found in both these places. Britain also shows a history of glacial activity as rocks such as coal, sandstone and limestone could not have formed in its present climate.2
Wegener’s pooled information from several subject areas to produce his theory of continental drift. However, his ideas were rejected by specialists. This was due partly to himself not being regarded as an expert but mainly because he was unable to produce an explanation of the mechanism of continental drift. He was unable to explain how a solid continent could freely move around the earth.
Since Wegener’s theory was first put forward new evidence emerged during the 1950’s and 60’s, this being the discovery of the Mid Atlantic ridge, the studies of palaeomagnetism in the 1950’s and the discovery of sea floor spreading. The mid Atlantic ridge is a constructive plate boundary formed by the meeting of the Eurasian and the North American plates. It was discovered while investigating islands in the Atlantic in 1948, Maurice Ewing noted the presence of a continuous mountain range that was around 1000km wide and 2500m in height. It was also noted that the rocks found here were formed by recent volcanic activity, later investigations also show similar under sea mountain ranges (thought previously to have been formed by ancient volcanic activity) in the eastern pacific stretching nearly 5000km, known now to be the boundary between the Australian and Pacific plate.
Studies of palaeomagnetism began in the 1950’s and involved studying the rocks formed by underwater volcanic eruptions with relation to the earth’s magnetic field. When basaltic lava cools on the sea floor individual minerals separate - especially iron, these minerals then align themselves on the sea floor in the direction of the magnetic pole (Fig 3). New technologies allow these rocks to be dated and with information (known before 1950) that the earths magnetic pole varies from year to year and (a more a recent discovery) that the earth’s magnetic field reverses periodically, it is possible to see an identical pattern between rock formations on either side of the mid Atlantic ridge. It has been claimed that there have been 171 reversals in 76 million year’s; these reversals show that when new basalt formed and the pole was on the south it aligns with that formed at the same time on the other side of the ridge.
The last recent discovery was that of sea floor spreading. In 1962 Harry Hess dated the rocks of the Atlantic sea bed from the ridge itself outwards to the coast of North America. He discovered that the newest rocks were at the centre near Iceland, and the oldest at the coast. However the conflict with the idea of sea floor spreading was that of the earths surface expanding and evidence of plate destruction was needed to prove this wrong. This evidence was found along the edges of the Pacific Ocean where a destructive plate boundary lies between the Pacific, Philippine, North American and Australian plates. It came from the plotting of major earthquakes and volcanic eruptions, which led to the development of the theory of plate tectonics.2
The structure of the earth was thought for many years to be a mystery, however, by studying earthquakes geologists could for the first time work out what lay beneath the crust. At the ‘Moho’ (Mohorovičič) discontinuity geologists found that shock waves from seismic activity travel faster, indicating a change in structure from solid to liquid. The ‘Moho’ discontinuity is the junction between the earths crust and the mantle; it varies in depth depending on the type of crust above it. The average depth under continental crust is around 35-40km, under mountain chains it’s around 70km and under oceanic crust it’s at 6-10km below the surface. Scientists were able to work out the structure of the earth by measuring how fast seismic waves travel from the focus of an earthquake, as different types of waves travel at different speeds through different densities.
The earth is made up of 3 distinct layers, the crust the mantle and the core. The crust is the outermost ‘layer’ and the thinnest. The visible part of the crust that we see is known as the Pedoshpere, comprised of soil , it is the uppermost part of the lithosphere which reacts to the atmosphere, hydrosphere and biosphere through soil forming processes. The crust and the rigid top layer of the mantle are known as the lithosphere, and is the uppermost part of the mantle, it remains rigid for long periods of geologic time deforming through brittle failure or gradual stretching. There are 2 types of lithosphere, oceanic and continental, the lower part of the lithosphere consists largely of peridotite.4 A dense, coarse-grained igneous rock formed through the cooling and solidification of magma or lava.5
Oceanic lithosphere is around 50-100km thick (however beneath mid ocean ridges it is no thicker than the crust) the oceanic crust is around 6-19km thick (average density 3.0) and consists of younger denser rock of basaltic composition, dominant in minerals of manly silica and magnesium (Sima). Continental lithosphere has a range in thickness from about 40-200km; however, the upper 30-50 km is crust. It is composed of lighter older rocks of granitic (average density 2.6) and some basaltic types, dominant in minerals of mainly silica and aluminium (sial). The crust is separated from the mantle by the ‘Moho’ discontinuity; which is distinguished by the change in chemical composition. The asthenosphere is a region of the upper mantle which is situated directly under the lithosphere (100-200km below the surface) it is highly viscous, weak and deforms under stress unlike the lithosphere. The boundary between the lithosphere and asthenosphere is defined as a difference in response to stress, as the asthenosphere deforms to accommodate strain where as the lithosphere is much more brittle. The core is the innermost layer made up of iron and nickel it is divided into two parts. The outer core is in a semi-molten state but the inner core - discovered in 1936 is solid, it is 6371 km below the surface and around 6200°c.
Plate Boundaries
The lithosphere is broken into tectonic plates; there are seven major and several minor plates (Fig 5). Although the plates themselves are rigid they flow freely over the surface of the earth on the underlying asthenosphere. The plates form different boundaries dependant on their type and relative movement at each boundary. The resulting boundaries can either be constructive (divergent), destructive (convergent) and conservative (transform) plate boundaries. Volcanic and seismic activities as well as mountain-building and oceanic trench formation can occur along all these boundaries. The plates themselves are moved by currents which form convection cells. The currents are created as a result of the underlying lithosphere having a higher strength and lower density than the asthenosphere. The currents are generated through the lateral variations in density through the mantle with the dissipation of heat from the mantle supplying the original source of energy driving plate movement.2[ ]
Convergent plate boundaries (also known as destructive plate boundaries) form when a plate with continental crust moves towards a plate with oceanic or another continental crust, forming a Subduction zone or a continental collision. This is dependant on the types of plates involved. A Subduction zone normally occurs when oceanic crust is sub-ducted under the continental crust (Fig 6). This is due to the continental crust being more ‘buoyant’ due to the nature of the rock. Continental crust is older than oceanic crust and therefore lighter, the heavier oceanic crust is forced under the continental crust where it is melted back into magma. Collision zones (collision plate boundaries) occur when continental crust meets another continental crust the resultant force over millions of years forces one crust to ‘buckle’ the resultant landforms are large mountain ranges known as fold mountains, such as the Himalayas and the Alps (the collision between India and Asia has been continuous for around 50 million years). Along this boundary both volcanic eruptions and seismic activity take place. 2[3]
The process of Subduction produces deep sea Trenches parallel to the plate boundary as well as island arcs with volcanoes. The Marians Trench is an example of a deep sea trench at over 11 km deep. It is located in the west Pacific Ocean and is produced by the Subduction of the Pacific plate beneath the Philippine Plate. The Peru-Chile sea trench is another example off the west coast of South America it is formed by the Nazca Plate sub ducting under the South American Plate which formed the Andes.
New Zealand lies on a destructive plate margin between the oceanic crust of the Pacific plate and the continental crust of the Indo-Australian plate. On its south island the volcanic activity has created a deep sea trench ‘Tonga-Kemadec’. This has resulted in the creation of numerous volcanoes and frequent seismic activity. The Subduction has pushed the edges of the continental plate upwards forming Fold Mountains called ‘the southern Alps’. Most of the seismic and volcanic activity on the Island is located in a 20-40km wide Taupo volcanic zone, stretching for 300km from mount Ruapehu to white island forming part of ‘the ring of fire’ – a ring of volcanic and earthquake hotspots that lines the edge of the Pacific plate. Since 1886 5 volcanoes have erupted in the zone, apart from the permanently active white island, Ruapehu is the most recent in 1996. The eruption ejected steam and huge rocks as well as causing several lahars. This resulted in many roads, railway lines and even airspace to close. However the biggest loss was to the tourist industry as two skiing season were lost. 2
Constructive (or divergent) plate boundaries (Fig 7) are formed when two plates move away from each other; this is known as sea floor spreading (when involving oceanic crust). It occurs most actively between oceanic plates and forms mid ocean ridges such as the Mid Atlantic ridge, where the Eurasian and North American plates are being forced apart by convection currents in the asthenosphere. Divergent boundaries between continental plates create rifts which form valleys. As the plates move apart magma rises through the gap to form new volcanic rock, which initially forms sub marine volcanoes that may grow to above sea level over time. An example of this is Iceland which sits directly atop the mid Atlantic ridge with a chain of volcanic activity running down its centre. The landmass is gradually growing as the plates are pulled apart and new rock forms; Surtsey is a volcano in the south of the island.
Conservative (or Transform) plate boundaries (Fig 8), such as the San Andreas Fault in California occur when two plates move parallel to each other. Frequent seismic activity occurs at these plate boundaries, with the boundary being characterised by the pronounced transform fault visible where rock is neither created nor destroyed. The San Andreas Fault forms the junction between the North American and pacific plates. Both plates are moving in a North West direction however, the pacific plate at a faster rate creating the illusion that they are moving in separate directions. The last major earthquake to occur was in 1989. If these plates continue to slide past one another Los Angela will eventually be an Island off the Canadian coast.
Anomalies: Plate tectonic theory
An exception when looking at the three types of plate boundary is the great African rift valley. The Atlantic Ocean was formed as the continent of Laurasia split in two (Fig 2), this may be a process that is repeating itself today. In East Africa the brittle continental crust has fractured leaving the broken section to drift apart (Fig 9). The central portion dropped down to form the great African rift valley (Fig 10) extending for 4000km from Mozambique to the red sea. Its width varies between 10 and 50 km but its sides can reach 600km in height. Where the land has dropped significantly it has been invaded by the sea - in this case the red sea.
Anomalies: Hot spot, human activity, Intra plate old fault etc
Foci
Shallow focus (focus same as hypocenter) earthquakes are much more common than deep focus earthquakes, and unfortunately they cause most damage on the surface because they are closer to the surface and therefore produce stronger shaking on the surface. For example, most earthquakes around the San Andreas Fault in California usually have a focus less than 20 km deep. Shallow focus earthquakes occur around a fault line such as the San Andreas Fault, and they are generally associated with mountain ranges or with mid-ocean ridges or trenches.
There are many examples of shallow-focus earthquakes, but among those best known were the 1906 San Francisco earthquake, the 1994 earthquake in Los Angeles, and the most recent earthquake in Italy.
Deep focus earthquakes have a focus greater than 300 km deep. (Below this depth any disruptions tend to be by flowing rather than breaking and faulting because of the extreme heat and pressure at such depths.) Deep focus (and also intermediate focus) earthquakes rarely cause damage on the surface. They are generally associated with deep water trenches in the ocean and with coastal mountain ranges such as those of South America and Japan.
An example of a deep focus earthquake was the 6.8 magnitude quake that occurred 349 km under the Sea of Japan on July 2007, 140 km off the coast of Honshu. This quake was probably caused by a release of stress as the Pacific Plate subducts beneath the Okhotsk Plate. There were no casualties.
Induced seismicity
Induced seismicity refers to typically minor earthquakes and tremors that are caused by human activity that alters the stresses and strains on the Earth's crust. Most induced seismicity is of an extremely low magnitude. There are a many of ways in which induced seismicity has been seen to occur. In the past several years, some energy technologies that inject or extract fluid from the Earth, such as oil and gas extraction and geothermal energy development, have been found or suspected to cause seismic events.
The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity. Induced seismicity is usually overlooked due to cost cutting during the geological surveys of the locations for proposed dams. Once the reservoirs are filled, induced seismicity could occur immediately or with a small time lag. The 6.3 magnitude 1967 Koynanagar Earthquake occurred in Maharashtra, India with its epicenter, fore- and aftershocks all located near or under the Koyna Dam reservoir. 180 people died and 1,500 were left injured. The effects of the earthquake were felt 230 km (140 mi) away in Bombay with tremors and power outages.
The 2008 Sichuan earthquake, which caused approximately 68,000 deaths, is another possible example. An article in Science suggested that the construction and filling of the Zipingpu Dam may have triggered the earthquake. However, researchers have been denied access to seismological and geological data to examine the cause of the quake further.
Extraction of fossil fuels and disposal of waste
Fossil fuel extraction can generate earthquakes. Hydraulic fracturing of natural gas wells produces large amounts of waste water. This contaminated water is often pumped into salt water disposal (SWD) wells. The weight and lubricity of this waste water has been shown to trigger earthquakes. As of 2013, the magnitude 5.7 earthquake in Oklahoma in 2011 which occurred after 20 years of injecting waste water into porous deep formations is believed to be the strongest earthquake induced by injection of material.
MEDC Case studies
Japan March 13 2011
Tōhoku earthquake March 13th 2011 undersea mega thrust earthquake Megathrust earthquakes occur at subduction zones at destructive plate boundaries (convergent boundaries), where one tectonic plate is subducted (forced underneath) by another. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the worlds largest, with moment magnitudes that can exceed 9.0. Since 1900, all six earthquakes of magnitude 9.0 or greater have been mega thrust earthquakes. No other type of known tectonic activity has produced earthquakes of this scale] off the coast of Japan that occurred at 14:46, 70 km off the Oshika peninsula in Northern Japan and lasted 6 minutes. Shifted the peninsula 5.3 m towards the epicentre and lowered it by 1.2 m. Hypocentre was at 32km (relatively shallow). The earthquake moved Honshu (the main island of Japan) 2.4 m east and shifted the Earth on its axis by estimates of between 10 cm and 25 cm. The earthquake was initially reported as 7.9 MW by the USGS before it was quickly upgraded to 8.8 MW, then to 8.9 MW, and then finally to 9.0 MW. Sendai was the nearest major city to the earthquake, 130 km (81 mi) from the epicenter; the earthquake occurred 373 km (232 mi) from Tokyo.
The first major foreshock was a 7.2 MW event on 9 March, approximately 40 km (25 mi) from the epicenter of the 11 March earthquake, with another three on the same day in excess of 6.0 MW. Following the main earthquake on 11 March, a 7.0 MW aftershock was reported at 15:06 JST (6:06 UTC), succeeded by a 7.4 MW at 15:15 JST (6:16 UTC) and a 7.2 MW at 15:26 JST (6:26 UTC). Over eight hundred aftershocks of magnitude 4.5 MW or greater have occurred since the initial quake. Aftershocks follow Omori's Law, which states that the rate of aftershocks declines with the reciprocal of the time since the main quake. The aftershocks will thus taper off in time, but could continue for years
It caused 15,878 deaths, 6,126 injured, and 2,713 people missing across twenty prefectures, as well as 129,225 buildings totally collapsed, with a further 254,204 buildings 'half collapsed', and another 691,766 buildings partially damaged. The earthquake and tsunami also caused extensive and severe structural damage in north-eastern Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. Around 4.4 million households in north-eastern Japan were left without electricity and 1.5 million without water.
According to EERI (2011), the main dam was reported to have begun breaching within 20 minutes of the earthquake .The uncontrolled discharge from the breach was channelled through a narrow valley, destroying a small village at the mouth of the valley, and killing 8 people (Towhata, 2011).
The tsunami caused nuclear accidents, primarily the level 7 meltdowns at three reactors in the Fukushima Daiichi Nuclear Power Plant complex, and the associated evacuation zones affecting hundreds of thousands of residents. Residents within a 20 km (12 mi) radius of the Fukushima Daiichi Nuclear Power Plant and a 10 km (6.2 mi) radius of the Fukushima Daini Nuclear Power Plant were evacuated. Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion. The Bank of Japan offered ¥15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions. The World Bank's estimated economic cost was US$235 billion, making it the costliest natural disaster in world history.
One minute before the earthquake was felt in Tokyo, the Earthquake Early Warning system, which includes more than 1,000 seismometers in Japan, sent out warnings of impending strong shaking to millions. It is believed that the early warning by the Japan Meteorological Agency (JMA) saved many lives. The warning for the general public was delivered about 8 seconds after the first P wave was detected, or about 31 seconds after the earthquake occurred. However, the estimated intensities were smaller than the actual ones in some places in Kanto and Tohoku regions. This was thought to be because of smaller estimated earthquake magnitude, smaller estimated fault plane, shorter estimated fault length, not having considered the shape of the fault, etc.
The surface energy of the earthquake was double that of the 2004 Indian Ocean earthquake.
This earthquake occurred where the Pacific Plate is subducting under the plate beneath northern Honshu (Philippine plate); which plate is a matter of debate amongst scientists. The Pacific plate, which moves at a rate of 8 to 9 cm (3.1 to 3.5 in) per year, dips under Honshu's underlying plate releasing large amounts of energy. This motion pulls the upper plate down until the stress builds up enough to cause a seismic event. The break caused the sea floor to rise by several meters. A quake of this magnitude usually has a rupture length of at least 480 km (300 mi) and generally requires a long, relatively straight fault surface. Because the plate boundary and subduction zone in the area of the rupture is not very straight, it is unusual for the magnitude of an earthquake to exceed 8.5; the magnitude of this earthquake was a surprise to some seismologists. The hypocentral region of this earthquake extended from offshore Iwate Prefecture to offshore Ibaraki Prefecture. The Japanese Meteorological Agency said that the earthquake may have ruptured the fault zone from Iwate to Ibaraki with a length of 500 km (310 mi) and a width of 200 km (120 mi).
The quake moved portions of north-eastern Japan by as much as 2.4 m (7.9 ft) closer to North America, making portions of Japan's landmass wider than before. Portions of Japan closest to the epicenter experienced the largest shifts. A 400 km (250 mi) stretch of coastline dropped vertically by 0.6 m (2.0 ft), allowing the tsunami to travel farther and faster onto land. On 6 April the Japanese coast guard said that the quake shifted the seabed near the epicenter 24 meters (79 ft) and elevated the seabed off the coast of Miyagi prefecture by 3 meters. A report by the Japan Agency for Marine-Earth Science and Technology, published in Science on 2 December 2011, concluded that the seabed in the area between the epicenter and the Japan Trench moved 50 meters east-southeast and rose about 7 meters as a result of the quake.
Soil liquefaction was evident in areas of reclaimed land around Tokyo, particularly in Urayasu, Chiba City, Funabashi, Narashino (all in Chiba Prefecture) and in the Koto, Edogawa, Minato, Chūō, and Ōta Wards of Tokyo. Approximately 30 homes or buildings were destroyed and 1,046 other buildings were damaged to varying degrees. Nearby Haneda Airport, built mostly on reclaimed land, was not damaged. Odaiba also experienced liquefaction, but damage was minimal.
The earthquake, caused by 5 to 8 meters upthrust on a 180-km wide seabed at 60 km offshore from the east coast of Tōhoku, resulted in a major tsunami that brought destruction along the Pacific coastline of Japan's northern islands. The tsunami warning issued by the Japan Meteorological Agency was the most serious on its warning scale; it rated as a "major tsunami", being at least 3 m (9.8 ft) high. The actual height prediction varied, the greatest being for Miyagi at 6 m (20 ft) high. The tsunami inundated a total area of approximately 561 km2 (217 sq mi) in Japan.
Just over an hour after the earthquake at 15:55 JST, a tsunami was observed flooding Sendai Airport, which is located near the coast of Miyagi Prefecture. A 4 m high tsunami hit Iwate Prefecture. Wakabayashi Ward in Sendai was also particularly hard hit. At least 101 designated tsunami evacuation sites were hit by the wave.
Like the 2004 Indian Ocean earthquake and tsunami, the damage by surging water, though much more localized, was far more deadly and destructive than the actual quake. There were reports of entire towns destroyed from tsunami-hit areas in Japan, including 9,500 missing in Minamisanriku; one thousand bodies had been recovered in the town by 14 March 2011.
Among several factors causing the high death toll from the tsunami, one was the unexpectedly large size of the water surge. The tsunami walls at several of the affected cities were based on much smaller tsunami heights. Also, many people caught in the tsunami thought that they were located on high enough ground to be safe.
The most severe effects of the tsunami were felt along a 670-km (420 mi)-long stretch of coastline from Erimo, Hokkaido, in the north to Ōarai, Ibaraki, in the south, with most of the destruction in that area occurring in the hour following the earthquake. The tsunami washed away the sole bridge to Miyatojima, Miyagi, isolating the island's 900 residents. A two meter high tsunami hit Chiba Prefecture about 2 1/2 hours after the quake, causing heavy damage to cities such as Asahi.
15:12 JST – off Kamaishi – 6.8 m (22 ft)
15:15 JST – Ōfunato – 3.2 m (10 ft) or higher
15:20 JST – Ishinomaki-shi Ayukawa – 3.3 m (11 ft) or higher
15:21 JST – Miyako – 4.0 m (13.1 ft) or higher
15:21 JST – Kamaishi – 4.1 m (13 ft) or higher
15:44 JST – Erimo-cho Shoya – 3.5 m (11 ft)
15:50 JST – Sōma – 7.3 m (24 ft) or higher
16:52 JST – Ōarai – 4.2 m (14 ft)
The JMA bulletin also included the caveat that "At some parts of the coasts, tsunamis may be higher than those observed at the observation sites."
A joint research team from Yokohama National University and the University of Tokyo also reported that the tsunami at Ryōri Bay, Ōfunato was about 30 m high. They found fishing equipment scattered on the high cliff above the bay. At Tarō, Iwate, a University of Tokyo researcher reported an estimated tsunami height of 37.9 m (124 ft) reached the slope of a mountain some 200 m (656 ft) away from the coastline. Also, at slope of nearby mountain from 400 m (1,312 ft) Aneyoshi fishery port of Omoe peninsula in Miyako, Iwate, Tokyo University of Marine Science and Technology found estimated tsunami run up height of 38.9 m (127 ft). This height is deemed the record in Japan historically, as of reporting date, that exceeds 38.2 m (125 ft) from the 1896 Meiji-Sanriku earthquake. It was also estimated that the tsunami reached heights of up to 40.5 metres (133 ft) in Miyako in Tōhoku's Iwate Prefecture. The inundated areas closely matched those of the 869 Sanriku tsunami.
A Japanese government study found that only 58% of people in coastal areas in Iwate, Miyagi, and Fukushima prefectures heeded tsunami warnings immediately after the quake and headed for higher ground. Of those who attempted to evacuate after hearing the warning, only five percent were caught in the tsunami. Of those who didn't heed the warning, 49% were hit by the water.
Seawalls which line at least 40% of its 34,751 km (21,593 mi) coastline and stand up to 12 m high, the tsunami simply washed over the top of some seawalls, collapsing some in the process.
An estimated 230,000 automobiles and trucks were damaged or destroyed in the disaster. As of the end of May 2011, residents of Iwate, Miyagi, and Fukushima prefectures had requested deregistration of 15,000 vehicles.
The Fukushima Daiichi, Fukushima Daini, Onagawa Nuclear Power Plant and Tōkai nuclear power stations, consisting of a total eleven reactors, were automatically shut down following the earthquake. Higashidōri, also on the northeast coast, was already shut down for a periodic inspection. Cooling is needed to remove decay heat after a reactor has been shut down, and to maintain spent fuel pools. The backup cooling process is powered by emergency diesel generators at the plants and at Rokkasho nuclear reprocessing plant.At Fukushima Daiichi and Daini tsunami waves overtopped seawalls and destroyed diesel backup power systems, leading to severe problems at Fukushima Daiichi, including three large explosions and radioactive leakage. Over 200,000 people were evacuated.
The aftermath of the earthquake and tsunami included both a humanitarian crisis and a major economic impact. The tsunami resulted in over 340,000 displaced people in the Tōhoku region, and shortages of food, water, shelter, medicine and fuel for survivors. In response the Japanese government mobilized the Self-Defence Forces, while many countries sent search and rescue teams to help search for survivors. Aid organizations both in Japan and worldwide also responded, with the Japanese Red Cross reporting $1 billion in donations. The economic impact included both immediate problems, with industrial production suspended in many factories, and the longer term issue of the cost of rebuilding which has been estimated at $122 billion. In comparison to the 1995 Great Hanshin earthquake, the East Japan Earthquake brought serious damage to an extremely wide range.
The tsunami created over 300,000 refugees in the Tōhoku region of Japan, and resulted in shortages of food, water, shelter, medicine and fuel for survivors. In response to the crisis, the Japanese government mobilized the Self-Defence Forces.
The economic impact included both immediate problems, with industrial production suspended in many factories, and the longer term issue of the cost of rebuilding which has been estimated at ($122 billion)
A further serious impact of the tsunami was the critical damage done to the Fukushima Daiichi Nuclear Power Plant, resulting in severe releases of radioactivity and the prospect of a long-term health and environmental hazard in need of an expensive cleanup.140,000 residents within 20 km (12 mi) of the plant were evacuated. The accidents have drawn attention to ongoing concerns over Japanese nuclear seismic design standards and caused other governments to re-evaluate their nuclear programs. As of April 2011, water is still being poured into the damaged reactors to cool melting fuel rods. John Price, a former member of the Safety Policy Unit at the UK's National Nuclear Corporation, has said that it "might be 100 years before melting fuel rods can be safely removed from Japan's Fukushima nuclear plant".
The number of the evacuees, as of 26 January 2012, was 341,411. Some earthquake survivors died in the shelters or in the process of evacuation. Many shelters struggle to feed evacuees and were not medically sufficiently equipped. Fuel shortages hampered relief actions. In the first week after the earthquake, supplies of food, water, and medicine had been held up because of a fuel shortage and the weather condition.
By 12 April 2011 the Japanese government estimated that the cost of just the direct material damage could exceed ($300 billion). An estimated 90% of the 29,000 fishing boats in Miyagi, Iwate, and Fukushima prefectures were rendered unusable by the tsunami.Miyagi Prefecture's fishing industry was almost completely destroyed. Twelve thousand of 13,000 registered fishing boats in the prefecture were destroyed or damaged. At least 440 fishermen were killed or missing. The damage to the prefecture's fishing industry was estimated at US$5 billion. The earthquake and tsunami have had significant immediate impacts on businesses such as Toyota, Nissan and Honda, which completely suspended auto production until 14 March 2011.Many seaside communities in Japan have reexamined their tsunami defenses and reaction plans in response to the disaster.
The reconstruction of damaged areas in Tōhoku beginning in 2011 produced a boom in construction jobs and business in the area. As a result, cities like Sendai benefited from an increase in residents and wages for construction-related jobs rose.
Japanese media reported in 2012 that up to 25% of special funds allocated by the government for disaster recovery and relief were being used outside the disaster area on projects unrelated to the earthquake and tsunami. The projects included ¥500 million for road construction in Okinawa, ¥330 million for repairs to National Stadium, ¥10.7 million in subsidies for nuclear research, ¥30 million for power shovels for prisons in Hokkaido and Saitama, and ¥2.3 billion to combat the Sea Shepherd Conservation Society. In the meantime, in October 2012 the damaged towns in Tōhoku reported that they were still struggling to recover from the disaster.
Some people devastated by the quake began, however, to question the government's effort in providing food, clothing, electricity, heat, and phone service. Chief Cabinet Secretary Yukio Edano later said, "In hindsight, we could have moved a little quicker in assessing the situation and coordinating all that information and provided it faster."
The U.S. Embassy in Japan had advised evacuation of all American nationals to outside a 50 mi (80 km) radius from the Fukushima power plant on 16 March 2011, which is a far greater distance than the 12.4 mile (20 km) evacuation zone the Japanese government had already recommended for all inhabitants of the affected region, but later increased to 18.6 miles (30 km) on 25 March 2011
Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion. The Bank of Japan offered US$183 billion to the banking system on 14 March in an effort to normalize market conditions. The World Bank's estimated economic cost was US$235 billion, making it the costliest natural disaster in world history.
Christchurch
Christchurch, New Zealand is located on the Pacific ‘ring of fire’ makes it vulnerable to tectonic hazards. It is much less vulnerable than for example Haiti because it has sophisticated monitoring, wealth and a small population of only 4.4 million. An earthquake struck on 4th September 2010 and was similar in magnitude to the Haitian earthquake in January 2010 (magnitude 7.0) measuring 7.1 on the Richter scale. In New Zealand there were no deaths and only 2 serious injuries in comparison with Haiti which suffered 300,000 casualties and 1.3 million displaced people. In comparison the disruption in New Zealand was quickly dealt with.
On February 22nd a 6.1 magnitude aftershock hit Christchurch on the South Island, New Zealand’s second largest city. This killed 181 people and damaged the city severely. It was the second most deadly disaster in New Zealand’s history and the estimated cost of rebuilding is around NZ$15 billion making it the country’s most expensive.
The cause of the earthquake was the boundary where the pacific plate converges with the Indo-Australian plate subduction – responsible for the volcanic activity on the North Island where the major earthquakes are located. Magnitude 5 earthquakes occur on average once every 10 years. The south Island experiences less large earthquakes and the September earthquake was the largest recorded for the Canterbury region. The plate boundary has resulted in the major Alpine and Hope fault lines, movement, strike-slip faulting and smaller faults cause the South island quakes.
The 2011 quake (aftershock) was cause by movement along a previously unknown fault running roughly east-west to the southwest of Christchurch. The relatively shallow depth of 5km of the earthquake resulted in its destructive power being high even though its magnitude was not particularly high. The epicentre was also much closer to Christchurch at 10km south west in port Hills. It was likely an aftershock although still remains debatable amongst geologists due to it having occurred on a separate fault than the 2010 quake.
The distance from the epicentre and geology compounded the destruction caused. The hard volcanic rocks of the Port Hills resulted in seismic energy being reflected back up to the surface. In addition liquefaction was caused as ground water levels were close to the surface (previously had been areas of lakes) causing further damage to infrastructure and buildings.
The country is well prepared to deal with tectonic hazards as a rich nation and previous history. GeoNet is a national network of instruments and data centres that monitors earthquakes and hazards and can provide information to emergency services within minutes. GeoNet is funded by the earthquake commission set up by the government to provide insurance to homeowners and education on ‘quake-safeing’ their homes. There are building codes (implemented as early as 1935 and updated today) protect buildings from damage during moderate earthquakes and in the case of major ones ensuring they do not collapse. Older building have to be enforced although only in the North island – this was not seen as essential in the south Island making Christchurch’s heritage buildings much more vulnerable.
New Zealand’s preparedness was not able to prevent the consequences of the earthquake for many reasons. The shallow focus and close proximity to the epicentre meant the effects were measured as 8 on the Mercalli intensity scale (measures building destruction). Many buildings had already been weakned by the September earthquake. The city was crowded at the time as it struck on Tuesday (weekday) at 12:51pm.
Almost half of the buildings in Christchurch were damaged or destroyed as the peak acceleration was 1.8 times higher due to gravity. The six storey Canterbury television centre collapsed, killing 85 people. Christchurch’s tallest building a 26 story hotel was displaced 0.5m and had to be demolished, more than 100,000 homes were damaged or destroyed and 100 more damaged beyond repair by an aftershock in June 2011.
Liquefaction was widespread in Christchurch and always posed a risk due to the city being underlain with soft sediments but was exacerbated in 2011 with the unseasonably high water content of the sub-strata. Many schools that were undamaged by the quake had to close due to liquefaction from the bursting of stressed pipes. The AMI stadium had deep foundations and a network of 10m stone pillars covering 12,000m square to reduce the risk of liquefaction, however this was not enough as 2 stands subsided around 40cm.
The port Hills area suffered considerable slope failure as previously vertical cliffs remnant of sea cliffs experienced rock and debris falls causing fatalities and building damage at the base.
Following the earthquake the government established the Canterbury Earthquake Recovery Authority with the estimated cost of recovery at $13 billion. The city was divided into 4 zones depending on the severity of damage.
The red zone was the residential area along the banks of the river Avon. The area suffered considerable lateral spreading as a result of liquefaction. The government agreed to buy over 5,000 of the worst affected insured properties which can not be repaired for over 3 years.
The orange zone there are 10,000 homes which have to be investigated before anything can be done on them.
The government immediately activated its National Crisis Management Centre, and declared a national state of emergency the day after the quake. Christchurch’s central business district remained cordoned off for more than a month after the earthquake. Electricity was restored to 75% of the city within three days, but water supplies and sewerage systems took a number of weeks to restore in areas affected by liquefaction.
In the weeks following the earthquake about 70,000 people were believed to have left the city due to uninhabitable homes, lack of basic services and continuing aftershocks. Timaru’s population swelled by 20% and thousands of pupils registered at schools in other cities and towns. However, many were expected to return to Christchurch as conditions improved.
LEDC Case studies
Indonesian Earthquake Dec 26 2004
The 2004 Indian Ocean earthquake was an undersea megathrust earthquake that occurred at 00:58:53 UTC on Sunday, 26 December 2004, with an epicentre off the west coast of Sumatra, Indonesia.
The earthquake was caused by subduction and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing over 230,000 people in fourteen countries, and inundating coastal communities with waves up to 30 meters high. Indonesia was the hardest-hit country, followed by Sri Lanka, India, and Thailand.
With a magnitude of Mw 9.1–9.3, the earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 centimetre (0.4 inches) and triggered other earthquakes as far away as Alaska. Its epicentre was between Simeulue and mainland Indonesia.The plight of the affected people and countries prompted a worldwide humanitarian response. In all, the worldwide community donated more than $14 billion (2004 US$) in humanitarian aid.
The hypocentre of the main earthquake was approximately 160 km, in the Indian Ocean off the western coast of northern Sumatra, at a depth of 30 km.
The northern section of the Sunda megathrust (a fault that extends approximately 5,500 km from Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia) which had been assumed dormant, ruptured; the rupture having a length of 1,300 km.
Splay faults, or secondary "pop up faults", caused long, narrow parts of the sea floor to pop up in seconds. This quickly elevated the height and increased the speed of waves, causing the complete destruction of the nearby Indonesian town of Lhoknga.
The only other recorded earthquakes of magnitude 9.0 or greater were offKamchatka, Russia, on 4 November 1952 (magnitude 9.0)[16] and Tōhoku, Japan (magnitude 9.0) in March 2011. Each of thesemegathrust earthquakes also spawned tsunamis in the Pacific Ocean. However, the death toll from these was significantly lower, primarily because of the lower population density along the coasts near affected areas and the much greater distances to more populated coasts and also due to the superior infrastructure and warning systems in MEDCs (More Economically Developed Countries) such as Japan.
The megathrust earthquake was unusually large in geographical and geological extent. An estimated 1,600 kilometres (1,000 mi) of fault surface slipped (or ruptured) about 15 metres (50 ft) along the subduction zone where the India Plate subducts under the overriding Burma Plate.
The India Plate is part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is drifting north-east at an average of 6 centimetres per year (2.4 inches per year). The India Plate meets the Burma Plate (which is considered a portion of the great Eurasian Plate) at theSunda Trench. At this point the India Plate subducts beneath the Burma Plate, which carries the Nicobar Islands, the Andaman Islands, and northern Sumatra. The India Plate sinks deeper and deeper beneath the Burma Plate until the increasing temperature and pressure drive volatiles out of the subducting plate. These volatiles rise into the overlying plate causing partial melting and the formation of magma. The rising magma intrudes into the crust above and exits the Earth's crust through volcanoes in the form of a volcanic arc. The volcanic activity that results as the Indo-Australian Plate subducts the Eurasian Plate has created the Sunda Arc.
As well as the sideways movement between the plates, the sea floor is estimated to have risen by several metres, displacing an estimated 30 cubic kilometres (7.2 cu mi) of water and triggering devastating tsunami waves. The waves did not originate from a point source, as was inaccurately depicted in some illustrations of their paths of travel, but rather radiated outwards along the entire 1,600-kilometre (1,000 mi) length of the rupture (acting as a line source). This greatly increased the geographical area over which the waves were observed, reaching as far as Mexico, Chile, and the Arctic. The raising of the sea floor significantly reduced the capacity of the Indian Ocean, producing a permanent rise in the global sea level by an estimated 0.1 millimetres (0.004 in).
More spectacularly, there was 10 m (33 ft) movement laterally and 4–5 m (13–16 ft) vertically along the fault line. Early speculation was that some of the smaller islands south-west of Sumatra, which is on the Burma Plate (the southern regions are on the Sunda Plate), might have moved south-west by up to 36 m (120 ft), but more accurate data released more than a month after the earthquake found the movement to be about 20 cm (8 in). Since movement was vertical as well as lateral, some coastal areas may have been moved to below sea level. The Andaman and Nicobar Islands appear to have shifted south-west by around 1.25 m (4 ft 1 in) and to have sunk by 1 m (3 ft 3 in).
Scientists investigating the damage in Aceh found evidence that the wave reached a height of 24 metres (80 ft) when coming ashore along large stretches of the coastline, rising to 30 metres (100 ft) in some areas when travelling inland.
Because the 1,600 km (1,000 mi) fault affected by the earthquake was in a nearly north-south orientation, the greatest strength of the tsunami waves was in an east-west direction. Bangladesh, which lies at the northern end of the Bay of Bengal, had very few casualties despite being a low-lying country relatively near the epicenter. It also benefited from the fact that the earthquake proceeded more slowly in the northern rupture zone, greatly reducing the energy of the water displacements in that region.
The northern regions of the Indonesian island of Sumatra were hit very quickly, while Sri Lanka and the east coast of India were hit roughly 90 minutes to two hours later. Thailand was also struck about two hours later despite being closer to the epicentre, because the tsunami travelled more slowly in the shallow Andaman Sea off its western coast.
Despite a lag of up to several hours between the earthquake and the impact of the tsunami, nearly all of the victims were taken completely by surprise. There were no tsunami warning systems in the Indian Ocean to detect tsunamis or to warn the general populace living around the ocean. Tsunami detection is not easy because while a tsunami is in deep water it has little height and a network of sensors is needed to detect it. Setting up the communications infrastructure to issue timely warnings is an even bigger problem, particularly in a relatively poor part of the world.
On 28 March 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean but did not result in a major tsunami.
Indonesia was the worst affected area, with most death toll estimates at around 170,000. According to the U.S. Geological Survey a total of 227,898 people died.
Many countries across Asia, including Indonesia, Sri Lanka and Bangladesh, have put forth efforts to destroy the coral surrounding their beaches, and instead make way for shrimp farms and other economic choices. On the Surin Island chain of Thailand's coast, Browne argued, people may have been saved as the tsunami rushed against the coral reefs, lessening its impact. However, there were many fewer people on these islands, which helps explain the lower death toll. Many reefs areas around the Indian Ocean have been destroyed using dynamite because they are considered impediments to shipping, an important part of the South Asian economy. Similarly, Browne argued that the removal of coastal mangrove trees may have intensified the effect of the tsunami in some locations. He argued that these trees, which lined the coast but were removed to make way for coastal residences, might have lessened the force of the tsunami, in certain areas. Another factor, Browne argued, is the removal of coastal sand dunes.
In mid-March the Asian Development Bank reported that over US$4 billion in aid promised by governments was behind schedule. Sri Lanka reported that it had received no foreign government aid, while foreign individuals had been generous.
The impact on coastal fishing communities and the people living there, some of the poorest in the region, has been devastating with high losses of income earners as well as boats and fishing gear. In Sri Lanka artisanal fishery, where the use of fish baskets, fishing traps, and spears are commonly used, is an important source of fish for local markets; industrial fishery is the major economic activity, providing direct employment to about 250,000 people. In recent years the fishery industry has emerged as a dynamic export-oriented sector, generating substantial foreign exchange earnings. Preliminary estimates indicate that 66% of the fishing fleet and industrial infrastructure in coastal regions have been destroyed by the wave surges, which will have adverse economic effects both at local and national levels.
But some economists believe that damage to the affected national economies will be minor because losses in the tourism and fishing industries are a relatively small percentage of the GDP. However, others caution that damage to infrastructure is an overriding factor. In some areas drinking water supplies and farm fields may have been contaminated for years by salt water from the ocean. Even though only costal regions were directly affected by the waters of the tsunami, the indirect effects have spread to inland provinces as well.
Both the earthquake and the tsunami may have affected shipping in the Malacca Straits, which separate Malaysia and the Indonesian Island of Sumarta by changing the depth of the seabed and by disturbing navigational buoys and old shipwrecks. In one area of the Strait, water depths were previously up to 4,000 feet, and are now only 100 feet in some areas, making shipping impossible and dangerous. These problems also made the delivery of relief aid more challenging. Compiling new navigational charts may take months or years.
China
On the 12th May 2008 a 7.2 magnitude struck 90km north of Chengdu pop. 3.9 million in Sichuan province South East China. Sichuan province is mainly rural and the death toll was nearly 70,000 1 month after the quake. China doesn’t lie on any tectonic plate boundaries however; the earthquake was caused by stress build up between the movements of the Tibetan Plateau and the converging with the underlying crust of the Sichuan basin. Thus is related to the Northwards movement of the India plate against the European plate of 50mm/year responsible for the Asian highlands and the eastwards movement of the crustal material.
There was extreme shaking in a North eastern direction from the epicentre near in Qingchuan county subsidence and street cracks were obsereved in some cities and 1.5km of faulting was observed. On May 25th there was an aftershock which measured 5.4 killing 8, injuring 927, and destroying 40,000 homes.
Although the area experiences earthquakes it was not prepared for such a strong magnitude earthquake, which was felt as far away as Taiwan, Thailand and Bangladesh. 70,000 people were killed and 350,000 injured. The earthquake affected over 45 million people in 10 different provinces. 5 million building collapsed and 21 million damaged in Sichuan. Towns including Beichuan and Wuolong were completely destroyed. The total economic cost was $86 billion. Rescuers struggled to gain access to the areas affected because of the rural locations, mountainous terrain and landslides which had blocked some roads. Landslides had created 34 barrier lakes (with combined rainfall) threatened 770,000 people downstream. More than 2,000 dams fractured resulting in rescue operations had to divert to containing the threat.
The earthquake was unpredicted and Sichuan was an area that has been largely untouched by Chinas economic rise. There was not a sufficient earthquake regulations till after 1976 Tangshan earthquake and building regulations are hard to enforce in the rural countryside.
80,000 troops were sent by the government to Sichuan and some had to be parachuted due to the rough terrain. Secondary hazards began to arise due to dam failure lakes such as the Tangliashan were diverted into the quake effected town of Beichuan. 55 billion yen was raised by both domestic and foreign nations and 95 million had been allocated by the government to the rescue operation.
Iran
The 2003 Bam earthquake was a major earthquake that struck Bam and the surrounding Kerman province of southeastern Iran at 5:26 AM Iran Standard Time) on Friday, December 26, 2003. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude (Mw) of 6.6; estimated by the United States Geological Survey. The earthquake was particularly destructive, with the death toll amounting to 26,271 people and injuring an additional 30,000. The effects of the earthquake were exacerbated by the use of mud brick as the standard construction medium; many of the area's structures did not comply with earthquake regulations set in 1989.
Due to the earthquake, relations between Iran and the United States thawed. Following the earthquake the U.S. offered direct humanitarian assistance to Iran and in return the state promised to comply with an agreement with the International Atomic Energy Agency which supports greater monitoring of its nuclear interests. In total a reported 44 countries sent in personnel to assist in relief operations and 60 countries offered assistance.
Following the earthquake, the Iranian government seriously considered moving the capital of Tehran in fear of an earthquake occurring there. Psychologically the earthquake had an impact on many of the victims for years afterwards. A new institutional framework in Iran was established to address problems of urban planning and to reconstruct the city of Bam in compliance with strict seismic regulations. This process marked a turning point, as government ministers and international organizations collaborated under this framework with local engineers and local people to organize the systematic rebuilding of the city.
There is little earthquake education in Iran although the International Institute of Earthquake Engineering and Seismology established a Public Education Department in 1990 to improve "the safety, preventing, and preparedness culture against the earthquake among all groups of the society." In October 2003, Bahram Akasheh, professor of geophysics at Tehran University, called the effects of public ignorance about earthquakes "poisonous".
Iran suffers from frequent earthquakes, this earthquake occurred as a result of stresses generated by the motion of the Arabian plate northward against the Eurasian plate at a rate of approximately 3 centimetres per year. Earthquakes occur as the result of both reverse faulting and strike-slip faulting within the zone of deformation.
The rupture length of the earthquake was estimated to be around 24 kilometers. Based on these results, scientists suggest that the Bam earthquake ruptured a hidden fault and that in this process an unusually strong asperity was involved, causing the widespread devastation of the tremor.
Damage and casualties
The quake occurred at 5:26 AM Iran Standard Time on December 26, 2003. Its epicenter was roughly 10 kilometres southwest of Bam. Maximum intensities were at Bam and Baravat, with the most damage concentrated within the 16 kilometres (10 mi) radius around the city.
The earthquake damage in Bam
At least 26,271 people were killed and 30,000 injured. Casualties from the earthquake were originally reported to be 41,000, but that figure was lowered when it was discovered that some victims were counted more than once. The BBC reported that a large number of victims were crushed while sleeping. 11,000 students were killed and 1/5 of the 5,400 local teaching staff were also. This caused a significant problem for the local education system.
Eighty-five to ninety percent of buildings and infrastructure in the Bam area were either damaged or destroyed, with 70% of houses being completely destroyed, plus 70-90% of Bam's residential areas. This left an estimated 100,000 homeless. Not a single house was standing in Baravat. An important regional center during the 16th and 17th centuries, Bam contained many buildings that were not constructed to survive such ruptures. Many houses in Bam were homemade, and its owners did not use skilled labor or proper building materials to resist earthquakes in the construction. These were often built in the traditional mud-brick style. On the other hand, Iranian regulations laid down in the 1989 Iran seismic code. were better enforced in high rise buildings and skyscrapers.
Damage to a building in Bam
One reason for the large amount of casualties was that when the walls began to fall down, the heavy roofs would collapse, leaving few air pockets in them. The dust and lack of oxygen contributed to the suffocation of survivors. The Iranian government promised to prosecute anyone who violated building regulations, even setting up a special unit to deal with the issue.
The Bam Citadel was considered one of the best surviving mud citadels before the quake. Most of it was demolished, including a large square tower.
Response Iran–United States relations
Due to the earthquake, relations between the United States and Iran thawed. The U.S. usually treated Iran as part of the "axis of evil", as its President George W. Bush called the nation. However, following the tremor White House spokesman Scott McClellan spoke on behalf of President Bush: "Our thoughts and prayers are with those who were injured and with the families of those who were killed."
Fairfax County Urban Search and Rescue squad inspect earthquake damage in Bam
The U.S. offered direct humanitarian assistance to Iran. Iran initially declined this offer, though later accepted it. On December 30 an 81-member emergency response team was deployed to Iran via U.S. military aircraft, consisting of search and rescue squads, aid coordinators, and medical support. These were the first U.S. military airplanes to land in Iran for more than 20 years.
In return, the state promised to comply with an agreement with the International Atomic Energy Agency which supports better monitoring of its nuclear interests. This led U.S. Secretary of State Colin Powell to suggest direct talks in the future. Sanctions were temporarily relieved to help the rescue effort. However, he also said that the U.S. was still concerned on other Iranian issues, such as the prospect of terrorism and the country's support of Hamas.
Relief - On January 8, the International Federation of the Red Cross and the U.N. launched an international appeal for relief together at a conference in Bam, appealing for $42 million and $31.3 million respectively. In response a reported 44 countries sent in personnel to assist in operations and 60 countries had offered assistance in the aftermath of the earthquake. By January 15, the U.N. World Food Program (WFP) had distributed approximately 100,000 rations of food.
During the nights following the earthquake, the temperatures would drop to "bitterly cold" extremes, effectively killing some survivors. These people were living in unheated tents among the rubble. For these reasons, thousands of families were moved to heated camps on the outskirts of Bam. This was not met without resistance; many residents wished to stay in place. The Iranian government was, conversely, criticized for not doing enough supplying of tents. Those that owned motorized vehicles were met with jammed traffic going both ways through Bam. Survivors loaded their belongings to move elsewhere while relief supplies, volunteers, and relatives were arriving.
Aftermath
Iran seriously considered moving the capital of Tehran following the Bam earthquake. The city lies on a major fault, on which scientists predicted a devastating earthquake.
In January 2004, the United Nations estimated that a reconstruction of Bam would cost between US$700 million and $1 billion
Given the failure of the mud brick buildings and lack of compliance with the 1989 Iranian seismic code, the reconstruction in Bam paid special attention to using earthquake durable materials.
Type of Volcano
Fissure eruptions - occur where an elongated crack in the crust allows lava to spill out over a large area. Typically tthese are found around spreading ridges where tension pulls the crust apart - for example, the eruption at Heimaey, Iceland in 1973. When the Eurasian and North American Plates pulled apart, existing topography was drowned in a vast lake of basaltic lava. Fissure eruptions are characterized by a curtain of fire, a curtain of lava spewing out to a small height above the ground.
Shield Volcanoes - are made of basaltic rock and form gently sloping cones from layers of less viscous lava. These volcanoes are known for producing the Hawaiian Islands and are some of the largest in the world, both in height and width. Shield volcanoes are squatty, being lower to the ground, yet having a huge base.
Composite / Stratovolcano - The most common type found on land. They are created by layers of ash from initial explosive phases of eruptions and subsequent layers of lava from the main eruption phases. They are characterized by a fairly symmetrical mountain edifice. They tend to have highly infrequent eruptions ----------------hundreds of years apart-- and typically form at Subduction zones.
Cinder Cone Volcanoes - These are steep-sided volcanoes formed from very viscous lava. As the lava cannot travel far, it builds up convex cone-shaped volcanoes. Lava may solidify in the vent and be revealed later by erosion. They usually remain comparatively small and are active only for a short time.
Calderas - Form when gases that have built up beneath a blocked volcanic event result in a catastrophic eruption that destroys the volcano summit, leaving an enormous crater where later eruptions may form smaller cones. In the case of Crater Lake in the US, the caldera has filled with water, while in the case of Krakatoa in Indonesia and Thera/Santorini in Greece, the sea has inundated the broken remains of the volcano.
Type of eruption
Hawaiian - This type of activity is the like of Mauno Loa and Kilauea Volcanoes. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of very fluid basalt-type lavas with low gaseous content. Eruptions are not centralized at the main summit as with other volcanic types, and often occur at vents around the summit. Mount Etna is also known to have Hawaiian activity.
Strombolian- This type of volcanic activity is named after the volcano Stromboli, which has been erupting continuously for centuries. Strombolian eruptions are driven by the bursting of gas bubbles within the magma. These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slugs. These grow large enough to rise through the lava column. Upon reaching the surface, the difference in air pressure causes the bubble to burst with a loud pop, throwing magma in the air in a way similar to a soap bubble. Because of the high gas pressures associated with the lavas, continued activity is generally in the form of episodic explosive eruptions accompanied by the distinctive loud blasts. During eruptions, these blasts occur as often as every few minutes.
Vulcanian - In Vulcanian eruptions, highly viscous magma within the volcano make it difficult for vesiculate gases to escape. Similar to Strombolian eruptions, this leads to the buildup of high gas pressure, eventually popping the cap holding the magma down and resulting in an explosive eruption. However, unlike Strombolian eruptions, ejected lava fragments are no aero dynamical. They are also more explosive than their Strombolian counterparts, with eruptive columns often reaching between 5 and 10km high. Lastly Vulcanian deposits are andesitic rather than basaltic. Example includes Sakurajima, Japan.
Pelean - Is a type of volcanic eruption, named after the volcano Mount Pelee. In Pelean eruptions, a large amount of gas, dust, ash and lava fragments are blown out in the volcano's central crater, and that often creates large eruptive columns. An early sign of a coming eruption is the growth of a lava spine, a bulge in the summit preempting to its total collapse. The material collapses upon itself, forming a fast-moving pyroclastic flow. These massive landslides make Pelean eruptions one of the most dangerous in the world. Volcanoes known to have Pelean activity are Mount Pelee and Mayon Volcano in the Phillippines.
Plinian - High explosive eruptions that occur mostly at stratovolcanoes. Eruptions can last anywhere from hours to days. Plinian eruptions are similar to both Vulcanian and Strombolian eruptions, except that rather than creating discrete explosive events, Plinian eruptions form sustained eruptive columns, which can reach up to 45km in height. The most dangerous feature are pyroclastic flows generated by material collapse, which move down the side of the mountain at up to 435m/ph. The ejection of hot material from the volcano's summit melts snow banks and ice deposits on the volcano, which mixes the tephra to form lahars, fast moving mudslides with the consistency of wet concrete that move at the speed of a river rapid. Major Plinian eruptive events include Mount Vesuvius in AD 79. The 1980 eruption of Mount St. Helens was a Plinian eruption.
Surtseyan - A type of volcanic eruption caused by shallow-water interactions between water and lava, named so after its most famous example, the eruption and formation of the island of Surtsey off the coast of Iceland. Surtseyan eruptions are the "wet" equivalent of ground-based Strombolian eruptions, but because of where they are taking place they are much more explosive.
MEDC Case studies
Mt St. Helens
Cryptodomes are formed when viscous lava forces its way up and causes a bulge. The 1980 eruption of Mount St. Helens was an example. Lava was under great pressure and forced a bulge in the mountain, which was unstable and slid down the north side.
Mt. St Helens is an active composite cone volcano in Skamania county Washington in the NW of the USA. It is close to the subduction boundary of the North American and Juan de Fuca (oceanic) tectonic plates.
In response to the growing threat posed by the volcano in 1980 there were many management schemes. The ‘red’ zone was an exclusion zone where no members of the public were allowed to enter, and the blue zone was restricted access. After the eruption blast helicopters were mobilised to search for victims that had ventured into the exclusion zone and makeshift hospitals were erected near to the affected area.
The ash fall an Yakima was managed by media response telling people to remain calm, immediate aid was requested from the federal and state governments and all emergency services were mobilised. A central communications centre was established in the town hall, and people were urged to wear safety masks to avoid ash inhalation when outdoors – the 3M Company diverted its whole supply of masks to Washington State for anyone who needed them. The city’s municipal airport was closed indefinitely and there was 24 hour monitoring of the city’s domestic water treatment plants to ensure no contamination. The city’s CBD was ordered to close so cleanup could begin along with all public services including schools and buses. Emergency shelters were opened for people who were stranded such as tourists and business people. The National Guard was activated to help with security and clean up.
The eruption began with forewarnings of a 4.1 mag earthquake on 20th March with increasing activity over the days following. Ash began to plume out of the summit after 125 years of dormancy on March 27th. There were concerns over the growing bulge on the north flank on April 30th. On may 18th the day of the eruption a 5.1 mag earthquake was recorded below the summit which triggered the largest landside in history, followed by a lateral blast that levelled 230square miles of forest and killed 57 people and billions of £ in property damage. The ash plume reached 80,000ft in less than 10 minutes and spread up to 22,000 square miles. For 6 years after the volcano continued to add material to the crater floor (97 mil cubic yards). From 04-08 125 mil cubic yards of material produced and 7% of the crater has been refilled with lava, since however, the volcano remains quiet.
Mt. Etna 1991-3
Mt Etna supports rich agricultural land and it is estimated that 25% of Sicily’s population live on its slopes. Classified as a decade volcano, it has seen an eruption every year since 2001, however, unlike Chaitén it is well monitored and actively managed. Its vulcanism stems from the Subduction of the African plate beneath the Eurasian plate.
It presents significant natural hazard due to the agriculture it supports, with vineyards and orchards spread on its lower slopes and the broad plain of Catania. Etna is a composite stratovolcano and displays a wide array of eruptions,that typically erupt basaltic lava which has a low viscosity (‘runny’) therefore able to travel large distances.
The volcano has the potential to damage the infrastructure surrounding the volcano, as well as large explosive events can lead to the formation of eruptive columns of ash; the fallout from which could present problems to settlement, infrastructure, agriculture and road/air traffic. Flank collapse is a major threat causing a huge avalanche of volcanic debris.
Between 1991-1993 the town of Zafferana was threatened by a lava flow. Earth barriers were constructed but proved useless, explosives were then used to redirect the flow and break up a very efficient lava tube system that had carried the lava 7km down the slope. This proved successful on 23 may 1993 when the lava was successfully redirected.
During the 2002 eruption dams of volcanic rock and soil were built to protect the tourist base at Rifugio Sapienza which helped divert the flow. The Italian army’s heavy earth moving equipment was used to block and divert lava flows. None of the towns on Etna’s slopes were damaged however, there were loses to agriculture and tourism. The Italian government pledged immediate financial assistance of more than $8mil and tax breaks for villagers.
There are only 77 recorder deaths on Etna all of which in recent years can be attributed to accidents and tourists straying of the designated paths.
The current monitoring on Etna is carried out by the Catania INGV which has monitored the volcano for the last 20 years. It has a permanent network of remote sensors (seismic, geodetic, magnetic, gravimetric and video) connected to the centre at Catania by radio.
LEDC Case Studies
Chaitén Chile May 02 2008
Chaitén volcano is located in south-eastern Chile, on a Subduction zone between the Nazca (Oceanic) plate boundary and the South American (continental) plate boundary. On May 2nd 2008 Chaitén erupted for the first time in 9,400 years, therefore was not considered and active threat. The volcano is one of many along the Nazca-South America plate boundary, with Chile having one of the longest active volcano chains in the world. The volcano which featured a lava dome within a caldera about 2.5km wide and 4km long is composed if viscous rhyolitic lava and pyroclastics. It is a caldera volcano, resulting in explosive eruptions from the build up of pressure and gas.
The initial eruption produced a plume of volcanic ash and steam that rose 17,000 km high. This was carried over the Andes into neighbouring Argentina and over the Atlantic. This caused flights to be diverted in Argentina and airports to close. Hundreds of domestic and several international flights were cancelled impacting both governments up to $2 million. The town of Chaitén had a population of 4200 and was situated 10km south of the volcano. The town was covered in a thick layer of ash, causing the deaths of many animals due to asphyxiation. However there were no deaths to inhabitants as a direct result of the eruption (although one death caused by shock). 4000 of the town’s residents were evacuated by boat, along with another 1000 residents from the nearby town of Futaleufu. Smaller settlements to the south east such as Chubut and Rio Negro also received heavy ash fall.
Timeline - First earthquakes were felt late on the 30/04/08 with the eruption beginning 01/05/08. There were nearly continuous ash emissions as high as 30km with intermittent large explosions continuing 2nd-8th of May. By late May the lava eruptions had generated a new dome (around 54,999m^2 in an area containing 55 million m^3 of new material). The height of the ash column is estimated at 20-30km at its peak. The subsequent collapse of the column brought a vast amount of ash onto the surrounding area. This Asphyxiated some animals, blocking roads and causing thunderstorms. Passing polar storm also meant that heavy rain combined with heavy rains causing flooding. By May 14th officials had announced that 90% of the town was flooded due to increased flows of the Rio Blanco and Rio Chaitén.
The volcano is not accurately monitored and the nature of the eruption gave serious cause for concern. As the rhyolitic nature of the lava and ash meant that an eruption was likely dominated by pyroclastics (aside from some reports of lava this was the case). The USGS reported that the ashfall had significantly impacted local communities. Lahars generated by intense rainfall cut communications making access difficult. Ash falls up to 15cm deep had blocked rivers and contaminated groundwater supplies.
Many animals were killed due to ash inhalation resulting in farmers loosing livestock and produce (if/when there farms were again inhabitable).Local hospitals treated many people for breathing difficulties. Up to 90% of the down was damaged and up to 30% completely destroyed (as well as flooding) , damage to airport and marine facilities hampered rescue attempts.
Chaitén airport was closed indefinitely (inc closures at Osorno, Puertto Mont – Chile and Bariloche, Esquel, Comodro Rivadavia – Argentina)
Prior to 2008 Chaitén was considered a low threat volcano although records showed it to be an explosive volcano; the length at which it had lain dormant meant it was not actively monitored. The remote location of Chaitén and low population density meant that it was not a high priority. Chile has only 20 volcanoes with completed geological studies seven of which have completed hazard assessments and seven more monitored to some degree. There is only one volcano observatory in Chile and until the USGS arrived on May 16th (14 days after the initial eruption) there was no real monitoring of the volcano.
The immediate threat the eruption posed caused the evacuation of over 4000 people (by the 3rd May the Chilean navy helped evacuate 3900) with forced evacuation orders. Emergency measures were also put in place including: Residents were told not to drink the water due to ash contamination; Officials distributed fresh water and protective masks; a 50km exclusion zone was placed around the town; the government issued monthly financial support to each family of between $1200 and £2200; and financial aid to small businesses was granted and a 90 day freeze on payments of loans to the state bank Banco Estado to help get businesses back on their feet. The town resembles a ghost town as people fear returning to it.
A key development and positive outcome of the disaster was the VDAP Volcano Disaster Assistance programme to aid monitoring and prediction of future eruptions. Real-time seismic monitoring began on 17th May. As a Volcanic Exclusivity Index VEI category 5 eruption (>1km^3 magma ash to 20+km) the monitoring was seen to be important in helping the Chilean government model future explosive rhyolitic eruptions. The volcano continued to experience minor eruptions for the duration of 2008, highlighting the difficulties agencies face in dealing with the aftermath of one volcanic event.
Soufriére Hills July 18 1995
Montserrat is part of a volcanic arc of islands in the Caribbean (still a British territory). In 1995 an active volcano started erupting. The MVO (Montserrat Volcano Observatory has divided the activity into four phases.
Phase 1: Summer 95 – early 98
Soufriere Hills was inactive for over 300 years there were warning signs of volcanic activity. Steam was rising from the vent and mud pools increased in temperature. The first eruption started on 18th July 95 causing the evacuation of Montserrat’s capital Plymouth and exclusion zone on the south of the Island. On June 29th at 1pm 1997 a large eruption occurred sending 5 mil m^3 of rocks and ash down the flanks of the volcano. These pyroclastic flows killed 19 people (who chose to return to their farms in the exclusion zone). The impacts of stage 1 were significant on the local population, as it caused the emigration of over half the islands population.
The activity in phases 2-5 has been significant to warrant the continuation of the exclusion zone.
Phase 2: Dec 99 – Summer 03
Phase 3: Summer 03 – spring 07
Phase 4: summer 08 – Jan 09
Phase 5: Oct 09 – Feb ’10
This phase began after 2 days of decreasing gas emissions and an hour of small earthquakes. Ash vented for the first 4 days as the dome grew and pyroclastic flows were recorded some reached places never before affected. This ended with the 5 vulcanian explosions (powerful eruptions of blocks of viscous lava/volcanic bombs) over 5 weeks Jan-Feb.
On the 11th of February 40 million m^3 (20% of northern lava dome) collapsed, causing many pyroclastic flows and surges. One blast headed down Farm valley (not previously affected) and was described by the MVO as being ‘a small lateral blast type pyroclastic surge’- familiar with the 1980 Mt St Helens eruption (adding 650 m of new coastline at Spanish Point).
The pyroclastic deposits are made up of ash and andesitic glass (porous light grey rock ejected at great speed, trapping water vapour from magma as it forms). Some can be less dense than water and floats, some contain crystals of proxene originating from mingling of Basaltic (silica-poor) and rhyolitic (Silica-rich) magma. Further explosions can occur when water comes into contact with hot ash insulated by layers on top, days after the initial explosion.
The 11th Feb event generated ash clouds 12000m high, the SW winds caused the ash flow to fall only on parts of eastern Montserrat mainly falling on Islands inc: Antigua, Guadeloupe, Dominica and St. Lucia.
Monitoring
Note: Volcanologists can at least know where eruptions can take place, however, seismologists do not have this slight advantage.
Current monitoring of Soufriere Hills is carried out by the MVO with several stations throughout the island, powered by solar panels to supply a continuous flow of data (however pyroclastic surges, flows and lahars put stations out of service). However on the 11th Feb a monitoring station was only 2m away from a singe zone of a pyroclastic flow. There are also 4 monitoring stations set up by a British-American research project (SeaCALIPSO) containing a tilt and strain meter in a 200m deep borehole. There are also 2 additional stations to detect air pressure variations caused by gas eruptions, as well as webcams on the MVO itself, however, completely useless in heavy cloud cover although there is a thermal camera overcoming the problems of low visibility.
Seismometers – Detect earthquakes appearing in swarms before and eruption, indicating if dome collapse is likely.
GPS units – Measure bulging of the island as magma builds up in the magma reservoir below the dome.
Gas spectrometers – detect patterns of release of sulphur dioxide, a measure of the permeability of the underground ‘magma tunnels’.
Montserrat – 63km^3
In the 1995 eruption the capital city, Plymouth was destroyed and villages and farmland to the south was evacuated. Agriculture, industry, landforms, land-use, demography, politics and culture have all undergone enormous changes as a result. Montserrat experienced a mass exodus of its population. Between 95-99 the population decreased from 10,000 to 3,000 and rising to just over 5,000 by 2006. The displaced islanders settled mainly in Antigua (a neighbouring island) the UK and the USA. Throughout the 20th century the island has experienced out migration, such as in the wake of hurricane Hugo in 1989. Those that left during the 90’s were predominantly from economically active age groups. Therefore the island experienced a loss of economic potential. Although another impact is that there have been and influx of workers from other Caribbean islands seeking work in mainly in construction.
One on the points of the islands sustainable development plan (08-20) is to achieve a sustainable population. The government hopes to develop and implement population, labour and immigration policies to enhance the growth of the population, and to attract its current population with new initiatives as well as to facilitate the growth in population.
Some of the people affected by the eruption have stayed on the island have experienced worsening of respiratory diseases (however these have been well controlled), caused by christobalite, an element found in ash. Although there have bee other health issues such as post traumatic stress disorder, not aided by the crowded evacuation centres post eruption.
Enrolment in all streams of school dropped from 2,672 in 95 to 620 in 98, causing the amalgamation of the two secondary schools on the island. Although there was problems in staffing the schools as most came form other Caribbean islands (8/35 staff left the school at the end of 2009). Since, a new community collage has opened next door to the secondary school in 2005, with new methods of teaching to improve the education and set put students on better footing for the future.
Economic impacts
The island is still struggling to deal with the economic impacts from the eruption. The land adjacent to the volcano was the most fertile, but was made agriculturally useless by the eruption, putting 300 farmers out of work. The island was previously self sufficient with many crops, but now relies heavily on imports (it was once famous for its lime crops which are now hard to come by). Although following a government campaign many households grow their own crops.
Manufacturing
The island hosted assembly-type and food production plants before the eruption, and the industry was strong dominated by rice mills. Until the evacuation on the capital city the island hosted its own offshore medical school (the American university of the Caribbean) which employed dozens of staff and 400 students – significant spenders in the local economy.
Future plans to rebuild the economy include increasing the ash processing industry, and construction of a new capital city in Little bay.
Tourism
The airport and port were in the exclusion zone with huge areas of the island out of bounds and advice given to tourists not to visit the industry suffered greatly. In 04 a £5mil grant was secured form the department for international development, some of which used for hotel and villa construction and some on hiring a consultant’s team from Scotland called ‘team tourism’. Targets were made to widen their tourist base. At the height of the eruption in 2007 the annual number of tourists was 4,000, by 04 a ferry twice a day linked Montserrat with Antigua with the estimated number of tourists reaching 15,000. However this ferry service ceased in 2005 and numbers shrunk to 9,500, Caused by the limited size of the airport and ferry.
Energy
Is one of the economic challenges facing the island. It relies upon insufficient diesel generators. The islands sustainable development programme identified renewable energy identified it as a priority. Geothermal energy id the main focus, with solar tidal and wind not efficient enough due to the location and other factors and a suitable aquifer and fresh water has been found in foxes bay in zone c of the exclusion zone. The planned capacity of this small plant would be 2-3 MV, enough to sustain the current population size. However, the project is struggling to fund meaning that the island is still susceptible to rising oil prices.
Environment
The ash from the 11th Feb eruption disturbed air travel over neighbouring Caribbean islands, mainly eastern Caribbean, as well as causing millions of pounds of damage to banana and other cash crops. Te eruption also destroyed 1/3 of the islands tropical rainforest and wildlife slowing the growth of vegetation in the short term. (although after time will improve the fertility of the soil)
Nevado Del Ruiz Nov (Columbia) 13 1985
On November 13 1985 after 69 years of dormancy, the Nevdo Del Ruiz eruption caught nearby towns unaware, even though the government had received warnings to evacuate the area from multiple volcanological organizations. Geologists observed an increasing level of seismic activity near Nevado Del Ruiz. Other signs of a forthcoming eruption included increased fumarole activity, deposition of sulfur on the summit of the volcano, and small phreatic eruptions.
The mission's report (indicating a direct release of magma into the surface environment.) delivered on October 22, 1985, judged the risk of lahars to be very high. The report proposed various simple preparedness techniques to local authorities.
At 3:06 pm, on November 13, 1985, Nevado del Ruiz erupted, ejecting dacitic tephra more than 30km into the atmosphere. The total mass of the erupted material (including magma) was 35 million tonnes—only 3% of the amount that erupted from Mount St. Helens in 1980. The eruption reached a value of 3 on the Volcanic Explosivity Index.
The eruption produced pyroclastic flows that melted summit glaciers and snow, generating four thick lahars that raced down river valleys on the volcano's flanks. They ran down the volcano's sides at an average speed of 60 km per hour, eroding soil, dislodging rock, and destroying vegetation. The lahars were directed into all of the six river valleys leading from the volcano. While in the river valleys, the lahars grew to almost 4 times their original volume. In the Gualí River, a lahar reached a maximum width of 50m.
One of the lahars engulfed the town of Armero which lay in the Lagunilla River valley, killing more than 20,000 of its almost 29,000 inhabitants (only one quarter).The second lahar, which descended through the valley of Chinchiná River, killed about 1,800 people and destroyed about 400 homes in the town of Chinchiná. In total, over 23,000 people were killed and approximately 5,000 were injured. More than 5,000 homes were destroyed.
The relief efforts were hindered by the composition of the mud, which made it nearly impossible to move through. By the time relief workers reached Armero twelve hours after the eruption, many of the victims with serious injuries were dead.
The event was a foreseeable catastrophe exacerbated by unawareness of the volcano's destructive history; geologists and other experts had warned authorities about the danger. On the day of the eruption, several evacuation attempts were made, but a severe storm restricted communications. Many victims stayed in their houses as they had been instructed, believing that the eruption had ended. The noise from the storm may have prevented many from hearing the sounds from Ruiz until it was too late.
Hazard maps showing Armero would be completely flooded after an eruption were (poorly) distributed more than a month before the eruption, but the Colombian Congress criticized the scientific and civil defense agencies for scaremongering.
Another factor was the storm that hit that evening, causing electrical outages and hindering communications. Civil defense officials from four nearby towns tried to warn Armero the lahar was approaching in the hour or so before it reached Armero, but failed to make radio contact.
Hours before the eruption there were several long-period earthquakes, which start out strong and then slowly die out, had occurred in the final hours before the eruption, the scientists who were studying the volcano at the time of the eruption were not able to read this signal.
As the Armero tragedy was exacerbated by the lack of early warnings, unwise land use (building in and around low lying land – rive valleys) (clearing land for agriculture), and the unpreparedness of nearby communities, the government of Colombia created a special program (Oficina Nacional para la Atencion de Desastres, 1987) to prevent such incidents in the future.
All Colombian cities were directed to promote prevention planning in order to mitigate the consequences of natural disasters, and evacuations due to volcanic hazards have been carried out. About 2,300 people living along five nearby rivers were evacuated when Nevado del Ruiz erupted again in 1989.
Mt. Pinatubo June 1991
In June 1991, the second largest volcanic eruption of the twentieth century* took place on the island of Luzon in the Philippines, 90 kilometers northwest of the capital city Manila. Up to 800 people were killed and 100,000 became homeless following the Mount Pinatubo eruption, which climaxed with nine hours of eruption on June 15, 1991. On June 15, millions of tons of sulfur dioxide were discharged into the atmosphere, resulting in a decrease in the temperature worldwide over the next few years.
Mount Pinatubo is part of a chain of composite volcanoes along the Luzon arc on the west coast of the island. The arc of volcanoes is due to the subduction of the Manila trench to the west. The volcano experienced major eruptions approximately 500, 3000, and 5500 years ago.
The events of the 1991 Mount Pinatubo eruption began in July 1990, when a magnitude 7.8 earthquake occurred 100 kilometers (62 miles) northeast of the Pinatubo region. In mid-March 1991, small earthquakes could be felt and vulcanologists began to study the mountain. (Approximately 30,000 people lived on the flanks of the volcano prior to the disaster.) On April 2, small explosions from vents dusted local villages with ash. The first evacuations of 5,000 people were ordered later that month.
Earthquakes and explosions continued. On June 5, a Level 3 alert was issued for two weeks due to the possibility of a major eruption. The extrusion of a lava dome on June 7 led to the issuance of a Level 5 alert on June 9, indicating an eruption in progress. An evacuation area 20 kilometers (12.4 miles) away from the volcano was established and 25,000 people were evacuated. On June 10 Clark Air Base, a U.S. military installation near the volcano, was evacuated. The 18,000 personnel and their families were transported to Subic Bay Naval Station and most were returned to the United States. On June 12, the danger radius was extended to 30 kilometers (18.6 miles) from the volcano resulting in the total evacuation of 58,000 people.
On June 15, the eruption of Mount Pinatubo began at 1:42 p.m. local time. The eruption lasted for nine hours and caused numerous large earthquakes due to the collapse of the summit of Mount Pinatubo and the creation of a caldera. The caldera reduced the peak from 1745 meters (5725 feet) to 1485 meters (4872 feet) high is 2.5 kilometers (1.5 miles) in diameter.
Unfortunately, at the time of the eruption Tropical Storm Yunya was passing 75 km (47 miles) to the northeast of Mount Pinatubo, causing a large amount of rainfall in the region. The ash that was ejected from the volcano mixed with the water vapor in the air to cause a rainfall of tephra that fell across almost the entire island of Luzon. The greatest thickness of ash deposited 33 centimeters (13 inches) approximately 10.5 km (6.5 mi) southwest of the volcano. There was 10 cm of ash covering an area of 2000 square kilometers (772 square miles). Most of the 200 to 800 people (accounts vary) who died during the eruption died due to the weight of the ash collapsing roofs and killing to occupants. Had Tropical Storm Yunya not been nearby, the death toll from the volcano would have been much lower.
In addition to the ash, Mount Pinatubo ejected between 15 and 30 million tons of sulfur dioxide gas. Sulfur dioxide in the atmosphere mixes with water and oxygen in the atmosphere to become sulfuric acid, which in turn triggers ozone depletion. Over 90% of the material released from the volcano was ejected during the nine hour eruption of June 15.
The eruption plume of Mount Pinatubo's various gases and ash reached high into the atmosphere within two hours of the eruption, attaining an altitude of 34 km (21 miles) high and over 400 km (250 miles) wide. This eruption was the largest disturbance of the stratosphere since the eruption of Krakatau in 1883 (but ten times larger than Mount St. Helens in 1980). The aerosol cloud spread around the earth in two weeks and covered the planet within a year. During 1992 and 1993, the Ozone hole over Antarctica reached an unprecedented size.
The cloud over the earth reduced global temperatures. In 1992 and 1993, the average temperature in the Northern Hemisphere was reduced 0.5 to 0.6°C and the entire planet was cooled 0.4 to 0.5°C. The maximum reduction in global temperature occurred in August 1992 with a reduction of 0.73°C. The eruption is believed to have influenced such events as 1993 floods along the Mississippi river and the drought in the Sahel region of Africa. The United States experienced its third coldest and third wettest summer in 77 years during 1992.
Overall, the cooling effects of the Mount Pinatubo eruption were greater than those of the El Niño that was taking place at the time or of the greenhouse gas warming of the planet. Remarkable sunrises and sunsets were visible around the globe in the years following the Mount Pinatubo eruption.
The human impacts were severe, in addition to up to 800 people who lost their lives, there was almost one half of a billion dollars in property and economic damage. The economy of central Luzon was horribly disrupted. In 1991, the volcano destroyed 4,979 homes and damaged another 70,257. The following year 3,281 homes were destroyed and 3,137 were damaged. Damage following the Mount Pinatubo eruption was usually caused by lahars - rain-induced torrents of volcanic debris that killed people and animals and buried homes in the months after the eruption. Additionally, another Mount Pinatubo eruption in August 1992 killed 72 people. Pyroclastic flow deposits still hold temperatures as high as 900°F (500°C) in 1996 and may retain heat for decades. [Global impact as well as Iceland]
Short comparison: Pinatubo – 800 deaths approximately 6 from the eruption itself, 70 from lahars suffocation and 700 from diseases such as cholera due to lack of immediate management (even though an evacuation happened). Good comparison with Mt St. Helens as both knew their volcanoes were about to erupt showing there is monitoring (inc monitoring equipment) at many if not most plate boundaries. So prediction technology saves lives (evacuation) Mt St. Helens only killed as direct result of pyroclastic flow when people went back into area.
Population density can result in more people at risk, although, a counter point – location size type, weather conditions. Economic damage to local’s government step in? St. Helens it was the local economy mostly tourism.
The United States military never returned to Clark Air Base, turning over the damaged base to the Philippine government on November 26, 1991. Today, the region continues to rebuild and recover from the disaster.
Fortunately, scientists from the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey had forecast Pinatubo's 1991 climactic eruption, resulting in the saving of at least 5,000 lives and at least $250 mislion in property. Commercial aircraft were warned about the hazard of the ash cloud from the June 15 eruption, and most avoided it, but a number of jets flying far to the west of the Philippines encountered ash and sustained about $100 million in damage.
1996 - About 20,000 indigenous Aeta highlanders, who had lived on the slopes of the volcano, were completely displaced, and most still wait in resettlement camps for the day when they can return home. About 200,000 people who evacuated from the lowlands surrounding Pinatubo before and during the eruptions have returned home but face continuing threats from lahars that have already buried numerous towns and villages. Rice paddies and sugar-cane fields that have not been buried by lahars have recovered; those buried by lahars will be out of use for years to come.
Example Essay – ‘Physical factors cause the greatest impact to volcanic events’ – discuss.
Volcanic events vary in size frequency and type around the world but it can be argued that these physical factors cause the greatest impact as they are uncontrollable and create the ‘initial’ impact which we can only manage and are therefore what causes the impact. On the other hand it could be said that there are many factors which affect the impacts, both human and physical.
As stated it could be argued that physical factors are what the impact of volcanic events depends primarily on, because these are the factors behind the event. The eruption of Iceland for example in 2010 had 2 phases both physically very different. On March 20th the first eruption began lasting for 6 weeks; it gained little interest from the rest of the worldwide media as the eruption was not dominated by explosive events and caused little impact to the rest of the world. This was due to the low viscous nature of the lava allowing trapped gas bubbles to escape, this also produced little ash. In contrast with the second phase on April 14th which caused a great impact globally, but mainly to Northern Europe. The physical factors which caused the impact to be so great was the high viscosity of the lava coupled with the fact that the volcano was ice capped, this produce vast amounts of ash (250,000m3)as melt water rapidly cooled the lava which was released straight into the jet stream, located directly above the volcano. The eruption measured 4 on the Volcano explosivety index, and the ahs was of a fine glassy consistency, this resulted in the force of the eruption able to project the material 27,000ft into the atmosphere which was then able to travel an extremely large distance (3000miles) over northern Europe. The impact of this was mainly economic closing airports in 14 nations for 6 days (14th-20th) costing the UK airline industry £10 million per day. As well as having wider effects on the developing world who could not sell their produce due to flights being grounded, consequently some businesses went out of business, arguably a result of the physical factor of the nature of the eruption.
Further to this volcanic eruptions also differ in frequency, length and magnitude as well as simply nature. The eruption of Mt. Etna in Sicily could be deemed to be ongoing as and eruption has been seen every year since 2001. Although these tend to have more of a localised impact due to the uncharacteristic low viscous nature of the lava, despite the volcanism being a result of seduction activity. It was this feature which caused the 1991 eruption to last for 2 years as the lava was able to travel a large distance threatening a considerable population on Etnas slopes and the town of Zafferana. Magnitude is another factor regarding the impact of volcanic events, the eruption of Mt. St. Helens on May 18th 1980 was measured as a 6 on the VEI it produced a plume of ash that rose 17km high. However, its real destructive nature came as a result of its lateral blast, which was both unexpected and deadly killing 40 people. The landslide was the largest recorded in human history and a result of the high viscosity lava which solidified and blocked the vent. All three eruptions were the result of a different underlying physical makeup that being the type of plate boundary, lava type and surface interactions. It can therefore be argued that it is the unique physical nature of each event which causes the impact.
However, I believe it is human factors such as population density, land use and infrastructure which exacerbate the initial impact and cause an event to become a natural disaster. During the eruption of Nevado del Ruiz in Columbia on November 13th 1985 4 large lahars were created by the mixing of ash and sediments with melt water from the melted glacier atop the volcano. The lahars raced down river valleys (at 60km/h) that provided a natural path towards settlement of whichmuch of the land had been cleared for agriculture providing little resistance. All 6 river valleys were filled, where nuch of the population was located as it provided as a means for travel. In some places they reached 50m wide and grown to almost 4 times their original volume. They engulfed the town of Amero which was located in the Lagurilla river valley killing more than 20,000 of the 29,000 inhabitants. The second lahar descended through the Chinchina river valley killing around 1,800 people and destroying 400 homes. This was the most destructive force of the eruption as it mixed with pyroclastic flows, in total killing around 23,000 people. If proper adherence to warning and land use and hazard mapping had been implemented more lives may have been saved.
Another factor which exacerbated the impact of volcanic events is preparedness. Although eruptions are essentially impossible to predict it is possible to estimate the level of danger and eruption may pose with adequate monitoring. The Chaiten eruption on May 2nd 2008 came as a surprise to inhabitants of the town of Chaiten, situated only 10km south of the volcano. Previous eruption records had shown the volcano to be a threat however, due to the length of time it has lain dormant (9000 years) it was not considered an active one. Chile only has one volcano observatory for a region that is very active in activity, prior to the eruption small scale seismic activity was observed. Although no warning of an imminent eruption was given the Chilean army and Navy evacuated 4000 residents of the town (with only one death caused by shock). This was due to the frequent nature of volcanic threats in the region, and although initially unprepared the government was able to mitigate the impact by quick and decisive action.
The ability for a government to provide aid following a natural disaster is also a factor which can both negate or heighten the impact. In response to the Nevado del Ruiz eruption the government sent relief workers to help with recovery however, relief workers took 12 hours to reach the town of Amero, by which time many victims who had survived the initial effects were dead. Added to this many workers lacked basic rescue materials such as shovels and tools due to insufficient provisions hindering relief efforts. In response to the Soufriere Hills eruption on Montserrat in July 1995 the infrastructure inadequacies and lack of, made communications difficult and aid hard to obtain. Although Montserrat is a UK colony it lacks many UK standards, during the eruption 50% of the water supply network was destroyed and it took days for international aid to arrive to relieve this. Some aid was also inappropriate and Montserrat now relies on diesel generators which put it in a difficult position for future development with rising fuel prices and inefficient energy production. In comparison with this eruption on Mt. Etna prompted the Italian government to provide $8 million in tax breaks to villagers following the 2002 eruption, indication that although a lack of or inadequacy in providing aid can be detrimental factor to the impact of such events it can also be a mitigating factor.
Lastly management is perhaps the most important human factor with regards to reducing or in some cases increasing the impact felt. During the 1991-1993 eruptions of Mt. Etna the town of Zafferana was threatened by a lava flow. The Italian government initially constructed earth and rock barriers to divert the flow but this failed to work. Explosives were then used to break up a very efficient lava tube system that had carried the lava 7km down slope which was successful in 1993. Only one house was destroyed a few hundred metres from the towns boundary. Again in 2002 earth barriers were constructed by the Italian government’s heavy earth lifting equipment which successfully stopped a lava flow destroying the tourist station and Refugio Saffarenza. Mt. Etna has constant sophisticated management schemes in comparison with Nevado Del Ruiz which had no permanent monitoring. Although geologists and other experts had warned of imminent eruptions which the Columbian authorities had chose not to convey the severity of to its people. Many victims had stayed in their homes as instructed. The event was a foreseeable catastrophe exacerbated by the unawareness of the volcanoes destructive history.
Overall the impact of volcanic events is dependent on both physical and human factors, it could be said that the larger the initial event the greater it is overall. However it is considerably made worse with the greater level of human factors that add to this impact. As there is nothing we as humans can do to prevent these events and much more to prepare and avoid them the emphasis is on impact should be aimed at humans seeking to cause it as little as possible, and not take for granted the physical factors which drive them and are much larger on a whole.
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