Geography- Restless Earth

AQA, A specification, Restless earth 1A, physical geography

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Tectonic Plates

  • We live on the earth's crust, its only 20km thick
  • At the centre of the earth there is a core made of solid nickel and iron
  • around the core is the mantle which is semi-molten rock which moves slowly 
  • the crust is divided into tectonic plates, 2 types
    • oceanic- thinner and more dense (5km thick)
    • continental- thicker and less dense
  • the plates are moving because the rock underneath the mantle is moving due to convection currents
  • the places where plates meet are called plate boundaries
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Destructive plate margins

(or compressional)- e.g. along east coast of Japan

  • push together- moving together
  • denser oceanic crust sinks below the lighter continental crust
  • oceanic crust sinks into the magma in mantle where it melts in the subduction zone
  • energy builds up, can be released as an earthquake
  • or the molten magma rises up causing a volcanic eruption- composite cones
  • the continental crust becomes crumpled into fold mountains or ocean trenches

(http://upload.wikimedia.org/wikipedia/commons/a/af/Destructive_plate_margin.png)

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Constructive plate margins

(or tensional) e.g. at the mid-Atlantic ridge

  • Moving in opposite directions- apart
  • mostly happens under oceans
  • plates move apart and the gap is filled by magma rising from the mantle which cools creating a new crust, shield volcanoes and volcano islands (like Hawaii)

(http://www.frankswebspace.org.uk/ScienceAndMaths/physics/physicsGCSE/bytesize%20images/techPlateBoundaries1.gif)

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Conservative plate margins

(or passive)

  • moving past each other (sideways)
  • move in same direction
  • or if one moving slightly faster, pressure builds up along the fault line until one plate jerks past the other which causes an earthquake
  • e.g. along west coast of USA

(http://4.bp.blogspot.com/-zrhRd2VNC8I/TZ32exvtFUI/AAAAAAAAABU/xiuHrVlzVqA/s1600/transform.jpeg)

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Ocean Trenches

  • mostly around sides of pacific ocean
  • subduction zone is an ocean trench- one wall is formed by sub-ducted ocean plate, the other by overriding continental plate
  • trenches are very deep
  • inaccessible to humans
  • ocean area of greatest importance- continental shelf
    • shallow zone- less than 200m deep, off the coast
      • used for fishing and drilling for oil and gas
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Formation of Fold Mountains

  • form along destructive plate margins
  • there were long periods of quite between earth movements and sedimentary rocks formed in huge depressions called geosynclines
  • rivers carried sediments and deposited them into the depressions
  • over millions of years sediments were compressed into sedimentary rocks like sandstone and limestone
  • sedimentary rocks were forced upwards into a series of folds when the oceanic and continental plates collide
  • sometimes folds simple up-folds (anticlines) and downward folds (synclines)
  • in some places the folds are pushed to one side causing over-folds
  • e.g. the Andes
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Physical problems of fold mountains

Relief: high and steep

  • mountain valleys= narrow and gorge like
  • little flat land for forming settlements

climate:, increasing height becomes colder, windier, wetter and more snow

  • short growing season
  • often impossible to grow crops at such high levels

soils- stoney, thin and infertile

Accessibility, roads and railways= expensive and difficult to build

  • travel disrupted by frequent rock falls, avalanches and bad weather

Are exceptions: parts of Andes well settled, Chile and Bolivia rich in minerals like silver and gold

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Uses of fold mountains

Farming: higher mountain slopes aren't good for growing crops so used for grazing animals like mountain goats

  • lower slopes used for growing crops, steeper slopes sometimes terraced to make easier

Mining: major source of metal ores

  • steep slopes make access difficult so zig-zag roads have to be carved out the sides of the mountain

Tourism: spectacular scenery which attracts tourists, winter- skiing, snowboarding, summer- walkers

  • tunnels have been cut through fold mountains to make straight fast roads improving communications

Hydro-electric power- steep sided slopes and high lakes makes them ideal

forestry- good environment to grow conifers, used for things like fuel and paper

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Case Study- The Alps

where? Europe, France/Italy border

Formation: about 30 million years ago by a collision between African and Eurasian plate

tallest peak: mont blanc at 4810m

population: about 12 million

Farming:

  • on the sunnier, warmer side of slopes
  • uses transhumance- seasonal movement of animals
    • summer- cattle taken to high Alps to graze allowing crops to grow
    • winter- return to valley floor in cattle sheds
  • change over years:
    • cable cars used to transport milk to dairy's
    • farmers buy additional food so can remain on valley floor all year
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Case Study- The Alps, tourism

Tourism:

  • 100 million tourists visit each year
  • 70% of tourists visit the Alps in the winter for skiing, snowboarding and ice climbing
    • flatter land on higher levels easier to build on
  • in the summer tourists visit for walking, mountain biking, climbing
    • steep slopes and scenery ideal
  • new villages have been built to cater for tourists e.g. tignes in France
  • worry is that winters are warming up so there is less snow
    • more people skiing on worn slopes
    • damages vegetation and the surface below
    • increases number of bare slopes and risk of soil erosion
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Case Study- The Alps, HEP, Mining, Forestry

Hydro-Electric Power (HEP)

  • steep slopes, high precipitation and summer melting of glaciers makes fast flowing rivers which are ideal
  • valleys are narrow
    • easier to dam and there are lots of lakes to store water
    • e.g. In the Berne area in Switzerland
  • some cheap HEP is used by industries which require high input of electricity e.g. sawmills and fertiliser manufacture
  • 60% of Switzerland's electricity is from HEP in the Alps, its used locally and transported further away

Mining- salt, iron ore, gold, silver and coper are mined

Forestry- Scots pine is planted because its more resilient to the goats which kill native tree saplings, the trees are logged and used for things like furniture

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Case Study- The Alps, adaptations and comparison

Adaptations:

Steep relief: goats are farmed- well adapted to live on steep mountains, trees and man-made defences used to protect against avalanches and rock fall

Poor soils- animals grazed in areas where soil isn't good for crops

limited communications: roads have been built over passes e.g. Brenner pass between Austria and Italy- takes long time and can get blocked by snow so tunnels have been cut through the fold mountains to provide fast transport links e.g. Schoenberg base tunnel

Comparisons to other fold mountains

  • not mineral rich like Andes
  • well populated compared to most fold mountains
  • countries are rich- able to overcome high mountain transport problems because have money and technology.
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Volcanoes

  • found at destructive and constructive plate margins
  • a volcano= cone shaped mountain formed by surface eruptions from magma chamber
  • At destructive margins
    • The oceanic trench moves down into the mantle, where its melted and destroyed
    • a pool of magma forms
    • the magma rises through cracks in the crust called vents
    • the magma erupts onto the surface (lava) forming a volcano
  • At constructive margins
    • magma rises up into the gap created by the plates moving apart
  • some volcanoes form over parts of the mantle that are really hot (hotspots) e.g. Hawaii
  • The worlds distribution of volcanoes shows almost perfect fit with tectonic plate margins
  • each time there is a volcanic eruption a new layer of lava is added to the surface of the volcano
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Types of volcano

Composite volcanoes- e.g. mount Fuji in Japan, Mount Etna, Vesuvius

  • lava is usually thick and flows slowly it hardens quickly forming a steep sided symmetrical volcano
  • made up of ash and lava in alternate layers, lava cools inside and next eruption there will be an explosion
  • subsidiary cones and vents form

Acid lava volcano (or cinder volcano, or Dome volcano) e.g. Mount Pelee in caribbean

  • made only of lava- steep cone with narrow base
  • lava is thick and flows slowly forming a steep sided volcano
  • eruptions are explosive

Shield Volcano- Mount Loa on Hawaiian islands

  • lava is runny and flows quickly and spreads over a wide area forming low, flat volcano, made only of lava, frequent non violent eruptions
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Picture of types of volcano

(http://media.tiscali.co.uk/images/feeds/hutchinson/ency/c02745.jpg)

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Super Volacanoes

A supervolcano is much bigger than a standard volcano, the erupt with massive volumes of material and develop over hotspots e.g. yellowstone national park

How?

  • magma rises through cracks in the crust forming large magma basin below the surface, the pressure of the magma causes a circular bulge on the surface
  • the bulge cracks creating vents for lava to escape through, lava erupts out of vents causing earthquakes and sending up gigantic plumes of ash and rock
  • as the magma basin empties the bulge is no longer supported so collapses
  • when the eruption finishes there is a big crater (caldera) left where the bulge collapsed, sometimes these get filled with water to form a large lake e.g. Lake Toba in indonesia

characteristics

  • flat, cover a large area, have caldera
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Global consequences of a super volcano

Last known eruption about 75,000 years ago

  • so much dust would circulate in the atmosphere it could lead to a 'volcanic winter' which would lower global temperatures because less sunlight would reach the surface- mini ice age
  • a thick cloud of super-heated gas and ash would flow at high speed from the volcano, killing, burying and burning everything it touches
  • releases a lot more material
    • Mount St Helens in USA in 1970 released 1km3 of material but if a supervolcano erupted it would alter the landscape of hundreds if not thousands of kilometres
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Volcanoes good or bad?

Primary effects- immediate impact

  • people die/injured
  • houses/buildings/businesses/ farm land destroyed
  • communications disrupted/destroyed
  • public services disrupted

Secondary Effects- medium and long term impacts

  • healthcare not able to access- more people die
  • loss of income/homeless/ no food- more die
  • economic problems- cost of rebuilding
  • grief- family stress
  • water contamination- disease and death

Benefits: fertile soil, tourism (hot springs) industry (minerals- sulphur, borax, pumice), generating power and heating things (geothermal power)

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Warning signs of volcanic eruption

  • Small earthquakes
  • increased emissions of steam and gases
  • visual signs of bulging around crater

in rich countries e.g. Italian volcanoes they are constantly monitored

  • electronic tiltmeters- measure very small changes in the profile of mountain
  • because of difficulties putting instruments into the crater satellites are used to measure the infra-red radiation and look for changes in heat activity
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Case Study- Montserrat- LEDC

The soufriere hills Montserrat

  • main eruption 25th June 1997, started in july 1995
  • 4-5 million m3 of rocks and gas released
  • 19-23 people killed

Cause:

  • above a destructive plate margin where the Atlantic plate is being forces under the Caribbean plate
  • magma rose up at weak points under the soufriere hills forming underground pool of magma
  • rock above pool collapsed, opening the vent and causing an eruption
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Timeline of Montserrat

July 1995- first eruption- signs of volcanic activity

August 1995- 50% population evacuated

1996- finally erupted-mudflows then pyroclastic flows, part of dome collapsed

April 1996- eruption continues

June 1997- eruption killed 23 people and lava became more explosive

Few months later- Plymouth burned to ground and covered with ash

Only 39/103 square kilometres were considered safe

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Case Study, Montserrat- Impacts

Primary:

  • large areas were covered with volcanic material- capital city Plymouth was buried under 12m of mud and ash
  • over 20 villages and 2/3 of homes on the island were destroyed by pyroclastic flows
  • schools, hospitals, the airport and the port were destroyed
  • vegetation and farmland destroyed
  • 19-23 people died and 7 were injured

Secondary:

  • fires destroyed buildings- local government offices, police headquarters and main petrol station
  • tourists stayed away, businesses destroyed- disrupting the economy
  • population decline- 8000/12000 have left since eruptions began
  • volcanic ash improved soil fertility
  • tourism now increasing as people come to see the volcano
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Case Study, Montserrat- Responses

Immediate:

  • people were evacuated from the south to safe areas in the north
  • shelters were built to house evacuees
  • temporary infrastructure built e.g. roads and electrical supplies
  • The UK provided £17 million of emergency aid
  • local emergency services provided support units to search for and rescue survivors

Long term:

  • A risk map and an exclusion zone is in place, south of island is off limits as volcano is still active
  • UK provided £41 million to develop north of island- new docks, airport and houses
  • the Montserrat Volcano Observatory has been set up to try and predict future eruptions
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Earthquakes

= vibrations in the earth's crust which shake the ground surface- some too small to feel

happen on all 3 plate margins

  • destructive- tension builds up when one plate gets stuck as its moving down past the other into the mantle
  • constructive- tension builds along cracks within the plates as they move away
  • conservative- tension builds up when plates are grinding past each other get stuck

Pattern= around tectonic plates

  • lots around west side of south American plate
  • lots around Philippine plate
  • on African plate marks out practically the whole margin
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The Richter scale

  • Measures magnitude (energy released) of an earthquake
  • measured using a seismograph
  • doesn't have an upper limit (normally between 1-10)
  • its logarithmic- means that an earthquake with magnitude of 5 is 10 times more powerful than one with a magnitude of 4
  • most people don't feel earthquakes of magnitude 1-2
  • major earthquakes are above 5
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The Mercalli Scale

Used to indicate intensity/effects of an earthquake

effects are measured by asking eye witnesses of what happened, and takes into account effects on Earth's surface, people and buildings

given a number between 1-12, sometimes Roman numerals

I (1)- rarely felt by humans

II-IV (2-4)- feeble to moderate effects- felt by people indoors

V-VII (5-7) strong effects, causing panic felt by everyone, structural damage

VIII (8) destructive to poorly built structures only slight damage to those well designed

IX-XII (9-12) ruinous, disastrous, total destruction

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Why Do Earthquakes Happen?

90% occur where plates are colliding

focus= point at which the earthquake originates- waves stronger and do more damage

Epicentre= the point on the surface directly above the focus where greatest force of the earthquake is felt

Shock-waves= radiate out in all directions gradually becoming less strong as you get further away from the epicentre

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Effects of Earthquakes

Primary:

  • collapsing buildings, bridges and roads- people are killed by being trapped
  • severity of primary effects depends on human and physical factors
  • chance effect- time of day- were fewer people closer to epicentre?

Physical and human factors of high magnitude earthquake

  • shallow focus
  • sands and clay vibrate more (e.g. Mexico city)
  • High density population lack of emergency procedures (e.g. Gujarat India)
  • residential area of city- self built housing, 

Physical and human factors of low magnitude earthquake

  • focus deep underground, hard rock surface (e.g.seattle)
  • low density population- urban areas with open spaces
  • earthquake proof buildings, regular drills
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Secondary effects of earthquakes

Fires- caused by fractured gas pipes, bringing down electricity cables- spread quickly in areas of poor quality housing

Tsunamis- giant sea wave- really dangerous in areas of low lying coasts

landslides- most likely on steep slopes and in areas of weak rock

disease- typhoid and cholera spread easily when pipes burst- leads to shortage of water and contamination

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Impacts of earthquakes

rich= specialist rescue teams with sniffer dogs and lifting equipment, medical teams and field hospitals, helicopters

poor= greater reliance on short term aid from overseas

medium term- quick return to normal life by replacing and repairing what has been lost and restarting economic activity focus from disaster aid ----> development aid

earthquakes cannot be predicted  need to be prepared

emergency services need to be trained and ready, disaster relief requires practise

tall buildings are more likely to remain standing if built using these methods:

  • damping and bracing to support from shocks
  • foundation piles made from alternate layers of steel and rubber to make flexible so its stiff vertically and flexible horizontally
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Case Study- Kobe MEDC

When: 17th January 1995

7.2 on the Richter scale

because the Eurasian and Philippine plate collided and it runs directly under city

6,430 died

the worst effected was around the bay

earthquake lasted 20 seconds but longer on reclaimed land

Kobe was 20km away from the focus (point at which earthquake originates)

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Case Study- Kobe,effects

Primary:

  • road and rail lines destroyed
  • buildings and houses destroyed- people killed
  • homes destroyed- old town mainly wooden structures so collapsed easily

Secondary:

  • because no road networks- hard for emergency aid
  • not enough space in hospitals and not enough services for those in need- more deaths
  • gas pipes broken- fires destroy homes and buildings, burn people to death and destroy businesses
  • No services- gas, electricity
  • supplies not getting through
  • grief because of loss of family and friends
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Case Study- Kobe, Aid

Short Term:

  • dig through rubble for survivors
  • water, food and medicine

long term:

  • rebuilding
  • redevelopment
  • prevention and planning
  • insurance claims
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Japan Physical and effects on Kobe

reclaimed land- allowed shock waves to travel through easily

string of islands

lots of plates so experience many earthquakes

many buildings designed to sway

Effects on Kobe

  • sannomiya- many houses collapsed, several fires and general damage
  • hanshin express way- multiple collapsed spans over 20km stretch
  • Hankyo, hanshin and JR railways- major damage to tracks and trains
  • Wangen (harbour) express way- badly damaged, partial collapse
  • Shinkasen (bullet train) major collapse
  • liquefaction cause collapse of sea walls and cranes in docks
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Case Study, Gujarat India LEDC

January 2001, 7.9 on Richter scale,result of plate movements

  • epicentre near Bhachau
  • 48hrs for rescue efforts, 20,000 dead, 16,000 injured, 600,000 homeless
  • economic loss US $2-4billion

Primary effects:

  • buildings destroyed- cheaply built, easily knocked down
  • people trapped in rubble
  • road networks destroyed

secondary effects:

  • international aid needed- poor country, little action plans and preparation in place
  • homelessness- camps, lack of food and sanitation
  • rescue workers had to use spades- took longer to find survivors so more died
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Case Study, Italy MEDC

L'aquila, Italy

6th April 2009

6.3 on Richter scale

movement along crack in the plate at a destructive margin

Preparation:

  • laws on construction standards but some hadn't been built to withstand earthquakes
  • Italy has civil protection department that trains volunteers to help with things like rescue operations
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Case Study, Italy- Effects

Primary:

  • 290 deaths, mostly from collapsed buildings
  • hundreds of people injured
  • thousands of buildings damaged or destroyed
  • thousands made homeless
  • a bridge near the Fossa collapsed and water pipe was broken near the town of Paganica

Secondary:

  • aftershocks hampered rescue efforts and caused more damage
  • fires in some collapsed buildings- more damage
  • broken water pipe near the town of Paganica caused a landslide
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Case Study, Italy- Responses

Immediate:

  • camps were set up for homeless people with water, food and medical care
  • ambulances, fire engines and the army were sent to rescue survivors
  • cranes and diggers used to remove rubble
  • international teams with rescue dogs were sent to look for survivors
  • money was provided by the government to pay rent, and gas and electricity bills were suspended

Long-term:

  • The Italian Prime Minister promised to build a new town to replace L'Aquila as the capital of the area
  • An investigation is going on to look into why modern buildings weren't built to withstand earthquakes
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Case Study, Pakistan LEDC

Kashmir, Pakistan

8th October 2005

7.6 on Richter scale

Movement along crack in the plate at a destructive margin

Preparation:

  • no local disaster planning
  • buildings were not designed to be earthquake resistant
  • communications were poor and were roads roads and they were badly constructed
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Case Study, Pakistan- effects

Primary:

  • around 80,000 deaths mostly from collapsed buildings
  • hundreds of thousands of people injured
  • entire villages and thousands of buildings destroyed
  • around 3 million left homeless
  • water pipelines and electricity lines were broken cutting off supply

Secondary:

  • landslides buried buildings and people they also blocked road access and cut off water supplies, electrical supplies and telephone lines
  • Diarrhoea and other diseases spread due to little clean water
  • freezing winter conditions shortly after earthquake caused more casualties and meant rescue and rebuilding operations were difficult
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Case Study, Pakistan- Response

Immediate:

  • Help didn't reach for days or weeks and people had to be rescued by hand without any equipment or help from emergency services
  • tents, blankets and medical supplies were distributed within a month but not to all areas affected
  • international aid and equipment such as helicopters and rescue dogs were brought in as well as teams from other countries

Long-term:

  • Around 40,000 people have been relocated to a new town from the destroyed town of Balakot
  • Government money has been given to people whose homes had been destroyed so they can rebuild them themselves
  • training has been provided to help rebuild more earthquake resistant buildings
  • new health centres have been set up in the area
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Case Study, Asian Tsunami LEDC's

26th December 2004

Earthquake off the west coast of the island of Sumatra between the Indian and Eurasian plate- triggered tsunami waves of up to34m high and the average speed was 500km/h

people displaced: about 2 million

people dead or missing: 220,000+

houses destroyed: over 500,000

Indian plate was being pushed under Eurasian

Happened along 1,040km fault line- the subduction zone

focus10km under earth's surface, epicentre 256km south of banda aceh (Indonesia)

as the sea level above earthquake returned to normal level the waves were created as it reached shallow water waves grew in height due to friction

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Case Study, Asian Tsunami

It affected many countries

affected most of the countries bordering the ocean: Indonesia, Thailand, India, Sri Lanka, Somalia and the maladives

the effects were so bad because there was no early warning system:

  • whole towns and villages were destroyed- over 1.7million lost their homes
  • infrastructure was severely damaged, Indonesia worst because closest
  • 5-6 million people needed emergency food, water and medical supplies 
  • massive economic damage
    • fishermen lost livelihoods- e.g. in Sri Lanka
    • tourism industry suffered because of destruction as people were afraid to go on holiday there- e.g. The Maldives
  • Environmental damage- salt from sea water meant plants can't grow in many areas, mangroves, coral reefs and sand dunes were destroyed by the waves
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Case Study, Asian Tsunami- Responses

Short Term:

  • within days hundred of millions of pounds had been pledged by foreign governments, charities, individuals and businesses to give survivors access to food, water, shelter and medical attention
  • foreign countries sent ships, planes and soldiers and teams of specialists to help rescue people, distribute food and water and begin clearing up
  • troops using bulldozers helped clear dead bodies into mass graves to reduce spread of disease
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Case Study, Asian Tsunami- Responses

Long-term

  • Billions of pounds has been pledged to re-build the infrastructure of the countries affected
  • as well as money, programmes have been set up to re-build houses and help people get back to work
  • A tsunami warning system has been put in place in the Indian ocean
  • Disaster management plans have been put into place in some countries. Volunteers have been trained so that local people know what to do if a tsunami happens again
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