Tectonic landscape


edexcel gcse geo
Chima  Power
Flashcards by Chima Power, updated more than 1 year ago
Chima  Power
Created by Chima Power over 9 years ago

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Distribution of earthquakes and volcanoes Earthquakes occur in long narrow bands on all three types of plate boundary both on the land and in the sea the biggest belt runs along the Pacific Ocean. Other major belts travel along the middle of the Atlantic Ocean and through the continents of Europe and Asia from the Atlantic Ocean to the Pacific Ocean. Bolcanoes also occur in long narrow bands longest called Pacific ring of fire going around the entire Pacific Ocean. Found at constructive and destructive plate boundaries, occuring on land and in sea. Sometimes found away from plate boundaries at hot spots where crust is thin.
Plate tectonics Explains why natural hazards are found at plate boundaries. The earth crust is divided into seven large and twelve smaller plates. The Earth's crust is between 10 and 100 km thick and consists of cooler solid rock floating on the hotter molten rock of the mantle.
Consistence of crust Oceanic crst is between 5 and 10 km thick denser than continental crust and being continually renewed and destroyed. Continental crust is between 25 and 100 km thick is less dense than oceanic crust and does not sink so is not destroyed.
Plate movement Most plates move a few centimeters a year causing the continents to move split apart and collide. The relative position of continents are still changing movement known as continental drifting.
Types of plate movement Some plates move toward each other convergent or destructive eg Nazca and South American Plate Some plate move away from each other divergent or constructive eg Nazca and Pacific plates Some plates slide past each other conservative or transform eg Pacific and North American plates
Plate boundaries Where plates meet also known as plate margins, areas of greast crustal stress, meeting points are where most of the world's earthquakes and volcanoes and other structural features such as fold mountains, rift valleys and ocean trenches occur.
Hotspots Where magma form the mantle erupts through the crust creating volcanoes that often rise above the ocean surface to form island. The Samoa chain formed as the Pacific crustal plate moved over the stationary source of magma or hotspot. Can be confirmed because the lava has been radiometric age dated on all the islands and Savai'l has dated at 5 million yrs old, whereas Vailulu'u is a new island that is presently being formed. This occurs as the plate moves the hotspot does not new islands are formed in progression with the youngest at the source of the hotspot.
Convergent or destructive boundaries characteristics Two plates move towards one another, where they meet on eplate is subducted below the other the cause of subduction is the difference in density between the two plates the more dense on is subducted below the ligher one there.
Convergent or destructive ocean to ocean boundaries: The Ryuku Islands are a direct relsut of destructive plate acitivity in the western Pacific. Philippine plte to the east is subducting beneath the Eurasina plate to the west. As is subducts the tremendous pressures that are released cause earthquakes. At about 100 km below the surface the subducting plate begins to melt and magma escapes to the surface fo form volcanoes. After several eruption shtes volcanoes break the ocean surface to form islands, when several islands form known as islandic arc.
Convergent or destructive ocean to continent boundary The oceanic plate is subducted by the continental plate from this a deep oceanic trench forms these are the deepest parto fo the ocean deeper than Mount Everest is tall in some cases. The heat from the mantle and friction between the two plates causes the oceanic plate to be destroyed. Consequently the friction and pressure causes earthquakes to occur along the subduction zone, the melting plate creates liquid magma that rises towards the surface to form volcanoes such as Aconcagua the highest peak in the Andes 6960m. Collision of plates also causes severe folding and uplift of the rock, process has contributed to the growht of the Andes.
Convergent or destructive continental to continental boundary Continental crust is less dense than oceanic crust and so when two continents collide the collision is slow rather than any marked subduction taking place. Results in intense folding, faulting and uplift and leads to the formation of mountains. The Indian plate grinds into the Eurasian plate at a rate of 5 cm a year.
Divergent or constructive boundaries Occur when two plates move away from each other and create a new crust, commonly occurs at the middle of the ocean. The convection currents that cause this movement are creating a gap called a mid oceanic ridge. Magma rises to fill the gap thus forming new land. Magma builds up above the surface of the ocean, volcanic islands form such as iceland
Conservative or transform boudaries Where plates move alongside each other no new crust is created nor is any destroyed and no new landforms appear. However there can be sites for violent earthquakes such as San Andreas Fault in California where both plates are moving in a north west direction but at different speeds. Pressures builds up if plate gets stuck due to friction and the plate jerk forward, sending shock waves to the surface and triggereing a sudden earthquake. There is no volcanic action because the crust is not being destroyed at conservative boundaries.
Mercalli scale Intensity of an earthquake is a measure of the violence of earth motion produced by the earthquake, mercalli determines the effect the earthquake has on humans building and local landscape through human perception. The magnitude, which has a unique value for a particular earthquake, depends on the distance of the place from the epicentre and the depth of the focus. Many places such as Hong Kong have adopted this uses 12 grades. Drawback of the Mercalli scale is a non specific set of definitions based on human perception so bias can occur also can not be used in rural areas.
Richter scale Designed to allow easier comparison of earthquake magnitudes regardless of their location created by CF Richter by taking the existing Mercalli scale and tried to add a scientific scale based on accurate measurments that could be recorded on a seismograph. This measured the violence of the ground when it suddenly moved. The richter scale measurments are logarithmic as each whole number represents a ten fold increase in power.
Focus and epicentre of an earthquake The point at which the enormous stress is released and the crust snaps si called the focus and is below the surface of the earth, the point on the ground surface immediately above the focus is called the epicenter and this is where the greatest damage usually occurs
Economic reasons for settling near volcanic activity Volcanic soils are espically fertile for instance in Naples there is a huge wine growing area, minerals such as tin, silver, gold, copper, diamonds can be found in volcanic rocks. Money tha can be made by mining these precious rocks outweighs the risk.
Social reasons for living in Volcanic activity Many people espically in LIC's can not afford to move as livelihood based on life and jobs they have in that area. People do not want to leave families and friends. People choose to stay for spiritual reasons as many people choose to live near Mount Merapi in Indonesia to worship ancient spirits which they believe will warn them of an eruption throw rice, jewellery and live animals into crater at full moon to calm spirits.
Environmental reasons for living in volcanic activity Some volcanoes are popular tourist destinations giving local population jobs for example Mount Etna in Sicily for where tourists travel to the crater by cable car.
Economic reasons to live in Earthquake activity Some earthquake areas like Turkey and Iceland are poplar tourist areas and provide many jobs for locals. Landslides triggered by earthquake tremors have caused a loss of lives . In 2007 an earthquake mesuring 7.7 hit an area of many large copper mines in Chile killing two but people make a living from mining
Social reasons for living in Earthquake activity People in MIC's feel safe in earthquake zones because of the advances that have been made in earthquake proof buildings. Since 1981 all buildings in Japan have been made earthquake proof. Also common to have disaster plans to tell people what to do in emergency. People believed the chance of them being affected by an earthquake is low.
Environmental reasons for living in Earthquake activity Some places are known for their beauty and som e individuals buy houses in exclusive areas despite potential earthquake risks eg Malibu California, people feel safer as buildings can now be built to be earthquake proof
Case study - Earthquake in Turkey 1999 Causes Earthquake of magnitude 7.4 hit Turkey, epicentre near industrial city of Izmit about 88 km east of Istanbul. Turkey sits close to the boundary of three tectonic plates Eurasia, Africa and Arabia, which are pushing into one another. The turkish landmass is a small tectonic place which is being squashed by the other plates, creating several faults throughout Turkey and the east Mediterranean. The Arabian plate is pushing the microplate west so there are earthquakes on the North Anatolian fault adjacent to the Eurasian plate . Izmit lies on this fault one of the most active faults in the whole world, has a length of 860m. Represents a conservative margin which slipped between 2 to 5 m to cause the earthquake. Moreover th ground in the area around Izmit is composed of very thick soft clay or loose sand layers which move much more than solid rock.
Case study earthquake Turkey 1999 Social effects Estimated 18,000 people died and 300,000 left homeless almost all deaths occurred due to collapse of buildings. Hospitals in the city of Gebze ran out of beds causing more suffering for the injured. memories of the earthquake remained long after the event and psychological problems increased, some people have trouble sleeping others have become withdrawn. When a relatively minor tremor shook Istanbul during the night thousands of people fled into the streets in panic. Two years after the earthquake 20,000 people are still living in temporary accommodation, some of them tents, most of them in prefabricated huts. In Golchuk there was a solid jam of vechiles along the main as people evacuated the area, caused problems for rescue workers trying to get to the devastated zone. Job of keeping lanes open for the rescue services lay on the hands of vigilantes who used sticks and in some cases guns to threaten people. Parts of the motorway between Ankara and Istanbul buckled causing cars to crash into each other.
Case study Earthquake 1999 Economical effects In Yalova alone 65000 houses destroyed, the most common type of housing in Turkey was twoto five storey building which were not constructed well enough to withstand the tremors. Destruction occured over wide area, buildings were destroyed in Turkey's largest city, Istanbul, 80km north west of Izmit. Worst hit region around the eastern end of the Sea of Marmara part of Turkey's industrial heartland.. Big businesses well recovered, small companies and entrepreneurs have suffered badly, although. Many shopkeepers were unable to reopen for business as thousands of their former customers migrated away from the earthquake zon and returned to other parts of the country. Had to either close down or suffer large loses rebuilding the region cost $10 billion, estimated. Earthquake caused tidal surge smashing boats, marooning a passenger ferry in the middle of an amusement park and drowning Turkish tourists 6m high. Subsequent waves repeatedly struck the shore at intervals an effect known as a seiche as the wave rebounded of ends of Izmit Bay.
Case study Earthquake Turkey 1999 Environmental effects Oil refinery at Tupras Turkey's largest oil refinery at Tupras with 700,000 tonnes of was sent on fire. Fire burnt itself out, but by then damage had been dealt out as large quantities of pollution was excreted into air, water and land. Causing health problems for local people who suffered from breathing illnesses like asthma. Oil dispersed over large are but Oil Spill Response company limited damage using booms and absorbent materials for containing and clearing up the oil.
Case Study Turkey 1999 Environment effects Oil refinery Korfez For days after the earthquake struck it was burning out of control causing considerable damage to the local ecosystem.
Case study Earthquake Turkey 1999 Environmental effects In Yalova next door to a chloring was a factory producing synthetic fibres where there was some chemical leakage, though it was brought under control quickly. Earthquake actually caused massive land movements on the Coast of the Sea of Marmara causing some land to be reclaimed from the sea. Toxic waste dump at Petkim was cracked, exposing waste which had been dumped there for years. Was also damage to nearby PVC factory and the waste treatment plant causing raw sewage to contaminate rivers killing fish. Throughout the area people suffered from diseases like diarrhea due to lack of water and spillages of untreated sewage. Concerns that diseases such as cholera could infect the area.
Causes of the Montserrat eruption Volcanic island of Montserrat situated on a destructive plate boundary, north American plate being subducted by the Carribean plate. Occure on 25 June 1997 Chances Peak volcano erupted catastrophically so catastrophic because was that the volcano produced thick sticky lava called andesite, lava so thick that it builds up at the top of the volcano in a dome until it becomes too heavy and the dome collapses. As the dome collapsed a huge ash cloud formed rising rapidly up to a height of estimated 10 km strong winds blew the clouds of ash westward over the island. Parts of Montserrat had black out conditions as ash cooled it fell back to some parts of the island depositing ash 2-3 mm thick. When dome collapsed hot rocks, gases and ash were ejected from the volcano causing pyroclastic flows.
Effects of eruption on people Exclusion zone was set up at the time authorised personal were in the exclusion zone to carry our essential tasks and monitor the volcanic activity. When an eruption looked likely all these people were able to evacuate safely by responding to the emergency sirens. Some unauthorised people were in the exclusion zone but didn't hear sirens 19 were killed by pyroclastic flow. Common injuries were severe burns to the feet as a result of walking on ash deposits also occured on other points of body, including burns to nose and mouth due to breathing in the hot gases. Of the 11000 that lived on Montserrat when the volcano erupted in 1995 7000 have been evacuated. 3000 to neighboring island Antigua and UK had 4000 rest to the US
Earthquake effect on transport Was cut off from air travel in 1995 when the volcano destroyed Bramble airport, air travel did not resume until the new Gerlad's Airport was reopened in July 2005 that international travel would resume.
Earthquake effect on buildings Villages of Farm and Trant wre completely buride by ash flow deposits destroying 100 to 150 houses, partially buried or burned. Aluminium window shutter were melted and twisted everything made of wood was burned. Other houses destroyed by direct impact of rock up to 5m in size. Houses in exclusion zoned desstroyed, farmers were producing crops to feed evacuees and believed that they were helping their country in crisis as most suitable land was south close to island.
Environmental effects of eruption Many rivers were blocked causing flooding, pyroclastic flows broke and flattened thousands of trees in some areas no vegitation left at all. Flow deposits completely filled Pea Ghaut and formed a thick, broad fan houses up to 200 metres from the edge of the fan were completely buried by deposits. some of rock deposited in Bethel were up to 5m in size caused widespread destruction. During eruption 5 million cubic metres of ash and rock was deposited.
Methods for predicting earthquakes and volcanic eruptions Despite sophisticated monitoring equipment it still remains very difficult to pinpoint exactly when an eruption or earthquake will happen, high risk areas are now constantly monitored. Sulphur dioxide is one of the main volcanic gases and changes in the amount of this gas can be an indication of an eruption. Pressure from rising magma deforms the volcano ground can change shape by rising , subsiding, tilting or forming bulges. Newest and most accurate way of measuring ground deformity is by using GPS involves satelittes and radio waves reciever set up close to the volcano then data can be transmitted between satellites data is obtained in just a few minutes and is extremely accurate. Seismometer and tiltmeters can also be used
Prevention: Education A lot of schools carry out an evacuation drill as part of the back to school routine. In the USA the Federal Emergency Management Agency (FEMA) gives information on how to prepare for an earthquake, states six ways to plan ahead: check for hazards at home Identify safe place in and outdoors Educate yourself and family members have disaster supplies on hand Develop an emergency communication plan Help your community get ready.
Earthquake proof structures Many building in earthquake zones in HIC's are now built with earthquake proof regulations. For example rolling wieghts on roof to counteract shock waves, identification number visible for helicopters assessing damage after earthquake, birdcage interlocking steel frame, reinforced lattice work foundations deep in bedrock, rubber shock absorbers between foundations and superstructure, open areas where people can assemble if evacuated, panels of marble and glass flexibly anchored to steel superstructure, reinforced lift shafts with tensioned cables, automatic shutters come down over windows to prevent pedestrians below being showered with glass.
Famous earthquake proof structures At the Tamaki building in Auckland the two wings of the main building block have been split by a movement joint, a gap of about 10 cm right across the building on all levels. Building designed to allow a controlled even movement that will dissipate the earthquake's force before it causes structural damage. The San Francisco International Airport uses many advanced building technologies to help it withstand earthquakes. One of these technologies involves giant ball bearing. The 267 columns that support the weight of the airport each ride on a steel ball bearing 1.5m in diameter. The ball rests in a concave base that is connected to the ground. In the event of an earthquake the ground can move 50 cm in any direction. The columns that rest on the balls move a lot less than this as they roll around in their bases which reduces the movement of the ground. When the earthquake is over gravity pulls the columsn back to the centre of their bases.
Volcano defences To divert or stop lava flow detonating explosives can be used in 1996 the Italian army detonated 7000 kg of mining explosives to successfully block a lava flow leading from Mount Etna and threatening villages below. Construction of earth walls can deflect lava. Diversion structures have been constructed in Hawaii to protect the Mauna Loa Observatory form future lava flows. Spraying large volumes of water can cool an advancing flow, one of the lava flows from Etna went to within 50m of the departure station of the cable car but was relatively small and cooled by spraying water onto the lava.
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