Hazardous Earth what to talk about for what question. What the question will be about The structure of the Earth. Plate movement

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1 What the question will be about The structure of the Earth Plate movement Evidence for continental drift and plate tectonics 1. pre 1950 evidence Alfred Wegener Evidence for continental drift and plate tectonics 2. Post 1950 the mechanism The global pattern of plates and plate boundaries What you should talk about Earth is divided into layers core mantle crust. You must refer to the asthenosphere (upper part of the mantle semi molten (can flow)) and the lithosphere solid layer above the asthenosphere. The boundaries between them are unclear. Crust is found as oceanic crust and continental crust. Lithosphere divided into sections called plates and these move. The accepted theory to explain movement was convection currents however slab pull is now thought to be the reason the movement created at a subduction zone pulls the rest of the plate along with it. Happens as a result of the different densities of the plates. 3 rd theory = ridge push. Variety of evidence built up over time which led the theory to become accepted. 1. Jigsaw fit (especially the continental shelf. 2. Fossil records, 3. Land masses far apart showed evidence of glaciation at the same time. This evidence was collected by Alfred Wegener but not accepted because he failed to provide an explanation. Paeomagnetism studying the magnetic record on the rocks on the ocean floor led to the theory of sea floor spreading. This allowed us to understand that the plates moved. This evidence was backed up by surveys of the ages of ocean floors showing that youngest rocks were at spreading ridges. 7 major plates and many minor ones 3 types convergent, divergent and conservatives. Most of the Examples/facts Where is the asthenosphere? km down. What is the thickness and density of oceanic crust? 5-10km thick, density: 3.3kg/m² What is the thickness/density of continental crust? 30-70km thick, density: 2.7kg/m² 97% of EQs at plate boundaries. 100% of deep focus EQs and 70% of shallow/medium around the Pacific plate.

2 associated with convergent (destructive) plate boundaries. associated with oceanic continental destructive plate boundaries associated with oceanic oceanic destructive plate boundaries associated with continental continental destructive plate boundaries associated with divergent (constructive) plate boundaries earthquakes and volcanic eruptions occur at or near plate boundaries. These are where the plates are moving towards each other. 3 types Oceanic continental Oceanic oceanic Continental continental Oceanic plate subducts under the continental plate because it is denser. This leads to melting of the plate along the Benioff zone and the large amount of magma produced leads to volcanoes. At the point of subduction the land is dragged downwards leaving an ocean trench. The collision of the plates leads to fold mountains. Where the two plate scrape past each other there are earthquakes. Still subduction as one is slightly denser than the other. Instead of volcanoes on land this leads to submarine volcanoes and the creation of island arcs. Still earthquakes, ocean trenches. No subduction because continental plates are similar density. Instead land crumples as fold mountains with deep mountain roots. These are where the plates are moving apart 2 types: Oceanic-oceanic Continental continental Other key location = alpine Himalayan belt = 23% shallow/medium EQs Intraplate EQs (not on plate boundaries = 3% 95% volcanoes at plate boundaries. 5% = hotspots Nazca plate being subducted under South American Plate: Peru-Chile Ocean Trench, Andes Mountain range. Chaiten Volcano in Chile Pacific plate subducted under Phillipines plate: Marianas Trench 11,000m below the surface deepest part of the ocean. Marianas island arc. Himalayan mountain building zone formed as India has crossed the Indian Ocean and collided with Eurasian plate 50,000 year ago.

3 associated with oceanic oceanic divergent plate boundaries associated with continentalcontinental divergent plate boundaries. associated with conservative plate boundaries Causes of volcanoes 2 oceanic plates pull apart and magma rises to fill the gap. Main feature = mid ocean ridges huge underwater mountain chains pushed upwards by rising magma, broken into segments by transform faults which can lock together and result in earthquakes. Where plates are moving quickly there are broad, smooth mountains with no rift valleys at the centre. Where plate movement is slow, mountains are steep with deep rift valleys. Magma can erupt onto the seabed and cool quickly as pillow lava. Magma can be built up as volcanic islands. Continents can slowly spread apart continental crust thins and is stretched leading to faulting and rift valleys with horst (raised bits) and graben (sunken bits) landscapes. Volcanic eruptions can occur as magma rises to the surface. Rift valleys can get wider and wider and eventually be inundated by the sea and continents can split apart. Plates sliding past each other either in opposite directions or the same direction at different speeds. No volcanoes as no magma can get to the surface. Build up of pressure leads to earthquakes. Sometimes there may be crinkled land at the plate boundary but no major landforms. Viscous lava found at convergent plate boundaries where melting of the subducting plate involves the inclusion of water in the resulting magma which forces its way to the surface because of differences in densities. Non-viscous lava found at divergent plate boundaries is runny and rises up to plug the gaps left by plates pulling apart. Mountains can be 3000m high Total length globally = 60,000km. Mid Atlantic ridge between the North American and Eurasian plates a slow spreading ridge with steep slopes and clear rift valley. Iceland is a volcanic island along the Mid Atlantic ridge. Example of a fast spreading ridge = East Pacific Rise East African Rift Valley where African plate is splitting into 2. Example of an associated volcano = Nyiragongo in the DRC. Red Sea is an example of a sea created as the Arabian Peninsular and Africa pulled apart. San Andreas fault along the boundary of the Pacific and North American Plates. Pacific plate moving NW at a rate of 5-9cm per year. N. American plate moving NW at a rate of 2-3cm per year 95% of volcanoes at plate boundaries. 5% at hotspots. See below for examples.

4 Variety of volcanic activity, landforms and landscapes No volcanoes at conservative plate boundaries because no magma generation. Volcanoes also at hotspots where mantle plumes bring magma to the surface Convergent plate boundaries = acidic, high silica viscous magma = explosive volcanoes with gas, dust, ash, lava bombs/tephra = steep sided stratovolcanoes, often in chains. Divergent plate boundaries = basic, low silica, low viscosity magma = effusive eruption leading to lava flows = gently sloping sided shield volcanoes/lava plateaux. Eruptions at hot spots Eruptions at hot spots Hot spots = mantle plumes places where magma = much closer to the surface. Plates move over a hot spot giving a slowly developing chain of volcanic islands such as Hawaii. There is also a hot spot under the East African Rift Valley and Iceland. Volcanoes usually basaltic lava effusive shield volcanoes as in Hawaii but can also be explosive stratovolcanoes as at El Tiede on Tenerife. Size and shape of different volcanoes Supervolcanoes Measuring and assessing volcanic activity Explosive eruptions = steep sided volcanoes made of layers of ash and lava. Effusive eruptions = gently sloping shield volcanoes made up of layers of lava tend to be bigger. Calderas- volcanoes that have collapsed leading to giant craters to form largest volcanoes come from super volcanoes. A volcano that erupts more than 1000km³ Form giant craters in the landscape. Can be measured by magnitude (amount of material) or intensity (speed of eruption). Most widely used Convergent plate boundaries There are 66 strato volcanoes along Nazca, S. American plate boundary e.g. Chaiten Divergent plate boundaries Skjaldbreidur = shield volcano on Iceland huge volcano extending horizontally for 10s of km. Hawaii centre of Pacific plate moving NW over a hotspot creating a chain of volcanic islands. Vast shield volcanoes created e.g. Mauna Loa and Mauna Kea in Hawaii rise 900m from the ocean floor East African rift valley is above a hot spot Afar region in Ethiopia = Erta Ale Volcano shield volcano See above Yellowstone in Wyoming, US has a caldera measuring 75 km across. Last erupted 70,000 years ago 0 on the VEI = Kilauea gentle, effusive eruption but scale not useful for gently erupting volcanoes. 4 = Eyjafjallajokull

5 Volcanic eruptions generate distinctive hazards Are the impacts of volcanoes long/short term and local/global? Causes of earthquakes measure is the Volcanic Explosivity Index which combines both. Logarithmic scale between 0 and 8. Lava flows basic lava = free flowing and can travel a long way. Acidic lava slow and destructive. Don t kill people, just property destroyed. Pyroclastic flows hot (500 degrees) gas, ash and rock travelling down the side of the volcano at 100km/h. Huge destruction. Tephra any material ejected from a volcano = ash to volcanic bombs. Buries farmland, grounds planes, buildings collapse because of the weight and can be hard to breathe. Gas Toxic gas such as carbon dioxide and sulphur dioxide = can poison people and lead to acid rain which damages crops and pollute water. Lahars Mudflows as ash mixes with water from rain, rivers or snow/ice melting on a volcano. Travel at 50km/h. Hugely destructive. Glacial outburst floods. When heat from a volcanic eruption melts large amounts of ice/snow leading to flooding. Tsunamis landslides/pyroclastic flows into the sea can cause displacement of water and tsunamis = waves travelling across the ocean then destroying coastlines Majority of impacts are short term and local however for really big eruptions or those which generate a lot of ash, the effects can be far reaching and have longer term impacts on climate change. Plate move, lock together, pressure builds up over time and is released as an earthquake. Happens at: Convergent plate boundaries subduction zones 8 Yellowstone 640,000 years ago Lava flows Kilauea, Hawaii, currently erupting Pyroclastic flows: Montserrat 1990s wiped out Capital city of Plymouth Tephra ash from Eyjafjallajokull led to cancellation of 100,000 flights Toxic gases current eruption of Kilauea emitting Sulphur dioxide Lahars - Eruption of Nevada del Ruiz Volcano in Colombia overwhelmed the town of Armero killing 23,000 people Glacial outburst floods Eyjafjallajokul led to glacial outburst floods of 57million cubic m of water. Tsunamis 1883 eruption of Krakatoa believed to have created tsunamis which drowned 36,000 peopl Subduction zone earthquake Japan 2011 which triggered the tsunami. Divergent plate boundary earthquake those that preceeded the eruption of Eyjafjallajokul

6 Shallow/Deep focus EQs Ways of measuring earthquake magnitude (strength) Ways of measuring earthquake intensity (impacts) The effects earthquakes have on landforms and landscapes Divergent plate boundaries along transform faults that split these into sections. Collision zones where continents collide Conservative plate boundaries (Basically all plate boundaries for different reasons) Can also have intraplate earthquakes can do huge damage because not expected and therefore buildings not earthquake proof. Can be caused by human activity: mining, building dams, fracking, nuclear explosions Shallow down to 70km common at all plate boundaries Deep km down happen at subduction zones more powerful and less frequent but do little damage Richter scale 1935 logarithmic scale, no upper limit. Problems gives no idea of damage and numbers at the upper end of the scale are inaccurate. Moment Magnitude scale preferred method for larger earthquakes. Measures physical movement which is a direct function of the energy released. More accurate for larger earthquakes Modified Mercalli Scale qualitative assessment based on observation and description. Problems: subjective and cant measure EQs away from habitation. Earthquakes associated with mountain landscapes may see patterns of folding and faulting in the landscape. Collison zone earthquake Nepal, 2015 Conservative plate boundary EQ San Francisco EQ % of EQs at plate boundaries. 100% of deep focus EQs and 70% of shallow/medium around the Pacific plate. Other key location = alpine Himalayan belt = 23% shallow/medium EQs Intraplate EQs (not on plate boundaries = 3% E.g. of intraplate EQ that did a lot of damage Gujarat 2001 old fault line reactivated. 7.7 of moment Mag scale 20,000 people died as 50 multistory buildings collapsed. Nuclear testing carried out by N. Korea. Shallow focus EQ: Nepal km down Deep focus EQ: Japan 2015 mag 7.8 eq did little damage because was 590km down 9 on the moment mag scale = Japan, 2011 Complex patterns of faults can be seen in the Himalayan-Karkoram range in Asia and also on the Tibetan Plateau to the north of the mountain range.

7 Rift valleys show evidence of faulting with inward facing fault scarps or escarpments: An escarpment is a long, steep slope, especially one at the edge of a plateau or separating areas of land at different heights. They create the horst and graben landscape which is areas of high and low land separated by escarpments. Horst and Graben landscape with escarpments found all along the East African Rift Valley. Hazards generated by earthquakes Ground shaking and displacement most extreme in locations close to the epicentre of a high magnitude quake on unconsolidated ground. Ground movements can lead to the collapse of buildings, rip apart infrastructure such as pipelines and disrupt drainage. Liquifaction where ground is unconsolidated and contains water shaking may lead to it behaving like a liquid which causes damage to building foundations. Landslides where EQs occur in regions with steep slopes. Made worse by deforestation and heavy rains. This can block roads and rivers and therefore lead to flooding as well as destroy villages. Avalanches EQs can trigger avalanches. Tsunamis under sea EQS cause the sea bed to rise which displaces water abve leading to powerful waves at the surface. Te height builds as the coastline shallows. Underwater landslides can also displace water leading to tsunamis which can have big local effects. Flooding can happen when landslides block rivers or lead to landslides into reservoirs which then overtop their dams. Mexico Earthquake with extreme ground shaking. 7.1 Moment magnitude scale. Mexico city is built on an old lake bed of soft, unconsolidated material. Mexico city 150km from the epicentre Liquifaction in Christchurch, New Zealand, 2011 led to 10,000 building having to be demolished after the EQ. Landslides and avalanches destroyed villages in the Langtan region in the Nepal EQ An avalanche on Everest killed 22 people. Tsunami caused by under sea EQ: Japan 2011 tsunami killed 20,000 Tsunami caused by underwater landslide triggered by an EQ 1998 Papua New Guinea killed 2,200 Flooding landslides in Sichuan (China) 2008 formed temporary dams across rivers which led to huge floods when the dams were breached.

8 There are a range of impacts experienced by people as a result of volcanic eruptions 2 case studies to show: Why people live near volcanoes The impacts of the eruption on people The environmental. Economic and political impacts on the country. In Italy in 1963, the collapse of a hillside above the Vaiont reservoir created a 100m wave which drowned 3000 people. 1. Iceland Nyiragongo 2002 There are a range of impacts experienced by people as a result of earthqaukes Modifying the Event Modifying people s vulnerability 2 case studies to show: Why people live in areas prone to earthquakes The impacts of the EQ on people The environmental, economic and political impacts on the country Not possible for most volcanic eruptions however in a couple of cases, lava diversion channels, spraying lava to cool it down (Heimay, Iceland) and dropping concrete blocks (Etna) have helped. Not possible for earthquake events although some secondary effects can be modified e.g. afforestation will reduce landslides after an earthquake. Education in what to do. Community preparedness e.g. having tsunami shelters and walls, having strong public buildings and key infrastructure such as hospitals. Prediction and warning better for volcanoes. Hazard resistant buildings advanced for earthquakes but nothing can be done for volcanoes. Having strict regulations for buildings in place and enforced. Hazard mapping e.g. mapping lahar routes/areas that would be affected by liquefaction. Land use zoning to avoid building in those locations. 1. Japan 2. Nepal

9 Modifying people s loss There are various strategies to manage hazards from volcanic activity. There are various strategies to manage hazards from earthqaukes How and why the risks from tectonic hazards have changed over time Emergency aid Disaster response teams and equipment Search and rescue strategies Insurance for buildings and businesses Resources for rebuilding. Case studies of two countries at contrasting levels of economic development to illustrate strategies used to cope with volcanic activity including: attempts to mitigate against the event, such as lava diversion channels attempts to mitigate against vulnerability such as community preparedness attempts to mitigate against losses, such as rescue and emergency relief. Case studies of two countries at contrasting levels of economic development to illustrate strategies used to cope with hazards from earthquakes including: attempts to mitigate against the event such as land-use zoning attempts to mitigate against vulnerability such as building design attempts to mitigate against losses such as insurance. Frequency of tectonic events not really changed but impacts have due to population growth and urbanisation putting more people at risk, however, this number may reduce n the future as strategies for coping with the risks improve in the future, especially for volcanoes. There is an increasing danger however, for earthquakes at least that there may be a million death quake in the future if 1. Italy 2. Indonesia 1. Japan 2. Nepal Cities at risk of a million death quake Tehran, Istanbul

10 The degree of risk and the probability of the tectonic hazards occurring the disaster risk equation a big earthquake occurs near a big city with poorly built buildings Future strategies to cope with tectonic hazards which may decrease the risks Monitoring and prediction of volcanic eruptions and planning for evacuation in the event of volcanic eruptions. Modelling of ash clouds may reduce the impact of cancelled flights in the future (occurred after Eyjafjallajokul eruption) However, people will always live near volcanoes because of the benefits they bring e.g. fertile land. This may also be put at risk by conflict and poor governance as in the case of Nyiragongo. See Japan and Nepal case studies to see what they are doing to decrease the risks from earthquakes