Component 1, Topic 1: Hazardous Earth [PLC]

Transcription

1 Hazardous Earth - Earth's Structure and Tectonic Processes Revision Booklet Component 1, Topic 1: Hazardous Earth [PLC] From 1-5 rank how confident you are for each argument. 1= not confident at all / 5 = very confident I can identify the layers of the earth. Before After EARTH'S STRUCTURE AND TECTONIC PROCESSES I can describe their temperature, density, composition and physical state (solid or liquid). I can describe how the earth s crust is broken up into tectonic plates. I can explain how radioactive decay causes convection currents and how this drives plate movement. I can describe the global distribution of tectonic activity (volcanoes and earthquakes). I can draw a diagram of a divergent plate boundary and explain how volcanoes are formed on them. I can draw a diagram of a convergent plate boundary and explain how volcanoes occur there. I can compare shield volcanoes on divergent plate boundaries with composite volcanoes on convergent plate boundaries. I can describe how the Richter scale measures the strength of an earthquake. I can explain the cause of an earthquake at convergent and conservative (sideways) plate boundaries. I can compare the primary and secondary impacts of two earthquakes; one in a developed country and one in a developing country. I can explain two ways in which volcanoes can be managed through land-use zoning and evacuation. I can compare earthquake resistant design for buildings in the developed and developing world. I can evaluate (successes and failures) for the response to one tectonic event. I can explain two ways in which volcanoes can be predicted.

2 The structure of the Earth Crust: Mantle: Outer Core: Inner Core: The outside layer which we live on. It is very thin compared to the rest of the Earth. We live on this part. Solid. This is the layer beneath the crust. It is semi-molten (the rock is hot and flows like jam). This is the layer between the inner core and mantle. It is liquid metal (nickel and iron). Over 4000 C This is found at the centre of the Earth. It is solid metal and spins. It is what creates Earth s magnetic field. Over 5000 C Lithosphere Mantle Core Layer Density (grams/cm 3 ) Physical state Composition Temperature ( C) Continental crust 2.7 Solid Granite Up to 900 C 35 Km Oceanic crust 3.3 Solid Basalt Up to 1200 C 10 Km Depth (Km) Asthenosphere Partially molten C 250 Km Peridotite Lower mantle Solid C 2800 Km Outer core Liquid Iron and C 5270 Km Inner core >12.2 Solid Nickel C 6370 Km Label and annotate the diagram showing the different Earth s layers. Provide relevant info for each layer.

3 Radioactive decay Some elements are naturally unstable and radioactive. Atoms of these elements release particles from their nuclei and give off heat. This is called radioactive decay. The heat from inside the Heart is called geothermal ( earth-heat ). The heat is produced by radioactive decay of elements such as uranium and thorium in the core and mantle. This raises the core s temperature to over 5000 C. Using the help of the diagram, explain how convection works. (4 marks) All this is linked by the Earth s tectonic plates. They move due to convection currents in the mantle. Earthquakes and volcanoes occur at the boundaries between the plates where they meet each other. Describe the distribution of earthquakes and volcanoes and give a possible explanation for your findings. Refer to the tectonic plates map.

4 Plate boundaries Boundary Type Plate Movement Example Hazard Divergent Away from each other Mid Atlantic Ridge Shield Volcanoes (spreading) North American and Eurasian moving away from each other Convergent Towards each other (subduction) Conservative Sideways alongside (usually in opposite directions) Collision zone Convergent boundaries where two continental plates of relatively similar density collide. Rift Valley in East Africa Pacific Plate moving underneath the Eurasian Plate (Japan) Pacific Plate moving alongside North American Plate (San Andreas Fault, California). Mountain ranges such as Himalayas and the Alps. Composite Volcanoes Earthquakes Earthquakes Earthquakes Divergent Plate Boundary Draw a cross-section in the box below. Include direction the plates are moving in, convection currents underneath, rock type and two plates that meet at a divergent boundary. Hazards at Divergent Plate Boundaries Shield volcanoes Minor earthquakes Label the picture of the shield volcano below. Label it to show its shape and physical features. Explain its shape using the type of lava erupted from a shield volcano. Case Study of a Shield Volcano E. Jokyll 2010 eruption in Iceland. Primary Hazard Description Secondary Hazard Basaltic lava (very hot lava over 1000 C) A limited amount of runny lava was erupted causing the volcano to have a wide flanked shape. Volcano caused snow to melt resulted in some small floods. Ash Cloud Large ash column and resulting cloud emitted from the volcano. Farmland was covered in ash. The ash cloud spread south-east over Europe, causing the cancellation of flights for a week and airlines losing millions of pounds.

5 Convergent Plate boundary Draw a cross-section in the box below. Include direction the plates are moving in, convection currents underneath, rock types and two plates that meet at a convergent boundary. Show how subduction causes volcanoes. Hazards at Convergent Plate Boundaries Composite volcanoes Earthquakes Label the picture of the composite volcano below. Label it to show its shape and physical features. Explain its shape using the type of lava erupted from a composite volcano. Case Study of a Composite Volcano Mt Pinatubo 1991 in the Philippines Hazard Description Development / Case Study specific information Lava Acidic lava, 800 C so more viscous, cools quickly creating a steeper, cone shaped volcano. Pyroclastic Flow Hot gases, ash and rocks around 1000 C flow down the volcano burning everything in their path. Tribal villages of the Aeta people and large areas of farmland destroyed. Large numbers of trees burnt. Ash Cloud Ash column 12 km high rises. Blocks incoming sunlight and when This kills 150 people. Lahars (mud flows) it lands it causes roof tops to collapse on houses. Ash from the volcano mixes with rainwater from a typhoon creating huge mud flows down river valleys. These kill 300 people. Kills 300 people. The type of magma affects the explosive threat of the volcanoes Basaltic Magma: divergent plate margins, low in silica, low gas content, fluid lava flow, relatively little explosive activity. High temperature (> 1000 C). Flows a long way. Andesitic Magma (derives from the Andean Mountains): convergent plate margins (where continental rocks are melted by magma), relatively low in temperature (< 1000 C), high silica, more gas, less fluid lava, more likely to explode. Granitic Magma: collision zones, lower in temperature (< 800 C), highest silica and gas content, sticky lava likely to get stuck before reaching the surface.

6 Exam question To what extent are volcanoes and their hazards determined by lava type? (8) Effects of volcanic eruptions Primary effects: caused instantly by the eruption. Secondary effects: in the days and weeks after the eruption. Label each of the following effects as primary (P) or secondary (S). Poisonous gases cause acid rain destroying crops and livestock. Many farmers could lose income. Widespread destruction leads to food shortage and limited access to clean water. Lava flows interrupt roads and railways, making more difficult to travel around and to bring help. Homes and economic activities are destroyed by lava flows and earthquakes. Lava flows and lahars destroy settlements and clear areas of woodland or agriculture. Ashes disperse in the atmosphere influencing the climate of the area for several months. If the ash from the eruption mixes with rain or melting snow, fast and deadly mudflows called lahars are created. People may need to move to overcrowded refugee camps. Governments around the world give aid to refugees. People might not afford to rebuild their homes, increasing the poverty of the area. Pyroclastic flows instantly change natural landscapes, attractions can be destroyed forever. Exam question For a volcano you have studied explain its primary impacts on people and property. (4)

7 Earthquakes Step 1. At convergent and conservative plate boundaries, plates are moving past each other. Step 2. Friction occurs as the plates get stuck. Step 3. Pressure builds up over time. Step 4. Rocks break and plates move suddenly. Step 5. Huge energy is released as seismic waves. These cause the ground to vibrate and fracture The Richter scale is used to rate the magnitude of an earthquake -- the amount of energy it released. This is calculated using information collected by seismographs. The Richter scale is logarithmic, meaning that whole-number jumps indicate a tenfold increase. A level 6 earthquake is 10 times greater than in a level 5 earthquake, and the amplitude increases 100 times between a level 7 earthquake and a level 9 earthquake. Comparison of Two Earthquakes Example and details Earthquake Impacts Port-au-Prince, Haiti January 2010 Developing World Christchurch, New Zealand March 2011 Developed World Magnitude 7.0 5pm Conservative plate boundary between Caribbean and North American Plates. Magnitude 7.1 4am Conservative plate boundary between Pacific and Australian Plates. Primary: deaths. Mainly caused by the collapse of poor quality slum housing with concrete roof and walls on steep slopes. Hospital and government building collapsed, airport runway destroyed. Secondary: 1 million people homeless. Cholera spread due to lack of sanitation and contaminated water supply. Damage to roads, port and airport meant very difficult to get aid into the country. Economic damage $8 billion. Primary: 185 deaths due to buildings collapsing. Much lower number than in Haiti. Mainly older buildings collapsed as newer ones were earthquake proof. Roads damaged. Secondary: Liquefaction caused ground to become unstable resulting in insecure house foundations causing homelessness people. High economic damage of $20 billion.

8 Exam Question For an earthquake in a named location, describe primary and secondary impacts on property and people. (6) Named location: Explain why earthquakes in the developed world have a lower death toll than in the developing world. (2) Response to earthquakes Response means what happens after the earthquake. The response can come from the government of the country or other governments or from international aid agencies like Oxfam. Response to Haiti earthquake Successful response Red Cross (charity / NGO) flew in planes of aid including tents to house people whose houses had been destroyed. Wateraid (the NGO) gave water purification tablets and installed toilets for people living in tents. US government gave $100 million to Haiti to help the relief effort. Unsuccessful response The first aid took 3 days to get into the country as the airport and port were badly damaged. This meant people with serious injuries were not treated and were forced to drink dirty water. The Haiti government could not organise the relief effort / response. This was because key buildings and communications were damaged. However, the government was highly corrupt before and had no serious plan in place for an earthquake. Sanitation arrangements for the temporary tents were poor and cholera spread. Explain why some of the Haiti s responses to the earthquake were not effective.

9 Prediction, Warning and Evacuation Volcanoes can be predicted, earthquakes cannot be predicted. Two ways volcanoes can be predicted are: 1. Monitoring volcanoes with seismographs to look for small earthquakes occurring. If the number of small earthquakes increases it shows magma is rising to the surface and an eruption is likely. 2. Monitoring gas emissions from the volcano, especially sulphur dioxide. If the amount increases, an eruption is likely. The monitoring of Mt Pinatubo in 1991 successfully predicted the eruption meaning that people living up to 20km away were evacuated. This saved thousands of lives. People can also prepare by storing food and clean water. Although earthquakes cannot be predicted we know where they are most likely to occur. This means that countries can be well prepared for an earthquake and also design buildings to withstand earthquakes. Schools in Japan hold regular drills to practise for an earthquake (crouch under desks) and everyone has an emergency pack to take out of their home when they leave after an earthquake including water purification tablets, a wind up torch, basic first aid and some food rations. Making buildings safer (mitigation) Developing Countries Hollow bricks (so lighter) Plastic roofing (no concrete used) Both means if the house collapses people are less likely to be injured / crushed. Cross bracing to prevent floors collapsing. Developed Countries Make very deep foundations for skyscrapers that include rubber to absorb seismic waves. Skyscrapers designed to swap and contain shock absorbers. Cross bracing of steel to prevent floors collapsing.

10 Exam Question For a named earthquake or volcanic eruption, describe the immediate response and relief efforts. (4) Named earthquake or volcanic eruption: Exam Question Describe two ways people can prepare for volcanoes before they happen (4)