1.1 How and why do the Earth s tectonic plates move? a The Earth s interior hasa layered structure, with different composition and physical properties; the Earth s core generates heat and convection currents drive plate motion. Interpret a cross-section of the Earth, with details (temperature, density, composition, physical state) of layered structure (including the asthenosphere); using rock samples to contrast continental and oceanic crust. Layers of the earth Lithosphere- the top bit of the mantle which is solid and the Earth s crust. Asthenosphere- The asthenosphere is a part of the Earth's mantle, lying just below the crust and the lithosphere. The asthenosphere is made up of rock which is soft due to the heat of the mantle. Inner Core- The inner core is the centre of the earth and is the hottest part of the earth. It is a solid mass of iron and nickel. The temperature of the core is around 5500 C Outer Core- The outer core is the layer around the inner core. It is also made up of iron and nickel though it is in liquid form. Mantle- This layer is made up of semi molten rock, known as magma. Crust- This layer is between 0-60km thick. It is made of plates of rock that float on top of the mantle. 1
Rocks The continental crust is thicker and lighter than the heavier, thinner oceanic crust. Continental crust is made of rocks such as granite. This is less dense than the oceanic crust. Oceanic crust is made of rocks such as basalt. This is more dense than the continental crust. Examine the core s internal heat source (through radioactive decay) and how this generates convection, which drives plate motion and generates the Earth s magnetic field. Why do plates move? The earth's tectonic plates are in constantly moving like giant 'rafts' on top of the semi-molten mantle below. However this movement is slow and rates vary from less than 2.5cm /yr to over 15cm/yr. The movement of the earth's crustal plates is believed to be due to convection currents which occur in the semi-molten mantle. These convection currents are created by heat from within the earth - much of which is generated by radioactive decay in the core. 2
b There are conservative, constructive and destructive plate boundaries, each with characteristic volcanic and earthquake hazards. Explain the distribution of the three plate boundary types and identify major plates. There are 4 different Plate Boundaries: Constructive (When 2 plates move apart.) Destructive (When an oceanic plate and continental plate move towards each other.) Conservative (When 2 plates move alongside each other.) Collision (When 2 continental plates collide.) Constructive (When 2 plates move apart.) 3
Constructive Plate Boundaries A volcano happens on a constructive plate boundary because two plates are moving apart, leaving a gap in the crust. The pressurised magma in the crust immediately rises through the gap and erupts as lava as it leaves the mantle and travels through the crust. This builds new land between the plates, and builds up to form a volcano shape (shield volcano, short and fat). As the crust moves apart over time more lava erupts from the mantle to fill the gap between the plates. The eruption of lava can also build up to form volcanic islands. The slow movement of the plates occasionally can be felt as earthquakes as the ground moves as the convection currents in the mantle pull the plates apart in opposite directions. Destructive plate boundaries Volcanoes form on a destructive plate boundary when an oceanic plate and a continental plate are being pulled towards each other by the convection currents, the oceanic plate is much denser and is therefore forced to sink underneath the continental plate (subduction). The oceanic plate is melted by the heat in the mantle and the friction of grinding against the continental plate. The melted oceanic plate releases carbon dioxide into the mantle, and is therefore pressurised. This magma finds a weak point in the crust and forces its way out, erupting as lava and making a volcano. 4
Destructive plate boundaries continued Earthquakes happen on destructive plate boundaries because the oceanic plate and continental plate are being dragged towards each other by convection currents, the denser oceanic plate forces underneath the continental plate and the plates grind together as the oceanic plate subducts into the mantle. The movement of the grinding and friction between the plates is felt on land as an earthquake. The oceanic plate can also become stuck against the continental plate until some of the crust breaks, making the oceanic plate descend suddenly into the mantle. This causes higher magnitude earthquakes. Conservative Plate Boundaries (When 2 plates move alongside each other.) Earthquakes happen on conservative plate boundaries because the continental plates are being dragged past each other, or in the same direction, by convection currents. They are not moving at the same speed which causes the friction felt as earth quakes. The plates grind together as they pass each other causing minor earthquakes. The movement of the grinding and friction between the plates is felt on land as an earthquake. The plates can also become stuck against each other until some of the crust breaks, as they are not moving at the same speed, when this happens the plates suddenly move past each other, this violent movement is felt on the plates as a higher magnitude earth quake. Collision Plate Boundaries Two continental plates collide (crash into each other) as they are travelling towards each other. The plates are equally dense, and therefore neither plate can sink. They therefore fold up to form Fold Mountains such as the Himalayas, like cars crumple in a crash. The impact of the collision can cause minor earthquakes which travel outwards in waves. THIS BOUNDARY IS NOT ASSESSED IN YOUR EXAM. 5
Examine the causes of contrasting volcanic (volcano type, magma type and explosivity) and earthquake hazards, including tsunami (shallow versus deep, magnitude) at contrasting example locations, e.g. Iceland and Indonesia. Measuring volcanoes and earthquakes Volcanic Explosivity Index The Volcanic Explosivity Index (VEI) shows the size or magnitude of explosive eruptions. It is 0-8 in terms of explosivity. Each number is equal to ten times the one below it. It accounts for ash fall, pyroclastic flows and other substances ejected the height of the eruption and duration. Richter Scale There are two ways to measure earthquake intensity; the Mercali scale and the Richter Scale. The Richter Scale is outlined below. 6
Mercali Scale The Mercalli Scale has an intensity score (1-12) with a descriptive word, e.g. instrumental. The magnitude on the Richter scale and a description of each category is below. Mercalli Scale Intensity Description Magnitu de Witness Observations 1 Instrumental 1 to 2 Detected only by seismographs. 2 Feeble 2 to 3 Noticed only by sensitive people. 3 Slight 3 to 4 Resembling vibrations caused by heavy traffic. 4 Moderate 4 Felt by people walking; rocking of free standing objects. 5 Rather Strong 4 to 5 Sleepers awakened and bells ring. 6 Strong 5 to 6 Trees sway, some damage from overturning and falling object. 7 Very Strong 6 General alarm, cracking of walls. 8 Destructive 6 to 7 Chimneys fall and there is some damage to buildings. 9 Ruinous 7 Ground begins to crack, houses begin to collapse and pipes break. 10 Disastrous 7 to 8 Ground badly cracked and many buildings are destroyed. There are some landslides. 11 Very Disastrous 8 Few buildings remain standing; bridges and railways destroyed; water, gas, electricity and telephones out of action. 12 Catastrophic 8 or greater Total destruction; objects are thrown into the air, much heaving, shaking and distortion of the ground. 7
More explosive volcanoes usually cause more damage. The focus is the point underground where earthquakes originate, the epicenter it the point above this on earth s surface. Shallow focus earthquakes (where the focus is much nearer the epicenter and therefore closer to earth s surface) cause more destruction than deep earthquakes, as they produce more shaking on the surface as the waves do not have to travel as far. DEEP FOCUS earthquakes or "intra plate" earthquakes, occur within the sub-ducting oceanic plates as they move beneath the continental plates. Appearing along fault lines, these are earthquakes with focus much deeper within the earth. SHALLOW FOCUS earthquakes are commonly occurring "crustal" earthquakes, caused by faults and movements of the continental plates. These are earthquakes with their focus nearer the surface of the earth. Montserrat Volcanic Eruption Causes- Atlantic plate subducting under the Caribbean plate- destructive plate boundary. Volcano Type-Composite volcano (layers of ash and lava, steep sides) Magma Type- Rhyolitic (basalt melted with silica from the earth, this is very explosive). Explosivity- 4 on VEI- large or very explosive. Laki (Iceland) Volcanic Eruption Causes- Constructive plate boundary- two plates move apart. The largest lava flow in recorded history was generated by a fissure eruption in south central Iceland in 1783. Known as the Laki flow, it erupted from a 25-kilometer-long fissure to produce 12 cubic kilometers of lava, filling two deep river valleys and covering an area greater than 500 square kilometers. Volcano Type- Shield (chocolate button shaped- gentle sloped sides and wide base). Magma Type- basaltic lava (fast flowing, spreads quickly) Explosivity- 6 on the VEI= colossal/very large. Kashmir Earthquake Causes- Collision plate boundary between Indian and Eurasian plates. Shallow focus-16.2 miles under the earth. This is very unusual. This is very deep for a crustal earthquake. Magnitude 7.6 on Richter scale. 8
Loma Preita Earthquake, California Causes- Conservative plate boundary; North America Plate (moving South) and Pacific Plate (moving North). Shallow focus- 11 miles under the earth. This is very deep for a crustal earthquake. Magnitude 7.1 on Richter scale. Asian Tsunami 26 th December 2004 Causes- (Earthquake on destructive plate boundary) The Asian tsunami of 2004 was caused by tectonic activity beneath the Indian Ocean. A fault twenty miles below the ocean surface ruptured, forcing one of the plates to be thrust upwards by as much as 40 feet. The ocean above was forced upwards and the displaced water moved out as a series of giant ripples. From the land, the first sign of a tsunami is the water being dragged out to sea. The vertical wall of the tsunami destroyed everything in its path Shallow/Deep- Shallow focus- 20 miles deep. Magnitude- 9.3 on Richter Scale. 9
1.2 What are the effects and management issues resulting from tectonic hazards? a Volcanic and earthquake hazards affect people in different ways and at contrasting locations. Investigate the primary and secondary impacts of earthquakes in two named locations, e.g. the 2005 Kashmir versus 1989 Loma Prieta earthquakes. To include reasons for contrasting impacts on property and people. Kashmir, Pakistan, 2005 (Developing Country) On 8 October 2005, an earthquake measuring 7.6 on the Richter scale hit the Kashmir region of Pakistan. The earthquake was the result of collision between the Indian and Eurasian plates. Effects: Primary effects Buildings collapsed. 79,000 people were killed. Landslides, and large cracks appeared in the ground. Secondary effects Broken sewerage pipes contaminated water supplies and spread disease. People died of cold during the harsh winter. Long term homelessness. Responses: Short term Help took 24 hours to arrive from abroad- locals surface searched themselves up to this time. Long term People were prosecuted for poor building construction. The army and emergency services arrived to join the rescue effort. Tents were given out by charities. Aid workers arrived from abroad to find survivors and treat the injured. Schools and hospitals were rebuilt. Building regulations were improved to reduce damage and the death rate in future earthquakes. Teams from Britain used specialist search and rescue equipment to rescue people from collapsed tower blocks. *You need to say HOW successful (evaluate) the methods used to respond to the Kashmir Earthquake and recongnise Pakistan needed aid, and that help took too long to arrive. 10
Loma Prieta Earthquake Tuesday, October 17, 1989, San Franciso, USA (Developed Country) Primary Impacts 63 people died. 3757 injured Cyprus Freeway (road on stilts) collapsed. Bridges collapsed. 10, 000 homes destroyed 30 fires broke out. Secondary Impacts Homes needed rebuilding. Cyprus freeway took 10 years to rebuild and was made more earthquake resistant. Many older homes which were destroyed were rebuilt to a higher standard. Transport issues- traffic. People who were now disabled needed benefits and homes adapting. Reasons the effects of the Kashmir and Loma Prieta earthquakes were different: Loma Prieta- collapsed freeway has immediate response to rescue trapped people, Kashmir Earthquake help took 24 hours from abroad. San Francisco had a larger search team than Kashmir. Building standards generally higher in San Francisco therefore less deaths and injuries. Kashmir 5x more powerful. 11
Examine the primary and secondary economic and social impacts of one volcanic event. Montserrat Volcanic Eruption Primary Economic Impacts Secondary Economic Impacts The biggest eruption in 1997 killed many farm animals and crops, these therefore couldn t be sold. People lost their farms and businesses (and therefore had no income, creating high unemployment). The port was destroyed, and the airport was unsafe to use, which halted exports (and therefore external income). Primary Social Impacts The biggest eruption in 1997 killed 19 people. People were traumatised and afraid. Schools, homes and transportation hubs were destroyed. The loss of farm land is still impacting Montserrat s development as it cannot grow as many crops and therefore has less income and has to pay for more imports. Key infrastructure including the main port, airport, businesses and schools have had to be rebuilt in the north, this was expensive. Montserrat had little tax income due to residents leaving and high unemployment; this meant the island relied on aid money to recover. Secondary Social Impacts 5000 out of the 10 000 residents left. Lack of educational facilities limited opportunities. Long term homelessness and unemployment caused a low standard of living. 12
b Management of volcanic and earthquake hazards, at contrasting locations, ranging from short term relief to long-term planning, preparation and prediction. Examine the role of prediction, warning and evacuation in relation to volcanic and earthquake hazards. Contrasting hazard resistant design in the developed and developing world. Developed Prediction- Seismometers monitor plate movements to sense earthquakes that could cause tsunamis. EARTHQUAKES CANNNOT BE PREDICTED but patterns of smaller earthquakes indicate plate movement and can come before bigger quakes. Tilt metres and seismometers sense magma movement and plate movements which can cause volcanic eruptions. Warning- Police and army can be used to do door- to- door evacuation. News- TV and radio. Leafleting. Automated phone calls. Evacuation- Police and army used to evacuate, all local governments have hazard management plans. Hazard Resistant Design: Retrofitting- flexible steel supports which sway with the earthquakes and reduce collapsing risk. Dampers-shock absorbing springs or dampers can be put under buildings to allow them to wobble or sway within their foundations. Bracing- corner supports to stop collapse. Pointing - replacing cement in house regularly to ensure bricks are well held together. Developing Prediction- Often little investment, Developed countries provide developing countries with warnings. Warning- Police and army can be used to do door- to- door evacuation, but there are too few staff. News- radios and TV used to warn. Leafleting- charities often use helicopters to drop in leaflets. Evacuation- People told to evacuate but resources are often not there to support. Army are used on occasion. Hazard Resistant Design: Ring beams- Circular beams around houses hold the walls together and prevent the roof collapsing inwards onto people. Sloped roofs- these prevent ash build up and roof collapse. In Nepal straw blocks are being used to build homes as it is cheap and will cause less injuries when the buildings collapse. Much safer than bricks or concrete. 13