Tectonic activity – The essentials

The earth’s crust is made of huge floating plates (rock). The earth is like a broken egg shell. These plates float on the mantle (molten material) in different directions a few cm/year. Plates meet at plate boundaries or margins There are 3 different types of plate margin: Constructive Destructive Conservative

World map showing plate boundaries and their movement

2 plates move away from one another. Magma rises from the mantle 2 plates move away from one another. Magma rises from the mantle. New crust is created. Volcanoes get formed.

At a destructive boundary the plates are moving towards each other At a destructive boundary the plates are moving towards each other. This tends to involve a continental plate (a plate carrying land) and an oceanic plate (a plate carrying ocean). The oceanic plate is denser than the continental plate so, as they move together, the oceanic plate is forced underneath the continental plate. The point at which this happens is called the subduction zone. As the oceanic plate is forced below the continental plate it melts to form magma. The magma collects to form a magma chamber. This magma then rises up through cracks in the continental crust. As pressure builds up, a volcanic eruption may occur.

At a conservative boundary the plates are sliding horizontally past each other. No land is created at a conservative boundary and none is destroyed. Volcanoes do not occur along these boundaries but earthquakes are very common. A very well-known example of a conservative boundary is the San Andreas Fault, which runs through the state of California in the USA.

How are fold mountains formed? (destructive margin) Fold mountains e.g. Alps, Rockies, Himalayas are formed when two plates move together (a destructive plate margin). This can be where two continental plates move towards each other or a continental and an oceanic plate. The movement of the two plates forces sedimentary rocks upwards into a series of folds. Fold mountains are usually formed from sedimentary rocks. When plates and the continents riding on them collide, the accumulated layers of rock crumple and fold like a tablecloth that is pushed across a table.

Case study fold mountains: The Andes – how do people use them? FARMING – subsistence farming occurs on steep slopes e.g. potatoes. Terraces (steps cut into hillsides to create areas of flat land) retain water and limit soil erosion. Most crops are grown in the valleys e.g. rice, cotton, soy beans. Llamas are use as pack animals (mainly males carrying equipment) and the females are used for milk and meat and wool is used in clothes and rugs. MINING – Andean countries are important for tin, nickel, silver and gold mining. Towns grow as a result of job creation. However, this brings an increased crime rate. HEP (Hydroelectric power). Steep slopes and narrow valleys can easily be dammed; there is lots of precipitation and spring melt snow to generate electricity TOURISM – There are many natural attractions e.g. mountains, volcanoes, glaciers and lakes. Some people follow the Inca trail (ancient people) to see famous early settlements e.g. Machu Picchu

World map showing the distribution of volcanoes (spread of)

A cross section of a volcano and its features

Composite Volcano The shape of a volcano depends on the type of magma and the kind of vent out of which the lava comes. If very runny magma erupts, the lava spreads out quickly to form a low, gently sloping shield volcano e.g. Mauna Loa, Hawaii. If a vent becomes blocked, smaller vents often break out around it (through cracks/weaknesses in the rock) and form small cones on the side of the main one (secondary). This is called a composite volcano. When thick sticky magma erupts through a central vent, the lava forms a steeper sided cone.

Cause/effects Montserrat eruption 1995-8 Destructive plate margin – Caribbean plate moves towards and underneath the North American Plate (gets subducted, as it is oceanic crust i.e. is heavier) Effects Primary: 2/3 of the island was covered in ash 50% of the population were evacuated to the north of the island to live in makeshift shelters 23 people died in 1997 Plymouth - the capital was evacuated The airport and port were closed Farmland was destroyed Many schools and hospitals were destroyed Effects Secondary: Floods as valleys were blocked with ash Forest fires caused by pyroclastic flows As most of the southern area was destroyed any remaining inhabitants have had to endure harsh living conditions in the North. Transport remains a problem for people travelling to the island as the port and airport remain closed. The tourist industry is still suffering with few visitors except for cruise ships looking at the volcano Over half the population left the island and have not returned

Immediate/long term responses Montserrat eruption 1995-8 Farmers quickly collected what harvest they could as first eruptions happened Inhabitants nearby were evacuated to a ‘safe zone’ in the north Long term: £41 million was given in aid by the British Government. Money was given to individuals to help them move to other countries (7000 left). Riots occurred as locals complained that the British were not doing enough to help the island The MVO (Montserrat Volcano Observatory) was set up to study the volcano and provide warnings for the future A Risk assessment was done to help islanders understand which areas are at risk and reduce problems for the future.

Monitoring and predicting eruptions How can you predict and monitor volcanic eruptions? Earthquakes are a sign of an impending eruption ‘Swelling’ (magma building up) on the sides of a volcano Tiltmeters detect a change in slope caused by shifting magma under the rock surface Global positioning systems (GPS) use satellites to detect movement as little as 1mm Digital cameras on the edge of craters allow volcanologists to make safe observations Changing gases escaping from a vent are a sign of an imminent eruption. Tiny robots called ‘spiders’ are now used to collect samples.

Supervolcanoes What is one? A supervolcano is a mega colossal volcano that has the capacity to erupt a 1000 times more material (ash, lava) than a normal volcano. What are its characteristics? Much wider and less steep than normal volcano Much bigger scale, emitting far more material than a normal volcano (1,000km cubed, instead of 1km cubed) They have large depressions (calderas – a collapsed magma chamber) instead of a cone shape) What are the likely effects of an eruption? The effects could be global e.g. dramatically affecting climate as an ash cloud could reduce incoming solar radiation (small ice age?) A huge area of land could be covered, resulting in crops failing, huge air transport problems and thousands of people dying

World map showing the distribution of earthquakes (spread of)

A cross section of an earthquake and related features

Key terms - earthquakes Epicentre – the point on the earth’s surface directly above the focus Focus – the point in the earth’s crust where the earthquake happens Shock waves – seismic waves generated by the earthquake, which pass through the earth’s crust Richter Scale – logarithmic scale (each increase in 1 means a 10 fold increase in energy) which measures the strength of an earthquake. There is no upper limit Mercalli Scale – a means of measuring earthquakes by describing and comparing damage done on a scale of 1 to 12.

Case study (MEDC): Kobe Earthquake, Japan 1995 Cause Kobe is near a destructive plate margin where the Pacific Plate (oceanic crust) gets subducted (forced underneath) below the Eurasian Plate (continental crust) as it is heavier.

Effects Primary: Nearly 200,000 building s collapsed and roads are destroyed e.g. Hanshin elevated highway Many bridges collapsed along 130km section of bullet train route 120 of 150 quays in the port are destroyed Secondary: Water pipes and gas mains burst. Electricity supplies disrupted Wall of fire up to 500m wide sweeps city (caused by broken gas pipes and ruptured electricity mains) 5,500 people killed; 40,000 injured; 180,000 houses destroyed 230,000 homeless – living in temporary shelters. Shortage of blankets, clean water and food) Major industries forced to close e.g. Panasonic and Mitsubishi 10 trains derailed Temples destroyed in nearby Kyoto

Responses Immediate: Friends and neighbours, joined by emergency services searched through rubble Hospitals struggled to cope, treating people in corridors Major retailers e.g. 7-Eleven, helped provide essentials e.g. food Motorola gave people telephone connections free of charge Railways were 80% operational within a month Long term: Infrastructure e.g. water, gas, electricity and phone services were fully operational by July 1995 All rail services back to normal by August Within a year, the port was 80% operational Rubber blocks were put under bridges to absorb shocks New buildings were built further apart (to prevent domino effect) and with flexible steel frames

Case study (LEDC): The Sichuan Earthquake, China, 2008 Cause The pressure resulting from the Indian Plate colliding with the Eurasian Plate, was released on 12th May 2008, leading to an earthquake measuring 7.9 on the Richter Scale.

Effects Immediate: 55,000 reported dead within 11 days and 18,000 missing 374,000 injured 5 million homeless In rural areas, 80% of buildings collapsed 5 million buildings collapsed, including a number of schools (one had 900 pupils which were killed). Communications (land and mobile phones) were cut and roads were blocked by landslides Long term: 2 months later, 69,000 are confirmed dead Landslides blocked rivers, leading to fears of flooding

Responses Immediate: 20 helicopters are sent to help by Chinese Government Troops parachute in to assess situation and 1000s of army troops help on the ground Rescue workers search for trapped survivors Land flattened to put up tents to shelter people from spring rains Teams from Japan, South Korea and Russia help rescue effort Donations to Red Cross exceed £100 million, much being spent on food, medicine, doctors, volunteers, tents, mattresses and blankets Long term: 1 million temporary small homes are built for homeless Chinese Government pledges $10 million rebuilding fund Banks write off debts owed by survivors without insurance

Prediction, protection and preparation The 3 Ps are the key to reducing the impact of earthquakes: PREDICTION – This involves trying to forecast when an earthquake will happen by: monitoring foreshocks (although their usefulness is limited if you want to evacuate an area); animal behaviour has been used but is sceptically viewed by many. PROTECTION – Building to an appropriate standard and using designs to withstand movement is the main form of protecting people. Buildings can have: an interlocking steel frame which can swing during earth movements; an automatic window shutting system to prevent falling glass; rubber shock absorbers at base (built into foundations); fire resistant building materials. PREPARATION – Involves hospitals, emergency services and people practising for disasters e.g. drills/code of practice, so people know what to do to increase their chance of surviving.

Case Study of a tsunami: SE Asia, Boxing Day 2004 Cause On 26th December 2004, an earthquake (10km below the sea bed, 150 miles off the coast of the island of Sumatra, Indonesia) measuring 9.1 on the Richter Scale happened at 7.59am local time (12.59am GMT). The earthquake was caused by the Indo-Australian Plate subducting (being forced underneath) beneath the Eurasian Plate.

Effects Estimates suggested more than 220,000 died, 650,000 were injured and 2 million made homeless as a result of tsunami waves, up to 25 metres high coming ashore in different countries. Public buildings e.g. hospitals and schools were wiped out in some areas. Up to 1,500 settlements were completely destroyed in the province of Banda Aceh, Indonesia. Map showing countries affected

Responses Rescue services and emergency teams were swamped by the scale of the disaster. Bodies littered the streets before being buried in mass graves. International Aid poured in e.g. fresh water, water purification tablets, food, sheets and tents. Medical teams and forensic scientists arrived. UK government promised £75 million and public donated £372 million. There were organisational issues following the collection of large sums of money but it has been spent on rebuilding projects in Sri Lanka and Indonesia. A tsunami warning system was set up in 2006 around the Indian Ocean to ensure that people know how to respond and that local authorities have plans in place in case a tsunami happens again.

Useful websites - animations http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundaryrev3.shtml (destructive/compressional plate boundaries) http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundaryrev2.shtml (constructive/tensional plate boundaries) http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundaryrev4.shtml (conservative/lateral plate boundaries) Geography at the movies - http://www.geographyatthemovies.co.uk/ (Tectonics)