Tectonic Hazards Flashcards
Describe the plate tectonic theory
The Earth’s crust is split into a number of plates about 100km thick. Plates move in relation to each other due to convection currents from deep within the earth. Tectonic activity at plate margins causes earthquakes and volcanoes.
Describe the distribution of earthquakes
Earthquakes occur mainly at the margins of tectonic plates where plates are moving and enormous pressures build up and are released. Some earthquakes do not occur at plate margins, these may be due to human activities such as underground mining or oil extraction.
Describe the distribution of volcanoes
Volcanoes are fed by magma from deep within the earth. This rises to the surface at constructive and destructive plate margins. Volcanoes also form at hot spots, where the crust is thin and magma is able to break though to the surface.
What happens at a constructive, destructive and conservative plate margin?
Constructive: two plates are moving apart. Magma forces it’s way to the surface and as it breaks through the overlying crust, it causes earthquakes. On reaching the surface it forms broad and flat volcanoes.
Destructive: Plates are moving towards each other. The more dense oceanic plate is subjected beneath the less dense continental plate. As the oceanic plate over downwards it melts. This creates magma which is less fluid than at a constructive plate margin. It breaks through to form steep-sided composite volcanoes. When two continental plates meet, there is no subduction, the two plates collide and the crust becomes crumpled and uplifted creating mountains and causing earthquakes.
Conservative: two plates move past each other. Friction between the plates causes earthquakes. Earthquakes occur due to the stresses gradually building up over many years.
What were the primary and secondary effects of the Chile earthquake?
Primary: 500 people killed, 12,000 injured, 800,000 affected. 220,000 homes, 4500 schools, 53 ports and 56 hospitals destroyed. Much of Chile lost power, water and communications. Cost of earthquake was $30B
Secondary: 1500km roads damaged mainly by landslides - remote communities cut off for days. Several costal towns devastated by tsunami waves. Fire at chemical plant near Santiago - area evacuated.
What were the primary and secondary effects of the Nepal earthquake?
Primary: 9000 dead, 20000 injured, 8 million people affected. 3 million left homeless. Electricity, water, sanitation and communications affected. 7000 schools destroyed and hospitals overwhelmed. 50% of shops destroyed, affecting foods supplies. Cost of damage was $5B
Secondary: Ground-shaking triggered landslides and avalanches, blocking roads and hampering relief efforts. Avalanches on Mt. Everest killed 19 people. Avalanche in Langtang lead 250 people missing.
What were the immediate and long-term responses in Chile?
Immediate: Power and water restored to 90% of homes within 10 days. National appeal raised $60M - enough to build 30,000 shelters. Temporary repairs made to route 5 within 24 hours enabling aid to be transported.
What were the immediate and long-term responses in Nepal?
Immediate: 300,000 people migrated from Kathmandu to seek shelter. Social media widely used in search and rescue operations. Field hospitals set up to support overcrowded main hospitals. Financial aid pledged from many countries.
Long-term: 7000 schools to be re-built or repaired. Stricter controls on building codes. Road repaired and landslides killed. Lakes emptied to avoid flooding.
Why do people continue to live in areas at risk from a tectonic hazard?
Volcanoes bring fertile soils, rocks for building, rich mineral deposits and hot water. Fault lines associated with earthquakes can allow water supplies to reach the surface, important in dry regions. Some people may not be aware of the risks and people living in poverty may not have a choice.
How does monitoring, prediction, protection and planning reduce the risks from a tectonic hazard?
Monitoring: Remote sensing - satellites detect heat and changes to the volcanoes shape. Gas - instruments detect gases released as magma rises. Geophysical measurements - detect changes in gravity as magma rises to surface.
Prediction: Identify locations that are most at risk using historic records. Increase in earthquake activity beneath volcanoes to make accurate predictions about eruption.
What is a natural hazard?
A natural event that has had a huge social impact.
What different types of natural hazards are there?
Volcanic eurptions, earthquakes, storms, tsunami, landslides, flootds
What factors affect hazard risk?
Climate change - warmer worlds means the atmosphere will have more energy leading to more intense storms and hurricanes, May also cause some parts of the world to become wetter with risk of flooding.
Poverty - Many people are forced to live in areas at risk. Shortage of housing leads people to build on unstable slopes prone to floods and landslides.
Urbanisation - Densely populated urban areas are at great risk from natural events such as earthquakes and tropical cyclones.
