Tectonic Hazards

• What is an earthquake?

  An earthquake is a sudden, violent period of ground-shaking.
• How doe earthquakes occur and where do they usually occur?

  Most occur at the margins of slow-moving tectonic plates. Friction and sticking between plates creates enormous pressures and stresses which build to breaking point
• What are tectonic plates?

  The Earth's crust and upper part of the mantle is cracked into a number of large pieces, known as tectonic plates
• What are the two types of crust?

  Dense, thin oceanic crust and less dense, thicker continental crust
• How do plates move?

  convection currents in the mantle
• What are volcanoes and what is their distribution?

  Volcanoes are large, often cone-shaped landforms formed over long-periods by several eruptions. They are fed by molten rock (magma) deep within the Earth's mantle and like earthquakes, most occur in belts along plate margins. But some occur at hot spots where the crust is thin and magma breaks through the surface
• What are three different plate margins?

  Constructive, destructive, conservative margin
• What happens at a constructive margin?

  -The two plates move apart and magma forces its way to the surface. As it breaks the crust it causes mild earthquakes

  -The magma is very hot and fluid allowing lava to flow a long way before cooling. This results in typically broad and flat shield volcanoes
• What is an example for a constructive margin?

  -Iceland sits on a constructive plate boundary

  -It is located on the North American and Eurasian plate and when these plates move away it forms the Mid-Atlantic Ridge
• What happens at a destructive margin?

  -Two plates move towards each other and dense oceanic plate is subducted beneath the less dense continental plate. Friction and the build up of pressure causes strong earthquakes

  -The sinking oceanic plate creates sticky, gas-rich magma which results in steep-sided composite volcanoes which erupt violently

  -When two continental plates meet there is no subduction, so no magma to form volcanoes. The crust crumples and lifts to form fold mountains and powerful earthquakes can be triggered
• What is an example of a destructive margin?

  The Nazca plate being forced under the South American plate

  -the Andes which are fold mountains
• What happens at the conservative margin?

  Two plates move past each other at different rates. Friction between the plates build stresses and trigger earthquakes when they slip. There are no volcanoes because there is no magma
• What is an example of a conservative margin?

  At the San Andreas Fault, the Pacific plate is moving in the same direction as the North American plate but faster
• Where do the majority of tectonic hazards occur?

  The majority of tectonic hazards occur at plate margins, some of which run through densely populated regions such as Japan, parts of China and southern Europe
• Why do people live in (tectonic) hazardous areas?

  -Volcanoes can bring benefits such as fertile soils , rich minerals deposits and hot water

  -Some people have no experience or knowledge of the risks

  -Poor people have no choice - money, food and family are seen as more important

  -Earthquakes and volcanic eruptions are rare, so not seen as a great threat

  -Earthquake-resistant building designs reduce the risk and effective monitoring of volcanoes and tsunami waves allow evacuation warnings to be given
• How can we manage the risk of tectonic hazards?

  We can reduce the risk from tectonic hazards through four main management strategies:

  -Monitoring

  -Prediction

  -Protection

  -Planning
• How can risks from Earthquakes be reduced by monitoring?

  Earthquakes generally occur without warning. Whilst there is some evidence of raised groundwater levels, bulging of the ground and microquakes before the main tremor, scientists have yet to discover a reliable ways to monitor earthquakes
• How can risks from Volcanoes be reduced by monitoring?

  All active volcanoes are now monitored using hi-tech scientific equipment which includes:

  -remote sensing: satellites detect heat and changes to the volcanoes shape

  -Seismicity: seismographs record microearthquakes

  -Ground deformation: changes to the shape of the volcano are measured using laser beams
• How can risks from Earthquakes be reduced by prediction?

  it is impossible to make accurate predictions about earthquakes due to the lack of clear warning signs. However historical records can help determine probability and so help in planning for them

  e.g. Istanbul, Turkey = Migration of the Earthquake along the North Anatolian Fault
• How can risks from Volcanoes be reduced by prediction?

  Monitoring is now allowing prediction and effective evacuation

  e.g. In 2010 an increase in earthquake activity beneath Iceland's volcano enabled scientist to make an accurate prediction about the eruptions that took place in March and April
• How can risks from Earthquakes be reduced by protection?

  Earthquake-resistant construction is the main way to reduce risk and this can be done through:

  -rubber shock-absorbers to absorb earth tremors

  -automatic window shutters to prevent falling glass

  -open areas where people can be assembled if evacuated
• How can risks from Volcanoes be reduced by protection?

  The sheer power of a volcanic eruption means that there is often little that can be done to protect people and property. However it is possible to use earth embankments or explosives to divert lava flows away from property and this has been done on the slopes of Mt Etna in Italy
• How can risks from Earthquakes be reduced by planning?

  Hazard maps have been produced for any of the world's most dangerous volcanoes showing the likely areas to be affected. The maps can be used in planning to restrict certain land uses or to identify which areas need to be evacuated when an eruption is about to happen
• How can risks from Volcanoes be reduced by planning?

  Hazard maps have been produced for any of the world's most dangerous volcanoes showing the likely areas to be affected. The maps can be used in planning to restrict certain land uses or to identify which areas need to be evacuated when an eruption is about to happen