Tectonic hazards and causes

Plate boundaries
1. Convergent
  1. Oceanic crust is denser than the continental plate and so when they converge the oceanic plate is subducted. Melting occurs 1000km below the surface
  2. Earthquakes are common at the Benioff zone where plates get locked due to the pressure and break after release.
  3. Philippines
    1. Samar Island
    2. Mount Mayon
    3. Bohol Island
2. Divergent
  1. Pressure from rising magma leads to a doming of the surface and the formation of a ridge.
  2. Close proximity of the surface and so the pressure is easily released.
  3. Eyjafllajoekull volcano, Iceland
3. Transform
  1. Haiti
  2. No magma is released or destroyed and no new crust is formed. Two crusts move in the similar direction.
4. Collision
  1. Two continental plates collide and can form new mountains.
  2. Balochistan, Pakistan
5. Hot spot
  1. Magma rises from the asthenosphere even they may not be necessarily close to a plate boundary. If the crust is thin or weak, the magma may escape.
What else causes tectonic hazards?
1. Fracking
  1. Way of extracting methane from shale rock. A mixture of water, sand and chemicals are injected under high pressure. This process triggers small earthquakes and explosions.
  2. Blackpool, UK
2. Isostatic rebound theory
  1. Lithosphere can change shape and tend as a result of a heavy mass (ice sheets). There is a point reached where the lithosphere is supported. As a result of climate change (ice sheet melted), the lithosphere can rebound as a result and produce small earthquakes.
What is the evidence for tectonic hazards?
1. Continental drift
  1. Alfred Wegner (1912) -this 300 million years ago was a single continent known as Pangea.
2. Magnetic magma
  1. Molten lava is magnetic, when it is liquid, it wants to align with poles, some rocks are aligned opposite as the magnetic field has changed. There are patterns (1000km) away symmetrically suggests they were once together.
What will happen in the future for tectonic hazards?
1. There is evidence that the Mediterranean is closing.
  1. Africa is colliding with Italy. This is shown in Mt Stromboli as water vapour is in the trapped gases.
2. Pangea Ultima
What is the deadliest tectonic hazard?
1. January 1556 in Shaaxi, China. There was a 8.0 magnitude earthquake and 1 million deaths.
2. The volume of deaths is because many people who live in Shaaxi live in caves. As an earthquake occurs, the caves are very soft and so the shockwaves caused the caves to collapse.
3. It may occur again as forty million people live there now.
What is the costliest tectonic hazard?
1. Sendai, Japan 2011
2. Direct loss of $210 million.
3. Reconstruction of $244 billion.
Hazard profiles
1. Frequency
  1. Volume of tectonic hazards that occur in an area.
2. Magnitude
  1. The higher volume of tectonic hazards, the lower the magnitude because there hasn't been a high level of pressure build up.
  2. Intensity of the hazard.
3. Areal extent
  1. What is the widespread extent effect of a tectonic hazard?
    1. Volcanoes have a wider areal extent because of the lava expelled.
4. Areal reliability
5. Duration
  1. Time taken for the tectonic event to take effect.
6. Speed of onset
  1. Time taken for the tectonic event to take effect.
What is the difference between a tectonic event, tectonic hazard and tectonic disaster?
1. A tectonic event is a physical occurrence that occurs as a result of the movement of the Earth.
2. A tectonic hazard is a tectonic event that has the potential to cause a loss of life or damage to property.
3. According to UNISDR: 10+ people are killed/ 100+ people are affected/state of emergency is declared/international aid is received.
What are the threats from tectonic hazards?
1. Earthquakes
  1. Ground outbursts
    1. Movement of the Earth's crust has an impact on buildings and infrastructure.
  2. Tsunamis
    1. Ocean waves with extremely long wave lengths caused by earthquake tremors.
  3. Landslides
    1. Movement of masses of rock and debris down a slope. Slope failure can occur as a result of an earthquake or heavy rain.
2. Volcanoes
  1. Lava flows
    1. This is the lava expelled from a volcano.
    2. Lahars
      1. They are known as mud flows where meltwater mixes with loose soil and ash.
  2. Tephra
    1. Explosive blasts.
  3. Glacial outbursts
    1. Masses of water/ice is released from a glacier and can be turned into a mudflow.
  4. Ash flows
    1. Ash flows also known as pyroclastic flows.
  5. Ash falls
    1. Very disruptive.
How are tectonic events measured?
1. Mercalli scale
  1. This measures the intensity; it quantifies the effects of earthquakes.
2. Richter scale
  1. It is calculated from the amplitude of the largest seismic wave during the event. It is a 10 logarithmic scale.
3. VEI
  1. Volcanic explosivity index
What are the causes of tectonic hazards?
1. Asthenosphere is heated by radioactive decay (of elements such as Uranium). As the radioactive source is heating the asthenosphere, the fluid magma circulates because of the convection currents leading to plate tectonics.

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	Created by Bethany. about 11 years ago