Tectonics

Geophysical hazards occur near plate boundaries. These plates move at different speeds and directions which can cause collisions, earthquakes and volcanic activity as shown in the map above.

➔ Earthquakes can also occur near the middle of plates (called intra-plate). The causes of this are not fully understood but it is assumed that plates have pre-existing weaknesses which become reactivated, forming seismic waves. For example, an intraplate earthquake may occur if solid crust, which has weakened over time, cracks under pressure.

➔ Volcanic hotspots, such as the Ring of Fire, are also situated amongst the centre of pates. This is a localised area of the lithosphere (Earth’s crust and upper mantle) which has an unusually high temperature due to the upwelling of hot molten material from the core. (First theorised by Tuzo Wilson in 1963)

➔ At hotspots, such as the Hawaii hotspot, magma rises as plume (hot rock).

➔ Usually, the most powerful earthquakes occur at convergent or conservative boundaries. OFZ (Oceanic Fracture Zone) – This is a belt of activity through the oceans and along the mid-ocean ridges through Africa, the Red Sea, the Dead Sea CFZ (Continental Fracture Zone) – This is a belt of activity along the mountain ranges from Spain through the Alps to the Middle East and to the Himalayas.

Soil Liquefaction

● Affects poorly compacted sand and silt.

● Water moisture within the soil separates from the soil particles and rises to the surface. ● This can cause the soil to behave like a liquid, which can cause building subsidence or landslides.

Landslides

● The shaking caused by the earthquake can weaken or damage cliff faces, hills and snow material. ● Unconsolidated material or loose rocks can collapse.

● Landslides can travel several miles and accumulate material on the way. ● Risk varies with topography rainfall, soil and land use.

Tsunamis

● When an oceanic crust is jolted during an earthquake, all of the water above this plate is displaced, normally upwards

● This water is then pulled back down due to gravity. The energy is transferred into the water and travels through it like a wave.

● The water travels fast but with a low amplitude (height).

● As it gets closer to the coast, the sea level decreases so there is friction between the sea bed and the waves.

● This causes the waves to slow down and gain height, creating a wall of water that is on average 10 feet high, but can reach 100 feet. www.pmt.educatio