Tectonic processes and hazards 5th set

Seismic waves

Shock waves released by the rupture of rock strata at the focus of an earthqauke. They travel through the rocks and are recorded on a seismograph

Sill

Horizontal intrusions of magma along the bedding planes of sediment rock

Soil liquefaction

The process by which water-saturated material can temporarily lose normal strength and behave like a liquid under the pressure of strong shaking. Liquefaction occurs in saturated soils (ones in which the pore space between individual particles is completely filled with water). An earthquake can cause the water pressure to increase to the point where the soil particles can move easily, especially in poorly compacted sand and silt.

Solfatara

Small volcanic areas without cones. Produced by escaping gases

Subduction

When a denser plate is forced under a lighter one as they collide into each other

Subduction zones

These are broad areas where two plates are moving together, often with the thinner, more dense oceanic plate descending beneath a continental plate. The contact between the plates is sometimes called a thrust or megathrust fault. Where the plates are locked together, frictional stress builds. When that stress exceeds a given threshold, a sudden failure occurs along the fault plane that can result in a 'mega-thrust' earthquake, releasing strain energy and radiating seismic waves. It is common for the leading edge to lock under high friction. The locked fault can hold for hundreds of years, building up enormous stress before releasing. The process of strain, stress and failure is referred to as the 'elastic-rebound theory'.

Tectonic hazard profile

A technique used to try to understand the physical characteristics of different types of hazards, for example earthquakes, tsunamis and volcanoes. Hazard profiles can also be used to analyse and assess the same hazards which take place in contrasting locations or at different times. Hazard profiles are developed for each natural hazard and are based on criteria such as frequency, duration and speed of onset.

Tephra

Any solid material from an eruption e.g. Volcanic bombs, ash particles

Trench

A deep crevice at the point of collision at a destructive plate boundary

Tsunami

The word comes from two Japanese words: tsu (port or harbour) and nami (wave or sea). Tsunamis are initiated by undersea earthquakes, landslides, slumps and, sometimes, volcanic eruptions. They are characterised by: low amplitude (wave height), 0.5-5 m, long wavelengths, typically 150-1000 km, fast velocities, up to 600 kph in deep water.

Volcanic gases

an impact of volcanic activity. Including carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine

Volcanic hazards

Associated with eruption events.

Volcanic landslide

landslide due to volcanic activity

Volcano

A landform that develops around a weakness in the Earth's crust from which molten magma, volcanic rock, and gases are ejected or extruded.