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Causes of Tectonic hazards (Tsunamis (Tsunami characteristics are…
Causes of Tectonic hazards
Volcanoes
Major volcanic eruptions frequently have more than one hazard associated with them. In some cases, these are secondary hazards, which are an indirect consequence of the eruption. This is especially the case with the violent eruptions associated with volcanoes at destructive plate margins.
Volcanic hazards
Lava flows
= extensive areas of solidified lava, which can extend several km from volcanic vents if the lava is basaltic and low viscosity. Can flow up to 40km
Pyroclastic flow
= very large, dense clouds of hot ash and gas at temperatures of up to 600’. They can flow down the flanks of volcanoes and devastate large areas.
Ashfall
= ash particles can blanket huge areas in ash killing vegetation collapsing buildings and poisoning water.
Gas eruption
= the eruption of co2 and sulfur dioxide which can poison people and animals in extreme cases.
Tsunamis
The violent motion displaces a large volume of water in the ocean water column, which then moves outward in all directions from the point of displacement.
The water moves at a vast ‘bulge’ in open water, rather than a distinct wave.
Tsunamis are mostly generated when a sub-marine earthquake displaces the sea bed vertically as a result of movement along a fault line at a subduction zone. However, they can also be generated by landslides and volcanic eruptions.
Tsunami characteristics are different from those of wind-generated ocean waters:
wave heights are typically less than 1 m
wavelengths are usually more than 100 km
Speeds are 500-950 km
Tsunamis are not noticeable in the open ocean. When the wave approaches the shore, they slow down dramatically and the wavelength drops, but the wave height of the wave increases. They also hit coastlines as a series of waves called a ‘wave-train’.
Submarine earthquakes that occur close to shorelines can generate intense ground-shaking damage, followed by damage from the subsequent tsunami.
The distribution is around 90% that occur in the pacific basin associated with activities in the plate margin. Most are generated at subduction zones.
Earthqaukes
As tectonic plates attempt to move past each other along fault lines, they inevitably ‘stick’.
Earthquakes are a sudden release of stored energy.
Allows strains to build up over time and the plates are placed under increasing stress
Generated because of sudden stress; called stick-slip’ behaviour
A pulse of energy radiates out in all directions from the earthquake focus (point of origin).
