Follows boundaries of tectonic plates - thought to be moved by large scale convection currents driven by radioactive decay of the Earth's core.
where new ocean floor accumulates on either side of a mid-oceanic ridge as plates move apart - causing SHALLOW FOCUS earthquakes
dense, oceanic plate is driven below a continental plate as they converge - causes DEEP FOCUS earthquakes in the subduction zone
plates slide past each other laterally and due to friction they have sudden and jerkey movements - causes SHALLOW FOCUS earthquakes
- some earthquakes occur far from the boundaries because they are on transform faults which run perpendicular to the plate boundary
Closely linked to the distribution of volcanoes.
where dangerous, volatile volcanoes are. violent erruption of viscous lava which is produced by the partial melting of oceanic plate material in the subduction zone.
lava plateus and shield volcanoes that form here, eg the ones in Iceland, are less explosive due to non-viscous lava - less disaster threat
not generally associated with volcanoes
occur on slopes wherever the SHEARING STRESS acting on the slope exceeds SHEARING RESISTENCE.
- coastlines undercut by waves causing collapse
- upland areas of high relief
- areas that have recently undergone deforestation
they occur when
- BANKFUL DISCHARGE has been reached in a river (fluvial flooding)
- when high tides drive seawater inland (coastal flooding)
- when water collects in depressions because of HIGH INTENSITY RAINFALL (pluvial flooding)
The pattern shows high occurance
-on the floodplains of major rivers
-areas with a monsoon climate, especially if there is deforestation
they are Low pressure weather systems which bring multiple risks; high wind speeds, heavy rainfall and flooding.
- 5 to 20 degrees North and South of the equator
- begin as a body of moisture over tropical ocean of 26degrees
- Coreolis force rotates the mass around an eye
- depressions form in the mid-latitudes between 40 and 60 degrees north of the equator where the tropical and polar air masses converge at the polar front (under conditions of divergent flow of the jet stream)
extended period of low rainfall relative to the expected average for a region.
They occur periodically:
- in mediterranean climates when the rainy season is late
- in the mid-latitudes because of changes in the behaviour of air masses and the jet stream eg UK droughts in 1976, 2006 and 2011
- either side of the pacific ocean due to ENSO cycles