Distribution of Volcanoes
Ocean ridges - Mid-atlantic Ridge. Mostly on sea floor. Only hazards to people when merge above sea level to form islands e.g. Iceland.
East African Rift Valley - line of 14 active volcanoes.
80% of worlds most active occur.
Oceanic plates subducted beneath continental plates.
Explosive volcanoes form e.g. Mt St.Helens + The Ring of Fire around the Pacific.
Distribution of Slides:
Mountainous areas after abnormally heavy rain or seismic activity.
Deforestation of hillsides in South East Asia and building on hills in Hong Kong - widespread slides following rain.
Global Warming may increase avalanches but deaths have slowed because of effective management.
High Mountainous Areas - Southern Alps of New Zealand or Rockies in North America (average of 100+ deaths per year)
Slopes steeper than 35'
Distribution of Drought:
Over 1/3 has exposure.
70% of worlds people and agriculture.
Causes: Variations in ITCZ - moves N and S through Africa; brings band of seasonal rain. High pressure zones expand and block rain-bearing winds.
Ethiopia and Somalia - famines.
El Nino - changes rain patterns; 2006 - drought in Australia & Indonesia.
Changes in mid-latitude depression tracks - Temperate regions = large amounts of rainfall.
If blocking anticyclones form - depressions track north = dry conditions; UK + France 2003 + 2006.
Distribution of Flooding:
Evident in some 33% of the worlds area.
Regional scale, high-magnitude floods frequent in India/Bangladesh & China.
Causes = Excessive rain due to atmospheric processes - monsoon rainfall + cyclones. Series of depressions can lead to prolonged rainfall = flash flooding.
El Nino - Mosambique 1997/2006.
Distribution of Storms:
Latitudes 5-20' North/South of the Equator
Move Westward once generated
26'C Sea Temperature - 70m depth
5'N or South of equator so coriolis effect can bring rotation of air
Cause: Heavy rain/ High wind + Velocity/ Very low central pressure = storm surges and coastal flooding
Most catostrophic are:
Localised areas of the lithosphere with an unusually high heat flow, magma rises to the surface as a plume e.g. hawaii.
As a lithospheric plate moves over a hotspot a chain of volcanoes is created.
Mudflows; (1983 mudflows from nevado del ruiz killed over 22,000 people.)