Distribution of Hazards

Distribution of Hazards

1. Geophysical

   • Volcanoes
     • Constructive (Divergent) plate boundary
       • Most of these volcanoes are on the sea floor and do not present a major hazard to people with the exception of when they emerge above sea level to form islands e.g. Iceland.
       • Rift valleys occur where the continental crust is being stretched. For example the East African rift valley has a line of 14 active volcanoes some of which can produce violent and dangerous eruptions (Mt Nyragongo in DR Congo).
     • Destructive (Convergent) plate boundary
       • 80% of the worlds volcanoes occur along destructive plate boundaries.
       • Oceanic - Oceanic, Soufriere Hills in Montserrat.
       • Oceanic - Continental, Mt St Helens in Washington.
   • Earthquakes
     • Primary hazards - Collapse of buildings and infrastructure (water pipes/ gas supply) Secondary hazards - Soil liquefaction, landslides, avalanches, tsunamis and exposure to adverse weather.
     • Destructive (Convergent) plate boundary
       • Continental - Continental Oceanic - Oceanic Continental - Oceanic These are where the most frequent and highest magnitude earthquakes occur due to the force of compression as the plates meet, causing stresses in the crust. When the pressure is released the ground above shakes violently.
       • Features - Fold mountains, highly damaging earthquakes
     • Conservative (Transform) plate boundary
       • This is where lateral crust movement occurs, i.e. San Andreas Fault in California. These produce frequent shallow earthquakes, sometimes of high magnitude.
     • Constructive (Divergent) plate boundary
       • These are usually submarine (Iceland is an exception)  and are associated with shallow, low magnitude earthquakes as the crust pulls apart.
     • Other areas
       • A small minority of earthquakes occur at intra-plate locations usually as a result of old fault lines e.g. Church Stretton fault in Shropshire.
       • Some earthquakes occur as a result of human activity, e.g. dam/resevoir building and fracking.

2. Slides

   • Landslides
     • 7th biggest killer, causing over 1400 deaths per year (more than volcanoes or drought).
     • They occur in mountainous areas, after heavy rain and after seismic activity. Human factors such as deforestation and building on hillsides also increase the risk of slides (Philippines)
   • Avalanches
     • Occur in high mountainous areas such as the S. Alps of NZ or the Rockies in N. America. Occur on slopes steeper than 35 dgs.
     • 150+ deaths per year caused by avalanches.
     • Global warming may be increasing avalanche occurrence. Trends in deaths have slowed due to effective managenent.

3. Hydro-meteorological

   • Droughts
     • Causes: Variation in the ITCZ which moves North and south through Africa bringing a band of seasonal rain. Sometimes high pressure zones block rain to areas like Ethiopia and Somalia.
     • El Nino can cause major changes to rainfall patterns, leading to drought in Indonesia and Australia.
     • Changes in mid-latitude depression tracks have caused droughts in UK and France (1976, 1989-92, 1995, 2003,2006)
   • Flooding
   • Storms