MT ST HELENS
-Causes The eruption was caused by the Juan de fuca plate moving east, towards the north American plate. because the Juan de fuca is more dense, it is forced below the lighter North American plate. these movements cause friction, which then cause a rise in temperature, melts the earths crust. then, because the magma from the mantle is less dense than the recently melted north American plate, the magma rose to the surface and caused the mountain to bulge (by about 1.5 meters a day). the pressure became so great that the mountain exploded sideways.
-Effects
>Short term
- laval flows and ash filling in Spirit Lake and log jams and ash blocking the channel of the Toutle River;
- 57 people died in the eruption - most from poisonous gases;
- large number of wildlife were killed by the blast and the volcanic ash with nothing surviving in the blast zone
- flooding resulting from blocked rivers washed away road and rail bridges
- crops were ruined and livelihoods of loggers were devastated with large areas of trees being flattened like
matchsticks.
>Long term
- Trauma
http://wiki.answers.com/Q/What_were_the_causes_of_the_Mount_St_Helens_eruption
http://geobytesgcse.blogspot.com/2007/01/volcano-case-study-mount-st-helens-1980.html