Mt St Helens 1980 Eruption - Case Study

Mt St Helens Eruption – Sunday 18^th May 1980

Location and Hazard:

·         In the Cascade mountains

·         A composite volcano with andesitic lava

·         Destructive plate boundary – Juan de Fuca and North American plates

·         In March 1980 there were a series of small earthquakes and a bulge appeared

·         On May 18^th there was a 5.1 magnitude earthquake followed by an eruption of volcanic material – rock, ash, steam and hot gases

·         The lateral blast covered an area of 600km² north of the volcano

·         Pyroclastic flows, lahars and floods

·         540 million tonnes of ash deposited across an area of 57,000 km²

Social Impacts:

·         57 killed

·         200 homes destroyed

·         Unemployment rose tenfold

·         Social facilities were lost e.g. impossible to fish in Spirit Lake (filled with toxic gases)

·         Telephone lines and electricity supplies were knocked out

Economic Impacts:

·         Total cost…