Volcanic Eruption at Mount St Helens
LOCATION
Washington State, North West U.S.A. The Rocky Mountains
CAUSE
| |This area is located on a destructive plate boundary |
| |N. American Plate (continental crust) and Juan de Fuca plate (Pacific plate(oceanic crust) collided – a subduction zone |
| |Pacific plate is sub ducted and pressure/heat causes rock to "melt" into magma |
| |increased pressure caused Mt St Helens to erupt above the magma hot spot |
ERUPTION
|May 18 1980 at 8.30am |
|An Earthquake of 5.0 on the Richter scale triggered the eruption |
|Huge lateral (sideways) blast of hot volcanic gases team dust and rock fragments released at over 100mph |
|Some lava erupted |
|Glaciers melted |
|Huge quantities of ash, steam and gas released |
|Biggest ever landside of soil, snow and rock ran down the mountainside and filled Spirit Lake - led to a huge mudslide |
RESULT
|520km of pine forests flattened up to 20km away from the eruption – landscape totally changed |
|ash and mud blocked roads, chocked rivers