Volcanic Eruption at Mount St Helens
Washington State, North West U.S.A. The Rocky Mountains
| |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 |
|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 |
|520km of pine forests flattened up to 20km away from the eruption – landscape totally changed | |ash and mud blocked roads, chocked rivers...