Mount St Helens is located in the Cascade mountain range in Washington in the United States and is famous for its devastating 1980 eruption, which killed 57 people. The victims closest to the eruption were killed almost instantly when an earthquake triggered a huge landslide that unleashed a sideways blast that sent clouds of hot gas, ash and rock speeding away from the volcano.
Mount St. Helens, Washington State, began its most recent series of eruptions in 1980 when a massive landslide and powerful explosive eruption created a large crater, and ended six years later after more than a dozen eruptions of lava built a dome in the crater.
The first sign of activity began in the spring of 1980 with a series of small earthquakes. After thousands of additional earthquakes and steam explosions, a catastrophic eruption occurred on the 18th of May 1980.
Mount St Helens lies close to a destructive plate boundary where the smaller Juan de Fuca plate is being forced into the mantle by the larger North American plate.
Friction and heat cause the plate to melt and, as it melts, molten rocks are formed. The molten rock builds up until it has the chance to reach the surface through cracks in the Earth’s crust.
The eruption had a huge impact on the landscape and the population, resulting in devastating outcomes.
The mountain was reduced from a height of 2950m to 2560m as the eruption created the largest landslide ever recorded.
All plant and animal life within a 25km radius of the volcano was killed, including fully grown trees.
Mud flows poured down the valleys choking rivers with rock debris, killing fish and ripping trees from their roots.
Sixty one people died due to mud flows, being crushed to death and poisonous gases, while 198 had to be rescued.
Mud flows destroyed bridges, houses and roads.
The explosion flattened buildings and trees and knocked out power supplies and telephone lines.
Ash clouds resulted in airline flights being cancelled.
Ash caused £100 million of damage to farm machinery and crops.