At 08:32 (local time) on 18 May 1980, Mount St Helens burst into life with power equivalent to 500 atomic bombs. Fifty-seven people lost their lives, including scientists who were studying the volcano at the time. Around 24,000 animals were killed and ten million trees were destroyed in the surrounding area. It's estimated that the volcano caused $2.500m worth of damage during one of the greatest eruptions ever recorded in North America.

The blast followed two months of intense activity which signalled that Mount St Helens was about to awaken once more. There were hundreds of small steam explosions, about 10,000 earthquakes and the northern side of the mountain expanded by around 80m (260ft).

When the volcano finally blew it shot a cloud of ash 24km (15 miles) into the air which was carried as far as 400km (250 miles) away. A pyroclastic flow of pumice, superheated ash and gas poured out of the crater, destroying some 240 sq km (150 sq miles) of the surrounding forest. The earthquake which followed measured 5.1 on the Richter scale, triggering an enormous landslide on the north flank of the mountain.

Geologists gathered valuable information about the landslide, which suggests that they are more common than was first believed. This has been of great help when assessing the risks of other volcanoes. The volcanic activity at Mount St Helens continued for another six years and lava was expelled inside the crater to form a dome.

Evidence suggests that Mount St Helens was active between 1600 and 1700 but before 1980 it had been dormant for 123 years, with only a few steam emissions around 1898, 1903 and 1921. In 1800 explorers, traders and missionaries heard about an eruption from local Native Americans, which signalled the start of the Goat Rocks Eruptive Period. Geologists began to study the volcano in the middle of the 19th century, and by 1857 the activity had formed the peak at the top of the mountain which was blasted away in 1980.