Mount St Helens is located in Skamania County, Washington State in the Pacific Northwest of the USA. It measures around 9.5km (6 miles) across its base and is 2,549m (8,364ft) high.

Mount St Helens is a stratovolcano, which means it has a conical shape with steep sides made up of layers of lava flows, ash and other volcanic debris. Native Americans who lived in the area knew that this was no ordinary peak and called it Louwala-Clough, meaning 'Smoking Mountain' or 'Fire Mountain'.

In 1792 a group of British explorers from HMS Discovery became the first Europeans to sight the mountain during a survey expedition around the Pacific coast of the north-west of America. It was named Mount St Helens by Captain George Vancouver in honour of British diplomat, Alleyne Fitzherbert, the first Baron of St Helens.

The Cascade Range, where Mount St Helens is located, has been active for 40,000 years or so, but the volcano itself didn't appear until around 2,500 years ago. It was then that magma (molten rock) first came to the surface and began to shape the mountain that we see today. Since then there have been five eruptive periods. The first of these that we have written records for is the Goat Rocks Period which began in 1800. It was during this time that the dome on the top of the volcano appeared, which subsequently collapsed when Mount St. Helens erupted once more in 1980.

Although there was minor activity the volcano was dormant from 1857 until 1980 and the local residents and visitors saw it as a picturesque, recreational haven rather than a deadly volcano with explosive potential. The area around the peak teemed with wildlife and the clear waters of Spirit Lake at the base of the northern flank became popular for various leisure activities like fishing, boating and camping.

The volcano is in the Gifford Pinchot National Park and in 1982 President Ronald Reagan designated the 445 sq km (110,000 acres) around it as the Mount St Helens National Volcanic Monument.