Formed on the Juan de Fuca plate (Oceanic crust) which moves towards the North American plate (Continental Crust) and is forced downwards.

On the 18th of May 1980 Mount ST Helens blew her top.

Early in May, the North side was bulging - this was an early indicator.

Mud exploded and moved down the mountain.

61 deaths were reported, most of which were caused by the release of poisonous gasses.

Trees within 30km radius were destroyed by the wind.

Floods prevented communication.