On 18 May 1980 a young geologist radioed a warning. Moments later he was killed by an explosion more terrible than any seen in North West America. The volcanic blast of Mount St Helens, that took his and 62 other lives, was 500 times the power of the Hiroshima bomb. For 30 kilometres it stripped the branches from the national forest and combed the tree trunks flat against the hills. Digging ash out of their mouths with their fingers, in order to breathe, survivors struggled for hours through a suffocating cloud which blotted out the sun.
Throughout the summer Horizon followed the geologists as they landed their helicopters in the mouth of the crater, measuring scalding pumice and toxic gas. St Helens had caught them by surprise, but now they are collecting new evidence from a mountain that could go on erupting for 20 years.
Narrator RAY MOORE
Spectacular footage (the DAILY TELEGRAPH) Constantly fascinating (THE GUARDIAN) Editor SIMON CAMPBELL-JONES
Written and produced by STUART HARRIS A Horizon production