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was now a Pelean type, and the gas and pyroclastic materials were able to move at speeds of up to 250 kilometres an hour. Part of this pyroclastic flow went into nearby Spirit Lake, throwing out the water entirely, while the rest went off down a valley, travelling some 28 kilometres before coming to rest.
The blast demolished the huge forest that lay to
(Below) The pyroclastic flow gets under way in this spectacular eruption from Mount Saint Helens.