<P> By the time this pyroclastic flow hit its first human victims, it was still as hot as 360 ° C (680 ° F) and filled with suffocating gas and flying angular material . Most of the 57 people known to have died in that day's eruption succumbed to asphyxiation while several died from burns . Lodge owner Harry R. Truman was buried under hundreds of feet of avalanche material . Volcanologist David A. Johnston was one of those killed, as was Reid Blackburn, a National Geographic photographer . Robert Landsburg, another photographer, was killed by the ash cloud . He was able to protect his film with his body, and the surviving photos provided geologists with valuable documentation of the historic eruption . </P> <P> Subsequent outpourings of pyroclastic material from the breach left by the landslide consisted mainly of new magmatic debris rather than fragments of preexisting volcanic rocks . The resulting deposits formed a fan - like pattern of overlapping sheets, tongues and lobes . At least 17 separate pyroclastic flows occurred during the May 18 eruption, and their aggregate volume was about 0.05 cubic miles (210,000,000 m). </P> <P> The flow deposits were still at about 300 to 420 ° C (572 to 788 ° F) two weeks after they erupted . Secondary steam - blast eruptions fed by this heat created pits on the northern margin of the pyroclastic - flow deposits, at the south shore of Spirit Lake, and along the upper part of the North Fork Toutle River . These steam - blast explosions continued sporadically for weeks or months after the emplacement of pyroclastic flows, and at least one occurred a year later, on May 16, 1981 . </P> <P> As the avalanche and initial pyroclastic flow were still advancing, a huge ash column grew to a height of 12 miles (19 km) above the expanding crater in less than 10 minutes and spread tephra into the stratosphere for 10 straight hours . Near the volcano, the swirling ash particles in the atmosphere generated lightning, which in turn started many forest fires . During this time, parts of the mushroom - shaped ash - cloud column collapsed, and fell back upon the earth . This fallout, mixed with magma, mud and steam, sent additional pyroclastic flows speeding down St. Helens' flanks . Later, slower flows came directly from the new north - facing crater and consisted of glowing pumice bombs and very hot pumiceous ash . Some of these hot flows covered ice or water which flashed to steam, creating craters up to 65 feet (20 m) in diameter and sending ash as much as 6,500 feet (2,000 m) into the air . </P>

Areas affected by mt. st. helens eruption