what was its impact on human from the 1980 eruption?
Fifty-seven people were killed; 250 homes, 47 bridges, of railways, and of highway were destroyed.
Mount St. Helens
Mount St. Helens is most notorious for its major eruption on May 18, 1980, the deadliest and most economically destructive volcanic event in US history. Fifty-seven people were killed; 250 homes, 47 bridges, of railways, and of highway were destroyed. 
what type of magma does mt st helens have Ash explosions and pyroclastic flows. where is it located? Skamania County, Washington, United States.
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Mount St. Helens [SEP] Introduction
As with most other volcanoes in the Cascade Range, Mount St. Helens is a large eruptive cone consisting of lava rock interlayered with ash, pumice, and other deposits. The mountain includes layers of basalt and andesite through which several domes of dacite lava have erupted. The largest of the dacite domes formed the previous summit, and off its northern flank sat the smaller Goat Rocks dome. Both were destroyed in the 1980 eruption.