This aerial view of Mount Saint Helens, Washington, shows the crater created by a massive volcanic explosion that destroyed part of the mountain in 1980.

Photograph by James P. Blair, National Geographic
  • On May 18, 1980, Mount St. Helens erupted in western Washington. It was the most devastating volcanic eruption in U.S. history. Fifty-seven people were killed. Hundreds of homes, businesses, roads, and bridges were destroyed. Material from the eruption—called a pyroclastic flow—destroyed 595 square kilometers (230 square miles) of forest. The volcano ejected a plume of ash 19-24 kilometers (12-15 miles) into the air, and volcanic ash was detected as far away as eastern Oklahoma. 
    The eruption of Mount St. Helens provided volcanologists with very useful data. Scientists tracked the volcano’s activity before it erupted, for instance, and noted that the eruption came after a series of earthquakes, the largest of which was a magnitude 5.1 that struck directly beneath the volcano just minutes before it erupted.  
    In 1982, the U.S. Forest Service established the Mount St. Helens National Volcanic Monument. The facility provides information and services for both tourists and researchers.
  • Term Part of Speech Definition Encyclopedic Entry
    data Plural Noun

    (singular: datum) information collected during a scientific study.

    destroy Verb

    to ruin or make useless.

    detect Verb

    to notice.

    devastate Verb

    to destroy.

    earthquake Noun

    the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

    eject Verb

    to get rid of or throw out.

    erupt Verb

    to explode or suddenly eject material.

    facility Noun

    a building or room that serves a specific function.

    forest Noun

    ecosystem filled with trees and underbrush.

    plume Noun

    single, upward flow of a fluid, such as water or smoke.

    pyroclastic flow Noun

    current of volcanic ash, lava, and gas that flows from a volcano.

    Encyclopedic Entry: pyroclastic flow
    research Noun

    scientific observations and investigation into a subject, usually following the scientific method: observation, hypothesis, prediction, experimentation, analysis, and conclusion.

    tourist Noun

    person who travels for pleasure.

    volcanic ash Noun

    fragments of lava less than 2 millimeters across.

    Encyclopedic Entry: volcanic ash
    volcano Noun

    an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

    Encyclopedic Entry: volcano
    volcanologist Noun

    scientist who studies volcanoes.