Did You Know?

Did You Know?

During the 1980 Mount St. Helens eruption, the ash cloud grew to 80,000 feet (24 km) in less than 15 minutes. It eventually deposited ash in 11 U.S. states and five Canadian provinces, turning day into night in cities like Yakima and Spokane WA.

The eruption of Mount St. Helens on May 18, 1980, remains one of the most significant geological events in modern American history. Here are five key facts about that day:

1. The Largest Landslide in Recorded History

The eruption began at 8:32 a.m. when a magnitude 5.1 earthquake struck directly beneath the volcano. This triggered a massive collapse of the mountain's north face, creating the largest debris avalanche ever recorded. The landslide traveled at speeds of 110 to 155 mph and filled the North Fork Toutle River valley with an average of 150 feet of debris.

2. A "Lateral Blast" Rather Than a Vertical One

Unlike most famous volcanoes that erupt straight up, Mount St. Helens exploded sideways. Because the landslide removed the "capping" rock on the north flank, the pressurized magma beneath was suddenly uncorked. This lateral blast reached speeds of 300 mph and temperatures of 660°F, leveling 230 square miles of forest in just minutes.

3. Significant Loss of Life and Property

The eruption claimed the lives of 57 people, including volcanologist David A. Johnston and resident Harry R. Truman. It was also the most economically destructive volcanic event in U.S. history, causing roughly $1.1 billion in damage (over $3.5 billion in today's value), destroying 200 homes, 27 bridges, and 185 miles of highway.

4. The Ash Cloud Circled the Globe

A vertical plume of ash rose 80,000 feet (about 15 miles) into the atmosphere in less than 15 minutes. The ash cloud drifted across the United States in just three days and completely encircled the Earth within 15 days. In eastern Washington, the ash was so thick that it turned daylight into total darkness, causing streetlights to turn on at midday.

5. Permanent Change to the Skyline

Before the eruption, Mount St. Helens was often called the "Mount Fuji of America" due to its symmetrical, snow-capped cone. The eruption removed the top 1,300 feet of the summit, replacing the peak with a massive, horseshoe-shaped crater. The mountain's elevation dropped from 9,677 feet to 8,363 feet.