WASHINGTON - Wednesday, May 18 marks 42 years since Mount St. Helens erupted, killing 57 people. The event has been called the deadliest volcanic eruption in U.S. history.
The catastrophic explosion not only changed and destroyed lives, but devastated around 230 square miles of surrounding landscape. An estimated 7,000 animals, including bears, elk and deer, were also killed.
- March 20, 1980: A magnitude 4.2 earthquake hits, signaling the "reawakening" of the volcano after 123 years, according to the United States Geological Survey (USGS).
- Spring, 1980: Rising magma pushed the volcano's north flank outward of about five feet per day, according to USGS.
- 8:30 a.m., May 18, 1980: Within minutes of a 5.1 earthquake that hit, the volcano’s north flank collapsed, triggering the largest landslide in recorded history.
- Within 15 minutes, a vertical plume of volcanic ash rose over 80,000 feet, according to USGS.
After the eruption, the summit of Mount St. Helens was gone, forests were obliterated and rivers followed new courses. More than 150 new lakes and ponds were formed, and existing lakes filled with sediment, flooding their banks. The eruption created a mosaic of disturbances where the landscape continues to change.
The volcanic ash cloud drifted east across the United States in three days and encircled Earth in 15 days, according to USGS. Lahars, or volcanic mudflows, filled rivers with rocks, sand, and mud, damaging 27 bridges and 200 homes and forcing 31 ships to remain in ports upstream.
In 1982, the Mount St. Helens National Volcanic Monument was established for all to observe both the awesome destruction and the remarkable recovery of plants and animals.
Of call the Cascade volcanoes, Mt. St. Helens is monitored the closest. During the past 4,000 years, Mount St. Helens has erupted more frequently than any other volcano in the Cascade Range, according to the USGS.
"Just based on its history of being so active recently, we would expect it will most likely be active again in the near future," said Cascades Volcano Observatory research geologist Emily Johnson in 2021.
Since the 1980 eruption, scientists have come a long way in monitoring Mount St. Helens.
"We have such better technology and greater distributions of seismometers and monitoring equipment that we can see things we never had the ability to see before happening at the subsurface of these volcanoes," said Johnson.
Between the Cascades Volcano Observatory and the Pacific Northwest Seismic Network, there are 18 seismometers within 10 kilometers of Mt. St. Helens. With the advancement of satellite imagery, geologists are able to see deformation at very small scales.