On May 18, 1980 – 34 years ago today — a cataclysmic eruption
occurred at Mount St. Helens. It was one of the most destructive
volcanic events ever recorded in the history of the United States.
Mount St. Helens is a 2549-meter (8363-feet) high
stratovolcano that
is located in Skamania County, Washington. It is the most active
volcano in the Cascade Range, which runs along the northwestern coast of
North America. The Cascade Range is part of the
Pacific Ring of Fire.
The eruption at Mount St. Helens on
May 18, 1980
was preceded by several geological events earlier in the year. Starting
on March 16, 1980, a series of small earthquakes struck the region, and
on March 27, 1980, a large amount of steam was vented from the volcano.
By mid-May, thousands of earthquakes had been recorded and a large
bulge had formed along the northern flank. The bulge extended outward to
approximately 140 meters (450 feet). All of this geological activity
indicated that magma was rising up into the volcano.
On the morning (8:32 a.m. PDT) of May 18, 1980, a 5.1 magnitude
earthquake struck and the bulging northern flank of the volcano
collapsed along with the summit. The collapse allowed hot pressurized
magma in the volcano to erupt and large amounts of material were ejected
over the course of the next nine hours. The ash plume from the eruption
reached a towering height of 24 kilometers (80,000 feet), and thick ash
blanketed the surrounding region.
Photograph of Mount St. Helens taken during the May 18, 1980 eruption. Image Credit: Oman/Combs, National Park Service.
The dense forest that covered the slopes of the volcano was reduced
to ash inside an area known as the inner blast zone, which extended
about 10 kilometers (6.2 miles) from the summit. Trees farther away from
the inner blast zone were also damaged by the searing heat.
Lahars, which are a type of volcanic landslide, formed rapidly from
the melting ice, snow and muddy debris released during the collapse of
the volcano’s flank and summit. The lahars caused extensive damage to
homes, roads and bridges in nearby communities outside of the inner
blast zone.
Fifty seven people including volcanologist David A. Johnston and
photojournalist Reid Blackburn lost their lives during the May 18, 1980
eruption at Mount St. Helens.
Mount St. Helens photographed seven years before the 1980 eruption. Image Credit: U.S. Forest Service.
Mount St. Helens photographed two years after the 1980 eruption. Image Credit: Lyn Topinka, U.S. Geological Survey.
Since 1980, Mount St. Helens has continued to experience periodic
earthquakes and volcanic eruptions, but not to the same extent of that
seen in 1980. The
Cascades Volcano Observatory
continues to monitor activity at Mount St. Helens, and while it is
still active, there are no current signs of a large impending eruption.
Bottom line: On May 18, 1980—34 years ago today—a cataclysmic
eruption occurred at Mount St. Helens. It was one of the most
destructive volcanic events ever recorded in the history of the United
States.
- EarthSky
