How Mount St. Helens “Disappeared”
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Mount St. Helens was once a beautiful, symmetrical volcano in Washington State, rising to about 9,677 feet (2,950 meters) above sea level. For generations, its snow-covered cone dominated the landscape and was sometimes compared to Mount Fuji. But in the spring of 1980, the mountain began showing signs that something enormous was happening underground. Small earthquakes started on March 16, and by March 27, steam explosions had opened a crater at the summit. As magma pushed upward, the northern side of the mountain began bulging outward by as much as several feet per day. By May 17, the bulge had grown about 450 feet, warning scientists that the volcano was becoming dangerously unstable.
Then, on the morning of May 18, 1980, everything changed. At about 8:32 a.m., a magnitude-5.1 earthquake struck beneath Mount St. Helens. Within seconds, the enormous bulge and the entire northern summit began collapsing in what became the largest debris avalanche in recorded history. Millions of tons of rock and ice rushed down the mountain. The collapse suddenly removed pressure from the magma system, triggering a massive lateral explosion. The blast traveled at speeds of at least 300 miles per hour and devastated forests across roughly 230 square miles. The upper part of the mountain had essentially been blown and carried away, making it look as though Mount St. Helens had “disappeared.”
The eruption continued with extraordinary force. A gigantic column of ash and volcanic material rose more than 80,000 feet into the atmosphere, while pyroclastic flows raced down the volcano. Ash spread across large portions of the United States, and darkness fell over communities hundreds of miles away. The eruption ultimately reduced the mountain's height by about 1,300 feet, from 9,677 feet to roughly 8,363 feet. A huge horseshoe-shaped crater replaced the former symmetrical summit. Tragically, 57 people lost their lives, including USGS volcanologist David Johnston, who had been monitoring the volcano from a nearby observation post.
But Mount St. Helens did not truly vanish. Instead, the eruption dramatically transformed it. After the main explosion, smaller eruptions continued, and lava began slowly building a new dome inside the enormous crater. Between 1980 and 1986, repeated episodes of lava-dome growth added millions of cubic yards of rock to the volcano. By the end of this period, a new lava dome had risen hundreds of feet above the crater floor. The mountain therefore became a remarkable example of how a volcano can destroy part of itself and then begin rebuilding.
Today, Mount St. Helens remains one of the most closely studied volcanoes in the United States. Its 1980 eruption changed the landscape, destroyed vast forests, reshaped the mountain, and taught scientists important lessons about volcanic hazards. The mountain's summit is still much lower and dramatically different from the cone that existed before 1980, but it is far from dead. Later volcanic activity occurred between 2004 and 2008, demonstrating that Mount St. Helens remains an active volcano. What looked like the disappearance of a mountain was actually a spectacular transformation and a powerful reminder of the enormous forces operating beneath Earth's surface.
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