News and Research
History of Mount St. Helens
by Christine Colasurdo
THE CASCADE RANGE
Mount St. Helens is one of many volcanoes in the West Coast’s Cascade Range, which stretches from Lassen Peak in California to Mount Garibaldi in British Columbia, Canada. A part of the Ring of Fire, the Cascade Range was created by the Earth’s tectonic plates slowly colliding over eons. Mount St. Helens is the result of a “subduction zone”—where one plate slides underneath another. At Mount St. Helens, the smaller oceanic Juan de Fuca plate is sliding under the continental North American plate.
MOUNT ST. HELENS’ GEOLOGIC HISTORY
On March 20, 1980, while the forests of Mount St. Helens lay under deep snow, earthquakes rocked the quiet woods—and stunned people across Oregon and Washington. How could such a tranquil mountain shake? Then, on March 27, steam and ash erupted from a small vent near the mountain’s summit. Suddenly Mount St. Helens was no longer a serene and snowy mountain but an ash-stained, active volcano.
Although the public was surprised by the small March eruption, geologists had been studying the volcano for years. They knew that it was the youngest and most active volcano in the Cascade Range—and overdue for an eruption. In 1978, the US Geological Survey published a bulletin alerting the public that Mount St. Helens was likely to erupt violently before the end of the twentieth century. Authored by geologists Dwight Crandell and Donal Mullineaux, the bulletin warned of mudflows, lava flows, ash fall, explosive gases, and avalanches. Crandell and Mullineaux concluded that “Future eruptions of Mount St. Helens are a near certainty.” The geologists even guessed at the location of future eruptions: a lava dome on the volcano’s north side called Goat Rocks.
Goat Rocks was only 150 years old. In fact, geologists had determined that most of the visible part of Mount St. Helens was a mere 1,000 years old. This young pile of rock sat atop an “older volcanic center” that had erupted more than 36,000 years ago. In terms of geologic age, even this ancestral Mount St. Helens was a relatively new volcano. And its most recent history was a violent one: for the last 4,000 years the mountain had erupted every 150 years or so to create and destroy itself time and again.
From March 27 through May 17, Mount St. Helens swelled with magma. The Goat Rocks area expanded five feet per day in April. By May 17, the volcano had ballooned into a deformed mass of magma, explosive gases and increasingly hot groundwater. Its snowy profile was peppered black by ash, and a stream of melting glacial ice was coursing down its north side.
Then, on the morning of May 18, Mount St. Helens burst apart. Shaken by a 5.1 earthquake at 8:32 a.m., the volcano’s entire north flank collapsed. Within seconds the crumbling mountain roared northward into Spirit Lake as well as into the Toutle River’s north fork, becoming the largest landslide in recorded history. As the mountain fell away, it also blew skyward. Blocks of glacial ice the size of small houses were hurtled for miles. Huge plumes of ash shot into the atmosphere, causing lightning storms and turning the sky in eastern Washington dark as night. Crows fell lifeless from the sky.
But the most powerful part of the eruption was its lateral blast. Instead of erupting upward, Mount St. Helens blew sideways. A 650-mile-per-hour wind of gas, rock, and ash swept over a 230-square-mile area, killing nearly everything in its path. The 600-degree F. blast vaporized the forest near the volcano. As it fanned outward, it uprooted and combed trees down, and then finally, losing force, it left trees standing but scorched to death. Hundreds of small forest fires caused by the blast burned for days.
The May 18 eruption of Mount St. Helens lasted for more than nine hours and killed 57 people through the force of its mudflows, lateral blast and ash fall. Countless elk, bear, cougar and other forest species perished. Lakes were cooked clean of fish, and millions of dollars’ worth of private property was destroyed.
THE NATIONAL VOLCANIC MONUMENT
After experiencing the awe-inspiring force of the 1980 eruption and its powerful lessons, the U.S. Congress and President Reagan signed into law in 1982 the creation of the Mount St. Helens National Volcanic Monument. This 110-000-acre national monument was set aside to:
- protect the area’s geologic, ecological and cultural resources
- protect the monument’s significant features
- ensure public health and safety
- permit scientific research within the monument
- provide for recreation
Situated within the Gifford Pinchot National Forest, the Mount St. Helens National Volcanic Monument is administered by the U.S. Forest Service. Most of the area affected by the May 18, 1980 lateral blast lies within monument boundaries. This blast-affected area is known as Mount St. Helens’ blast zone.
THE VOLCANIC LIFE CYCLE AT MOUNT ST. HELENS
Although many people believed that Mount St. Helens had obliterated all life forms in the path of its lateral blast, scientists discovered a month after the eruption that life had indeed survived—in protected pockets. Hibernating animals and dormant plants protected by heavy snow survived the eruption to recolonize the blast zone.
In the last three decades, life has returned to the blast zone far more quickly than scientists expected. Beetles were among the first animals discovered after May 18, and now more than 300 species of beetles thrive near the mountain. Lupines were among the first plants to root in the deep volcanic ash, and scientists are still studying how their presence helps other species return to the harsh volcanic landscape. A new forest of Douglas fir and Pacific silver fir is growing higher every year, and forest inhabitants such as elk, deer, cougar, bear, fish, birds and amphibians have found new homes in the returning forest.
Thanks to the creation of the Mount St. Helens National Volcanic Monument, people around the world can watch and study how life returns on its own, without human involvement, after a major eruption. The public can witness the natural cycles of life and death that have occurred for millennia throughout the Cascade Range.
THE VOLCANO SINCE 1980
Since May 18, 1980, the volcano has erupted many times. The eruptive cycle that began in 1980 continued until 1986, with a new lava dome appearing on the crater floor. After 1986, the volcano lay mostly quiet for more than a decade, then began a new eruptive cycle in September 2004, which lasted until July 2008. The second eruptive cycle created a new, larger lava dome with fresh lava appearing as fast as a dump-truck load in volume every second.
With its glaciers beheaded by the May 18, 1980 eruption, the volcano has lost its summertime glacier-white crown. But it has gained a new glacier in its crater. Known as the Crater Glacier, this growing mass of ice was halved in two by the dome-building eruptions of 2004-08. The lava dome is now encircled by glacial ice.
The U.S. Geological Survey monitors Mount St. Helens intensively. A team of scientists stationed at the Cascades Volcano Observatory keeps a close watch on the volcano’s seismicity, deformation, gas and steam emissions, debris flows, ash fall, and other hazards.
Sources: USGS Bulletin 1383-C (1978); Colasurdo (1997); Geological Survey Professional Paper 1250 (1981).
