Worst Volcanic Eruption in U.S. History
After weeks of earthquakes and eruptions that have only grown in intensity, geologists and citizens are anxiously waiting to see just what the Kilauea volcano has in store for the island of Hawaii. It is an odd and melancholy coincidence that during this time we recognize the anniversary of a similar major geological event.
On May 18, 1980, Mount St. Helens, a long dormant volcano in southwestern Washington state, let loose in a devastating eruption that the National Oceanic and Atmospheric Administration has labeled “the deadliest and most economically destructive volcanic event in the history of the United States.”
We can only hope that we do not witness an eruption on the scale of 1980 there, in Hawaii, or anywhere, for a long, long time.
Mount St. Helens is part of the Cascade Range of the Pacific Northwest, about 95 miles south of Seattle and 55 miles north of Portland, Ore. It is also part of the Ring of Fire, a 25,000-mile chain of volcanoes and active fault lines that rings the Pacific Basin and is home to 75 percent of the world’s volcanic eruptions and 90 percent of its earthquakes.
Geologists have determined that Mount St. Helens had a rich geological history going back 300,000 years with periods of violent activity followed by dormant intervals that sometimes lasted thousands of years. Many of these eruptions helped shape the volcanic mountain over time, with mudslides, solidified ash, and pyroclastic flow raising it to a height of 9,677 feet.
Mount St. Helens was discovered by Europeans in 1792 by a surveying mission led by Commander George Vancouver of the British Royal Navy. He named the mountain after Alleyne Fitzherbert, the First Baron St. Helens. No one realized at the time that it was a volcano. That came in 1835, after geologists and historians pieced together information from local Native American tribes and uncovered geological evidence from the region.
The mountain displayed minor volcanic activity in the early 1800s, producing ash plumes and low-level seismic rumblings. The last recorded eruption took place in 1857, after which the volcano was labeled dormant. There were small explosions that emitted from St. Helens in the early 1900s, but these were only steam ventings caused by molten rock deep underneath the mountain coming in contact with underground water sources.
In March 1980, Mount St. Helens woke up from its short geologic nap. Beginning on March 15, a series of small earthquakes rattled the area around the volcano. Scientists determined that they were caused by magma movement beneath the mountain. On March 27, a steam explosion caused by magma heating groundwater smashed rock within the crater at the summit and sent a plume of ash 7,000 feet into the air.
The earthquakes and venting continued throughout March and April, and a noticeable bulge had formed on the north face of the mountain. It pushed outward at the rate of about six feet per day, formed by magma pushing up from deep underground. By mid-May, the bulge measured more than 400 feet. Geologists feared that it would eventually give way, creating a landslide that would “uncap” the volcano and cause a major eruption.
Geologists and tourists flocked to Mount St. Helens, eager to catch one of its sporadic moments of venting. Nearby residents were at first encouraged to leave the area for their own safety, but later encouragement turned into a direct order to evacuate.
Harry Truman (no relation to the former president), 83-year-old owner of the nearby Mount St. Helens Lodge, refused to leave and became a national celebrity in the process.
“If the mountain goes, I’m going with it,” he told reporters. “The mountain is a mile away, the mountain ain’t gonna hurt me.”
During this time, earthquakes began to build in strength and frequency, and there was a general sense that this activity was going to lead to a major event. But no one knew what that event would look like or when it would happen.
On May 18, they got their answer. At 8:32 a.m. local time, a magnitude 5.1 earthquake struck below the north slope of the mountain. It dislodged the entire north face of Mount St. Helens, which slipped down into the North Fork’s Toutle River valley in a massive landslide. This landslide travelled at speeds of up to 155 miles per hour, with much of it filling the valley 600 feet deep with trees, mud, and other debris. This displaced much of the water in nearby Spirit Lake, which in turn caused more mudslides.
The landslide exposed the magma under St. Helens’s surface, which exploded outward seconds after the landslide began. A massive outburst laterally ejected extremely hot volcanic gas, ash, and rock. This pyroclastic flow travelled several times faster than the landslide underneath it, at one point reaching the speed of sound. The amount of thermal energy released was measured at 24 megatons.
The ash column reached 12 miles into the sky, dumping 540 million tons over an area of 22,000 square miles. Volcanic ash fell in tremendous quantities in nearby cities and towns and was later found in 11 states. In two weeks’ time, the dissipated ash cloud circled the globe.
The Mount St. Helens eruption completely devastated an area measuring 230 square miles. More than four billion board feet of timber was destroyed. Crops were wiped out for miles by ash and debris. More than 5,000 deer and 1,500 elk were killed, and 12 million salmon fingerlings died in their hatcheries.
At least 57 people were killed, including Truman, whose lodge was buried under 150 feet of volcanic debris in the opening moments of the eruption. More than 200 homes, 47 bridges, 185 miles of highway, and 15 miles of railway were destroyed. The devastation totaled $1.1 billion ($2.75 billion in 2018 dollars).
Mount St. Helens is 1,280 feet shorter after the 1980 eruption, and it is still active. Its last volcanic eruption was in 2008, and small earthquakes occasionally rumble from underneath. Geologists are not overly concerned about the current activity, but are keeping a close eye on things. We can only hope that we do not witness an eruption on the scale of 1980 there, or anywhere, for a long, long time.
Be sure to check out this amazing collection of photographs from before and after the 1980 eruption of Mount St. Helens.