Geologists May Have Finally Solved The Mystery At The Heart Of America’s Deadliest Volcano

When the mighty peak of Mount St. Helens exploded on May 18, 1980, it sent a shockwave of destruction across the state of Washington. But for decades, scientists struggled to understand exactly what had happened. Apparently, this was far from a typical eruption; now experts have begun to figure out its secrets.

Thirty-four years after the deadly eruption, a group of researchers from a number of different institutions came together to study the mysterious volcano. Dubbed the Imaging Magma Under St. Helens project, or iMUSH, it sought to understand what was happening beneath the volatile peak. And now, four decades after the disaster, the experts have released some of their results.

Using a combination of cutting-edge techniques, researchers have spent years building up a clear picture of the geology of the volcano. And finally, they believe that they know what caused it to erupt. Unlike the neighboring peaks of the Cascade Range, Mount St. Helens does not sit above a mass of molten rock – so what exactly fuelled the fatal inferno?

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Located in southwest Washington, the 8,363-foot peak of Mount St. Helens is impressive even when it lies dormant. But although it is not the tallest mountain in the Cascades, it is definitely the most dangerous. In fact, this typically snow-capped mass is one of the most treacherous volcanoes in the entire United States.

According to experts, the geological turmoil that would ultimately lead to the formation of Mount St. Helens began some 275,000 years ago. For countless millennia, lava and ash spewed out of a rift in the ground, eventually creating a volcanic peak. However, much of what we see today is the result of comparatively recent activity.

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Over the past 3,000 years, a series of eruptions across the flanks and summit of Mount St. Helens have all made their mark on the shape of the volcano. And even today, that process remains ongoing. In fact, when settlers arrived in the region towards the beginning of the 19th century, they observed eruptions on the northern side of the peak.

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For the next half a century, Mount St. Helens continued to erupt on occasion. However, that did not stop a number of towns and settlements from springing up in the surrounding area. And when the volcano went dormant in 1857, the local residents may well have believed that the giant had gone to sleep for good.

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Sadly, that was not the case. More than 100 years later, on March 20, 1980, an earthquake shook the ground beneath Mount St. Helens, a clear indicator that the peace was about to be shattered. Afterwards, huge plumes of ash shot upwards into the sky, some reaching heights of up to 16,000 feet.

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As the weeks passed, new craters began to open up and researchers detected signs that magma was on the move beneath the volcano. And throughout April, Mount St. Helens continued to rumble, occasionally sending clouds of ash into the air. Towards the end of the month, however, things grew quiet once more.

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As April turned into May, researchers flocked to Mount St. Helens, keen to learn more about this strange and volatile beast. In order to keep a closer eye on the volcano, an observation post known as Coldwater II was constructed on the ridge of another mountain close by. From there, experts watched the simmering peak with bated breath.

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According to reports, the main point of interest was a bulge that had formed on the northern flank of Mount St Helens. Alarmingly, observers had noted that it was growing in size at a rate of five feet every day. Then, on May 7, the volcano began to rumble and smoke once more. After five days of this activity, another earthquake caused a huge avalanche on the northern side of the peak.

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All this time, the strange bulge had continued to grow. On the evening of May 17, volcanologist David Johnston arrived at Coldwater II to take care of the overnight shift. And in the early hours of the following day, he reported to the United States Geological Survey, or USGS, in Vancouver, WA. According to him, the anomaly had now reached more than a mile wide.

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Sadly, it was the last time that the USGS would receive a report from Coldwater II. Later that morning, just after 8:30 a.m., an earthquake measuring 5.1 on the Richter scale sent a shudder through Mount St. Helens. High above the volcano, two geologists in a private aircraft watched as a huge crack spread across the peak at lightning speed.

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Within moments, the entire northern side of the volcano slid away in the largest above-water landslide in recorded history. But the most terrifying part was still to come. As it fell, the rock relieved the pressure on the boiling magma beneath, causing an explosive – and deadly – eruption.

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Traveling at speeds of up to 80 miles an hour, the explosion devastated Mount St. Helens and the surrounding area. At Coldwater II, Johnston had just enough time to inform his colleagues in Vancouver about the eruption before he was consumed by the blast. Forty years on, his remains have never been found; in all probability they will never be recovered.

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A few miles away, the Washington Department of Emergency Services’ Gerry Martin watched helplessly as the explosion engulfed Coldwater II. According to The Seattle Times newspaper, his last words were ominously prescient. “It’s going to get me, too,” he is reported to have said. In fact, as many as 57 people would lose their lives in the deadly eruption.

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Indeed, the eruption was so violent that debris from the volcano was discovered as far as 17 miles away. In the surrounding area, some 230 square miles of forest were destroyed in temperatures that reached 660°F. Meanwhile, a column of ash stretched into the sky, climbing to a staggering height of 80,000 feet. In some places, it blocked out the light from the sun.

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As some 1.4 billion cubic yards of ash fell on the area around Mount St. Helens, the devastation continued. And as well as the human loss of life, countless animals perished in the disaster. In total, some 220 homes sustained damages, while buildings and waterways up and down the state of Washington were affected by the volcano’s wrath.

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Despite the death and destruction, however, some incredible stories of miraculous escape emerged in the aftermath of the explosion. At nearby Green River, some fishermen managed to survive the oncoming inferno by leaping into the water. Meanwhile, a family out hiking in the area were protected from the disaster by the bulk of another mountain.

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Moreover, it’s likely that the death toll would have been far higher were it not for the work of researchers like Johnston. Months earlier, a group of experts had successfully lobbied the authorities to prevent free public movement in the immediate area surrounding the volatile volcano. And while some had protested at the time, these actions likely saved hundreds of lives.

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Nevertheless, the eruption of Mount St. Helens would go down in history as the deadliest in the history of the United States. And afterwards, the science of vulcanology was forever changed. Before the disaster, many Americans had been unaware of the potentially lethal force lurking just beneath the surface: this was their wake-up call.

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For the first time in history, modern researchers were able to study a volcanic eruption and its aftermath up close. Previously, scientists in the discipline had been divided, but now they came together to utilize the opportunity, setting a precedent for the future of natural science. And through their work, more effective ways of forecasting future disasters were developed.

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Forty years later, the volcano has yet to stun the world with another violent and deadly eruption. However, that doesn’t mean that researchers have been resting on their laurels. Instead, they have turned their attention to an age-old mystery: why is there a volcano at Mount St. Helens at all?

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Although the mountain is considered part of the Cascade Range, it is actually located some 25 miles to the west of the other volcanic peaks. And according to experts, the rock in this specific region is not hot enough to produce the fiery magma that burst forth from Mount St. Helens decades ago. So where did the force of the eruption come from?

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It’s this question that the team at iMUSH have been attempting to answer since 2014. Using a number of different techniques, the researchers worked together to reveal exactly what was happening beneath the surface of Mount St. Helens. And now, they believe that they might have gotten to the bottom of its mysterious firepower.

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Like a lot of volcanoes around the world, those in the Cascades sit at the point where two tectonic plates meet. As one slides under the other, it plunges deep beneath the surface of the Earth, where high temperatures transform the rock into magma. And ultimately, this molten material bursts through the planet’s crust.

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But while this explanation fits most of the volcanoes in the Cascades, it does not work for Mount St. Helens. In fact, the deadly peak sits just 42 miles above the lower plate, where the temperatures are not hot enough to create magma. However, experts believe that an unusual underground reservoir of molten rock might have formed underneath the mountain.

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Over the course of four years, the team at iMUSH performed a variety of experiments in and around Mount St. Helens. In one approach, researchers placed devices that emit seismic waves across the volcano. By monitoring how these waves traveled underground, they were able to build up a picture of what was lurking beneath the surface.

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In another experiment, researchers intentionally set off a series of blasts around the volcano so that they could monitor the movement of the waves. Elsewhere, specialist instruments were set up to record seismic conditions at Mount St. Helens over the course of two years. Meanwhile, another iMUSH team busied themselves with studying the chemistry of the mountain itself.

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According to reports, the team studied conductivity too, using electric and magnetic fields to learn more about the rocks beneath the ground. Altogether, it was an approach that left no stone unturned. In a May 2020 interview with National Geographic magazine, Seth Moran from the USGS explained, “As far as the group was able to do, the kitchen sink got thrown at St. Helens.”

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Eventually, this thorough approach began to deliver results. According to reports, the tests revealed that seismic waves were making their way slowly through a zone to the east of the volcano. Moreover, this was occurring at between ten and 25 miles beneath the surface. Could a relatively shallow reserve of magma have been the reason for its sluggish speed?

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With this evidence in mind, researchers have proposed a solution to the conundrum. Perhaps magma forms as expected deep beneath the main volcanoes of the Cascade Range, but some is pushed westwards towards Mount St. Helens? Apparently, a study of rocks from the region supports this theory.

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If true, these findings could change the face of vulcanology for good. In the National Geographic article, geophysicist Geoffrey Abers explained, “[It] suggests we need to look more broadly than just right below a volcano if we’re going to understand where the magma is coming from.”

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However, scientists are currently unclear about exactly what caused this reservoir of magma to form. According to some, the process may have begun 50 million years ago, when a region called Siletzia collided with North America. In the process, the ocean that once separated these two landmasses disappeared, morphing mud and debris from the seafloor into stone.

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Millions of years later, iMUSH researchers believe that they have located the site of this geological anomaly – right underneath where Mount St. Helens sits today. Moreover, the team also identified a lump of ancient magma that effectively plugs the reservoir beneath the volcano. And while these are two different discoveries, they may work together in an explosive way.

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According to reports, the plug may serve to prevent magma from reaching the surface to the east of the volcano. Meanwhile, the ocean sediments, known as metasedimentary rocks, draw the displaced molten matter towards the peak of Mount St. Helens. At the same time, in the west, another layer of metasedimentary rock keeps the flow in place.

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But while the team at iMUSH have come up with some fascinating theories throughout their research, there is much about Mount St. Helens that remains unknown. In the National Geographic article, Moran explained, “One of the general rules in geophysical imaging is the deeper you go, the less you know.”

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However, the project is far from over. In fact, researchers are still picking through the vast cache of data collected by various experiments over the years. In the future, they hope to understand more about how this complex system has evolved over the years – and how it ultimately exploded with such deadly force.

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In the meantime, Mount St. Helens has not remained entirely dormant since its violent eruption four decades in the past. For example, in 2004 a steady stream of lava began erupting from the volcano. And by the time that it finally stopped some 16 months later, almost three billion cubic feet of molten rock had been expelled.

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Two years later Mount St. Helens’ active period ended once more; the volcano has remained dormant ever since. However, experts insist that another eruption could happen again at any time. Luckily, the work of organizations such as iMUSH has helped the world to prepare – and hopefully we will have plenty of warning when the time comes.

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