The eruption of Mount St. Helens revisited

The 1980 eruption of Mount St. Helens was the culmination of a prolonged period of volcanic unrest. We will go through the events that lead in May 1980 to one of the largest eruptions in the history of the United States. 

By Kathelijne Bonne. 

The early morning of Sunday 18 May 1980 was one like any other in the Pacific Northwest. But 'rest' is a relative concept in places where two tectonic plates collide. The ocean floor of the Pacific Ocean slowly plunges below the North American continent, in a process known as subduction. Earthquakes and volcanic eruptions are common in such areas. Mount St-Helens, together with Mount Baker and Mount Rainier, lies in a string of volcanoes that runs along the entire west coast of the American continent. 

Mt Saint Helens: signs of unrest

Months before the fatal Sunday morning, Mt St. Helens started showing signs of unrest. From the 15th until the 21rst of March that year, seismographs registered more than 100 earthquakes. Ash and vapor rose from the summit. The volcano rumbled along, and snow avalanches slid down its slopes. At some places large fissures started to open up. 

After a couple of stronger quakes, the US Geological Survey urged people to stay away from the volcano and its immediate environment, including the area of Spirit Lake. A bulge started to form on the north slope of the volcano. It was a sign that magma was being injected from beneath. Ash clouds rose, up to three kilometers high. Ash that had rained down was studied in the lab, and was apparently not formed from 'fresh' magma, but from older volcanic material. Maybe that was an indication that the newly injected fresh magma was still residing at a considerable depth. Nevertheless, volcanologists were not at ease. 

State of emergency

Mount St. Helens became increasingly restless. Quakes became more intense and the intervals between the quakes became shorter. Gas explosions occurred as pressure built up inside the volcano, and the hot material caused the groundwater to violently  evaporate. 

On the 3rd of April, the state of emergency was declared. The area was marked as a red zone and whoever hung around without permission was given a 500-dollar fine or six months of jail. Meanwhile, the bulge on the north flank had reached a thickness of 90 meter, only to further increase in size. Behind the protrusion, the area was sinking. 

Geologists realized that this protruding, convex slope, was at risk of failure, and capable of producing a landslide. If that would happen, the magma underneath would be released. But nobody could predict if, and when the slope would fail. All that could be done was wait. By the start of May, the rumbling increased again. 

Silence before the storm

Then, on the 15th of May, Mount St. Helens fell silent. Not much more happened and the attention the volcano had received in the last few weeks, weakened. Homeowners became nervous, looking forward to check upon their properties. On May 17th, they were given permission to visit their homes to collect belongings. 

In the early morning of May 18th, the volcano looked exactly the same as the day before. A geologist who made observations from 10 kilometers away saw nothing unusual compared to the previous days and weeks. 

North slope collapses

At 8.32 am on 8 May 1980, an earthquake of magnitude 5.1 hit just below the protruding bulge. It just sat there for a few seconds, but then the entire north flank of the volcano began to move. 

The largest landslide ever witnessed by modern humanity, raged in the direction of Spirit Lake. The sliding mass followed a river valley all the way down, reaching speeds of 175 to 250 kilometers per hour, over a distance of 20 kilometers.

Landslide and lateral blast

The magma underneath was released in an explosive way, producing a massive lateral eruption, now forever known as the infamous lateral blast. The explosivity is due to the gasses that were locked under high pressure in the magma. You can compare it to a bottle of champaign you first shake and then open. 

Gasses and shattered volcanic material formed a huge cloud, a pyroclastic flow that cascaded down the slopes, reaching an incredible speed and quickly overtaking the gigantic landslide. Entire forests were destroyed over a large area. For decades to come, tree trunks were seen floating on Spirit Lake. The sight of lake itself had changed beyond recognition. 

The water of the river and part of the lake evaporated in a loud bang and hissing sound, which could be heard as far away as Canada. 

Mud, molten glaciers and fine ash

Ten minutes after the lateral blast, an ash column rose from the summit to a height of more than 20 kilometers. For ten hours, Mt St-Helens spewed volcanic material, in the form of ash and debris. Lightning bolts in the ash cloud added to the spectacle. More landslides, of a mixture of ash, lava and mud shoved off the slopes. Molten glacier water created deadly lahars, a kind of mudflow, that raged through the river valleys.

The finest ash stayed in the atmosphere and drifted to the east, carried by the winds. In the hours following the eruption, the ashes were reported in increasingly distant areas. In Yellowstone, then in Colorado and Minnesota, and finally the ashes circled the earth. 

Direct blast to standing dead zone

The destroyed area was later categorized into three concentric areas with different levels of destruction. Near the volcano was the direct blast zone. Everything was destroyed and obliterated, even soil had been blown off. A bit further was the channelized blast zone. In some areas, especially behind topographic obstacles, soil with seeds were protected and survived. Fallen and broken trees all lay in the same direction away from the direction of the blast. In the searing zone or standing dead zone, trees still stood upright, but were charred. 

57 people died. Amongst them were a few geologists, photographers and homeowners. Tragically, Robert Landsburg was found curled up; he had died, using his body to protect his camera, which was undamaged. 

Aftermath of the eruption

The eruption of Mount St-Helens was the most devastating in the recent history of the United States. In addition to the people who died, huge expanses of forest and timber were destroyed, elk and deer were killed, and more than ten million salmon and other riverine life in the rivers surrounding the mountain also died. Roads, bridges and crop land were destroyed, and air traffic was disrupted. Cleaning up the ashes was a huge job that lasted for weeks. 

And Mount St-Helens itself? It looked completely different, lower, and with a large, gaping horseshoe-shaped crater. The top had literally been blown off. The volcano remained active and several smaller eruptions have occurred since. 

In the meantime, the volcanoes flanks have become regrown with vegetation and there's a new, small volcano rising from the big crater. 

What nature takes away, she somehow returns, in an endless cycle. No matter our perspective or point of view, nature always has the last word. And nothing reminds us of that more resoundingly than a volcano.

-----

Since I posted this article in 2020 on the 40th anniversary of the eruption of Mount Saint Helens, I've written about other volcanoes. Read about Campi Flegrei in Italy and the volcanoes of Europe (with a few unknown ones). There is an article too on the Gulf of Naples were a plastic eruption is imminent and on the three heads of hellhound Cerberus, on the unpleasant mix of volcanic risk, mafia and pollution in an otherwise jaw-dropping landscape. A few ideas and perspectives are shared in my post on supereruptions and how to survive them. 

Kathelijne: I am intrigued by how earth, life, air, ocean and societies interact on geological and human timescales.

Why I started GondwanaTalks.

Donation?

An immense effort is poured into GondwanaTalks.

Are my articles somehow meaningful to you? Let a few coins roll my way through this secure link. Support my work so I can keep GondwanaTalks afloat. Your contribution makes an ultra-Plinian difference. Make a one-off or recurring donation of your choice. I suggest your become become my:

Stromboli Strategist
(€2/month)

Tambora Trailblazer
(€4/month)

Vesuvian Visionary
(€7/month)

Magmatic Maecenas (other amount)

~

Already donating? Thank you very much!

------

Recent posts:

Do you like this article? Subscribe to my short newsletter (every couple of weeks, no large files or annoying gifs), to let you know I published something new.