Plinian Eruptions

This past Sunday marked 34 years since Mount St. Helens in Washington erupted and entrenched itself in the history books as the most economically devastating volcanic event in United States history. Throughout world history, there have been many other Plinian eruptions, which refer to similarly explosive eruptions that are accompanied by hot plumes of ash and often result in brutal destruction. This week’s trivia post will cover some of the most famous Plinian eruptions.

Mount St. Helens – Washington, USA 1980

Mount St. Helens hibernated for 123 years before earthquakes in March of 1980 indicated re-emerging activity and foreshadowed its future explosion.  After an “earthquake swarm”, which was marked by a two-day period of 174 earthquakes greater than magnitude 2.6, the volcano started its first eruptions. The original summit crater expanded to 250 feet wide and a second crater began to form. These two craters eventually combined as molten rocks smashed into the crater walls. Ash and smoke rose over 7000 feet into the air, forming ash clouds that produced lightning storms around the peak’s slopes.

The Washington governor declared a state of emergency and forbade anyone from entering a “red zone” surrounding the volcano. By this time, Mount St. Helens’ northern slope began bulging, and geologists warned of the imminent danger of a landslide caused by the bulge. Then, on May 18th, 1980 at 8:32 AM, an earthquake triggered a landslide on the north face, which travelled as fast as 155 miles per hour. If it is assumed that the entire face was made of granite rock, then 7.9×1012 kilograms of rock was moved. This would be equivalent to the mass of over 4 million NASA Space Shuttles sliding off the mountain in just minutes.

Pyroclastic flows followed immediately after the landslide. Pyroclastic flow is a mixture of hot gas and molten rock that harnesses gravitational potential energy and flows at incredibly high speeds, hugging the mountain and slithering down like a giant grey molten basilisk. The pyroclastic flow of Mount St. Helens accelerated to speeds known to be as fast as 670 miles per hour, and it is possible that it even broke the speed of sound. A large column of smoke and ash flowed from the giant crater into the atmosphere and released more than 500 million tons of ash. There are some traces of ash still in today’s atmosphere. Ash deposited up to 5 inches thick near Washington and accumulated in measurable amounts (about ½ inch of ash) as far as 2000 miles away in Oklahoma.

Over fifty-seven people were killed due to the landslide and eruption. Without downplaying the loss of those involved in the disaster, there could have been more fatalities had the volcano not erupted the day before when loggers were working in the area and had United States Geological Survey scientists not warned locals to close Mount St. Helens to the general public.

One of the lives lost was that of 83-year-old Harry Randall Truman. Truman lived on Mount St. Helens and, when the governor ordered all civilians off of the mountain, Truman refused. He lived a mile away from the peak and believed the lake, trees, and distance would keep him safe. If those couldn’t let him live, then he swore that if “the mountain goes, he [sic] is going with it.”

Reid Blackburn was another notable figure who died at Mount St. Helens. He was a photographer and journalist assigned to cover the volcano’s activity. He had climbed Mount St. Helens before the eruption sequence began and earned the assignment to document the volcano’s progression. His assignment was only supposed to last until May 17, the day before the eruption, but he decided to prolong his stay. He was camping 8 miles away from the eruption, but pyroclastic flows reached him in just seconds. His camera was discovered in his vehicle, but the film was unsalvageable. Just this last December, an undeveloped roll of film was found with shots that Blackburn had taken a month before the eruption.

One of the most famous individuals who died on Mount St. Helens was USGS volcanologist David A. Johnston. Johnston was one of a handful of individuals who believed that Mount St. Helens would have its northern face burst off. Still, as a fervent geologist, he devoted the last few days of his life to studying the volcano. The day before the bulging slope did explode, Johnston and his colleagues at climbed the mountain the collect samples. Johnston was photographed scaling the bulge less than 24 hours before his fate was sealed. As the volcano erupted, Johnston famously radioed, “Vancouver! Vancouver! This is it!” before pyroclastic flows likely reached his post 6 miles from the peak.

Mount Vesuvius

The eruption of Mount Vesuvius in the year 79 AD is how Plinian eruptions got their namesake. The Roman poet Pliny the Younger, nephew of naturalist Pliny the Elder, witnessed the eruption and described it in great detail. A plume of volcanic gas, stones, ash, and fumes reached 20.5 miles into the sky while burying the Roman towns Pompeii and Herculaneum.

Pliny the Younger, safely situated at the Bay of Naples twenty miles away from the volcano, described the eruption as it happened over a period of two days. The eruption was marked by billowing clouds of volcanic material and pyroclastic flows. His description was used as an outline to describe Plinian eruptions.

Pliny the Elder, also twenty miles away and safe, ordered the formation of a rescue fleet. He commanded ships across the bay but encountered a hail of hot volcanic rock. His helmsman advised him to return, but Pliny the Elder reportedly countered “Fortune favors the brave.” Amidst fleeing villagers and burning buildings, Pliny the Elder and his crew found a safe place to sleep. Soon, volcanic rock and ash had crept toward their building and threatened to corral the rescuers. Pliny’s men attempted to wake Pliny, who had been sleeping soundly and snoring loudly. He struggled to escape and when he arrived on the beach, Pliny sat down on a sail. He could not rise again, even with assistance, and likely collapsed and died, possibly due to an asthmatic attack or heart failure.

Eyjafjallajökull

The most recent Plinian eruption was that of Eyjafjallajökull. The volcano, located in Iceland, is translated to mean “Island mountain glacier”. In April 2010, eruption began and a large ash cloud formed over the volcano. The ash travelled across the North Sea into Europe and disrupted air travel for more than 20 countries and over 10 million travelers.

With the eruption, “volcano tourism” began causing problems for Icelandic authorities. Tour companies offered trips to see the volcano up-close-and-personal, while authorities attempted to reinforce restricted access regulations and station stand-by search and rescue teams. The volcano was actually very remote though and is typically buried under an ice sheet. Consequently, there were no deaths directly resulting from the eruption. The eruption officially lasted until October 2010.

There have been many other recorded Plinian eruptions. The catastrophic eruption of Krakatoa, which killed over 36,000 and had the energy 4 times greater than the largest nuclear weapon ever detonated, was a Plinian eruption. In 1991, Pinatubo ejected about 10 times more material than Mount St. Helens and is considered the largest eruption to impact a densely populated area. Volcanic activity is unpredictable and devastating, and it’s unlikely that Plinian eruptions will disappear anytime soon.

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One thought on “Plinian Eruptions

  1. I still have a Christmas Ornament that I bought from the Davis Family Nursery that was blown glass from the ash of Mount St Helen… I bought it in 1984….

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