Mount St. Helens: What we learned from America’s largest volcanic eruption

What impact did it make on climate change?

FILE - In this May 18, 1980, file photo, Mount St. Helens sends a plume of ash, smoke and debris skyward as it erupts.  May 18, 2020, is the 40th anniversary of the eruption that killed more than 50 people and blasted more than 1,300 feet off the mountain's peak.
FILE - In this May 18, 1980, file photo, Mount St. Helens sends a plume of ash, smoke and debris skyward as it erupts. May 18, 2020, is the 40th anniversary of the eruption that killed more than 50 people and blasted more than 1,300 feet off the mountain's peak. (Copyright 1980 The Associated Press. All rights reserved.)

The eruption of Mount St. Helens in Washington State on May 18, 1980, was the largest volcanic event ever in the United States. It was so powerful it turned day into night as ash eclipsed sunshine. The calamity killed 57 people and thousands of animals in the pyroclastic fire.

Yet from the destruction, the eruption led to a better understanding of how volcanoes shape climate change.

What comes spewing out of the belly of the earth during major explosive eruptions is a mixture of volcanic gas, aerosol droplets, and ash some of which cool and potentially warm the planet.

Volcano cooling power. Is it due to ash or gas?

Scientists discovered it wasn’t the ash but sulfur dioxide which led to long-term planetary cooling. Researchers came to this conclusion after comparing St. Helens to a smaller Mexican eruption two years later at El Chichon that led to a drop in global temperatures five times colder than that of St. Helen’s.

FILE - In this May 19, 1980, file photo, clouds of ash from the eruption of the Mount St. Helens volcano move over the Ephrata Airport in Ephrata, Wash. May 18, 2020, is the 40th anniversary of the eruption, which darkened skies and sent volcanic ash falling for hundreds of miles. (AP Photo/Mike Cash, File) (Copyright 1980 The Associated Press. All rights reserved.)

Even though El Chichon released less ash into the atmosphere, the eruption was higher in the sky, well above where everyday weather takes place. At this level called the stratosphere, ash doesn’t stick around long and most falls out within a few days or weeks. This proved it wasn’t the ash that cooled the planet but rather the sulfur dioxide gas.

Suspended sulfur aerosols worked as microscopic sun reflectors blocking the warming rays which were more effective at cooling the planet for a longer time compared to ash.

Compared to the cooling effect, carbon dioxide gases are also released in volcanic eruptions. Carbon dioxide is a greenhouse gas that traps heat so naturally one would think volcanic greenhouse CO2 could be responsible for the recent rise in global warming over the past century?

It turns out not the case.

Mount St. Helens vented approximately 10 million tons of CO2 into the atmosphere in only nine hours. While this appears like an excessive amount of harmful gasses, humans are much harder on the atmosphere releasing about 200 million tons of carbon dioxide annually, according to the U.S. Geological Survey (USGS).

In comparison, the natural source of CO2 is so trivial that the US Geological Survey found that the carbon dioxide released in contemporary volcanic eruptions has never caused detectable global warming of the atmosphere.

Global warming keeps coming back to humans.

Carbon dioxide levels have increased at measuring stations around the world despite the rare major eruption that may only occur once every 10 years on the planet.

Humanity’s relentless emissions release is why scientists say the run-up in temperatures since the industrial revolution is related to our activities and not part of a natural cycle.


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