Mount St. Helens Blew Up 40 Years Ago This Week

Mount St. Helens erupting in May, 1980. At this point in the photo, the entire
north side of the volcano is falling away in a massive landslide
as the ash cloud just begins to rocket upward and laterally. 

This isn't a weather or climate story per se, but it is related.

People in Washington State are this week marking the 40th anniversary of the dramatic eruption of Mount St. Helens.  

It was the worst volcanic eruption on record in the continental United States, killing 57 people.

As the Seattle Times notes, the north flank of the volcano collapsed in an enormous landslide that buried 23 square miles of a river valley to an average depth of 150 feet. The blast sent rocks and a superheate ash cloud that toppled 230 square miles of forest in just three minutes.

Large swaths of a Washington State went dark as night under the immense ash cloud.

The blast had some effects on the skies around the nation for days afterwards.  I remember the ash cloud a few days after the eruption turning the May blue sky over Vermont a sickly slate gray.  The setting sun didn't seem to hit the horizon. Instead, it faded to nothing in the haze as the sun sank low in the west.

As dramatic and huge as this eruption was, it was actually too small in the grand scheme of things to actually affect worldwide weather and climate to any noticeable degree.  Or even that week here in Vermont. As the ash dimmed the skies over Vermont, daytime temperatures the week after the Mount St. Helens eruption rose into the 70s and 80s.

Large volcanic eruptions - much bigger than Mount St. Helens - can belch so much ash and soot into the air that it circles the globe and dims the sun, temporarily cooling the surface of the Earth.

One relatively recent example of this was Mount Pinatubo, which erupted in the Philippines in 1991. It pumped enough gunk into the upper atmosphere to briefly stop the upward trend in global warming around 1992.

A more dramatic example was Mount Tambora in what is now Indonesia back in 1815.  That massive volcano is thought to have created the "Year Without A Summer" in 1816. It caused global cooling, with some examples of that in Vermont. There was a June snowstorm that year, and hard frosts and freezes in July and August.

The effects of these massive eruptions on climate tend to last only a couple years as the ash particles from these volcanos slowly fall out of the atmosphere.