May 18 – Pop Life

Today’s factismal: There have been over 1,200 earthquakes under Mount St Helens since 2010.

If you’ve been reading the news (or Facebook), you’ve probably heard that there has been a recent swarm of about 20 earthquakes under Mount St Helens. And that can be sort of scary because thirty-six years ago today, Mount St Helens reminded us of just how powerful nature can be when it erupted some 4 billion cubic yards of rock. The eruption tore off most of the top of the mountain by noon, shrinking it from  9,677 ft tall to 8,363 ft and spread ash across fifteen states. The forest was blasted away for 17 miles from the northern side and the Columbia River shipping channel 70 miles away was blocked by the largest landslide in recorded history. And yet, thanks to the work of the vulcanologists on the scene, only 57 people lost their lives in the eruption.

The eruption was actually fairly small as such things go (Image courtesy USGS)

The eruption was actually fairly small as such things go
(Image courtesy USGS)

But will the mountain erupt again? If you ask a geologist, the answer is both yes and no. Because Mount St Helens is on an active subduction zone, we know that it will keep getting fed magma so it will definitely erupt sometime. But because we’ve seen similar swarms for the past decade, it is unlikely that Mount St Helens will erupt any time soon. There have been more than 1,200 earthquakes since 2010; that works out to be about ten per month. So getting twenty in two weeks isn’t that unusual. And because the recent swarm is about the same place that previous swarms have been, it is unlikely that the events are due to large amounts of magma moving around; indeed, they could have been caused by magma cooling and contracting which would reduce the chances of an eruption!

The location of earthquakes over the past decade show that the recent swarm isn't that unusual (Image courtesy the Pacific Seismometer Network)

The location of earthquakes over the past decade show that the recent swarm isn’t that unusual
(Image courtesy the Pacific Northwest Seismometer Network)

Scientists have been monitoring the volcano for years, starting well before the 1980 eruption. They monitor the earthquakes associated with magma movement  with a number of seismometers and have flown over the volcano repeatedly to capture images of changes in the mountain slopes; they have also put instruments into place to measure the tilting of the ground and its temperature. This information allowed them to predict when the volcano would erupt in 1980 and continues to help us understand what will happen next.

Mount St. Helens is just one of many, many volcanoes on the Pacific coast (Image courtesy USGS)

Mount St Helens is just one of many, many volcanoes on the Pacific coast
(Image courtesy USGS)

That information is important because most people forget is that Mount St Helens isn’t the only volcano in the Cascades range. There are over 100 volcanoes stretching from California to British Columbia. All of them are caused by the subduction of the Juan de Fuca and Gordo plates under the North American plate; this is also what has created the Cascades mountains and the large number of large earthquakes in the region. And it is that motion that tells us that someday (geologically) soon, one of them will erupt just as Mount St Helens did.

California's earthquakes and Washington's volcanoes have the same cause (Image courtesy USGS)

California’s earthquakes and Washington’s volcanoes have the same cause
(Image courtesy USGS)

If you’d like to help scientists learn more about volcanoes and predict the next eruption, then why not join NetQuakes? You’ll keep a seismometer in your home and help monitor earthquakes and volcanic eruptions!
http://earthquake.usgs.gov/monitoring/netquakes/

One thought on “May 18 – Pop Life

  1. Pingback: January 18 – Children Of The Sun | Little facts about science

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