Geoscientists say that a swarm of earthquakes has intensified to the point that there are now 40 a week.
The earthquakes could be a clue that magma is building up under Mount St. Helens, much as did before the famous eruption on May 18, 1980. That event was the deadliest volcanic explosion in American history, killing 57 people, pumping 540 million tons of ash into the air and triggering the largest landslide in recorded history . The ash cloud spread as far at the central US.
“Since the start of 2016, an earthquake swarm has been detected underneath the currently quiet Washington (state) volcano,” Erik Klemetti, a professor of geosciences at Ohio’s Denison University, wrote in Wired. “USGS volcanologists and seismologists are interpreting this swarm as a response to the slow ‘recharging’ for the volcano, where new magma is rising up underneath St. Helens  as it slumbers.”
The quakes are more “vigorous” than swarms of quakes in 2012 and 2014, he wrote, explaining that they are generated by the shifting of rocks by magma or lava building up underground. Last year, United States Geological Survey (USGS) scientists discovered that there are two giant magma chambers underneath Mt. Helens. When the chambers become completely full of magma, Mount St. Helens or other nearby volcanoes like Mount Adams go off.
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Scientists actually do not know when Mount St. Helens, or its neighbors, will erupt. They can only guess, using an advanced network of USGS sensors in the area to monitor the situation. Most scientists say another eruption, even if it is minor, is still a few years away.
“The magma that will likely take part in the next eruption is working its way up towards the surface, likely stopping along the way to crystallize and interact with the residue of previous eruptions,” Klemetti wrote.
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“… [W]hat we can say is that no volcano is truly ‘dormant’ when it’s not erupting. It’s just that most of the action is happening far beneath our feet.”
It’s Not Just St. Helens
Mt. St. Helens is not the only dangerous volcano in the mainland United States. Volcanologists have identified some other mountains that could blow again. The list includes:
- Mount Rainer in Washington State. Volcanologists rate this mountain as the third most dangerous volcano in America. Mount Rainer goes off every 500 to 1,000 years, and it could cover nearby cities like Seattle and Tacoma with mud and other deadly debris.
- Mount Hood in Oregon. Volcanologists worry about this mountain because people live right on it. There have been two major eruptions at Mount Hood in the last 1,500 years, National Geographic reported.
- Mount Shasta in California. The USGS rates this scenic wonder in Northern California a very high threat. It could erupt with deadly mudflows and an ash cloud similar to that which occurred when St. Helens erupted in 1980.
- South Sister in Oregon. This mountain just west of Bend, Oregon, is rated a very high threat by the USGS. Magma has been building up under it for years but no eruption has occurred.
- Lassen Peak or Lassen Volcanic Center in Northern California. This is actually a collection of several volcanoes near Redding that last erupted during World War I. https://www.youtube.com/watch?v=nZD9K4q55jk
- Crater Lake volcano, in Oregon. This national park is actually a volcano that once erupted with 42 times the force of Mount St. Helens.
The volcanic danger in the United States is far greater than most of us imagine. There are 169 active volcanoes  in the US, and 54 of them are considered high threats by the USGS.
What do you remember about the last time Mount. St. Helens erupted? Share your thoughts in the section below: