Baby, It's Cold Inside: Mount St. Helens Has No Magma

A research published in Nature Communications has revealed the unthinkable: instead of finding a chamber of hot magma below the volcano, scientists discovered a cool wedge of serpentine rock. The volcano responsible for the most destructive eruption in the history of the United States of America is literally cold inside.

This is yet another reason for scientists to consider Mount St. Helens as an anomaly. For a volcano that contains no magma, Mount St. Helens had caused a devastating eruption in 1980. This traumatizing incident resulted in the deaths of 57 people and billions of dollars in property damage.

"This hasn't really been seen below any active arc volcanoes before," Steven Hansen, a geologist from the University of New Mexico, shared with Science News. Already considered strange because of its location, Mount St. Helens is part of the Cascade Arc, a string of volcanoes that runs parallel to the Cascadia subduction zone from California to British Columbia. Mount St. Helens, however, is located 50 km (31 miles) to the west of the rest of the arc's mountains. Since it sits on top of a wedge of cold mantle instead of scorching magma, scientists have no explanation why Mount St. Helens is located where it is.

In order to solve the mystery of Mount St. Helens, Hansen and his team planted thousands of sensors around the mountain to measure ground movements. They also drilled 23 holes into the volcano, filling them with explosives to trigger minor quakes around the volcano.

Those seismic waves generated presented an unusual discovery: instead of a chamber of hot magma below the volcano Mount St. Helens was on top of a cool wedge of serpentine rock. This presents yet another mystery for Hansen and his team to solve: where does Mount St. Helens get its fuel?

One possible answer the team presented is that the magma source might be in the east, near the rest of the Cascade Arc. There, magma temperatures are above 800 degrees Celsius (1,470 degrees Fahrenheit) and could possibly erupt out of Mount St. Helens due to the deep earthquakes in the region. However, Hanson and his team would need more data to before drawing any more conclusions.

"Mount St. Helens is pretty unusual," Hansen stated in an interview. "It's telling us something about how the arc system is behaving, and we don't yet know what that something is."