According to a paper published Nov. 1 in Nature Communications, Mount St. Helens, home to a volcano, is actually cold inside. While most people would imagine the volcano sitting on a large quantity of boiling magma, the researchers have found that the volcano is actually a cold stone slab, stealing magma from far away from its peak.
Before the lethal eruption that took place in southern Washington state on May 18, 1980, magma began to leak months ahead of the event. The geologists observed the small earthquakes in the area in March that year, after which the magma formed a bulge on the north side of the mountain's summit. During the eruption, it released 250 million tons of ash.
Decades after the event took place, the origins of the magma were still uncertain. The mountain is a Cascade volcano, one of the many across the Northwest Pacific and Northern California. However, most of them are located on a continental arc, which has contributed to the high seismic activity in the region, but not Mount St. Helens. The volcano is located on an oceanic plate, slipping under the North American plate, which creates a subduction zone and results in a chain of volcanoes.
Back in 2014, a $3 million project was funded in order for iMUSH to be launched, aimed to understand the ground underneath the volcano. The scientists took measurements of the seismic waves as part of the project, during which time roughly 1,000 stations were placed around the mountain. Analyzing the seismic activity, the readings reflected structures that suggested the deeper layers are made of rocks at different temperatures.
The study's findings concluded that the Mount St. Helens volcano is actually sitting on a cold mantle wedge, which is a geologic formation under 1,300 °F. The findings' revolutionary conclusion is that the mountain doesn't actually produce its own lava.
While the study has managed to answer a series of questions, even more mysteries are yet to be solved. For instance, the types of minerals existing at the boundary between the Earth's crust and the mantle are significantly distinct on the eastern and western sides of the mountain, according to the seismic reflections. The discoveries make the entire area very special in terms of geological characteristics, and the reason why this is so remains to be discovered.
"Mount St. Helens therefore presents a thermal paradox because it lies directly adjacent to the cold mantle wedge and yet still produces arc derived magmatism which requires elevated temperatures," says the study.