Deep magma chambers seen beneath Mount St. Helens
I know the title to this post seems like stating the obvious given the events that have occurred here in the past but…
Recent tomography (imaging using waves) has shown that there are three separate magma chambers that show more about this system in particular and some about the internal structure of volcanoes in general. These magma chambers seem to be connecting not only Mount St. Helens but also Mount Adams and the dormant Indian Heaven volcanic field to the east.
Researchers were able to map this out using a combination of 2500 seismometers in the ground on trails and logging roads around the mountain and 23 explosive shots, each with the force of a small earthquake. The energy waves from the blast went into the crust and seismometers picked up reflections. Since waves travel more slowly through magma than they do with rock, they were able to piece together an image (seen above). 75 seismometers are presently onsite to record tremors that travel through the Earth –or “teleseismic earthquakes” — so to produce a more robust map down to 80 kilometers.
The goal of this mapping is to match this new data with earthquake data from the 1980 eruption to better understand how it occurred. In the weeks leading up to the eruption, there were a series of small earthquakes that could be connected to magma traveling to the upper chamber which then pressurized to the point of eruption. Since these are only initial findings, there is no way to fully confirm the hypothesis of a two-chamber system for all volcanic eruptions (seen in the 1980 eruption and the Yellowstone supercaldera in Wyoming but not in the 2009 Mount St. Helens eruptions).
For more information about the research findings and methodology, check out this article from Science Magazine.