St. Helens Rumbles


We all remember what Mt. St. Helens did back in 1980, it’s eruption blew out the entire north flank of the mountain in a spectacular lateral eruption blasting pyroclastic flows out over hundreds of square miles of forest and sending lahars 50 miles out reaching the Columbia River. 57 people were killed in the eruption.

St. Helens isn’t done, of that you can be sure, and it’s lava dome continues to build as magma under pressure intrudes into crevices beneath it. A lava dome is a dead give-away that a volcano is active and planning something unsavory. Below we see the lava dome formed in the breached crater of St. Helens.

St. Helens Lava Dome

Yesterday on the VALT seismograph station there appeared traces of activity that tell us St. Helens is very much awake and active. The VALT station is a broadband seismograph that sits just in front of that lava dome, and is one of several seismograph stations on and around the mountain. St. Helens is one of the volcanoes I like to keep an eye on and I check her seismographs every day.

This morning while having my coffee and getting my seismofix I came across elevated activity at St. Helens on the VALT station’s record from late yesterday. This happened after I’d checked it earlier, so I didn’t see it until this morning.

Even non-seismogeeks can see that this is telling us something. I don’t mean to be alarmist at all here, and this is not a precursor to another VEI 5 eruption by any means, but it does tell us that the magma chamber under St. Helens is under pressure, and it’s that pressurized magmatic system that is building the lava dome in the breached crater there.

That little blue triangle at top is the VALT broadband seismograph station, the other two in the crater there are short period stations. The lava dome is quite obvious in this picture. It’s growing and got a good push yesterday. We might expect some limited venting of gases and ash in the near future if this keeps up or increases, which it might well do. Lava domes have a way of functioning as a plug in a volcano under which pressure builds to the point of eruption, and that might well happen too, although I don’t expect it to be anything on the order of the 1980 eruption, or any time soon, but I’ll be watching the seismographs there just the same because this is just fascinating stuff!

And just now, checking back on St. Helens I see this:

That blue trace is most likely the magnitude 6.8 quake that hit the Aleutians this morning while I was writing this, and just after it we see a long harmonic, which I’m going to hazard a guess is the shock waves from it passing through the magma chamber under St. Helens. It suggests magma rocking around in the chamber to me, but I could be wrong.

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About Martina Vaslovik

Volcano nerd and seismogeek
This entry was posted in Uncategorized, Volcanology. Bookmark the permalink.

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