Berkeley blog - Mount St. Helens and earthquakes

Flying back from Germany a week ago Saturday, our plane was diverted over Iceland to get north of the ash cloud blowing from the Eyjafjallajökull volcano towards Spain. This caused a delay of two hours, not bad compared to what others have experienced, and I got to see the ash cloud from the south-facing windows. First time I have ever seen an erupting volcano. Pretty cool, even though it was a volcanic eruption. The dark cloud was nearly vertical, before it topped out, and then headed off towards Spain.

Anyway, it is now thirty years since the last large volcanic eruption in the conterminous United States at Mount St. Helens. The Berkeley Seismo Blog has a nice description of the harmonic tremors that reflected the magma moving within the volcano, and then the 5.1 magnitude earthquake that triggered slope failure of the mountain and the explosive volcanism.

Small earthquakes continue to occur. Check out the graphics and info at the Pacific Northwest Seismic Network.

Mount St. Helens, May 18, 1980

Twenty-nine years - how time flies!

from The Pacific Northwest Seismic Network

"Graphs show average number of events occurring per day (blue) and average seismic strain energy release (square root of seismic energy) per day (red). The times and types of eruptions are shown at the top of each figure with the length of the symbol roughly proportional to the size of the eruption. Magmatic explosive eruptions are those which had a significant amount of new, juvenile magma ejected into an ash cloud. Phreatic explosions are steam or gas explosions involving little or no magmatic material. Dome growth eruptions are relatively quiet, non-explosive eruptions of lava onto the lava dome.

"This plot is for the explosive eruption period of 1980. The first phreatic eruption occurred on Mar. 27, 1980 and the cataclysmic avalanche, lateral blast and plinian ash eruption occurred on May 18 1980... In the 1980s the sensitivity of the seismic network was much less than it is today and thus only larger earthquakes were located. During the pre-cataclysmic eruption period before May 18 over 600 earthquake greater than magnitude 3 were located and 12 around magnitude 5. During this same period, both because of network sensitivity but also because the seismic noise level was so high that small earthquakes could not be well recorded, there were only 6 events located with a magnitude less than 2.

"After the major eruption on May 18 the seismic noise level was usually much less and smaller earthquake could be more easily located, thus the energy plot after May 18 is very small while the number of events continues to have bursts of activity at moderate levels. "

I like the multidimensional data on the graphs.

Half a lifetime ago (for me).

Redoubt webicorder

I didn't realize that there was actually a name for the online digitized seismograms I have shown from time to time. According to the Alaska Volcano Observatory (AVO), these are called webicorders.

Mt. Redoubt has been spewing ash, and the AVO has reports, tweets, photos, videos. But of course, here, we need to focus on seismograms of those harmonic tremors that accompany themagma moving in the volcano.

The webicorder at Redoubt is pretty intense right now. Have a look. The image at the time of this blog entry is shown below. Click on it for an enlarged image.

Mt. Asama volcano in Japan

Mt. Asama volcano is erupting.

Both earthquakes and volcanoes are endothermal processes, both are very related to platge tectonics, and both can be monitored by real-time geophysics.

Thus, while I don't meant to go off forever on a volcano tangent, since they are nicely covered elsewhere, it is interesting to follow another developing volcanic scenario in Japan.

More news can be found where the photo came from, The Japan Times.

In light of what you can see about Redoubt at the Alaska Volcano Observatory, it is interesting how little you can find out about Asama from the Japanese Meteorological Agency. Just a brief update (although, nicely, this can be read in English), and a very static volcanic ash advisory map. No video, no seismographs. Yet Japan is very conscious of the natural hazards - earthquakes, volcanoes, cyclones - that it faces, so I wonder why the basic data seem so hard to come by? There are some video clips online, but mainly from the British press, such as The Guardian.

"It's gonna blow... Volcano"

(Lyrics from the pop song Volcano, by Presidents of the United States of America)

I only have time for a short entry, but it looks like Mt. Redoubt in Alaska may erupt. One of the omens is the occurrence of harmonic tremors that accompany movement of magma through a volcano. Volcano seismicity is physically different from the tectonic earthquakes that we usually talk about.

Check out the situation at the Alaska Volcano Observatory.

Photo: Redoubt Volcano from the AVO observation hut. The dark flow was growing while work was performed on the Redoubt webcam. Taken 27 Jan., 2009. (www.avo.alaska.edu)