It would seem that seismic data has stopped coming out of Columbia, at least for the Ruiz-Tolima massif. Several of the seismographs at Ruiz ceased updating online on the 20th, and shortly before midnight on the 21st the rest of them at the Ruiz-Tolima massif quit altogether, at Cerro Machin, Cerro Bravo, and Nevado del Ruiz. This has seriously impacted my morning seismofix.
I am not able to find out the reason for this, but I’m still digging and I hope those seismographs come back online soon. It might be that they are having equipment problems, perhaps routers had to be moved or reconfigured, there was some quite serious seismicity at Cerro Machin on the 13th that shook things up a lot, and that may have something to do with it. The helicorders at Galeras are still updating online, and that volcano is very quiet.
Ruiz, Machin, and Bravo where the most entertaining and interesting things a going this week, and now I can’t even see their charts. No webcams that I know of there either. Data stopped being updated on Merapi back on August 8th and has not resumed. That was the only Indonesian volcano with online webicorders that I knew of.
Now I am left with Cascadia, the Aleutians, Iceland, and Yellowstone, none of which is doing anything interesting, and then there is Tambora, which seems to have stabilized according to the most recent report I can find, although it’s alert status has not as yet been lowered. Two people climbed to the summit three days ago, ignoring official channels to do so, and said that visually everything seems okay, although they did feel some tremors. We can always count on someone to ignore official channels where volcanoes are concerned.
Mt. St. Helens continues to twitch, there having been several small volcanic quakes there overnight recorded on the VALT station near the lava dome. These recorded before midnight were followed by more afterwards.
Mt. Etna in Italy has been putting on a show, reportedly it’s 14th paroxysm occurred at it’s new Southeast crater, and while clouds obscured the volcano visually it’s being said that it’s seismographs showed it to be undergoing a major eruptive episode with seismic activity as 30 times normal background levels. Sorry I missed that here, I was focused elsewhere.
I had not found seismographs for Etna until this morning, my Italian not being all that good, (I can sorta read it and figure out what it says) and those I’ve found show nothing beyond background seismicity this morning, so I guess the show at Etna is over for now.
Until recently Etna was regarded as mainly an effusive volcano, producing running lava flows for the most part, but recent studies indicate it is capable of highly explosive plinian eruptions, and indeed it did produce one of those in 122 BC. Since the late 1970’s Etna has demonstrated an ability to produce explosive summit eruptions which it displayed dramatically from 1995 to 2001 with over a hundred lava fountains (paroxysms) and high ash plumes.
It might be that we see some action from Mt. St. Helens, the quakes under the lava dome last night have become continuous tremor there at the VALT broadband station in front of the lava dome. This has continued for over 40 minutes so far. I’ll be updating as I watch this.
After over two hours of continuous volcanic tremor under Mt. St. Helens this morning things seem to have grown quiet again. I’ll keep watching. This may indicate rising magma and it might well start up again at any time.
Mt. St. Helens is composed mostly of dacite making up a glassy rhyolitic matrix containing amphibole and plagioclase phenocrysts (Whittington, 530). The dacite that Mt.St. Helens is composed of is hydrous. Hydrous dacite cools at a rate that results in increased crystal fraction, decreased temperature, and massive volatile loss. This results in a very low viscosity magma that causes violent, explosive eruptions.