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Possible 'Hazardous Event' At Mount St. Helens
babynerd writes "Seismologists believe there's an increased likelihood of a hazardous event at Mount St. Helens due to recent changes in the mountain's seismic activity. That increased activity on Sunday prompted the U.S. Geological Survey
and the University of Washington to release a "notice of volcanic unrest.""
Although it was a fairly big explosion, some 1500+ feet of the mountain were completely blown off. It's probably not likely to be anywhere near that big of a boom again.. also, even though it was a pretty large boom, only something like 57 people died as a result of it..
*numbers may be a little fuzzy
I was just researching the whole thing on Friday,when I saw this article come up on Fark.. was trying to explain to a coworker of mine (who was born in 1981, in South Africa.. so had never heard of Helen) the whole thing..
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Ummm, dumbass? You might want to take a quick look at what caldera actually means.
Who lets these freakin' idiots in here?
Worse could happen:
People of Earth, your attention please. This is Prostetnic Vogon Jeltz of the Galactic Hyperspace Planning Council....
In seriousness:
Seismic activity at Mount St. Helens has changed significantly during the past 24 hours and the changes make us believe that there is an increased likelihood of a hazardous event, which warrants release of this Notice of Volcanic Unrest.
So there have been changes of a large magnitude, in a small time scale.
The swarm of very small, shallow earthquakes (less than Magnitude 1) that began on the morning of 23 September peaked about mid-day on 24 September and slowly declined through yesterday morning. However, since then the character of the swarm has changed to include more than ten larger earthquakes (Magnitude 2-2.8), the most in a 24-hr period since the eruption of October 1986. In addition, some of the earthquakes are of a type that suggests the involvement of pressurized fluids (water and steam) or perhaps magma. The events are still occurring at shallow depths (less than one mile) below the lava dome that formed in the crater between 1980 and 1986.
I think it is time to change the alert, even if it means changing the lightbulb!
Damn I love British comedy!!!
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Mt. Asama in Japan (near Nagano) has been erupting the last few weeks. Check out this short video of a continuous stream of ash leaving the top. Some of it reached Tokyo!
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The Cascade volcanoes, including St. Helens, Ranier, Hood, Jefferson, Three Sisters, Mazama, Adams, Jefferson, Lassen, Shasta, etc... are formed by the same general phenomenon: subduction of the Juan De Fuca and Gorda plates at the Cascadia subduction zone off the coast of Washington, Oregon, and California.
Based, however, on extensive worldwide research of volcanoes, including those in the Pacific Northwest, it is very safe to conclude that the magma system of the volcanoes are not linked. In other words, activity on any one peak is completely unrelated to activity anywhere else in the Cascade Range. There is no readily imagined mechanism by which pressurization in one magma system of one Cascade volcano could pressurize the next.
As I stretch my imagination, I suppose a large earthquake could theoretically destabilize an already critically pressurized system, as happened in the St. Helens 1980 eruption (although in that case the mountain caused its own triggering earthquake), but the scenario is really a bit outlandish for one volcano triggering another: one mountain triggering another would require a very large earthquake as the quake amplitude would be considerably attenuated by the time it reached any other Cascade volcano, and these mountains can't readily produce very large earthquakes, let alone that the fact that none of the other Cascade volcanoes is about to blow its top!
It's also worth noting that volcanoes are really good about giving lots of advance warning before they blow up. Earthquakes basically can't be predicted, but volcanic eruptions make themselves known long before they finally go off. It's not like you wake up one morning and discover that Mt. Hood all-of-a-sudden dropped 550 million tons of Ash on downtown Portland. For a volcano to erupt, the magma that is going to erupt needs to reach the surface. As it moves up through the earth you get lots, and lots, and lots of warning, particularly before a really big eruption: ground inflation, earthquake swarms, frequent small earthquakes at shallow depths below the mountain, changes in groundwater chemistry, changes in hot springs, changes in outgassing, volcanic tremors, etc... If these things didn't occur, you wouldn't be reading this article or these comments!
Finally, what Mt. St. Helens is doing is not like what it did before the 1980 eruptions. Right now we're looking at small earthquake swarms. They could amount to nothing, but they most certainly are not a multi-hundred-meter bulge on the side of the mountain.
Another large eruption like the 1980 eruption is also unlikely because much of the original volume of the mountain collapsed away during that eruption, so even in the very unlikely event that any really sizable volume of magma reached the surface, it wouldn't result in the huge lateral blast and landslide that swept away a huge piece of the mountain 24 years ago.
It's also worth noting that these mountain-destroying eruptions are uncommon in Cascade volcanoes. Usually the mountains erupt out of a fairly nice clean crater, or pour a bit of sticky lava down a flank. When another Cascade volcano erupts, it will likely not result in the collapse of the entire mountain. The greatest danger is probably from lahars -- volcanic mudslides -- that form when snow and glaciers on the mountain melt and mix with ash to form a fast flowing torrent of hot wet mud with all the typical material properties of moist cement. (Rainier in particular poses a large threat in this respect.)
Anyway, I'd worry a lot more about the weather when visiting Hood than about a small, hypothetical, eruption of Mt. St. Helens, or even a large eruption on Mt. St. Helens (although a lot of ash could make the climb down rather uncomfortable if it blew your way). As for Tabor, it is part of the Boring volcanic fields (no, I'm not making that up!) which are not part of the Cascades and were probably formed by almost totally unrelated processes. The Boring lavas last erupted at least 100,000 years ago, and pos
Mount Tabor (here as well) is an extinct volcano on the east side of Portland, OR. There are many homes on it and a park on top. It is only around 650 feet above Sea Level and 400 feet above the surrouding area. It is not in the same chain as Mt. St. Hellens.
Mount Hood is a "potentially active" volcano appoximately 60 miles to the east of Portland. This one is in the same range as Mount St. Hellens and could be potentially active. On the other hand, I am very sure that there would be signs coming from Hood if it was going to erupt any time soon, not just signs from St. Hellens.
Another interesting note from my geology class:
The Cascade Range (the mountain chain containing Mount Hood and Mount St. Hellens, but not Mount Tabor) is actually two separate geologic regions, one on top of the other. Towards the western side of the range, there is a much older, and more heavily eroded area with relatively low hills and mountains. On the eastern side of the Cascades, the much younger and taller Mountains were formed on top of the older mountains. The new mountains are formed by the subduction zone of the Juan de Fuca Plate (a small plate stretching from the northern end of Vancouver Island to the Northern part of California) under the North American plate.
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