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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.""
People who live new the mountain shouldn't panic at all, because whatever the mountain does is unlikely to be very big.
One interesting thing (of many, really), however, is that St. Helens is one of the few fairly low latitude mountains in the Western hemisphere with a low-elevation glacier acumulating ice. The glacier is accumulating at only between about 6500 or 7000 feet.
That ice, however, if it were heated suddenly, could be one of the more notable volcanic hazards on the mountain. My instinct tells me it probably couldn't cause much damage because it would have to flow a long ways before reaching anything too critical, and over that distance the flood wave would be much attenuated, and there's really not much redevelopment (there wasn't too much development before the initial eruption either) downstream of the crater.
In the near vicinity of the crater rock fragments, ash, and small landslides might be possible, but only researchers are allowed in that area anyway, so these represent little threat to the general public.
Personally, I think it would be kind of neat to see some activity out of this volcano. It's pretty been quite for several years now. A rumble from St. Helens would certainly be better than an eruption from most other other Cascade volcanoes -- a sizeable eruption from Hood or Ranier could be very dangerous.
> People who live near Mt. St. Helens shouldn't panic just yet. This just means it's possible, not that it's going to happen within the next few days. Just thought I'd point that out.
That's easy for you to say from Flori...
Never mind.
Sheesh, evil *and* a jerk. -- Jade
...an increased chance of a hazardous event
The Sizemologists were shocked and embarrassed by the premature eruption.
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