Slashdot Mirror
VolcanoCam Back On The Air
Cyberherbalist writes "Over a year after the camera went on the fritz, the Mount Saint Helens VolcanoCam is finally back on the air. It's just in time to catch the famous firework as its earthquake level rises dramatically. All MSH climbing permits have been cancelled due to the danger of rocks and such flying from the lava dome inside the crater. If the weather holds, you may get some good views if the volcano continues ramping up its activity."
You might or might not remember that in 1980 it blew up and killed 67 people, destroyed a couple hundred square miles of forest, and in general caused quite a fuss. It was one of the most destructive volcanic events ever recorded in recent history, so naturally everybody's forgotten about it in favor of tripe like jpegs that capture your computer or some such rot.
"The generation of random numbers is too important to be left to chance."
Unless you're sitting in the crater, you're probably someplace safe and quiet. The last eruption, to my knowledge, was a fairly small (as these things go) effusion of ash in 1990.
Right now the likelihood of various things happening goes something along these lines:
Likely -- nothing happens but the earthquake swarms diminish
Less likely -- there's a steam explosion in the crater that blasts some rock to other parts of the crater.
Rather Unlikely -- magma reaches the surface and some ash erupts or minor dome building occurs.
Basically UnbelievableAt This Point -- a significant eruption capable of disrupting anything on the lower flanks of the mountain or beyond occurs.
Mt. St. Helens is in SW Washington state, about 50 miles north of Portland Oregon. It is a member of the Cascades mountain range, a line of active, dormant, and extinct peaks extending from Northern California, to Southern British Columbia. The next major volcano to the north of Mt. St. Helens is Mt. Rainier, and the next major Cascade volcano to the south is Mt. Hood. All three mountains are volcanoes that we can reasonably expect to erupt again.
The Cascade volcanoes are formed by the subduction of the Explorer, Juan De Fuca, and Gorda oceanic plates beneath continental North America. Subduction is the process by which oceanic lithosphere (crust, the surface of the earth, plus a layer of the underlying mantle that moves with the crust as a rigid unit) slides underneath the continents and back in to the deeper mantle. The Cascadia subduction zone, where these plates subduct beneath the Pacific coast of North America, is notable (among other reasons) because it has no observable trench. This is in part due to the youth of the hot, relatively low-density lithosphere subducting there, and partly because the Columbia River dumps a huge volume of sediment off the continent in to the ocean where a trench might otherwise form. The location where the subduction zone starts (where a trench would normally sit) is a ways off shore beneath the Pacific Ocean.
Interesting aside: The subduction zone, besides producing volcanoes, also has the potential to create very large earthquakes just offshore. The subducting plates don't readily slide past one another, and are currently locked tightly together. When they break free a huge amoung of energy is released in the form of seismic waves. The last time this happened was about 350 years ago, and researchers have identified a recurrence interval for these quakes at about 500 years. In other words, we can expect one any time. California might have more earthquakes, but the strike slip faulting of the San Andreas fault simply isn't capable of producing the stresses that can build up in subduction megathrusts, so Oregon and Washington can expect a truly enormous earthquake someday soon.
As the plates descend in to the mantle, at a depth of around 100 km to about 150 km the descending slab of oceanic lithosphere induces the formation of magma in the overlying mantle. The fairly narrow depth at which partial melting occurs leads to a narrow trace of volcanoes on the earth's surface above the descending slab. Since the subducting slab formed the surface of a sphere, as it subducts the trace of its volcanoes forms an arc. Thus these volcanoes are known as arc volcanoes, and they occur all around the Pacific Ocean, albeit generally due to the subduction of plates other than the Explorer, Juan De Fuca, and Gorda. (A really nice view of this arc shape is visible in the Aleutians). The Cascades aren't long enough or formed by a large enough subducting plate to form a very distinct arc on a map.
The young active Cascade volcanoes do, however, form a very narrow line of peaks, and these peaks are superimposed on the eroded roots of older Cascade volcanoes. Besides Mt. St. Helens, other volcanoes in the High Cascades (as this sharp, distinct, line of young or recently active volcanoes is known) include: Mt. Bachelor, a popular ski resort; Mt. Hood, just east of Portland OR; Mt. Rainier, which threatens Olympia Washington with volcanic mudslides when it erupts again; Mt. Jefferson; Mt. Shasta, a massive mountain in Northern California; Mt. Lassen, which last erupted 1915; and Crater Lake, also known as Mt. Mazama, which emptied nearly 50 cubic kilometers of material during its climactic eruption; and many other mountains.
Geologically speaking, in the short term the entire High Cascades range can be considered active. Eventually, however, the Cascadia subduction zone will probably die out. There are major transform boundaries between the Pacific plate and North America to the north and south of the the Cascadia subduction zone, and over many millions of yea