As everyone not living under an (extrusive igneous) rock probably knows, Mt. St. Helens is in an active period again. Today's volcanocam currently looks quiet, we've already had two steam-and-ash bursts; if magma's working its way up, things could start happening in a hurry.
When the major eruption happened in 1980, I was seven years old -- I remember being amazed by the pictures at the time, and later by a National Geographic article that showed how, compared to other eruptions in recorded history, the St. Helens eruption was fairly small. Later on, as a grad student, I went on a field trip to St. Helens -- though we couldn't go into the crater itself, we had climbing permits, and hiked to the summit, which is really just a point on the south rim of the crater.
The pictures I took at the time are still sitting around on a webserver; mostly what I remember from that time is to what extent the mountain seemed more like a big pile of debris than a solid thing. The nature of a given volcano is largely determined by the chemistry of its magma; stratovolcanoes like St. Helens are fuelled by viscous, silicon-rich magma that doesn't flow easily, and can trap large amounts of gas. That's one of the main reasons why their eruptions are so explosive -- the magma tends to resist flowing, until the gas pressure builds up enough to force it out. As a result, the mountian's made up of pumice and ash (bits of bubbly or pulverized magma) as much as of actual lava flows.
It's an incredible place, well worth visiting (assuming it quiets down enough to be safe to approach). What's sobering about this is that there are a number of other volcanoes in Cascadia that could erupt in similar fashion -- Mount Rainier looms over Seattle when the weather is clear, and it's as much a volcano as St. Helens is. Better watch for that harmonic tremor...
If this thing doesn't erupt soon, I'm going to blow my stack!
Posted by: mamster | October 05, 2004 at 02:04 PM