Why was there no lava flow at Mt. St. Helens yet there is a lava dome
built up in the crater now?
Max Shanks
Hi Max,
The lava dome at Mt. St. Helens is the viscous equivalent of a lava flow. That
dacite lava is so cool and so high in silica that the poor thing can barely
flow. It just sits there like a big blob. Every once in a while (although not
for the past few years) pressure under or within the dome builds up and part of
it is exploded away.
Mount St. Helens has produced more fluid lava flows in the past. It just so
happens that the material that is presently being erupted is cool and viscous.
There is a very good section about lava domes in the
"Fire and Life"
section of the "volcanic parks and monuments" section of Volcano
World.
Sincerely,
Scott Rowland, University of Hawaii
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