Why aren't Hawaiian volcanoes violent? Mt. St. Helens violently exploded,
but the pictures of Hawaiian volcanoes I've seen seem to just slowly
ooze lava.
Don Packe
Dear Don,
The short answer is that Hawaiian magmas are a good deal hotter than those
of volcanoes like Mt. St. Helens. This hotter magma is much less viscous
than the cooler magma and therefore much poorer at allowing pressures to
build up within the volcano. The dramatic fountains of lava that you see
photos of from Hawai'i are more like constant releases of gas pressure as
opposed to explosions that can occur when gas pressures get really high.
You can think of the viscous magma at Mt. St. Helens as a much more
effective pressure cap on the volcano, allowing gas pressures to get much
higher and therefore for the eruptions to be much more violent.
Scott Rowland, University of Hawaii
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