What happened to the top?
 San Francisco
Peaks are the remnants of the only stratovolcano
in the San Francisco volcanic field. For decades, volcanologists suggested
that the mountain now called San Francisco Peaks had simply worn away
over time, eroded bit by bit to form its current bowl-shaped top. Then,
in 1980, the catastrophic explosion of Mount St. Helens forced us to rethink
our ideas about volcanoes.
You see, stratovolcanoes are known for their powerful explosive
eruptions, but they usually force their way upwards, producing a gaping
crater at the top. Mount St. Helens on the other hand, blasted sideways,
leaving a bowl-shaped amphitheater where a nearly symmetrical mountain
top once stood.
Take a look at the two photographs below. On the left side is
Mount St. Helens before the 1980 eruption; on the right is a photograph
taken after the eruption.
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| Mount St. Helens before the 1980 eruption.
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Mount St. Helens after the 1980 eruption
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Compare
the photographs above with the two below. On the left side you'll see
post-1980 eruption Mount St. Helens again; on the right are the San Francisco
Peaks with a line showing the pre-1980 eruption outline of Mount St. Helens.
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| Mount St. Helens after the 1980 eruption
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San
Francisco Peaks with Mount St. Helens outline superimposed.
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Notice any resemblance? Well, so did several volcanologists! Many
volcanologists now feel that the scooped-out shape of the San Francisco
Peaks may be the result of a catastrophic sideways blast like that of
Mount St. Helens. |
