Technology:

Prelude to a Catastrophe: “The Unusual Character of the Seismic Activity Became Clear”  (Scientific American)

Mount St. Helens from Spirit Lake. Skamania County,
Washington. August, 1975. The volcano exploded in 1980.
(Image courtesy Donal Mullineaux, USGS.)

Mount St. Helens had always been more seismically noisy than her siblings. Studies in the early 1970s found two types of earthquake: typically “volcanic” quakes high on the mountain, and classically tectonic quakes a few kilometers beneath to the northeast and southwest. Further studies revealed the earthquakes with “volcanic” signatures to be glaciers grating down the mountain. None of this was unusual for an ice-covered volcano in a tectonically feisty area.

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