American Notes Geology

Almost 80 years after the great earthquake of April 1906, which killed more than 700 people, another tremor hit the San Francisco Bay Area last week. Measuring 5.3 on the Richter scale, vs. an estimated 8.3 for the '06 temblor, the quake for four seconds shook shelves and nerves from Santa Rosa to San Luis Obispo. Damage was minimal: some 21,000 people lost power briefly, but the San Francisco skyscrapers merely swayed, as they are designed to do. The tremor, along with another mild one the previous Saturday, was the latest in a series that has shaken the area in the past decade.

Meanwhile, on an island southwest of Anchorage, the 4,025-ft. Mount ( Augustine volcano erupted for the second time, after being dormant since 1976. University of Alaska Geophysicist David Stone explained that the Mount Augustine eruptions, which shot ash eight miles into the sky, are loosely related to the earthquakes in that both are caused by the same "gross global mechanism": the glacial movement of the Pacific tectonic plate, which is inching north below California and diving under southern Alaska.