Driving south on I-5 into Seattle, the Cascadia Subduction Zone came to mind, especially when the highway dipped into a gloomy tunnel beneath Seattle’s relatively new skyscraper district. This fault line runs along the Pacific coast from north of Vancouver down into California. The western “plates” move implacably east and downward under the North American plate, building up massive tectonic forces that can produce some of the most violent megathrust earthquakes on the planet.
The zone also accounts for a chain of volcanoes that tend to produce titanic explosions rather than eruptions of lava and ash as seen in the hula movies. The most recent expression of this tendency was Mt. St. Helens in 1980, an impressive cataclysm by the standards of our fine-tuned complex civilization, but a junior event of its type compared to, say, the blow-off of Mt. Mazama 7,500 years ago, which left Crater Lake for the tourists. A publicity-shy correspondent writes:
By all acounts Mazama was floating upon a vast lake of steamy rhyolite. It was a structurally unstable stratovolcano the size of Mount Shasta with a net volume of 80 cubic miles. A 5 minute Triple Junction 9.3 Richter Scale shaker uncorked the Mount Mazama champagne bottle via massive lahars which removed the overpressure. Geologists estimate that the eruption lasted for about one day.
It’s only been in the last thirty years that Seattle hoisted up its tombstone cluster of several dozen office and condo towers. That’s what cities do these days to demonstrate their self-regard, and Seattle is perhaps America’s boomingest city, what with Microsoft’s and Amazon’s headquarters there — avatars of the digital economy. A megathrust earthquake there today would produce a scene that even the computer graphics artistes of Hollywood could…