Sunday, October 04, 2015

The Great Quake and the Great Drowning

[Hakai Magazine] In the year 1700, on January 26, at 9:00 at night, in what is now northern California, Earthquake was running up and down the coast. His feet were heavy and when he ran he shook the ground so much it sank down and the ocean poured in. “The earth would quake and quake again and quake again,” said the Yurok people. “And the water was flowing all over.” The people went to the top of a hill, wearing headbands of woodpecker feathers, so they could dance a jumping dance that would keep the earthquake away and return them to their normal lives. But then they looked down and saw the water covering their village and the whole coast; they knew they could never make the world right again.
That same night, farther up the coast in what is now Washington, Thunderbird and Whale had a terrible fight, making the mountains shake and uprooting the trees, said the Quileute and the Hoh people; they said the ocean rose up and covered the whole land. Farther north still, on Vancouver Island, dwarfs who lived in a mountain invited a person to dance around their drum; the person accidentally kicked the drum and got earthquake-foot, said the Nuu-chah-nulth people, and after that every step he took caused an earthquake. The land shook and the ocean flooded in, said the Huu-ay-aht people who are part of the Nuu-chah-nulth, and people didn’t even have time to wake up and get into their canoes, and “everything then drifted away, everything was lost and gone.”
Here’s what geologists say: the earthquake that almost certainly occurred on the night of January 26, 1700, ruptured North America’s Pacific Northwest coast for hundreds of kilometers, from northern California, through Oregon and Washington, to southern Vancouver Island. Along this coast, the Juan de Fuca plate was pushing under the larger North American plate, had gotten stuck—locked—but kept pushing until it released, abruptly and violently. The earthquake that resulted was probably a magnitude 9, about as big as earthquakes get. The coast dropped by as much as two meters, and a tsunami brought floods more than 300 meters inland.
Geologists now know that the Pacific Northwest has been having these earthquakes and tsunamis irregularly every 500 years or so; their oldest record in sediments goes back at least 10,000 years. The evidence is massive: subsided marshes, drowned forests, sediment layers showing enormous landslides that flowed out on the ocean floor, seismic profiles of the Juan de Fuca plate, and satellite measurements of a coast deforming from the stress of a plate that’s once again locked. In the next 50 years, the chance of another magnitude 9 earthquake there is 1 in 10. Read More