By KIRK JOHNSON
c.2013 New York Times News Service
COUPEVILLE, Whidbey Island —
The violent energy of the Earth can sometimes feel predictable.
An earthquake striking a steep slope of gravel or boulders creates an outcome that even a nongeologist could foresee. Volcanoes can literally move mountains.
The huge landslide that struck early Wednesday morning near Coupeville on Whidbey Island was the kind of event, though, that can make things feel more fickle.
The landslide, which destroyed one home and left more than a dozen others cut off from access by road, sent the equivalent of 40,000 dump-truck loads of earth — about 200,000 cubic yards — heaving toward Puget Sound.
A road was shifted about 80 feet vertically and to the west. A forest at the top of a cliff was pummeled to splinters on the beach. No one was injured.
Scientists at the state Department of Natural Resources said Thursday in a report that unlike, say, an ordinary mudslide or avalanche — both of which have seasonal or environmental triggers, especially around precipitation — the Whidbey slide was considered “deep-seated.”
That means, the report said, that the earth on Whidbey Island has in fact been moving slowly for years — since at least 2002 — as part of a larger “landslide complex” that may date back as far as 11,000 years.
In other words, the slide was ultimately predictable in its inexorable, gravity-fueled outcome, but unpredictable as to when a major slip might occur. Around 4 a.m. Wednesday, the great load shifted and started moving.
“Once an area slides, it will try to stabilize itself,” the Department of Natural Resources said on its blog, Ear to the Ground.
“The land will slowly move in an attempt to do this. The chance of another catastrophic movement is low; but possible.”
Meanwhile, other expressions of the earth’s restless energy are already in play at the site.
Wave action is eroding the tons of rubble piled onto the beach, with small sections — small by landslide standards, anyway, ranging up to 10 cubic feet in size — calving out into the water with the tide.
