Landslide on Puget Sound part of a geological pattern. Is it over?

The massive landslide on Whidbey Island near Seattle this week is part of a larger complex of slides on Puget Sound islands going back thousands of years. It may not be over yet.

Mike Siegel/The Seattle Times/AP
University of Washington geologist Terry Swanson surveys the damage from a landslide on Whidbey Island, Wash. The slide severely damaged one home and isolated or threatened more than 30 on the island, about 50 miles north of Seattle in Puget Sound.

The massive landslide on Whidbey Island about 50 miles north of Seattle may have happened in seconds, but its history is measured in geological time, so it may not be over yet.

It’s a small portion of a much larger landslide complex about a mile and a half long that may date back as far as 11,000 years, according to Washington State geologists, and it’s still moving, however slightly.

For now, the evaluation and recovery effort is focusing on assessing damages – particularly to the homes that residents have not been allowed to return to.

No one was killed or injured in the slide, which occurred at about 4:00 a.m. Wednesday morning.

But it did move one beachside home – now deemed uninhabitable – some 200 feet off its foundation, Eric Brooks, deputy director for emergency management at Island County (which includes nine islands in Puget Sound), told the Seattle Times. It also took out 300 to 400 feet of a road leading to the beach, leaving 17 homes unreachable and without power because the slide also took out the utility poles.

The slide displaced some 200,000 cubic yards of earth, or approximately 40,000 dump truck loads, state officials said. Twenty properties on a scenic island hillside were damaged by the slide, with some suffering structural damage and others losing portions of their yards, reports the Associated Press.

The landslide into Puget Sound lifted the beach as much as 30 feet above the previous shoreline, state geologists said in a preliminary report Thursday.

"It looks like a giant shovel pulled the hill down to the water," Central Whidbey Fire Chief Ed Hartin told Reuters. "We heard a lot of rumbling and snapping of trees."

The homes in the Ledgewood Beach area are a mix of year-round and vacation properties that sit high on a bluff overlooking the waters of Puget Sound.

A local home owned by Microsoft chief executive Steve Ballmer did not appear to be immediately threatened, Chief Hartin said.

At a community meeting Thursday evening in Coupeville, Whidbey Island’s country seat, residents wanted to know when they can get back into their homes. They're also worried about looters. The sheriff's office plans extra patrols.

While the ground continued to move Thursday, the geologists said the land will slowly try to stabilize itself.

"The chance of another catastrophic movement is low, but possible," their report said.

The area "still has a bit of slippage here and there," Terry Clark of the county’s emergency management department told the AP. "It can be a handful of dirt to a barrel-full. It's still an active event."

"It's probably one of the largest ones we've seen in Washington State, much less along the coast," Mr. Clark said of the landslide. "We're used to little slides here and there, but this happens to be way beyond what our expectations were."

As usual with such natural disasters, the Whidbey Island landslide may raise questions about where residential and commercial structures and facilities should be built.

“It’s taken a while to soak it in to realize that life changes in five minutes,” Whidbey resident Nancy Skullerud told KING5 News in Seattle. “Mother Nature always wins.”

The Pacific Northwest can be soggy, but rainfall appears not to have been a cause of the Whidbey Island slide.

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