KEENE - Landslides are common across New York, but the slow-speed collapse of a sodden mountainside in the Adirondacks is something else.
Andrew Kozlowski, an associate geologist at the State Museum, said Friday that 82 acres of glacial sediment on Porter Mountain in Keene Valley is moving because the winter's heavy snowpack and intense periods of rain this spring left it soaked and allowed the mixture of clays and sands to start shifting.
"We have landslides from Long Island to Buffalo. We deal with them all the time," Kozlowski said.
What makes Porter Mountain different, he said, is that it's an "earthflow," not a rock slide or "debris avalanche" that typically happens rapidly.
There's no telling when the hundreds of thousands of tons of earth on the east-facing slope will stabilize, Kozlowski said. It could be days, weeks or years.
Since the slide started on May 4 or 5, the earth at the top of the 1,500- to 1,800-foot mountainside has dropped 8 to 12 feet, creating a new cliff along a 0.8-mile stretch. And it's still sliding 2 to 12 inches a day, depending on how much rain falls and other conditions.
One vacation home on the mountain already has been wrecked, four others are threatened and two seasonal homes below could be engulfed over time.
Kozlowski said the owners of the remaining home nearest to the cliff have shored it up with steel beams and plan to move it farther back from the edge.
But figuring out how far back will be safe is difficult, he said, and homeowners were told retaining walls or other structures would be no match for the force of nature.
Kozlowski said the earth that's moving was deposited on the slope during the Ice Age, when valleys in the Adirondacks' High Peaks were dammed and became lakes.
For now, the slide is at a fairly steady pace. He said a large, quick drop isn't expected.
"But if we got another 9 inches of torrential rainfall," Kozlowski said, "that could be a game changer."
-Copyright 2011 Associated Press