By Zach Howard
NEW YORK (Reuters) - A mile-wide landslide that is unleashing hundreds of millions of tons of debris in New York's Adirondack Mountains is the largest in the state's history, but also one of its slowest.
Geologists say an 82-acre piece of earth on Little Porter Mountain in Keene Valley, New York, is creeping downhill at a rate of between just six inches and two feet per day, dragging boulders, trees and house foundations along with it.
Andrew Kozlowski, associate state geologist at the New York State Museum, said the uncommonly lazy slide was triggered by excessive groundwater from this year's heavy snows and rain.
The slide began May 6 and could last considerably longer, from a few months to many years, he said.
"That's the side of a mountain that's in full motion right now," Kozlowski said. "This thing isn't even close to being at equilibrium yet. There's every indication that this is going to continue to move for some time."
The landslide's mass is at least hundreds of millions of tons, he said. Measuring 0.8 of a mile wide, it is the largest landslide in New York history, he said.
One home has been destroyed and at least five others sit precariously near the slide's edge, which overhangs a 30-foot drop in some places.
Among those in jeopardy is the dream retirement home of Jim and Charity Marlatt on woodsy Adrians Acres Lane. They have enlisted a house-moving company to relocate it to a new foundation about 150-200 feet away from the landslide's edge.
But they must do so at their own expense -- at a price tag of at least $150,000 -- because routine homeowner's insurance policies will not pay for landslide damage, they said.
"My heart is broken," Charity Marlatt told Reuters in an interview. "Because we're only human and this is Mother Nature and God's will, we have no idea what will happen."
By late June, movers had hoisted the home from its foundation and slid it 30 feet from the brink, where it will stay "parked" until geological tests confirm the new foundation is in a secure location, Jim Marlatt said. With the right test results, the house will then be moved to the new foundation.
Unfortunately, initial drilling tests reaching 85 feet down into the soil there found no stable bedrock on which to anchor the house.
"Why did the landslide stop where it did?" wondered Stan Barber, owner of Larmon House Movers in Schuylerville. "That's the thing -- you don't know if it's ever going to change or get worse."
Geologists say landslides are common across the continent, particularly in the U.S. West and in parts of the Northeast. But they are problematic to forecast.
The United States Geological Service says they occur in every state and kill between 25 and 50 people every year nationwide. They cause in excess of $1 billion in damage, making them potentially more devastating than all other such natural hazards combined.
The May 18, 1980 eruption of Mount St. Helens, a volcano in the Cascade Mountain Range, in Washington State, caused the world's biggest landslide, encompassing an area of 23 square miles, according to USGS.
In New York, 80 percent of the state has a low susceptibility to landslide hazard. But in the Adirondacks, the high peaks are particularly vulnerable to slides because of vast swaths of land where loose soil is piled atop bedrock, geologists say.
"We have these glacial lake clays and sediment with very fine grain, and often they don't have a lot of strength to them," he said. "When they get deposited on hillsides, the steeper the slope the more likely they are to fail. All you need is a lot of ground water, and they slide and slip."
Indeed, slides occur all over the Northeast. In Vermont, several smaller slides occurred this month due to similar lake clays eroding because of heavy spring rains, Kozlowski said.
Speed is not always of the essence in landslides. According to the Utah Geological Survey, the Springhill slide in North Salt Lake has picked up speed since its start in 1998, and is currently moving at a pace of one to two inches per week.
(Editing by Barbara Goldberg, Cynthia Johnston and Greg McCune)