Thursday 14 July 2011

Bad news travels fast. Well, two feet a day at least.

The Adirondacks Mountains in NY are somewhere most people would go to relax. Even the tourist website invites you to "slow down this summer and camp out under a canopy of stars." Although you may wake up with your tent far from where you pitched it. The Adirondacks, for the past month and a half have been experiencing a landslide. It's moving up to 2 ft each day, fairly fast for an area where most move only a few inches. Although it's excuricatingly slow for the owners of the (now condemned) house, teetering at the edge.

A house teetering at the edge of the slope
The whole side of the hill, about 82 acres of forest, boulders, house foundations and earth, is being dragged down the sides of Porter mountain after this year's heavy snow and rain caused a build up of groundwater. The groundwater seeped into the 12,000 year old glacial till and sands, and the increased water pressure reduced the overall strength of the hillside, and started the movement. The USGS states that 80% of NY is not susceptible to landslides, but if there's a steep slope, like the high peak of Porter Mountain, then it's very easy for the top loose sediment layer to slip, like treacle, down the slope. 

Porter Mountain seen from a distance, the steep slopes causing the landslide are visible
With one house already destroyed and several others moving perilously close to the steep drop at the edge of the scarp, some residents have enlisted house movers to pick up their entire houses and park them at safer locations on the mountain flanks. Although, they have yet to drill a borehole in any property which can find stable ground. With each rainstorm the slide moves faster and the residents are now praying for summer, when the trees will take up more water and hopefully slow the pace. 

Andrew Kozlowski , a geologist for New York, states that there is no way of knowing how long the slide will last for, "It could stop in a few weeks. Or it could keep moving for three months. Or three years. We just can't tell. It has to reach a new equilibrium." There was no warning of the Adirondacks slide and it's possible there are many other areas which could landslide in the mountain range. The last big slide in New York occured in 1993 about 150 miles south west of the current slide.  Slow moving landslides are common in America, and the USGS is also monitoring one in North Salt Lake City, Utah which has been sliding for twelve years. Despite causing up to $2 billion worth of damage in the US alone, they are still one of the least studied natural disasters. 

Landslides turn catastrophic when they turn suddenly into mud of debris flows which travel extremely fast and can cause billions of dollars worth of destruction and high death tolls. If there's another heavy rainstorm it's possible the landslide could take the house right over the edge or worse. State Geologists, however, remain confidant they are well versed in monitoring the speeds of landslides and most catastrophic movement is preceeded by gradual acceleration which can be measured. There is also now a proposal to map the area using LIDAR (a way of mapping the topography beneath the forest) to determine if they can find any areas which are also susceptible.