The day after Hurricane Irene drenched the Adirondacks, state forester Kris Alberga flew over the High Peaks and saw so many new debris slides that he lost count of them.
Since then reports and photos of new slides—some taken from the air—have been trickling in. A guy who goes by the nickname of Mudrat has started compiling a list on Adirondack High Peaks Forums. In his first post, he listed sixteen that had been created or expanded by the storm, but there probably are many more.
The large slide depicted above, on the north side of Saddleback Mountain, was among those on Mudrat’s list. Brendan Wiltse, who took the photo, climbed it the day after storm before the state Department of Environmental Conservation closed the High Peaks Wilderness. He named the slide Catastrophic Chaos.
Now that DEC has reopened most of the trails in the Wilderness Area, many hikers will be eager to climb the new slides (and in winter, they will get skied). DEC spokesman David Winchell said the department is not prohibiting people from hiking on the slides, but he warned that debris on some slides is unstable.
It’s been estimated that that there are more than four hundred slide scars in the Adirondacks. They are most common in the High Peaks region, where soils are thin and slopes are steep.
Andrew Kozlowski, associate state geologist, said debris slides occur when heavy rains saturate the soil to the point where it starts slipping downward. “Once it starts moving, it starts accelerating,” he said, “and then it rockets down the slope”—taking trees and other vegetation with it.
Since the soils remain wet from Irene, he said, the High Peaks may see more slides if another storm hits, even one less powerful than Irene, which dumped about ten inches of rain.
If a slide strips a slope clean to the bedrock, he said, it can take centuries for vegetation to grow back. First, lichens cling to the bare rock, followed by moss. These pioneers trap bits of organic debris that decompose to form soil. Eventually, small seedlings take root, which in turn trap more debris. If rubble or dirt remain on the slide, the process is speeded up.
Kozlowski, who works for the New York State Museum, said debris slides are very different from the slow-motion mudslide discovered on the side of Little Porter Mountain in Keene this spring.
In that case, some eighty-two acres are slowly creeping down the mountain. The mudslide has destroyed, damaged, or imperiled a number of houses in the Adrian’s Acres subdivision.
The soil in the vicinity of the mudslide has been measured up to 250 feet deep, whereas the soil where debris slides takes place may be only a few yards deep. The speed of the mudslide on Little Porter—or whether it continues at all—depends on the depth of groundwater, Kozlowski said.
Kozlowski said the groundwater depth has dropped six feet since July. Right after Irene, it rose two feet. In the following days, it went up another half-inch. “What we’re anticipating is that the water levels will keep rising,” he said.
At its peak, the mudslide moved up to two feet a day. Although its movement is now “imperceptible,” Kozlowski said, if the groundwater reaches a certain level, the slide could speed up again. But he doesn’t know for sure what that level is.
“If the water levels recover in the in the four-to-six-foot range, things might start happening,” he said.
Click here to read a detailed account of the Keene mudslide on the Adirondack Explorer newsmagazine’s website.
Photo of Saddleback slide by Brendan Wiltse.