(Host) Geologists say landslides like the one near Montreal last week are the result of surface conditions that formed thousands of years ago.
A landslide in the town of Saint-Jude, Quebec created a massive hole several hundred yards wide that swallowed a house and killed a family of four.
Geologists say two kinds of clay formed in our region as glaciers receded 13,000 years ago – a freshwater clay, and saltwater clay. Speaking Monday on Vermont Edition, UVM geologist Charlotte Mehrtens said the marine clay is more likely to cause a landslide:
(Mehrtens) "Both types of clay can undergo this slippage, but certainly there is an implication that the salt in the Champlain Sea clay makes it even – along with the grain size difference – makes it extra specially unstable."
(Host) The freshwater clay formed just ahead of glaciers as they receded from this region. The marine clay formed in the saltwater environment that followed after the glaciers.
State geologist Larry Becker says landslides have occurred in Vermont in both types of clay, including one in Jeffersonville in 1999, and one much further back:
(Becker) "There was a slide in Weybridge back in the 1960s, and it’s right on the edge of whether it was marine or lake clay. But it had a very, a similar quality to the slide, from pictures that I saw of the Quebec slide, in that its stepback was a relatively shallow slope, and its stepback took out a state road that led up to Route 17."
(Host) Becker says the Vermont Geological Society is working with several colleges and Vermont Emergency Management to identify unstable slopes and potential landslide areas.