It is difficult to overstate the impact that glaciers have had on Vermont’s landscape. During the Last Glacial Period (115,000-11,700 years ago) – the official name for the most recent wave of the Quaternary Glaciation – our entire landscape was scoured clean by a continental glacier known as the Laurentide Ice Sheet. The enormity of the ice sheet is nearly unfathomable. It covered most of Canada and extended as far south as Long Island here in the east. At the glacial maximum some 25,000 years ago, if you stood on the summit of Mt Mansfield (Mozdebiwajo) – Vermont’s highest peak at 4,395’ – you would still be under nearly 1,000’ of glacial ice. To the north, the glaciers were more than two miles thick. And they were heavy – just a single square foot stacked one mile thick with ice weighs about 250,000 pounds. So heavy were these glaciers that the continent actually buckled under its weight and the continent was depressed down into the underlying asthenosphere – the upper layer of the mantle that bends and moves like a plastic – some 1,000’!
As more and more snow accumulated at the center of the ice sheet, the margins were pushed ever outward (imagine pushing down on a ball of dough and squeezing the edges outward). This advancing ice sheet acted much like a snowplow with it’s blade set too low. It plucked boulders from the bedrock, which, once caught in the ice, acted like sandpaper further grinding down the once Himalayan-sized Green Mountains down to gentle hills. The boulders were fractured, broken, and crumbled into smaller and smaller pieces and transported along with the moving glaciers. Beneath the moving ice, a hard packed, unsorted jumble of rocks, sands, silts, and clays, called glacial till (or hardpan to the early hill farmers), was pasted down atop the entire state. In the image below, you’ll notice that the vast majority of soils in the state are derived from glacial till.