A Glacial Lake

A Glacial Lake. . A river of ice over 2,000 feet thick moved down this valley. Lake McDonald is evidence of its passing. , , When the glacier receded more than ten thousand years ago, it revealed a changed landscape. The ice had quarried away huge amounts of rock. A terminal moraine dammed McDonald Creek, impounding Lake McDonald. , , Glaciers are slow-moving rivers of ice. Like conveyor belts they transport large volumes of material. As rocks and dirt pile up along the edges of the melting ice, they form moraines. Material that builds up at the snout is called a terminal moraine; debris deposited along the sides forms lateral moraines. The ridge across the lake and the ridgeline behind you are covered by lateral moraines left by the glacier. , , The lake fills a steep-sided glacial trough and is the deepest lake in the park at 472 feet (144 meters).