Nature
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A river of ice more than 2,000 feet thick moved down this valley, and Lake McDonald remains evidence of its passing. When the glacier receded more than ten thousand years ago, it revealed a changed landscape after quarrying away huge amounts of rock. A terminal moraine dammed McDonald Creek and impounded Lake McDonald. Glaciers are slow-moving rivers of ice that transport large volumes of material like conveyor belts. As rocks and dirt pile up along the edges of melting ice, they form moraines: material that builds up at the snout forms a terminal moraine, while debris deposited along the sides forms lateral moraines. The ridge across the lake and the ridgeline behind 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).
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