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How do hanging valleys form after glaciers retreat?

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esker: Nunavut — glacial landform Eskers, or narrow ridges of gravel and sand left by a retreating glacier, wind through western Nunavut, Canada, near the Thelon River.

Hanging valleys form due to the differential erosive power of glaciers within a system. Large trunk glaciers, which carry a greater volume of ice, possess significantly more erosive capability than the smaller tributary glaciers that feed into them.1

As the trunk glacier moves, it deepens and widens the main valley floor much more rapidly than the tributary glaciers can erode their own paths. Because the depth of ice is a dominant factor in this process, the tributary troughs are carved to a shallower level than the main valley.12

When the ice eventually retreats, these tributary valleys are left at an elevation substantially higher than the floor of the main valley, creating a discordant junction known as a hanging valley. In many instances, postglacial streams flowing from these elevated valleys descend into the main valley, often forming dramatic waterfalls, such as those found in Yosemite National Park.12