| A hanging valley is a valley eroded by a tributary glacier to the main, or trunk glacier in the main trough. The thickness of the ice in a tributary glacier is less than that of the trunk, because it drains a smaller area and has a smaller discharge. Because of this difference in thickness, the elevation of the valley floors is not the same, although the ice surfaces were probably at the same level during maximum glaciation, when the troughs were cut. When the ice melts, a cross-profile of the tributary valley or cirque is exposed. Note that river valleys also hang, although the difference in elevation between trunk stream and tributary beds is seldom more than a few meters, and is usually under water! |
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