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An entrenched river is a river that is confined to a canyon or gorge, usually with a relatively narrow width and little or no flood plain, and often with meanders worn into the landscape. Such rivers form when the base level of erosion is rapidly lowered, so that the river begins downcutting into its channel faster than it can change course (which rivers normally do on a constant basis). This may occur due to tectonic uplift of the region, a lowering of the oceans, the collapse of a moraine-dammed lake downstream, or by capture of the river by another. Meanders established before the lowering of the base level of erosion may be preserved as the river channel deepens subsequently. Examples of entrenched meanders may be seen in the Snake River Canyon in southern Idaho, and in many canyons of the Colorado Plateau.
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