Shut-in (river)

This article is about the type of rock formation found in Appalachia. For the watercourse in Missouri, see Shut-in Creek.

Johnson's Shut-Ins panorama

A shut-in is a type of rock formation found in streams in the Ozarks, comprising pools, rivulets, rapids and plunge pools. The term has an origin in Appalachia.

Description

A shut-in is a rock formation that carves through a mountain range, causing a complex of pools, rivulets, rapids and plunge pools. They are found in streams in the Ozarks. Shut-ins are inherently confined to a narrow valley or canyon, with the river valley widening out both above and below the formation. Because the rock resists downcutting, streams typically descend at a relatively steep gradient through shut-ins, with the downstream terminus of the formation often marked by a very large plunge pool. The river becomes unnavigable at shut-ins even by canoe due to the rapids and narrow channels.

Etymology

The term has an origin in Appalachia, where it was used to refer to a narrow river gorge confined by resistant rock layers.

Examples

Johnson's Shut-Ins State Park in Missouri, with its hard rhyolite and a diabase dike that divert the Black River into many small streamlets following a complex joint system, is the best-known example. More than ninety other shut–ins occur within and around the St. Francois Mountains region of southeast Missouri. In southern Illinois, the Burden Falls Wilderness area includes a narrow canyon below a waterfall that is confined by a resistant sandstone layer; the gorge is referred to as a shut–in, following the Appalachian usage for the term.

See also

• Downcutting – Process of deepening a stream channel by erosion of the bottom material