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A shut-in is an Ozark term for a river that's naturally confined within a deep, narrow channel. The river becomes unnavigable even by canoe due to the rapids and narrow channels produced as the stream encounters a more resistant rock that is more difficult to erode. In the Johnson's Shut-Ins State Park in Missouri hard rhyolite and a diabase dike diverts the stream into many little streamlets following a complex joint system "shutting" the river.〔 The term had an origin in Appalachia where it was used to refer to a narrow river gorge confined by resistant rock layers.〔Beveridge, p.39 - 62〕 Examples can be found in Johnson's Shut-Ins State Park in Missouri, where the Black River has become confined in a shut-in.〔 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 * 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shut-in (river)」の詳細全文を読む スポンサード リンク
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