Shut-in (river)

A shut-in (also known as narrows or a water gap) is a geological landform characterized by a narrow, steep-walled passage through which a river or stream flows. Shut-ins are typically formed where a resistant rock layer constricts the river channel, forcing the water to cut a narrow gorge or canyon through the rock. They often feature exposed bedrock, rapids, and constricted flow.

Shut-ins are commonly found in areas with differential erosion, where some rock layers are more resistant to weathering and erosion than others. Over time, the river erodes the less resistant rock, leaving the resistant rock layer to form the walls of the shut-in. Tectonic activity, such as faulting or folding, can also contribute to their formation by creating zones of weakness in the rock that are more susceptible to erosion.

The constricted flow and exposed bedrock in shut-ins can create unique aquatic habitats, often supporting specialized plant and animal communities adapted to the fast-flowing, turbulent water. Shut-ins may also present challenges to navigation, requiring experienced boaters and specialized equipment. Due to their scenic beauty and unique geological features, shut-ins are often popular recreational areas for activities such as hiking, swimming, and kayaking.