How Arches Are Formed

In the Windows area, many stages of arch formation can be seen. Entrada Sandstone, the rock in which arches are formed, was deposited here as sand more than 150 million years ago. Over time it was buried by new layers, hardened into rock, and shaped by erosion. A series of uplifts and collapses caused severe cracking in the 300-foot layer of buried Entrada Sandstone. When overlying rock layers eroded away, the Entrada was exposed to weathering, the cracks slowly widened, and parallel rock walls called fins were formed. Rainwater continually dissolves the natural cement that holds sandstone together, and with the pressure from water freezing in tiny cracks, causes the sandstone to flake and crumble. Eventually enough rock falls out of a fin that an opening is formed. These holes continue to erode, and in time the same forces of weathering that created arches will destroy them.

Moab, Utah · United States