Ventifact

Photographed by Michael P. Klimetz

WYOMING

A ventifact is a rock that has been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals. These geomorphic features are most typically found in arid environments where there is little vegetation to interfere with aeolian particle transport, where there are frequently strong winds, and where there is a steady but not overwhelming supply of sand. A ventifact can be abraded over time into an eye-catching natural sculpture. In moderately tall, isolated rock outcrops, mushroom shaped pillars of rock may form as the outcrop is eroded by saltating sand grains. This occurs because, even in strong winds, sand grains can't be continuously held in the air. Instead, the particles bounce along the ground, rarely reaching exceeding one meter above ground level. Over time, bouncing sand grains can erode the lower portions of a ventifact, while leaving a larger less eroded cap. The results can be stone pillars with a mushroom shape. Individual stones, such as those comprising desert pavement, are often found with grooved, etched, or polished surfaces where these same wind driven processes have slowly worn away the rock. When ancient ventifacts are preserved without being moved or disturbed, they may serve as a paleo-wind indicators. The wind direction at the time the ventifact formed will be parallel to grooves or striations cut in the rock.

Photographed by Michael P. Klimetz

Cheyenne

WYOMING

Photographed by Michael P. Klimetz

Cheyenne

WYOMING

Photographed by Michael P. Klimetz

Cheyenne

WYOMING