Radial Stress Fracture
January 02, 2023
Photographer: Thomas McGuire
Summary Author: Thomas McGuire
This image shows unusual fracturing in a boulder in the remote Circle Cliffs area of Southern Utah. The boulder is a massive (unlayered) siltstone, a sedimentary rock type common on the Colorado Plateau. Whether it weathered in place settling on top of the white sandstone surface or was moved onto the sandstone surface isn’t clear. Soft siltstone would not survive being moved very far.
Radial fractures are rare. An impact or explosion might create this kind of fracture. But I conjecture that this it occurred as the boulder came to rest on a relatively hard, flat sandstone surface with a protruding point, or on another, smaller boulder.
Burr Trail, Escalante-Grand Staircase National Monument, Utah Coordinates: 37.7902, -111.1534
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