Radial Stress Fracture

January 02, 2023


TomMc_EPOD.RadialFracturedSiltstoneBoulderOnSandstone (002)

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                                                                               

Related Links:

Conchoidal Fracture

Stress Fractures

Pillow Basalt with Radial Cooling

Author's Earth Science Books