A roadcut exposes the internal structure of the debris avalanche deposit that formed during collapse of Mount Shasta during the Pleistocene. This deposit contains large angular sections composed of rock and crushed matrix of similar material (like the light-gray area in this photo), in direct contact with other lithologies (brown) from other areas of the pre-collapse volcano. This is due to different sections mixing as the debris avalanche traveled across the landscape.

Photo by Lee Siebert, 1981 (Smithsonian Institution).

This image is made available under the Public Domain Dedication CC0 license, but proper attribution is appreciated.

Keywords: outcrop | stratigraphy | geology | debris avalanche deposit

Shasta