13 August 2013
Absaroka volcanic breccia
Posted by Callan Bentley
Two images of a “textbook” example of volcanic breccia from the Eocene-aged Absaroka/Gallatin volcanic series, a thick stack of lava flows and lahar deposits from southern Montana and western Wyoming. It features poor sorting, ashy matrix, angular clast shape, and of course, volcanic lithologic provenance for the clasts.
The sample is rotated from one shot to the next. The reason I took two shots was I felt like the background was insufficiently contrasted in the first image (something I subsequently went in and modified with Photoshop). But the second shot seems exposed for the grass, not the rock, with the result that I think I actually like the first shot better.
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
Using your blog in my Southwest Wyoming Geology course! Thanks for posting!
-Dana
http://www.wyomingwilds.blogspot.com