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31 January 2020
Friday fold: tension gashes near Sunflower, Arizona
Reader John Christian shared these folds with me via email last week. They are quartz veins in slightly metamorphosed Precambrian igneous rocks found near Sunflower, AZ in the Mazatzal Mountains. The second photo is a close-up shot of the curviest, cleanest batch of folds from the first shot. These are beautiful examples of folds in similarly oriented quartz veins; we call them “en echelon” for the way you have a …
11 July 2019
A submarine slump complex at Sandy Cove, Newfoundland
Traveling in Newfoundland, Callan visits a seaside outcrop showing a Proterozoic submarine slump complex, overprinted by tectonic cleavage and weathered by the sea.
3 May 2019
Friday fold: Monarch Canyon
When a dike is subjected to shear, how does it deform? A guest Friday fold from Darrel Cowan of the University of Washington teaches a nice little lesson. Join the field trip in Monarch Canyon of Death Valley National Park…
25 January 2019
Friday folds: more Marli Miller
Four Friday folds from Marli Miller’s online photo archive of geological images.
18 January 2019
Friday fold: Saluda Dam, South Carolina
Scott White (@SeafloorScott) of the University of South Carolina pitched in with today’s Friday fold: Click to enlarge This shows a section of high grade gneiss in the spillway of the Saluda Dam in Columbia, South Carolina. Zooming in there, you can see a nice fold hinge on the left edge: Although I don’t know the precise location of this outcrop, I did a bit of internet sleuthing… According to …
21 November 2018
Brittle overprinting ductile in the South Mountains metamorphic core complex, Phoenix, Arizona
Today, we take a look at the structural geology that reveals the deformation evolution (first ductile, then brittle) of the South Mountains metamorphic core complex, south of Phoenix, Arizona. Expect lots of photos of smeared-out rocks, broken by faults.
26 October 2018
Friday folds: Mather Gorge Formation
It’s been a very Billy-Goaty week for me. Three times since Sunday afternoon, I’ve taken people to the Billy Goat Trail’s “A” loop in C&O Canal National Historical Park. On Tuesday and Thursday, it was my NOVA Physical Geology students. On Sunday, though, it was just my son and me. Good news! He helped me discover a new fold by exploring some new rock outcrops and climbing on them. He …
19 October 2018
Friday fold: the Brooks Range, Alaska
It’s Friday, thank goodness. Today our “Friday fold” feature heads north, way north, to the Brooks Range of Alaska. There we find a trio of mountainsides exposing folds photographed in the 1990s.
11 October 2018
Q&A, episode 6
A reader asks about Callan’s source of inspiration, a fitting question given the advent of Earth Science Week, which this year has as its theme “The Earth as Inspiration.” Brace yourself for a tantalizing cavalcade of gorgeous images of patterns in rocks!
28 September 2018
Friday fold: Big Cottonwood Fm., Slate Canyon, Utah
It’s Friday and that means it’s time for a fold. Today we head to Cottonwood Canyon, Utah, with reader Octavia Spencer, for a lovely antiform.
Callan Bentley is an assistant professor of geology at Northern Virginia Community College. He is a fellow of the Geological Society of America and the 2018 National Association of Geoscience Teachers' James Shea Awardee. 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. Callan served as a contributing editor at EARTH magazine for many years. He is Past President of the Geological Society of Washington and the Geo2YC division of NAGT. He lives in the Fort Valley of Virginia.