Here’s a sample from my 2004 geology M.S. thesis work in the Sierra Crest Shear Zone of eastern California. The rock is a sheared ignimbrite (ashflow tuff) tuff bearing a porphyritic texture and a nicely-developed “S-C” fabric. With annotations, showing the S- and C-surfaces, and my kinematic interpretation: S-C fabrics develop in transpressional shear zones: … Read more
There is an old Chinese aphorism that “the beginning of wisdom is to call things by their proper names.” One of the naming conventions that tends to trip up NOVA students who hike the Billy Goat Trail with me is the difference between a “terrace” and a “strath.” This morning, I created a graphic that … Read more
In January, a large landslide occurred in the Hunza Valley of Pakistan’s Karakoram Range, near the village of Attabad. Like the Madison River landslide in Montana (1959), or the Gros Ventre landslide in Wyoming (1925), a river was dammed by the slide debris, and the impounded waters began to rise. At Gros Ventre, the landslide-dammed … Read more
…. And on the other side, we have secondary (tectonic) structures, focused on folds and faults:
One of the things I managed this week was to fill up a new display case in our Student Study area with a structural geology display. On one side is primary structures, both igneous and sedimentary….
In today’s post, I’ll finish up with my geologic discussion of the falls of the James River in Richmond Virginia, south of Belle Isle. Previously, we’ve examined the bedrock at this location (the Petersburg Granite) and a series of fractures – some faults and some extensional joints – that deform that granite. Now we come … Read more
In my previous post, I introduced you to the Petersburg Granite, as it is exposed south of Belle Isle, at the falls of the James River in Richmond, Virginia. I mentioned that it was fractured, and I’d like to take a closer look at those fractures today. The geologically-imparted fractures were exploited by human granite … Read more
Last Friday, NOVA colleague Victor Zabielski and I traveled down to Richmond, Virginia, to meet up with Chuck Bailey of the College of William & Mary, and do a little field work on the rocks exposed by the James River. Our destination was Belle Isle, a whaleback-shaped island where granite has been quarried for dimension … Read more
I mentioned going out in the field last Thursday with Liz Johnson‘s “Geology of Skyline Drive” lab course at James Madison University. We started the trip south of Elkton, Virginia, at an exposure where Liz had the students collect hand samples and sketch their key features. Here’s one that I picked up: Regular readers will … Read more
Searching around for the current Where on Google Earth, I found this astonishing place in western New Zealand: That’s Mount Taranaki, and evidently the vegetation change you see in the circular colored shape around the mountain must be due to a protected-area boundary. Check out the radial drainage pattern on that sucker! Check it out … Read more