https://www.youtube.com/watch?v=1SXaMH8gV6I Earth fissures are long, narrow cracks in the ground that form where the ground is sinking. They can erode very quickly, posing a hazard to nearby infrastructure. In Arizona, land subsidence--the sinking of the earth--is caused by groundwater withdrawal, meaning that earth fissures are a man-made--or anthropogenic--hazard. This video that I made as part… Continue reading Understanding Earth Fissures: A Man-Made Geohazard
Category: structure
Glaciated breccia: A three-part rock story
This piece of glaciated breccia from the Brussels Hill meteorite impact structure in Brussels, Wisconsin is probably one of my favorites in my collection. It’s not the oldest, nor is it necessarily the prettiest, but it holds one of the best stories. This rock began its life ~440 million years ago during the Silurian Period.… Continue reading Glaciated breccia: A three-part rock story
Meteorite Impact or Maar?
Looking at the two images above, they appear quite similar: both are of very large (~1 mile wide), nearly perfectly circular craters in the ground. However, one was formed by a meteorite impact and the other is a maar formed by an explosive volcanic eruption. Think you can figure out which one is which? From just… Continue reading Meteorite Impact or Maar?
Which way is up?
No, your eyes aren’t deceiving you, these rock layers are nearly vertical! Although they were once horizontal, these Paleozoic sedimentary units have been tilted so that they now dip nearly 90 degrees. These rocks are located in northeast Tennessee and are part of the Appalachian foreland fold-thrust belt. Though built by multiple orogenies, the Alleghenian… Continue reading Which way is up?
How do you make a green rock?
Typically when we think of rocks, we don’t often picture them as having vibrant hues. Minerals themselves often come in a spectacular array of colors, but rocks overall tend to have more muted tones and earthy colors. These rocks (pictured above) from the Buckskin Mountains in western Arizona stand out in stark contrast to the… Continue reading How do you make a green rock?
Van Hise Rock
If you’re a structural geologist or geology student in the midcontinent region, you’ve most likely made the pilgrimage to Van Hise Rock. Located near Rock Springs, Wis., in the Baraboo quartzite range, Van Hise Rock is among the best-known structural geology landmarks in the Midwest. Van Hise Rock provides spectacular exposure of the nearly vertical… Continue reading Van Hise Rock
Folds and cleavage
Folded quartzite and phyllite, with axial planar cleavage in the phyllite South limb of the Baraboo (Wis.) syncline Image by author
Crater Hunters Find New Clues to Ancient Impact Storm
The Earth will never catch up to the moon (let’s hope), but the number of Ordovician craters may soon takeoff. That’s because it’s easier and cheaper than ever to sniff out the shocked minerals that confirm an impact. My work on my impact site, Brussels Hill in Wisconsin, is featured in this article, which is… Continue reading Crater Hunters Find New Clues to Ancient Impact Storm
Shock metamorphism & shatter cones
Above: A shatter cone in dolomite from the Kentland, Indiana impact structure (Specimen from Lawrence University.) Meteorite impacts are pretty amazing things. An impact crater forms instantaneously on a human time scale, with the shock wave from the impact propagation through the target rock in the following stages: contact and compression, crater excavation, and crater modification. Some… Continue reading Shock metamorphism & shatter cones
Glaciated breccia
Had a great day out at my field site with my professors! Spent a bit of time in the quarry and most of the afternoon trekking through the forest in search of outcrops. Here’s a photo of some lovely, smooth glaciated breccia we found!
Emily Zawacki, Ph.D. 