Urth Picture Post: Kowallis

Showing posts with label Kowallis. Show all posts

Saturday, March 1, 2014

Microcracks and Macrocracks

Photos of fractures from small microfractures to large macrofractures.

Healed microcracks in a quartz grain in granite from the Wolf River Batholith of Wisconsin. Two sets of prominent microcracks are preserved now as trails of liquid filled bubbles and may give clues to the paleostress history of these rocks. In addition a couple of cracks healed with dark iron oxide can also be seen. The horizontal length of the photo is about 5 mm.

Another quartz grain from the granite of the Wolf River Batholith, but stress concentrations along the grain boundary in this grain have created a swarm of cracks radiating out from the triangular shaped feldspar at the top of the photo into the quartz.

A quartz (top yellow) and feldspar (bottom dark and light stripes) in this photo show the microcracks that form along the grain boundaries. The oval spots on the quartz grain are artifacts of the ion milling process used to produce the microcrack sections.

Microcracks in a sample of granite dyed with a fluorescent dye and then illuminated under UV light. The rock which to the eye appears very strong and solid has an extensive network of microcracks, many of them along grain boundaries.

Thin section of a basalt with lath shaped plagioclase feldspar crystals, dark Fe-Ti oxides, and multicolored lumpy pyroxene. A few cracks can be seen cutting across the feldspars.

Scanning electron microscope photo of an open crack in a basalt from Iceland. The oval spots again were produced by ion milling when the sample was being prepared.

A healed crack network on a slab of limy mudstone from the Green River Formation. I am not sure of the mode of formation for these cracks, but they may be formed in a similar fashion to the septarian cracks that are found in some concretions.

Three massive ash flow tuffs in central Nevada (look carefully in the bottom center of the photo for the group of people as a scale). The middle tuff unit has well developed columnar jointing and a dark vitrophyre at the base of the flow. The top of this middle flow is also less welded and forms a slope covered with sage brush. The lower ash flow (light yellow tan) just above the group of students does not have columnar jointing but it also grades up into a softer, less welded top that forms a slope just below the black stripe of the overlying vitrophyre.

Friday, September 21, 2012

Ferry Bluff on the Wisconsin River

Yesterday I visited Ferry Bluff on the Wisconsin River west of Sauk City with assorted nephews, nieces, in-laws, and out-laws. It was a beautiful day and the first time all summer that I have done any hiking (even though it was a fairly short hike). It was good to be able to tag along with the rest of the family and visit a spot that my brother-in-law, Douglas Clark, loved to visit. He would have enjoyed the trip.

David Clark, Julee Kowallis, Steven Clark, Karen Clark, Adrienne Celt, Kimberly Madison, Rachel Robinson, Ryan Clark, Aaron Robinson, Karl Kowallis standing atop Ferry Bluff.

Looking west along the Wisconsin River from Ferry Bluff.

Sandbar across the Wisconsin River south of Ferry Bluff.

Late summer asters in bloom along the sandstone outcrops of the bluffs.

The Wisconsin River from Ferry Bluff, looking to the east.

Cross-bedded Cambrian sandstones underlie the bluffs and are exposed here because the ice-age glaciers that covered most of Wisconsin did not cover this area, known as the "driftless area."

Bright lichens on a juniper tree atop the bluffs.

Wild grape vines lit by the late summer sun.

Blue harebells grow well in the sandy soil on top of the bluff.

This year's drought has stressed many of the trees including this oak that is trying its best to show its colors for fall even with many of the leaves half dead.

The boardwalk atop the bluff is knotted together with rope.

Juniper roots are exposed in places along the sandy top of the bluffs.

The vertical tubes on this face of the weathered sandstones of Ferry Bluff were made by ancient animals that burrowed into the sand along the Cambrian sea.