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Question
River rock
River rock  
Hi there. I noticed these narrow criss-cross channels running through the rock in the river near me and was wondering what kind of process might have caused this kind of pattern?

Thanks for your help!

Answer
Hi John,
What your seeing is a joint fracturing in the rock.  What happens is the rock fractures in a pattern, usually parallel or sub-parallel.

This happens in different ways depending on the type of rock, and the kind of stress acted upon it.  Sometimes the cement between layers in the rock erodes more quickly than the rest of the rock.  More commonly the rock expands because the pressure of overburden is removed due to erosion or the melting back of the thick ice of continental glaciers.  

Here are a few examples of jointing around the world.

http://www.yosemite.ca.us/library/geologic_story_of_yosemite/final_evolution.htm

http://il.water.usgs.gov/asian_carp/images/Ship_Canal/10-Joint%20Pattern%20Sugar

http://www.sublime.ag/things/?tag=geology

http://outsidetheinterzone.blogspot.com/2013_06_30_archive.html

http://agustgudmundsson.co.uk/?attachment_id=175

Hope this helps.

Bob

Geology

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C. Robert Reszka, Jr.

Expertise

I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.

Experience

I have been working for the State of Michigan for 36 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.

Organizations
Michigan Basin Geological Society

Publications
Decade of North American Geology.
Bedrock Geology of Michigan

Education/Credentials
BS Wayne State University

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