Physics Photo of the Week

April 10, 2009

Contrasts in Geology


US19, Nicholas County, WV
(Phoro by Donald Collins)
Buckner Gap Roadcut, I26, Madison County, NC
(Photo by Vicki Collins)

When travelling through mountainous regions, you can learn lots about the Earth's history from roadcuts.  Notice the contrast in rock formations between Central West Virginia and Madison County, NC. 

Most of West Virginia, and many parts of the southeastern United States west of the main Appalachian Mountains were once at the bottom of an ocean.  Thus the rocks consist of horizontal, layered sedimentary rocks.  The ocean floors were uplifted, but the horizontal layered structures were maintained.  You can also notice a thin coal seam near the top of the West Virginia road cut.  The coal was produced by about 100,000 years of plant material having been buried under other sediments for millions of years.

The geology of Madison County, NC has been much more violent than simple burial of sediments for millions of years.  The mountains were formed by continental collisions and thrust faults - where the ancient rock deposits were not only lifted, they were folded by the tremendous compressive forces lasting millions of years.  The folding in the North Carolina mountains was so extreme, that the rocks were exposed to excessive heat in addition to the pressure.  The heat results in two major transformations in the rocks: a) the heat (with pressure) transforms the mineral structures of the rocks - metamorphizing them into harder minerals - similar to firing clay pottery; and b) the rocks became plastic and deformable during the metamorphic processes.  Thus the rocks exposed in Buckner Gap roadcut show extreme deformation.




Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to dcollins@warren-wilson.edu. 

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