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.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
