A simple glance at the Grand Canyon is enough to know that forces
have acted upon the rock formation to transform the canyon into the shape we
see today. Two of these contributing forces are faulting and folding, and both
occur as the earth’s crust is strained. Faulting occurs when the stress on a
landscape is so great the landscape responds by breaking, creating a fracture
on the surface. As opposed to earthquakes which are experienced as faults occur,
the fault itself is the physical evidence left behind. Faults are caused by
stress in the form of compression, extension, and side-by-side movement. Compression
creates thrust faults, extension creates normal faults, and side by side motion
creates strike-slip faults.
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| http://media.tiscali.co.uk/images/feeds/hutchinson/ency/c00948.jpg |
According to the National Park Service, faults can
be seen in most of the canyon’s rock layers. The movement measures from 15 to
16000 feet. One of the most famous faults at the Grand Canyon is Bright Angel Fault.
Bright Angel Fault began as a normal fault 1700 million years ago, but has been
reactivated twice since that time as a thrust fault, then again as a normal
fault.
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| http://www.wvgs.wvnet.edu/www/geoeduc/SedimentaryRocks/CSR09.jpg |
Folding occurs when the stress on the landscape is not
enough to cause it to snap, but enough to deform it or bend the landscape.
Synclines are distinguished by their downward fold, anticlines through their dome
like upfolds, and monoclines by a single slight bend.
At the Grand Canyon, most
of the folds are monoclines. One of the most distinguishable folds is known as
the East Kaibab monocline. I remember looking out of the observatory station of
the Desert Watchtower, but little did I know I had the best view of the East Kaibab
monocline. I plan on visiting the Grand Canyon again, and next time I will know
whether I’m staring at a fault or fold.
Sources
http://www.physci.mc.maricopa.edu/Geology/FieldTrips/GrandCanyon/GrandCanyon_2004_Fall/GrandCanyon_2004_Fall_Images_640/DSC04383.JPG
http://www.nps.gov/grca/naturescience/upload/2-Grand-Canyon-Geology6-2009.pdf
http://www.physicalgeography.net/fundamentals/10l.html
http://www.nps.gov/grca/naturescience/faults.htm
