The Moab region of eastern Utah offers prime
landscapes where tourists can view abundant evidence of rock decay, whether
physical or chemical. Such evidence contributes in part to the distinctive
physical geography of Moab.
Joints
are fractures in rocks that allow for processes of weathering to occur. Joints
are visible on numerous rock formations in and around Moab, including Arches
National Park.
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Numerous joints are visible on the left-hand
side of this rock formation. This arch is located
in Hunters Canyon near Moab, Utah. (Photo by:
Katie Logar)
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Humans,
for means of rock climbing in the region, utilize joints; however, the primary
result of jointing is the promotion of weathering and later, erosion.
Joints
can form in two ways: either by contractional cooling/thermal expansion or by folding, faulting, or plate tectonics. In regards to sedimentary rock, which is
abundant in Moab, joint contraction is a key process in creating features like
arches and natural bridges.
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Landscape Arch, located within Arches National Park, boasts
prime examples of jointing. Joints weaken the rock and allow
for weathering to break down the rock. (Photo courtesy of:
http://upload.wikimedia.org/wikipedia/commons/c/c9/
Landscape_Arch_in_Arches_National_Park.jpg)
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While
joints pave the way for future weathering and erosion, other physical decay
process take their toll on the desert landscape. One such process is salt
decay, which can cause cavernous decay. Alveoli and tafoni are forms that evidence
cavernous decay. Both are examples of vertical weathering characterized by
holes found in rock surfaces. Alveoli are small, relative to the size of one’s
finger, while tafoni are larger—roughly the size of one’s fist. Both forms are
visible in the Moab region, due to its desert-like climate.
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This sizable cave located near Corona Arch houses examples
of tafoni and alveoli. These holes in the surface of the rock
are caused by cavernous decay. (Photo by: Jessica Logar)
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While salt decay
creates unique landforms, wind does not. Simple physical and chemical decay
processes shape unique formations, like many of the arches located in Moab. This
is evidenced by their rough—not smooth—surfaces.
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This diagram demonstrates the process of arch formation by
physical and chemical decay processes--not by wind formation.
Wind lacks the power to shape such formations over time.
(Photo courtesy of: http://thelifeofyourtime.files.wordpress
.com/2012/04/archformation.jpg)
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In addition to physical
decay, chemical decay also occurs in the Moab region. One product of rock decay is the
formation of new crystals, which leads to the creation of rock varnish. This
provides a backdrop for ancient rock art, which is abundant near Moab.
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Rock varnish on a panel near Moab provides a dark backdrop
for petroglyphs. Similar Indian rock art panels can be found
elsewhere in the region. (Photo courtesy of: http://www.real
-dream-catchers.com/images/KokoHunt.jpg)
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Tourists
can observe evidence of physical and chemical rock decay around Moab, Utah.
References:
"Decay of Earth's Rocks (weathering): the Key to our Beautiful Earth" Lecture Notes
http://upload.wikimedia.org/wikipedia/commons/c/c9/Landscape_Arch_in_Arches_National_Park.jpg
http://thelifeofyourtime.files.wordpress.com/2012/04/archformation.jpg
http://www.real-dream-catchers.com/images/KokoHunt.jpg
http://www.discovermoab.com/rockart.htm
