Mechanical Weathering,
the breakdown or decay of rock, is responsible for most of the current
landscaping of the earth. Most people believe that Mechanical Weathering is
powered solely by the wind, this is not the case. Joints, or fractures in the
rocks create fissures that are the key to all types of mechanical weathering. There
are six types of Mechanical Weathering; Frost, Pressure Release, Salt, Thermal
Expansion and Contraction, Expansion and Contraction from Wetting and Drying,
and Pressure Roots. Frost, Salt, and Root Mechanical Weathering are the most
common in Glenwood Springs.
In Frost Weathering,
water goes into fissures then expands and contracts inside it. This increasingly
expands the size of the fissure, as shown in figure 1. Frost Weathering occurs
mainly in High altitudes with numerous freeze/thaw cycles. The location of Glenwood
Springs, nestled in the Rocky Mountains with our mild yet stormy winters,
provides the perfect conditions for Frost Weathering.
 |
|
Figure 1: A diagram of the
process of Frost Weathering.
("Mechanical weathering
processes," )
|
On my many trips to
Glenwood Springs I have seen trees growing out of rocks and wondered how that
was possible. What I now know is that I was witnessing a form of weathering;
Pressure of Root Weathering to be more precise. Plant roots can spread into
fissures in rocks expanding the fissure as the plant grows or even breaking the
rock.
Salt Weathering occurs
in two processes, Crystallization and Heating and Cooling. Crystallization Salt
Weathering occurs when salt particles crystallize in the fissures, and porous
areas of rocks. These crystals exert an outward force on the affected rocks
causing them to expand and weaken and eventually break apart. Heating and
cooling of the salt crystals cause the crystals to expand and contract, also
exerting pressure on the rock. Cavernous Salt Weathering creates Tafoni, craters in
the surface of a rock. An example of these craters is shown in figure 2. Salt
Weathering formed the Vapor Caves in Glenwood Springs, seen in figure
3.
 |
|
Figure 2: A sample picture
of Tafoni. (Boxerman, 2008)
|
 |
|
Figure 3: A picture of the
Glenwood Springs cavern. You can see Tafoni in the upper portion of the picture
as well as the smooth texture of the rock. (Alden, 2010)
|
Wind does play a part
in Mechanical Weathering; wind blows small granules of rock and salt spreading
salt to other rocks. It helps send ice crystals deep into fissures during
storms and helps to deliver seeds to fertile ground. Wind also smooth’s out
rocks giving them the shiny silky look found in some caves.
Resources
Alden, A. (2010). Glenwood
caverns: Geology of glenwood springs, colorado. Retrieved from http://geology.about.com/od/geology_co/ig/glenwood-springs-CO/glenwood-caverns.htm
Boxerman, J. (2008). Tafoni_8:
Tafoni-from coastal northern california. Retrieved from http://tafoni.com/Gallery/Pages/Northern_California.html
Dr. Allen, C. (2012). Decay of
earth’s rocks (weathering): the key to our beautiful earth. (University of Colorado Denver )Retrieved from http://clasfaculty.ucdenver.edu/callen/1202/Battle/Destroy/Wx/Wx.html
Mechanical weathering processes. (n.d.). Retrieved from
http://itc.gsw.edu/faculty/bcarter/physgeol/weather/mechwth.htm
