Short Description of Area:
These are not way-points, per se, but will help
you easily and efficiently get to the EarthCache site, without
parking in an unauthorized area, or spending a lot of time going
cross-country, so you might want to load them into your
GPSr:
Parking: N 35º 21.467' W
80º 5.433'
Put-in: N 35º
21.636' W 80º 5.341'
When you park, please do not block the entrance to the horse
trail/fire road. Parking is possible on both sides of the
road, but is limited to a relatively few cars. Walk down the
Park road to the put-in location, take a left, and follow your GPS
to the EarthCache site. This is The Eye of The
Needle. If you're short, skinny and brave, you can
"thread the eye of the needle."
As you walk towards the site, you go up a small ridge and will
see numerous rock outcrops. Once at the site, you will be
able to see examples of
weathering. Weathering is caused by a
rock physically breaking apart or by the action of
chemicals. Note that erosion is the
actual transporting of bits and pieces of rock by water, wind, or
glaciers.
Mechanical
Weathering is the breaking of rocks into smaller and
smaller pieces, but each of the pieces retains the same
characteristics of the original rock. As you can see,
the largest boulder has split in two, freeing up both sides of the
split to be weathered. The following image by Dr. John Stimac of
Eastern Illinois University demonstrates that as the pieces of a
rock get smaller and smaller, more and more surface area is subject
to weathering.
One form of mechanical weathering that is quite important here
in the Piedmont is frost wedging. When liquid
water freezes, it expands about 9%. Small droplets in a tiny crack
in a rock can freeze and exert tremendous force on the surrounding
rock. In Fall and Winter, this can happen repeatedly. Eventually, a
piece of the rock will break off and further increase the exposed
surface area, accelerating the weathering process.
Chemical
Weathering. You have probably seen images of
geologists banging away at rocks with a hammer, as they examine an
outcrop. Chemical weathering involves a series of chemical
processes, and "blurs" the true structure and composition of rocks
and minerals, so the geologist needs to get beyond such weathering
to get a "clean" view of the real rock and minerals. Chemical
weathering can be simple, as in the dissolving of bits of rocks or
minerals into water (rain, dew, snow, or ice), and being washed
away, or it can be quite complicated, involving acids assisting
dissolving, reactions with oxygen to create completely different
minerals, and hydrogen ion reactions that create fairly complicated
processes resulting in a variety of minerals. All this sounds
esoteric, but that ever-present red clay we see in the Piedmont is
due to the rust formed upon exposure of iron-bearing rocks to
oxygen. Chemical weathering is not esoteric stuff -- it's
happening on every exposed rock and mineral on the earth!
One final thought: Differential
Weathering is variation in the rate of weathering and
erosion. Rocks that are harder than their neighbors will
seem to grow out of the ground, as if that caused the outcrops
here. In reality, the rocks in the outcrop are largely
staying in place, while the softer rocks in the ground around them
are eroding away.
Other Educational Information:
Logging
Questions:
Please DO NOT post a picture of you and your
party at the rock formation.
Send me an e-mail – not part of your log
– responding to the following:
1. Make the first line of the e-mail “GC24JFF, The
Deconsolidators: Weathering"
2. How many people were in your party?
3. On the upper side of the Eye, there is a small
tree that appears to be growing out of the rock
itself. Scrape away the leaves at the base of the tree,
and also look at the base of other trees which seem to be growing
out of the rock:
How are these trees contributing
to mechanical weathering?
4. Examine the surface of the big rock.
a. What evidence of
chemical weathering do you see?
b. What evidence of
mechanical weathering do you see?
Note: For other EarthCaches in the Uwharrie Mountains and the
Gold Hill mining district, go here.
Platinum EarthCache Master
Bibliography:
http://www.ux1.eiu.edu/~cfjps/1300/weathering.html
. Mechanical and Chemical
Weathering.
Tarbuck, E., and Lutgens, F. Earth: An
Introduction to Physical Geology. Pearson
Prentice Hall, 2005.
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