Tallulah Gorge: A Product of Rock and Water EarthCache
Tallulah Gorge: A Product of Rock and Water
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Tallulah Gorge State Park is located in Tallulah Falls, GA.
There is a $4 parking fee. This is a log only cache that
requires a strenuous climb down a 1000 steps to the Hurricane
Bridge. Park at N34.44.326 W083.23.839.
Rock and Water: Natural Forces Sculpt Tallulah Gorge
The Tallulah Gorge is one of the oldest geological features in
North America. The cliffs of Tallulah Gorge are made up of
quartzite, one of the hardest rocks on the earth. Yet these tough
rocks were at one time layers of sand, covered by ocean waters. As
layers of mud and sand grew thick under water, the sand was
compacted and cemented into rock, called sandstone. The tremendous
heat and pressures of mountain building transformed the sandstone
into quartzite.
As the Appalachian Mountains rose, the quartzite and surrounding
rocks were thrust forward and folded over themselves. Great
contortions of land can be seen in the tilted rock layers
throughout the gorge, evidence of powerful geological forces.
It is a theory that at one time the Tallulah and Chattooga rivers
were headwaters of the Chattahoochee River and flowed southwest to
the Gulf of Mexico. The young Tugaloo-Savannah River was located
just southeast and flowed to the Atlantic Ocean. Rivers move
backward by undermining rocks at their source. Cutting back through
soft rock, the Tugaloo-Savannah River finally joined with the
Chattooga and Tallulah Rivers. The Tugaloo-Savannah was lower than
the Chattahoochee and a waterfall formed at the junction. The force
of gravity from the drop in elevation enabled the Savannah to
“steal” the waters of the Chattooga and Tallulah away. This process
is called “stream capture”. The “elbow” or angle of this capture
gives the state line of Georgia its distinctive shape.
The Tallulah, strengthened by its descent into the Savannah, cut
more deeply into the quartzite - - carving the gorge with greater
speed. Waterfalls became a major way the river cut the gorge. A
waterfall moves backward by undermining the caprock (rock surface
of a riverbed) which eventually collapses, and the process starts
over.
In Geological Terms:
When rocks deform in a ductile manner, instead of fracturing to
form faults, they may bend or fold, and the resulting structures
are called folds. Folds result from compressional stresses
acting over considerable time. Because the strain rate is low,
rocks that are normally considered brittle can behave in a ductile
manner resulting in such folds.
There are several different kinds of folds. (See photo gallery
below)
Monoclines: are the simplest types of folds. Monoclines
occur when horizontal strata are bent upward so that the two limbs
of the fold are still horizontal.
Anticlines: are folds where the originally horizontal strata
has been folded upward, and the two limbs of the fold dip away from
the hinge of the fold.
Synclines: are folds where the originally horizontal strata
have been folded downward, and the two limbs of the fold dip inward
toward the hinge of the fold. Synclines and anticlines usually
occur together such that the limb of a syncline is also the limb of
the anticline.
Domes: are deformational features consisiting of
symmetrically-dipping anticlines; their general outline on a
geologic map is circular or oval. The strata in a dome are upwarped
in the center; if the top of a dome is eroded off, the result will
be a series of concentric strata that grow progressively older from
the outside-in, with the oldest rocks exposed at the center.
Folds can be classified based on their appearance.
-If the two limbs of the fold dip away from the axis with the same
angle, the fold is said to be a symmetrical fold.
- If the limbs dip at different angles, the folds are said to be
asymmetrical folds.
- If the compressional stresses that cause the folding are intense,
the fold can close up and have limbs that are parallel to each
other. Such a fold is called an isoclinal fold.
- If the folding is so intense that the strata on one limb of the
fold becomes nearly upside down, the fold is called an overturned
fold.
- An overturned fold with an axial plane that is nearly horizontal
is called a recumbent fold.
- A fold that has no curvature in its hinge and straight-sided
limbs that form a zigzag pattern is called a chevron fold.
To gain credit for this find, go to the listed coordinates which
will require a strenuous hike down a 1000 steps and end up in the
middle of a pedestrian suspension bridge. Post your photo of the
rock formations with your GPS in your log. Email us with what type
of folding you think is present at Tallulah Gorge and why. The
purpose of this cache is to learn something about the world around
us so we will be lenient as long as there is a photo and an email.
Congratulations to Cowboy59 and Family for
FTF!
Additional Hints
(No hints available.)