The Split-Sphinx Rocks on Grandfather Mountain EarthCache
The Split-Sphinx Rocks on Grandfather Mountain
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This EarthCache will take you to the Grandfather Mountain
Park located off of Highway 221 near Linville, NC. During inclement
weather, be sure to check for Park Closings at: Phone
800-468-7325
Many thanks to the Park Naturalist staff for their help and
permission to list this EarthCache. Please visit the Grandfather
Mountain web site prior to making your visit: http://www.grandfather.com/
Summer Flora By The
Rocks
The Blue Ridge Mountains of Western North Carolina and
Eastern Tennessee are the result of the action of plate tectonics.
This shifting of the plates occurred during what is termed the The
Alleghenian orogeny. The Alleghenian orogeny is one of the
geological mountain-forming events (an orogeny) that formed the
Appalachian and Blue Ridge Mountains. Approximately 350 million to
300 million years ago, in the Carboniferous period, Gondwana (later
to become Africa) and what became North America collided, forming
the super continent, Pangaea. This collision exerted massive stress
on what is today the Eastern Seaboard of North America, resulting
in a large-scale uplift of the entire region. During this orogeny,
some volcanoes occurred as found at the nearby Mount Rogers and
Whitetop Mountains, but there is no evidence of volcanic action
here at the Grandfather Mountain.
Pangaea
Grandfather Mountain is at the heart of a geologic wonder
known as the Grandfather Mountain Window, a region covering several
hundred square miles in northwestern North Carolina. During the
Alleghenian orogeny as discussed in the above paragraph, vast
sheets (the crusts) of rock were pushed over each other. The Blue
Ridge Thrust Sheet moved more than 60 miles to cover what is now
Grandfather Mountain. Many geologists believe that these mountains
were once much, much higher than they are now. Erosion over
millions of years has opened a "window" where younger rock shows
through. The window is like a sack of potatoes with a hole in it.
The potatoes are the younger rock and the sack is the older rock.
Having this window permits the study of the sequence of rocks
ranging in age from old to young.
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Grandfather Mountain also holds the distinction over other
southern mountain terrains as having the most outcrops and
boulders. The earlier mentioned erosion that occurred over hundreds
of millions of years has carried away most of the rocks to form
thick layers of sediment all across the Piedmont, Coastal Plain,
and in the Atlantic Ocean. So, Grandfather's loss was other areas
gain!
The Rocks
The rocks you will find on the Grandfather Mountain are
basically metamorphic which is one of the three major rock groups.
The other two of the three are sedimentary and igneous. Great
pressure, heat, and the introduction of new substances cause
metamorphism which changes the basic nature of the
‘mother’ rock. Changes include the development of new
minerals, making the rock, which has been deeply buried and
compressed, look very different from the original rock. At the
Split Rock and the Sphinx Rock you will encounter
metamorphosed conglomerate. The rocks are referred to as
metaconglomerates.
The Split Rock
Now just where did these wonderful and very large bounders
come from? They are certainly not ‘outcrops’ as found
at the top of the Mountain. As we said earlier, they couldn’t
be a result of volcanic action because there were no volcanoes
here! So, just where did they come from? The most likely origin of
the Split Rock and the Sphinx Rock was the top of
Grandfather Mountain. Thousands, maybe millions of years ago, the
bounders broke from the upper outcrops on Grandfather Mountain and
fell (rolled?) to their current resting places. Before arriving at
their current locations the rocks were most likely underwater. The
type of rock (metaconglomerate) also means they were created
millions of years ago as a stream bed in a previous mountain
formation that likely pre-dated the current Appalachians. Unlike
the Appalachian and Blue Ridge Mountains, the rocks are thought to
be over 650 million years old!
The Sphinx
Rock
The split in Split Rock occurred over many, many winters.
It all began as a small crack that allowed water to seep into the
rock. After repeated freezing and thawing, the split grew to
it’s current size. Be sure to carefully observe the split.
Later, you will need to answer a question regarding the crack.
NOTE: In order for you to claim a find of the
Split and Sphinx Rocks you must email answers to the
following questions: 1. Estimate the height and width of
both rocks. 2. After carefully examining the
‘crack’ in the Split Rock, estimate the average
width of the split. 3. Find the nearby sign and give the
estimated weight of the Sphinx Rock. Last, please post a photo of
the two rocks. While the photo is necessary and it would be nice,
you do not have to appear in the picture. The Grandfather Mountain
Park has many wonders to see and do. There are miles of trails and
several picnic areas to enjoy. Also, be sure to visit the Nature
Museum and the animal habitat. Take care and have fun.
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