In geology a fault is a crack in the
earth along which there has been movement along either side of the
crack. There may be a crack without movement but that is called a
joint. Faults may vary in length from a few millimeters to
thousands of kilometers. The largest faults are caused by movement
of tectonic plates.
Faults are produced by stress in the
earth’s crust. Stress is a force which causes a change in
shape by squeezing or stretching. This change in shape may be
elastic if the object returns to its original shape when the stress
is removed. The change may be inelastic if the object does not
return to its original shape when the stress is removed. A stressed
object may also fracture or break into pieces.
Rock may deform elastically under
small stress and inelastically under higher stress. Rocks which are
brittle fracture with little or no inelastic deformation. Cold
rocks are more brittle than rocks which are hot. Rocks are less
brittle under pressure. For these reasons most faults occur in the
top six miles of the earth’s surface. Below six miles rocks
tend to bend and fold.
Rocks may experience stress in the
following ways:
1. tension- pulls rocks apart,
pushing rocks away from each other
2. compression- squeezes rocks,
pushing opposites sides into each other
3. shearing- pushes opposite sides
against each other in opposite parallel directions
At the listed coordinates you get a
very good look at the Glenita fault. It is very evident in the
exposed bluff between VA 871 and the tunnel. This fault occurs in a
structural weakness between the gently folded Rye Cove syncline (a
downfold) and the more tightly folded Purchase Ridge syncline.
According to geologists with the Virginia Division of Mineral
Resources the cause of the Glenita fault is tectonic in origin. It
is the result of the collision of the African continent with North
America. This collision resulted in the formation of the
Appalachian Mountains during the Paleozoic Era. The Glentia fault
continues on through the Natural Tunnel and was very important to
its formation.
To claim a find
you must post a picture (optional) of yourself with the fault in
the background and answer the following:
1. Estimate the
height of the bluff in front of you.
2. Estimate the
width of the crack in the rock at its widest point.
When traveling into the quarry area be careful of meeting
dump trucks. A very small part to the left of the dirt road is used
as a spoils area by VDOT but the traffic here is very
light.
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