They include the Bluegrass, Knobs, Pennyroyal, Eastern Kentucky
Coal Field, Western Kentucky Coal Field, and the Mississippi
Embayment. These six regions reflect the underlying geology of that
particular area. Each region is characterized by distinctive
landscapes produced by erosion and deposition of different rock
types and is broken down into sub regions. Physiography, also
called geomorphology, is the study of land surface features. This
earth cache will focus on the Pottsville Escarpment. This plateau
is the transitional area of the Eastern CoalField, the Blue Grass
and The Knobs Physiographic Regions.
The Bluegrass region is located in central Kentucky and is
underlain by Ordovician limestone that are about 475 To 440 million
years old. This region is characterized by gently rolling hills,
sinkholes, and springs, which are typical of karstic areas.
Productive farmland is typical of this region. This is due to the
underlying limestone, which enriches the soils with beneficial
minerals.
The Knobs Region forms a horseshoe shaped band around the
Bluegrass Region. It is underlain by shales, sandstones, and
limestone from the Silurian, Mississippian, and Pennsylvanian
Systems, which means they were deposited approximately 440 to 330
million years ago. This region's topography is quite different from
the gently rolling hills of the Bluegrass. The Knobs is typically a
very rugged region, marked by steep conical shaped hills.
The Pennyroyal Region is located in south central and western
Kentucky. Like the Bluegrass region, the Pennyroyal is underlain by
limestone which leads to similar topographies between the two
regions.
The Mississippi Embayment is in the far western end of the state
and is located in the Gulf Coastal Plain of the central United
States and consists of alluvial deposits and loess.
The Western Kentucky Coal Field is in the western end of the
state. It comprises the southern edge of a larger geologic feature
called the Illinois or Eastern Interior Basin, which includes the
coal fields in Indiana and Illinois.
The Eastern Kentucky Coal Field covers the eastern end of the
state, stretching from the Appalachian Mountains westward across
the Cumberland Plateau to the Pottsville Escarpment. The Eastern
Kentucky Mountains include that part of the state east of the
westward-facing Pottsville Escarpment. Coal mining is the major
industry.
Escarpments are frequently formed by faults where the earth has
folded and tilted. When a fault displaces the ground surface so
that one side is higher than the other, a fault scarp is created.
This can occur in dip-slip faults, or when a strike-slip fault
brings a piece of high ground adjacent to an area of lower
ground.
The Pottsville Escarpment is a resistant sandstone belt of
cliffs and steep sided, narrow crested valleys in eastern Kentucky.
The eastern edge of the Eastern Kentucky Coal Field is called the
Pottsville or Cumberland Escarpment. This escarpment is formed from
resistant Pennsylvanian-age sandstones and conglomerates.
The escarpment is steep in south-central Kentucky because
several thick, resistant sandstones are separated by less resistant
shale. The manner in which the sandstones weather and are eroded
along the escarpment results in some locations as sheer
cliffs,steep-walled gorges, rock shelters, waterfalls, natural
bridges and arches and caves. Intensive erosion of the
Pennsylvanian sandstones and shale developed the region into an
landscape of steep hills and narrow valleys. Erosion over time
enters the picture and depending on the rate of action, shapes the
landscape and degree of the escarpment.
As you travel up Kentucky Route 67 known as the Industrial
Parkway, you will notice the landscape change from narrow ridges
and rounded hills capped with siltstone and limestone and separated
by wider valleys to irregular narrow crested ridges and deep narrow
valleys with little bottomland. These changes mark the boundaries
between the Knobs, the Pottsville Escarpment and the Eastern Coal
field of the Appalachian Basin.
The Pottsville Escarpment is a resistant sandstone belt of
cliffs and steep sided, narrow crested valleys in eastern Kentucky.
By definition the scarp is described as the zone between lowlands
and continental plateaus which have a marked, abrupt change in
elevation due to erosion at the base of the plateau.The crest of
the Waverly Escarpment in the vicinity of the Ohio River is at 1200
to 1300 feet from which the upland level drops off with the dip to
the southeast to about 1,100 feet at the western edge of the area
of Pottsville. Farther east along the Ohio and Big Sandy rivers the
topography rises to 900 feet. Here the crest of the Pottsville
Escarpment is at about 1400 feet from which the hilltop level drops
off down the dip to form a lowland area at about 1000 feet.
To the South, the Pottsville Escarpment rises above the
Pennyroyal and attains an altitude of about 1,800 feet in southern
Kentucky. The Pennyroyal surface slopes southward from 1,300 to
1,400 feet to about 1,000 feet in southern Kentucky, above which
the Pottsville Escarpment stands some 700 feet higher. To the
southeast of this there is general increase in hilltop level, and
with it relief, to altitudes of 2000 feet and more, above which
Pine Mountain and others to the east rise.This slope suggests a
southward tilt which, in conjunction with the northward tilt of the
Pottsville Escarpment, involves a peculiar twisting of this surface
on opposite sides of the plateau. Both are topographic features
carved out of lower Pottsville sandstones and conglomerates along
and near the Ohio River.
Decline of the crest of the Pottsville escarpment northward is
at least to some extent a matter of the less resistant character
and thinning of the conglomerate rock structure in this direction.
There is also a great thinning of the Limestone northward and these
beds contribute to the forming of the Escarpment. With less
effective cap to the north there must have been more rapid
recession of streams and lowering or eroding of the landscape. The
shape of the land surface is controlled by the effects of
weathering and erosion of the bedrock.
An escarpment is a landscape formed by differential erosion.
Differential Erosion means lower or higher erosion of different
rocks depending on their resistance. In sediments, there are always
harder and softer layers, so weathering of this rock will always
produce escarpments. The hard rocks form cliffs, as the softer
layers below are eroded faster, undermining the hard rocks above.
So the hard rock is breaking down, forming sharp edges, instead of
being rounded by erosion.
If the layers are horizontal, the result is called a cliff. If
they are sloping with a dip less than 30°, the result is called
escarpment or cuesta, an asymmetric ridge with a steep side across
the layer and a shallow side on the top of the layer, sloping with
the dip of the layer itself. Below is a Schematic cross section of
a cuesta, dip slopes facing left, and harder rock layers in darker
colors than softer ones.
Around the perimeter of the Appalachian Basin, the edge of the
sedimentary rock layers is tilted upwards. Where this edge is
exposed it has become a ridge formation, also known as a cuesta.
Cuestas are ridges formed by gently tilted rock layers.Every cuesta
has a steep slope where the rock layers are exposed on their edges,
called an escarpment. They also have a more gentle slope on the
other side of the ridge called a 'dip slope'.When you are driving
across the Escarpment on the Industrial Parkway north to south you
drive up the dip slope to the cuesta of the escarpment.
It is much easier to understand what the escarpment is when you
understand the formation that it is a part of. The Pottsville
Escarpment is sharp face of a ridge that is at the edge of a much
larger formation called the Appalachian Basin. The Appalachian
Basin is a roughly circular depression in the earth's crust
centered under the state of Kentucky. It is formed of layers of
sedimentary rock that were created over 420 million years. The
Basin used to be the location of an inland sea. This sea has shrunk
and grown in area several times between 445 million and 420 million
years ago (a period of 25 million years).Because these layers were
laid down along the bottom of the sea floor, these layers gently
tilt upwards at the edges where the old seashore would have been.
The last layers that formed underwater cover a smaller area than
those below them because the sea was shrinking for the last time.
These last layers were formed mainly from clay and sand, and so are
primarily shale and sandstone.
Over time, differential erosion kicks in as the limestone and
sandstone erode at different rates and waste the earlier laid areas
away to form the escarpment.
To perform the calculations for this Pottsville Escarpment Earth
Cache-
1. Travel to the Industrial Parkway intersection with US Route
23. TAKE AN ELEVATION READING AT THE INTERSECTION. Travel to the
coordinate provided above where Sullivan Cemetery Road intersects
the Parkway and pull off. Here you will find rock cuts and a view
to the north of how high sitting the escarpment is. TAKE AN
ELEVATION READING AT THE INTERSECTION HERE. Calculate the
difference in elevation you traveled as you drove up onto the
Pottsville Escarpment from US 23 to this location.
A/ 100' B/ 200/ C/300' D/ 400'
2. Take a Picture of the view to the north from the Pottsville
Escarpment Terrace with your GPS in the long shot.
3. Look to the east side of the Industrial Parkway Highway to
the rock cut. You will note that the rock formations tilt upward
and fold to some degree. Walk or drive to the coordinate 38 29.140N
and 82 47.819W. Notice the uplift of the older rock at the bottom
of the outcrop. What begins as a larger layer of sandstone narrows
at the uplift creating a fault.
Estimate the height of sandstone exposure at the fault where it
is narrow. Follow the rock as the layer increases in height to the
location of it's greatest height of exposure. What is the
difference in height of the sandstone layer from the narrow point
to it's greatest height at the first bench of the rock cut?
A/ 2' to 20' B/ 3' to 30' C/ 4' to 40'
4. Mark a point at the location where the sandstone on the lower
formation has it's greatest height. Travel to where it is the
shortest in height in exposure. What is the distance from the
greatest height to the lowest height where the fault narrows.
A/ 150' B/ 175' C/ 200'
5. What is the total height of the rock cut here from top to
bottom that represents Mississippian and Pennsylvania age
formations?
A/ 150' B/ 180' C/ 225'
Time has worked the landscape with elements of erosion shaping
scenery we see today.
