Falls on Athens-Boonesboro Road EarthCache
Falls on Athens-Boonesboro Road
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This waterfall is along Athens-Boonesboro Road (Hwy. 418) in Clark
County. There is room to pull off the road. Please be
cautious with children and pets as you exit/enter your
vehicle.
Falls on Athens-Boonesboro Road
WHAT IS A WATERFALL?
A waterfall is usually a geological formation resulting from water,
often in the form of a stream, flowing over an erosion-resistant
rock formation that forms a sudden break in elevation.
Waterfalls may also be artificial, and they are sometimes created
as garden and landscape ornament.
Some waterfalls form in mountain environments where erosion is
rapid and stream courses may be subject to sudden and catastrophic
change. In such cases, the waterfall may not be the end
product of many years of water action over a region, but rather the
result of relatively sudden geological processes such as
landslides, faults or volcanic action.
Waterfall
Erosion
The pounding of the water at the base of a waterfall is a powerful
force for erosion, especially if the water contains suspended
sediment. Even at the lip of the fall, the water gains extra
erosive power as it accelerates approaching the brink. For
this reason, waterfalls are temporary phenomena, geologically
speaking. While the surging water tears away at the base of
the falls, removing its rock foundations, the scouring of the lip
grinds back the brink of the falls, decreasing the overall
height. Often, the rock stratum just below the more resistant
shelf will be of a softer type, meaning undercutting, due to
splashback, will occur here to form a shallow cave-like formation
known as a rock shelter (also known as a rock house) under and
behind the waterfall. In some cases, the removal of the
underlying rock leads to a collapse of the lip itself, adding
blocks of rock to the base of the waterfall. These blocks of
rock are then broken down into smaller boulders by attrition as
they collide with each other, and they also erode the base of the
waterfall by abrasion, creating a deep plunge pool. The time
it takes for these processes to erode the river bed to a gentle
slope depends on the volume of water flowing over the drop, the
amount of sediment available to grind away the bed, and the
hardness of the rock over which the river flows. Even
waterfalls on smaller rivers can last for millions of years.
This is also true of large rivers where the bedrock is resistant to
erosion. But in geologic terms, waterfalls are quite
temporary, and their presence is a sure sign of the special
geologic conditions that produced them. In a sense, they are
like the flip side of lakes, which are also temporary, mostly
because lakes gradually fill with sediment and eventually turn into
marsh and meadow.
This waterfall on Athens-Boonesboro Road, like the majority of
waterfalls, has been formed by erosion processes. It cuts
down through layers of rock composed of different degrees of
hardness. Hard layers are more resistant to erosion.
Soft layers are quickly removed. The rock in this part of the
Kentucky River valley, which is exposed along the 'Palisades of the
Kentucky River,' is made of resistant limestone or dolomite.
The softer argillaceous, or clay containing limestone or dolomite
layers, remain protected beneath resistant caps. As the
stream flows over a lip composed of a layer of resistant limestone
or dolomite that lays atop a softer layer of argillaceous material,
the water will remove the soft layer beneath the limestone at a
faster rate than the lip itself. In this way, waterfalls
often become undercut as this soft material is worn away.
This results in the caves found beneath many waterfalls.
Eventually, the undercut becomes so large that the weight of water
on the unsupported layer of limestone will be sufficient to
collapse the layer. At this time, amidst a catastrophic
collapse, the cave disappears, and the cliff face moves further up
the valley. In many cases, the hard-soft layer relationship
remains, and the falls simply migrates upstream. This creates
a gorge of recession in front of the waterfall. As long as
the hardness differential remains, the waterfall will
persist. This phenomena is visible in this waterfall on
Athens-Boonesboro Road.
WATERFALL FORMATION
Three main processes create waterfalls:
- Recent uplift or down-dropping of part of the
Earth's crust,
- Diversion of a river by blockage of a preexisting
channel, or
- Differential erosion of valleys, especially in
glaciated areas.
In all cases, where a major river plunges over a waterfall,
geological processes must have been active within the past few
million years. Rarely are large waterfalls older than a few
tens of millions of years, and most are less than a million years
old. Invariably the rock at the crest of the falls is one of
the harder varieties, resisting the downcutting effects of the
river.
Uplift
A striking example of the first type of waterfall is Victoria Falls
on the Zambezi River in southern Africa. The geologically
recent uplift of east Africa and the faulting associated with the
African Rift Valley system provides the Zambezi River with the
power necessary to cut into the hard basaltic rock over which it
flows. At the edge of the basalt, the river has eroded away
softer layers below and has gradually carved a canyon upstream into
the basalts. The fracturing of the basalts is most intense in
two nearly (but not quite) parallel directions, and the river has
cut a zigzag path working upstream, first along one direction of
weakness, then the other. Presently it appears to be just at
the point where it will take another sharp bend.
River
Diversion
Niagara Falls is the archetype for the second kind of waterfall;
namely, one produced by the diversion of a preexisting river.
The ancestral Niagara River followed a course more or less parallel
to the current river for part of its course, and carved a gorge
similar in scale to the modern gorge. During the last ice
age, the old gorge was filled with glacial debris, diverting the
river into a new path across the dolomite upland. The new
gorge began at the escarpment near Queenston, Ontario, which is
where the diverted (modern) Niagara River fell over the edge of
this upland. Away from the Niagara escarpment, the hard
dolomite shielded the underlying soft shales from erosion.
Flowpaths beyond the escarpment traversed areas not protected by
this dolomite cap, and hence gradually eroded the underlying
glacial deposits. Over thousands of years, the differential
erosion created a vertical waterfall. It is estimated that
12,000 years ago, the falls were 7 miles downstream from their
present position. The continuous removal of the shales at the
base of the falls has steadily undermined the dolomite cap, causing
its collapse and hence the ongoing retreat of the falls
upstream. Today the erosion continues, but human
modifications of the river's flow have reduced the erosion
rate.
Differential
Valley Erosion
Probably the best example of the last type of waterfall is Yosemite
Falls in California. Yosemite Falls (and many of the other
famous waterfalls in Yosemite National Park) is the result of the
powerful erosion of Yosemite Valley by a glacier flowing down from
the High Sierra. The glacier in the main valley was larger,
and especially thicker, than the tributary glaciers that flowed
into it. The thick ice stream carved a deep, flat-floored
valley, and was much more effective in doing this than the smaller,
thin tributary ice streams. When the ice melted away, the
result of the differential erosion between the main and tributary
glaciers left the floors of the smaller glacial valleys perched
high above the main valley floor. Rivers such as the Yosemite
now leap over immense drops to meet the Merced River, which flows
at the bottom of the main valley.
ONGOING EVOLUTION
In all of these examples, the geologic activity producing the
waterfalls is quite recent — perhaps 10,000 to 15,000 years for
Niagara Falls and Yosemite, and probably somewhat longer in the
case of Victoria Falls. However, the uplift of east Africa
still may be occurring, likely at a rate of about 1 inch each
year.
Without active geologic change, whether variations in climate as in
the case of ice ages, or the slow, but inexorable motions of plate
tectonics, waterfalls would soon cease to be part of the
landscape. Their beauty is a combination of their ephemeral
nature, the magnificence of motion painted in the air, and the
insight they provide into the underlying working of the
Earth.
WATERFALL CLASSIFICATION
The International Waterfall Classification System is the generally
accepted scientific method of classifying the world's
waterfalls. Waterfalls are grouped into 10 broad classes
based on the average volume of water present on the fall using a
logarithmic scale. Class 10 waterfalls include Niagara Falls,
Paulo Alfonso Falls and Khone Falls. Classes of other well
known waterfalls include Victoria Falls and Kaieteur Falls (Class
9); Rhine Falls, Gullfoss and Sutherland Falls (Class 8); Angel
Falls and Dettifoss (Class 7); Yosemite Falls and Lower Yellowstone
Falls (Class 6).
Types of waterfalls
- Block: Water descends from a relatively wide stream or
river.
- Cascade: Water descends a series of rock steps.
- Cataract: A large waterfall.
- Fan: Water spreads horizontally as it descends while remaining
in contact with bedrock.
- Horsetail: Descending water maintains some contact with
bedrock.
- Plunge: Water descends vertically, losing contact with the
bedrock surface.
- Punchbowl: Water descends in a constricted form, then spreads
out in a wider pool.
- Segmented: Distinctly separate flows of water form as it
descends.
- Tiered: Water drops in a series of distinct steps or
falls.
- Multi-Step: A series of waterfalls one after another of roughly
the same size each with its own sunken plunge pool.
GEOLOGY
The bedrock in the Bluegrass Region of Kentucky is composed of
limestones and shales from the Ordovician Period (510 to 440
million years ago). Much of the Ordovician strata lies buried
beneath the surface. The oldest rocks at the surface in
Kentucky are limestones from the Late Ordovician Period
(approximately 450 million years ago), which are exposed along the
Palisades of the Kentucky River. The Palisades can be seen
from this road. They are the rock walls you see towering on
the other side of the river from this location. This unnamed
waterfall cuts down through multiple layers of the following types
of ancient Ordovician limestone.
Tyrone Limestone and Oregon Formation
(Lower Ordovician - Middle Ordovician)
Tyrone Limestone:
Primary Lithology: Limestone
Limestone, light-brownish-gray to light-yellowish-gray, dominantly
cryptograined (lithographic, micritic), with conchoidal fracture;
in thin to thick even beds. Some beds are composed of
cryptograined limestone with included tubules and blebs of sparry
calcite, commonly oval or circular in cross section (birdseye
limestone). Other beds are cryptograined limestone mottled
with dark patches or bands that contain diffuse microscopic specks
of opaque material. Upper half of unit includes thin zones of
argillaceous limestone and several beds of cryptograined limestone
interlaced with finger-like bodies of brownish-yellow dolomite
lithologically similar to interlaced limestone and dolomite
commonly found in the Camp Nelson Limestone. A 4-inch-thick
bentonite bed directly underlying the Lexington Limestone was seen
in a culvert west of Interstate 75 just north of its crossing of
the Kentucky River. Another bentonite bed, roughly 20 feet
below the upper contact, is nearly one foot thick and may persist
throughout the area. Lower third of unit intertongues
northeastward with upper part of Oregon Formation.
Oregon Formation:
Primary Lithology: Calcareous dolomite
Calcareous dolomite, brownish-orange to brownish-yellow, fine- to
medium-crystalline dolomite rhombs with calcite cement (rock
effervesces strongly in dilute hydrochloric acid), generally occurs
in thick, even-surfaced beds and bedding sets some of which show
lamination when weathered; certain zones, mottled and banded in
shades of orange and gray, are similar in pattern to mottled zones
in the overlying Tyrone. Where streams cross thick zones of
dolomite waterfalls are common. Here steep cliffs or undercut
faces are carved in the weathered dolomite by exfoliation and
spalling of curved, smooth-surfaced tablets and blocks. In
most areas the Oregon consists of a basal unit of thick, blocky
bedded dolomite, 25 to 35 feet thick, commonly marked at or near
basal contact by a thin layer of poorly resistant, argillaceous
dolomite; an intermediate unit of cryptograined limestone in part
interlaced with finger-like bodies of dolomite, a few very thin
beds of dolomite, and, at least locally, at the top an argillaceous
unit containing at its base a 6-inch-thick bed of pale-green
swelling bentonite (approximately 38 feet above base of Oregon);
and an upper unit of even-bedded, very fine to medium-crystalline
dolomite with a few cryptograined limestone interbeds. In the
north this upper unit is as much as 15 feet thick. In the
southwest it thins and intertongues with the Tyrone, and beyond its
pinchout the top of the Oregon was mapped on top of the thick basal
dolomite unit.
Camp Nelson Limestone
(Lower Ordovician - Middle Ordovician)
Camp Nelson Limestone:
Primary Lithology: Limestone and dolomite
Limestone and dolomite: Limestone, light-brownish-gray,
cryptograined; dolomite, brownish-yellow, very finely crystalline
to medium crystalline, occurring as irregularly shaped finger-like
blebs in limestone. When viewed in the plane of bedding some
dolomite inclusions exhibit dendritic branching though most show no
regular pattern; differential weathering of dolomite and limestone
gives rise to honeycomb weathered surfaces characteristic of this
lithologic type; contains several zones of tabular-bedded
cryptograined limestone and less resistant argillaceous limestone
in upper part. A thin zone of cryptograined limestone was
seen well down in the Camp Nelson near the mouth of Jouett Creek.
Base of unit not exposed.
Area Map: Falls on Athens-Boonesboro Road
Reference: Kentucky Geological Survey at the University of
Kentucky, the Kentucky Geologic Map Information Service,
NationMaster.com, MountainNature.com, and
WaterEncyclopedia.com.
DIRECTIONS
From I-75, take exit 95 and proceed east on Boonesborough Road
(Hwy. 627). Cross the bridge over the Kentucky River and
enter Clark County. Immediately turn right onto
Ford-Boonesboro Road (Hwy. 1924). Immediately turn right onto
Athens-Boonesboro Road (Hwy. 418). Proceed to the
EarthCache.
DO NOT LOG AS A FIND UNTIL YOU HAVE A PICTURE READY TO POST.
To get credit for this EC, post a photo of you (I do not accept
pictures of just a hand) at the posted coordinates with the falls
in the background (like my photo above) and please answer the
following questions.
- How wide and tall is the waterfall?
- What is the general shape of the waterfall?
- What process caused this waterfall to form?
- What is located to the right of the waterfall?
Do not wait for my reply to log your find. I will contact you
if there is a problem. Logs with no photo of the actual
EarthCacher/Geocacher (face must be included) logging the find or
failure to answer questions will result in a log deletion.
Exceptions will be considered if you contact me first (I realize
sometimes we forget our cameras or the batteries die). Logs
with no photos will be deleted without notice. I have used
sources available to me by using google search to get information
for this earth cache. I am by no means a geologist. I
use books, the Internet, and ask questions about geology just like
99.9 percent of the geocachers who create these great Earth
Caches.
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