The Mountains Appear
If you stand on one of the lofty peaks of the Great
Smoky Mountains and view the wavelike sequence of ridges which finally
lose themselves in the hazy distance, you are awed by the grandeur that
nature has lavished upon this mountainous region. Its landscape is the
product of almost incomprehensible forces. Here, throughout countless
ages, the surface of the land has undergone profound change. The main
story has been one of erosion, but let us go back many millions of years
and begin the geologic account with the rock-making and the building of
the mountains which took place in another age, for the Smokies are a
part of the oldest range of mountains in the country.
Most of the rocks that compose these mountains belong
to a group called the Ocoee series. They were formed from
sedimentsmuds, sands, and gravelsderived from a very ancient
land mass and deposited in great quantities, probably on the floor of a
shallow sea. Here they gradually accumulated in extensive layers to a
thickness of 20,000 feet or more. Deep burial and compaction, plus the
chemical action of water depositing natural cement among the particles,
changed the sediments to rock.
So ancient are these Ocoee rocks that they contain no
fossils of plants or animals, having been formed before life was
abundant on the earth. According to geologists, these rocks antedated
the Cambrian period of the Paleozoic era, more than 500 million years
ago.
Mount Le Conte (elev., 6,593 ft.), as seen from
Newfound Gap. The prominent scars on the side of this mountain resulted
from a cloudburst which occurred on September 1, 1951. Most of the
dark-colored, spired evergreens are red spruce. Courtesy, Tennessee
Conservation Department.
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The vast thickness of the sediments and the theory
concerning their source captures the imagination. What was it like, this
land mass from which the silts, sands, and gravels were derived?
Some of the rocks of the Ocoee series . . . are made
up of innumerable pebbles of quartz and feldspar; these pebbles were
derived from the breaking apart, under the influence of weather, of
individual crystals of an ancient granite mass. The conglomerate looks
somewhat like granite and is composed of the same materials but these
materials have been broken up, transported, reconstituted in strata, and
once more consolidated. The granite from which the conglomerates were
derived probably stood as mountain ranges at the time when the Ocoee
series was being formed. (See "Selected Bibliography," King and Stupka,
1950.)
The accumulation of sediments extended over long
periods in geologic time. Following this, the land surface was raised
and subjected to tremendous lateral pressures which caused the rock
formations to buckle into folds and to break in many places, forming
overthrust faults. This major disturbance of the earth's crust is known
as the Appalachian revolution, an epoch of mountain-building in the
Eastern United States which transpired some 200 million years ago. The
uplift that brought the higher Rocky Mountains into being came at a much
later time.
The overthrust of rock formations is well exemplified
in the scenic valley of Cades Cove. Here the Ocoee rocks were thrust
several miles, causing them to override much younger formations in the
valley section to the north. Those younger rocks, mostly limestones,
were formed during the Ordovician period of the Paleozoic era. In
contrast to the older, lifeless Ocoee series, the younger rocks contain
fossil remains of primitive sea animals. In the ages following the
overthrust, constant stream erosion gradually cut through the ancient
rocks and revealed the younger limestones beneath. Even though all rocks
exposed to the weather are altered, not all are equally susceptible;
thus the limestones, once exposed, weathered and eroded with comparative
rapidity, producing a level-floored valley almost entirely surrounded by
steep-sided mountains. Today in this scenic cove you can stand almost
encircled by mountains composed of rocks 200 million years older than
the rocks of the valley floor.
Following the Appalachian revolution and the uplift
of the land, the relentless forces of rock-weathering and erosion began
carving the valleys. This was evidently renewed several times; each time
erosion reduced the entire region to an almost featureless plain, but
again the processes of cutting down were renewed by uplifts in the land.
Evidence of these ancient plains can be seen as a series of high ridges
of approximately equal height. The valleys as we see them today have
been carved from what was once a much higher land surface. Geologists
explain it in this manner:
The present ridges and mountains are not caused by
upheaval, but by erosion, whereby the valleys have been carved out of
the same rock formations as those that still project above them. One may
therefore conclude that the landscape of Great Smoky Mountains is not
made up so much of ridges rising between the valleys as of valleys cut
between the ridges (King and Stupka, 1950).
Your appreciation of the landscape will be increased
by an awareness that these valleys were carved by stream erosion, a
phenomenon we witness almost daily. Every year thousands of tons of soil
and rock fragments are washed down the slopes and are carried away by
the streams. Usually, this is a very slow process, but there have been
cases of tremendously accelerated erosion, when tons of material have
been removed in a matter of minutes. On the south face of Mount Le Conte
are huge scars which bear testimony to the tremendous force of flood
waters. Here a cloudburst caused complete destruction to parts of a
mature forest, stripping large trees from the mountainside and piling up
debris for miles in the valley below.
Little River, one of many fine trout streams in
the park. These cold, rock-strewn watercourses are, for some visitors,
the outstanding attraction in the area.
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It is intriguing to imagine the enormous amounts of
sediments that have been removed through the ages to produce the valleys
that we see today. When we consider the present depth of the valleys and the fact that these mountains stood
thousands of feet higher in the geologic past, we get some idea of the
grand scale of erosion in this area. As one geologist, George H.
Chadwick, has stated, "Even the Grand Canyon fails to dwarf what is here
visible."
In the time of the last geologic epoch, the
Pleistocene, glacial ice spread over a large part of the land surface of
the world. It covered Canada and extended into the northern United
States. During one period, the ice sheet moved as far south as the Ohio
River, but it never reached the Great Smoky Mountains. Perhaps, during
the ice ages, the highest ridges of the Smokies were bare of trees and
were covered with snow. The cold climate of that time left its mark upon
the landscape in this area. The huge boulders, or "graybacks," lying on
the slopes and in the valleys were moved there by forces that are no
longer evident. It appears that these rocks were broken off and removed
from the mountaintops by frost action, and they gradually accumulated
as boulder fields on the slopes and in the valleys below. You may see
examples of such boulder fields along both the Big Locust and the
Buckeye Nature Trails, adjacent to U.S. 441.
As the great Pleistocene ice moved slowly southward,
many Canadian-zone plants and animals migrated before it and found a
haven in the southern Appalachians, well beyond the limits of glacial
ice. In the Great Smoky Mountains, most of the species of forest trees
survived the rigorous climate which prevailed. Here, in the heart of the
deciduous forest region of Eastern North America, there are more kinds
of native trees than in any area of comparable size in the United
States. In fact, in all of Europe there are not many more tree species
than grow in Great Smoky Mountains National Park. The outstanding
attraction of this area is its flora; so profusely does it grow that it
covers the mountains everywhere with an unbroken mantle. There is no
timberline here, and rock exposures are uncommon. But beneath the living
layering of green, and the thin crust of soil which nourishes it, is the
great mass of solid rock which has no life and whose secrets have become
dimmed through unnumbered centuries.
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