The Southern Appalachian Region

The Southern Appalachian region consists of physical, biological, and human landscapes. The physical landscape can be described by its climate, geology, topography, soils, and drainage. The biological landscape is defined by the biomes or biological communities found in the region. The physical and biological landscapes have also been modified by the people who have lived there and defined the cultural landscape. The environmental history of the region describes these interactions between the landscape and the people that inhabit it.

There are many ways to organize knowledge about the physical landscape. For some purposes, it is easiest to organize knowledge into the subjects of Geology, Climate, Regolith and Soil, Topography and Physiography,  and Hydrology.

For other purposes, organizing the physical landscape knowledge spatially makes more sense. here, our spatial organization focuses on the physiographic provinces:the Piedmont, Blue Ridge, Ridge and Valley, and Appalachian Plateau Provinces.

In this hypertext encyclopedia system,we can show both views.  However, we recommend the reader peruse the Geology section first because it provides an excellent overview of the birth of the Southern Appalachians as well as a geologic time table for periods discussed in other sections.

We begin this section on the geology of the Southern Appalachian Mountains with a streamlined description of geologic history by Sandra Clark, retired geologist from the US Geological Survey."The history recorded by humans spans only the past several thousand years on a planet that is 4 1/2 billion years old. Although we know little of earliest times, the history of the last billion years is well recorded in the rocks, much like pages in a book. The record is not one of permanence and stability, but one of continual change. On a scale of millions of years, continents and oceans form and disappear, change in shape and move. Mountains rise out of the sea and later wear down to their roots" (Clark 2002).

Beyond this streamlined description of the geologic history by Sandra Clark, there is much more detail needed to provide a useful understanding for practicing natural resource managers.  It is helpful to examine a geologic time scale in order to understand many of the concepts presented in this geology of the Southern Appalachian Mountains (Table:Geologic Time Scale).

The Appalachian Mountains are the oldest on the continent. Many of their geologic structures were formed more than 200 million years ago during the Paleozoic as the African Continent collided with the North American Continent. This collision compressed, thrust, and folded the North American Continental Plate. Vertical forces pushed up high mountain ranges so that by the end of the Paleozoic these mountains were high and steep and very likely glaciated, perhaps similar to the Swiss Alps today.

During the Mesozoic and Cenozoic, a broad, gentle, vertical crustal uplift predominated,producing folding and thrust falling. As uplift rates decreased, the mountains swiftly began to erode away, so that low mountains replaced the alpine peaks. During these times, erosion of the high mountains poured huge volumes of sediments into the seaways and onto the downwarped crust to the west of the mountains. These sediments now make up the rocks of the Ridge and Valley and the Appalachian Plateau Provinces.

Although glaciation was limited to the Appalachians north of the glacial advance, the Ice Age climate profoundly affected the Appalachian landscape during the Cenozoic. The intense cold associated with the ice age greatly increased the rate of physical weathering processes such as frost wedging.Landforms and deposits, such as sorted patterned ground, are clearly glacial in origin, and much of the hillslope colluvium and talus in the Appalachians probablywere formed inglacial times.

State geological surveys are making available via their Internet sites an increased number of geologic maps, publications, and other geologic information.  New material (e.g. geospatially referenced, digital geologic maps) useful to land managers are being added to these sites periodically, as well as basic geologic information useful for educational and interpretive programs.  Links to these state geological survey sites and to the U.S. Geological Survey site are listed below:

• North Carolina Geological Survey
• Virginia Division of Mineral Resources
• South Carolina Geological Survey
• Tennessee Division of Geology
• U. S. Geological Survey

Note that the Georgia Geological Survey no longer exists.

Although generalized and somewhat outdated in specific areas, a detailed geologic map of the State of North Carolina provides a good overall reference for the distribution of geologic units across the state.

Old Rocks

The rocks at the core of the Appalachian Mountains formed more than a billion years ago. At that time, all of the continents were joined together in a single supercontinent surrounded by a single ocean. Remnants of the supercontinent make up much of the North American core and contain minerals that are more than a billion years old. We can see fragments of the billion-year-old supercontinent (shown in red in the figure) at the surface in many places in the Appalachian Mountains. Examples include Blowing Rock in northern North Carolina and Red Top Mountain in northern Georgia.

In this section, we will start at the beginning of the history recorded in the rocks and look at the major stages in the development of the mountains and landscape.

• The Supercontinent Breaks Up: About 750 million years ago, the supercontinent began to thin and rocks at depth pulled apart like warm taffy.
• Continental Collision: About 470 million years ago, the motion of the crustal plates changed and the continents began to move toward each other.
• Another Continental Breakup: After the continental collision that formed the Appalachian Mountains about 240 million years ago, the continental mass began to pull apart again.
• Carving the Mountains: For the last 100 million years, erosion has carved away the mountains, leaving only their cores standing on the ridges of today.
• What Next? Today, the age old geologic processes continue. Change is constant. Alist of suggested reading is made available for those wishing to further explore the changing geological landscape of the Appalachian Mountains

Atlantic Ocean

Although a collision of continents caused the formation of the Appalachian Mountains, the present-day margin of North America is the result of a reversal in crustal plate movement. After the continents collided, the masses began to pull apart. About 240 million years ago, at the beginning of the age of the dinosaurs, a new ocean basin began to form the present-day Atlantic. The Atlantic Ocean is still widening today, with the ocean crust pulling apart at the mid-Atlantic Ridge.

Glaciation

While the Atlantic Ocean was still in its infancy, the Appalachians were already being attacked by erosion. At the time they formed, the Appalachians were much higher than they are now, more like the present-day Rocky Mountains. For the last 100 million years, erosion has carved away the mountains, leaving only their cores standing in the ridges of today.

Four times during the past 2 to 3 million years, great sheets of ice advanced steadily southward from the polar region. The glaciers did not extend as far south as the Southern Appalachians, but the resulting change in climate did. Animals and plants migrated southward. Species more common to northern climates, such as the saw-whet owl, established themselves in the Southern Appalachians and persist to this day at high elevations. Hunters who were ancestors to the Cherokees also migrated to the east and south during the most recent ice age.

Alum Creek

Effects of the ice ages also can be seen in the rocks. When water freezes in cracks or between rock layers, it gradually wedges the rocks apart. With repeated freezing and thawing in extremely cold climates, boulders accumulate on treeless slopes and at the bases of cliffs or ledges. In the Southern Appalachians, concentrations of boulders can be seen in the present-day forested mountainsides at many places. They are silent testimonies to the ice age.

Even though glaciers have retreated, the process of erosion continues. Mosses and lichens grow on rocks and begin the process of breaking them down. Plants grow in fractures, slowly widening them and enhancing the process of soil development. Rock layers slip along inclined surfaces, break off, and produce landslides. Wind and water continue the process of breaking down the rocks and returning them to the ocean. The sediments from the Southern Appalachians move toward the Atlantic Ocean and the Gulf of Mexico, where they are, once again, deposited on the ocean floor.

Whats next? The age old processes continue. Change is constant.

Wax Lake

Today, the age-old processes continue. Long after we have lived our lives, these sediments will become layers of rock that might again be uplifted into new mountains. At some time in the far future, they may become the host rock for new mineral deposits, or they may be invaded by molten rock. Processes acting upon these materials may move them great distances from their place of origin.

While we don't know the fate of rocks not yet formed, we do know that on this dynamic Earth, the one characteristic that we can count on, even though we may not perceive it in our lifetime, is change.

Our brief summary of the geologic history of the southern Appalachian Mountains should be viewed as only a starting point. We have included a list of published books and papers for further reading to guide those readers interested in delving deeper.

General

Carpenter, P.A., III, 1989, A geologic guide to North Carolina?s State Parks: North Carolina Geological Survey Bulletin 91, 69 p.

Carter, M. W., Merschat, C. E., and Wilson, W. F. 1999. A geologic adventure along the Blue Ridge Parkway in North Carolina. North Carolina Geological Survey Bulletin 98, 60 p.

Cox, W.E., 1998, Great Smoky Mountains: The story behind the scenery (6th printing): Las Vegas, Nev., K.C. Publications, 48 p.

Technical

U.S. Geological Survey and U.S. Bureau of Mines, 1968, Mineral resources of the Appalachian region: U.S. Geological Survey Professional Paper 580, 492 p.

Wooten, R. M., Carter, M. W., and Merschat, C. E. 2003. Geology of Gorges State Park. North Carolina Geological Survey, Information Circular 31, 60 p.

About 750 million years ago, the supercontinent began to thin and rocks at depth pulled apart like warm taffy because of expansion of the continental crust. Then, about 540 million years ago, the continental crust split into pieces that drifted away from each other. Seawater spread into low areas between crustal plates and, in time, formed new oceans.

Ocoee Basin

During the early part of the expansion of the continental crust (about 750 million years ago), a deep basin, known as the Ocoee Basin, formed on the margin of the supercontinent in what is now the western Carolinas, eastern Tennnessee, and northern Georgia. Seawater filled the basin. rivers from the surrounding countryside carried clay, silt, sand, and gravel to the basin, much as rivers today carry sediment from the midcontinent to the Gulf of Mexico. The sediment spread out in layers on the basin floor. The basin continued to subside, and over a long period of years, a great thickness of sediment accumulated.

The sediments of the Ocoee Basin now form the bedrock of the Great Smoky, Unicoi, and Plott Balsam Mountains. The layers in which these sediments were deposited on the ancient sea floor can still be seen in outcrops of the bedrock. In some rocks, even the pebbles and grains of sand are preserved.

The rocks that formed from coarse sediments, such as pebbles and sand, are very hard and are resistant to weathering and erosion. They form the high peaks and ridges of today. Rocks composed of fine-grained sediments, such as clay and silt, are softer and break down more easily. These rocks can be found in the lower areas. Erosion of the alternating layers of hard and soft rocks makes many of the landforms that we see today. As rivers cut their way through the layers, hard rocks form ledges that make waterfalls, and alternating layers of hard and soft rock make the riverbeds that produce whitewater rapids.

In 1843, a prospector who was looking for gold near Ducktown, TN, found copper instead. Disappointed, he moved on. Within 7 years, mining of the rich copper deposits near Ducktown began, and in time, the Copper Basin became the largest metal mining district in the Southeastern United States.

At the same time thatsediments and minerals were being deposited to form the Ocoee Basin, other areas that are now Virginia, the Carolinas, and Georgia were being subjected to volcanic eruptions.Still other areas,that are now the Valley and Ridge Province, were covered by a shallow inland sea.

When sediments were being deposited and mineral deposits were forming in the Ocoee Basin, volcanoes were erupting in areas that are now Virginia, the Carolinas, and Georgia. Lava from some volcanoes flowed in slow-moving sheets like lava from the Hawaiian volcanoes, but other eruptions were explosive, like Mount St. Helens.  Although volcanic activity ended hundreds of millions of years ago, rocks that formed from these ancient volcanoes are still visible.  Fragments that erupted from ancient volcanoes and minerals that filled holes where gas bubbles had escaped can be seen in some rocks at White Top Mountain in the Mount Rogers National Recreation Area of southern Virginia.

Amphibolites, that were most likely sea floor basalts before being metamorphosed during the Paleozoic, are common, and locally areally extensive in the Eastern Blue Ridge province.  These basalts likely formed in a rift environment similar to the Ocoee Basin.  It is important to understand that amphibolites weather to more basic soil types, and can support different plant communities than those that dominate on soil types derived from less fertile, weathered metasedimentary rocks.

An Inland Sea

The rocks of the Valley and Ridge Province formed in a setting very different from that of the Ocoee Basin. For millions of years, a vast, shallow, inland sea covered the area. Shells and other hard parts of ancient marine plants and animals accumulated to form limey deposits that later became limestone.

The weathering of limestone now exposed at the land surface produces the lime-rich soils that are so prevalent in the fertile farmland of the Ridge and Valley Province. Limestone is important in the economy of the region because of its use in building and road construction, agriculture, and many other activities.

Black Smoker

The rocks of the Ocoee Basin contained some of the most important deposits of copper, zinc, iron, and sulfur in the Eastern United States. The origin of these metals and sulfur was a mystery until the late 1970s when submersibles were used to study the deep oceans and geologists saw dark plumes of hot fluids emerging from vents along fractures in the ocean floors. Fluids from the "black smokers," as these vents are called, contain metals that are deposited in mounds around the vents. The deposits that were mined in the area now known as the Copper Basin (near Ducktown, TN) and other places in the Southern Appalachians probably formed in the same way when hot, metal-bearing fluids vented onto the floor of the Ocoee Basin. Copper from vents like these contributes to the economic growth of the country, as well as the region.

Copper Basin Devastation

During the early days of mining in the Copper Basin, people did not understand or take measures to prevent the adverse effects that mining and smelting can have on the environment. Metal-bearing rocks were roasted in outdoor heaps to free the metals. The proces also released harmful sulfur dioxide fumes into the atmosphere. Sulfur dioxide also mixed with the moisture in the air and fell as acid rain, sterilizing the soil and killing what vegetation hadnt been already cut for fuel. In time, a stark, deeply gullied, barren landscape developed. Twenty-three thousand acresof land, an are large enough to be seen by astronauts in space,became a biological desert.

Copper Basin Restoration

At the turn of the century, a method was discovered to convert the sulfur dioxide into sulfuric acid for fertilizer production. With the application of this discovery, release of sulfur dioxide into the atmosphere finally ceased. In the 1930s, efforts to restore the vegetation began, but it was not until the 1970s, when new methods were used, that trees started to flourish. Most of the area has now been revegetated through cooperative efforts of Federal and State agencies, universities, and mining companies.

While sediments and minerals were being deposited to form the Ocoee Basin, other areas that are now Virginia, the Carolinas, and Georgia were being subjected to volcanic eruptions. Those areas in the current Ridge and Valley Province were covered by a shallow inland sea.

Continental Plates

How did rocks that formed on sea floors and islands become the mountains and valleys of today? The ocean that formed during the continental breakup about 540 million years ago continued to expand. During that time bacteria, algae, and many species of invertebrates flourished in the oceans, but there were no plants or animals on land. Then, about 470 million years ago, the motion of the crustal plates changed, and the continents began to move toward each other. As the continental plates moved closer together, fragments of oceanic crust, island arc volcanoes (such as the islands of Japan and the Aleutian Islands), and other continental masses collided with the eastern margin of ancestral North America. By this time, plants had appeared on land, followed by scorpions, insects, and amphibians. The ocean continued to shrink until, about 270 million years ago, the continents that were ancestral to North America and Africa collided. Huge masses of rocks were pushed westward along the margin of North America and piled up to form the mountains that we now know as the Appalachians.

As blocks of continental crust rode across one another, some rocks became so hot that they melted. Where the temperature is high but below the melting point of the rocks, solid rock flows occur and create metamorphic rocks. The collision of continental plates is also expressed in the rocks by folds (bends) and faults (breaks). Earthquakes happen because of slippage along a fault. Faults act as channels for migration of fluids and were a key factor in localizing gold in certain zones. The collision of continents hundreds of millions of years ago also set the stage for the patterns of human settlement, travel, and transportation routes in the region.

Igneous Plutons

As blocks of continental crust rode across one another, some rocks became so hot that they melted. Molten rock at the Earths surface erupts to form either volcanoes or quiet lava flows. When molten rock remains deep below ground, it cools and crystallizes to form bodies of rock that are called igneous plutons.

Plutons are scattered throughout the Southern Appalachians like plums in a pudding. Some plutons are now exposed at the land surface due to erosion of overlying rock; they weather to form unusual, smooth-sided domes like Looking Glass Rock, south of Asheville, N.C. The plutons are composed of granite and similar rocks. People use granite that has a uniform texture and few fractures, such as the Mount Airy granite, in buildings, bridges, statues, and monuments. The next time you visit a cemetery, you may see granite that formed millions of years ago far below the land surface.

Some molten granitic rock cools very slowly and forms coarse-grained veins called pegmatites. These have been the source of high-purity minerals, such as feldspar, quartz, and mica, and gemstones, such as emerald and beryl. The main uses of feldspar are in glass, pottery, and ceramics.

Quartz has many uses, including as gemstones and in high-quality optical lenses. Native Americans used mica for ornaments, and now it is used as an insulator in electronic and electrical equipment. Ultra-high purity quartz mined and processed in Spruce Pine, North Carolina is vital to the computer industry worldwide.

Looking Glass Rock

Rockfall

When continental masses, islands, and the sea floor collided with the margin of ancestral North America, they were subjected to intense pressure and heat deep beneath the ground surface. Where the temperature is high but below the melting point of the rocks, the rocks deform and recrystallize in a solid state to become metamorphic rocks. The components separate into bands, and some flow with a consistency like that of toothpaste. In many places along the Blue Ridge Parkway, there are metamorphic rocks with bands of light- and dark-colored minerals, which in some places look like the folds and swirls in a marble cake.

Original layers are partly retained if metamorphic temperature and pressure are low, as happened with some of the sediments that were deposited in the Ocoee basin. During metamorphism, minerals recrystallized in sheets to form rocks (slate or schist) that split easily into thin, smooth layers. When these rocks are near rivers or creeks, they make excellent skipping stones.

The smooth surfaces are also excellent slip planes. These planes can cause serious problems, especially when the layers are steeply inclined. Rocks overlying smooth, inclined surfaces are very prone to sliding downslope, especially when heavy rainfall increases water pressure at the surfaces.

Geologic Window

The collision of continental plates is also expressed in the rocks by folds (bends) and faults (breaks). Damaging earthquakes happen because of slippage along a fault. Although earthquakes are now rare in the Southern Appalachians, during the time of continental collision, earthquakes were a common occurrence.

One place where the effects of the faulting can be seen is in Cades Cove in the Great Smoky Mountains National Park. In a normal sequence, younger rocks are deposited on top of older ones. However, in Cades Cove, the limestone that makes up the floor of the cove is younger than the rocks in the surrounding mountains. The older rocks of the surrounding mountains moved over the limestone on a low-angle fault. Erosion made an opening to expose younger rocks below the fault, in a feature called a window. The rocks that we see through the Cades Cove window formed in the inland sea that once covered this area.

Many faults have been identified throughout the Southern Appalachian Mountains and the Ridge and Valley province. Huge masses of rock moved along these faults for distances of 60 miles or more. A major fault area can be seen at Linville Falls, north of Asheville, N.C. The rocks that make up the mountains above the falls are older than the resistant ledges that form the falls. Ground-up rocks of the fault zone are between the older rocks above and the younger rocks below the falls in Linville Gorge.

Faults act as channels for migration of fluids and were a key factor in localizing gold in certain zones. Although the date that white settlers discovered gold in the Southern Appalachians is uncertain, there is no doubt that gold caused profound changes in the human history of the area. The Cherokees living in the region knew about the gold, but it did not have the same significance for them as it did for the new settlers.

In 1829, newspaper articles described vast riches of gold in Cherokee land in Northern Georgia. Thousands of miners quickly flocked to the area with dreams of quick riches. They washed gravel from banks of the streams to search for gold.

The frenzy caused by the discovery of gold hastened the removal of the Cherokees by a forced march to Oklahoma during the winter of 1837-38. More than one-third of the Cherokee people who started the march died along the way, on what is now known as the Trail of Tears.

Gold Miners

Trail of Tears

The collision of continents hundreds of millions of years ago also set the stage for the patterns of human settlement and transportation. When the continents collided, folds and faults formed with northeast-southwest alignments. These structures are the framework that controls the ridges and valleys of today. The northeast-southwest-trending ridges and valleys were both the main routes of travel for people and ideas. They also were barriers to travel perpendicular to them.

Sandstone Ridges

A less obvious result of the collision was a telescoping of contrasting rock types. The juxtaposition of rocks that had formed in diverse environments set the stage for the diversity of landscape, habitat, and life forms that characterizes the Southern Appalachians today. Differences in underlying rocks also influenced profoundly the patterns of regional development. Some land and soils were better suited for farming, mining, or timber than others. The location of industry, and subsequently, the location of population centers, was based on availability of raw materials and transportation routes.

Sand, clay, and interlayered limey ooze that formed on the floor of the shallow, inland sea became the bedrock of theRidge and Valley Province. The resistant sandstone layers now cap ridges and form cliffs. Limestone, on the other hand, erodes more readily, forming valleys. Limestone provides nutrients for crops and is also conducive to forming caves and sinkholes, which contain unique living communities. The occurrence of iron ore, limestone, and nearby coal deposits in the Ridge and Valley Province and the Appalachian Plateau, formed a basis for early economic development. The limestone also contained major zinc deposits in some places, further enhancing the economic development of the region. However, the value of the metals mined has been far exceeded by the total value of the industrial minerals extracted. These minerals include the limestone itself, which is used for making cement and concrete.

Sandstone Outcrops

The pebbles, sand, and clay that were deposited in the deep Ocoee Basin became the bedrock of the Great Smoky Mountains. The hard, metamorphosed sandstone forms outcrops and cliffs that are habitats for scattered communities of rare plants and animals. Metal-rich layers produce the acidic soils that some species, such as red spruce, need to flourish.

Lava and sediments that were deposited on the ocean floor form the bedrock of the Blue Ridge Mountains, to the east and north of the Great Smokies. Some of these rocks produce soils that are favorable for timber and for farming in the narrow valleys between ridges. However, like the Great Smoky and Unicoi Mountains, the special value of the area isfor recreation. Some of the rock types form highly specialized habitats, such as balds, high-elevation rocky summits, and granite domes. Some volcanic rocks produce soils that favor oak forests. Some fragments of crust from deep beneath the ocean floor were caught in the continental collision. These fragments of rock lack nutrients and produce soils that have sparse or stunted vegetation. Such areas form habitats for some rare plant communities.

Islands and continental masses that were offshore before the collision of the ancestral North American and African Continents were added to North America during the collision. They now form the bedrock of the Piedmont Province, which slopes gradually southeastward from the Blue Ridge.

The understanding of Appalachian geology has advanced greatly in the last few decades, owing to the development of the plate tectonics theory. Many geologic concepts, timeframes, and theories, once held as fact, have changed radically with the development of the new plate tectonic theory. Scientific theories will continue to change with advances in research.

According to this theory, the Earths upper layer, or lithosphere (composed of the crust plus the uppermost mantle), is divided into a small number of rigid plates that rest on weaker underlying rock (the aesthenosphere) and move relative to one another at rates of a few centimeters per year. Two adjacent plates may move apart along a zone of divergence, with new crust forming along their margins as magma rises into the gap between them. Alternatively, they may slide past each other along a zone of lateral movement. Finally, they may collide along a zone of convergence. Upon collision, one plate commonly slides beneath the other at a "subduction zone." Where two continental plates collide, however, they are too light to be subducted, and the result is a massive collision, producing zones of intense compression characterized by melting, metamorphism, and more peripherally, folding and thrust faulting.

In Precambrian times, North America was joined to Europe and Africa.

Plate Tectonics

During the late Precambrian, the North American plate and the African plates began to spread apart near what is now the Atlantic Coast of the Eastern United States. This spreading produced an ancestor of the modern Atlantic Ocean, as well as two seaways separating the North American Continent from two strips of land. During the Paleozoic Era, however, the plates reversed direction and began to converge. Slowly but inexorably the two strips of offshore land were crushed against the east coast. As convergence continued, the African oceanic plate began diving beneath the American plate. Finally, near the end of the Paleozoic the African Continent itself collided with the North American Continent. This collision produced tremendous compressive forces that thrust huge slabs of crust many kilometers to the west. It also folded formerly flat-lying rock layers. This compression, thrusting, and folding created many of the geologic structures seen in the Appalachians today. At the same time, vertical forces pushed up high mountain ranges, perhaps similar to the Swiss Alps today. During these times, erosion of the high mountains poured huge volumes of sediments into the seaways and onto the downwarped crust to the west of the mountains. These sediments now make up the rocks of the Ridge and Valley and the Appalachian Plateau Provinces.

(Table:Geologic Time Scale)

The most intense mountain building episode in the Appalachians took place in the Permian Period at the end of the Paleozoic, as Africa crashed into North America. With the end of the Paleozoic, such mountain-building in the Appalachians came to an end. At that time the mountains were high, steep, and very likely glaciated. As uplift rates decreased, however, the mountains swiftly began to erode away, so that low mountains replaced the alpine peaks. Crustal forces were not dead, however. In the Triassic and Jurassic Periods of the Mesozoic Era, North America and Africa began to pull apart. The modern Atlantic Oceanwas born. Itcontinues to expand even today as North America and Africa drift farther apart. This drifting produced many rift basins, mainly in the Piedmont. Crustal uplift also continued irregularly during the Mesozoic and Cenozoic, but of a much different type. Instead of a lateral compression producing folding and thrust faulting as well as uplift, a broad, gentle, vertical uplift predominated. The rate of uplift was also much lower than during the Paleozoic.

(Table:Geologic Time Scale)

Changes in stream drainage during the Mesozoic

A major change in stream drainage also took place in the Mesozoic. Today, many streams in the Southern Appalachians drain to the Atlantic Ocean. When the high Paleozoic Appalachians dominated the topography, however, most streams flowed to the northwest. We know this because the flow-direction indicators found in Paleozoic rocks in the Ridge and Valley and Appalachian Plateau Provinces show that the sediments that make up these rocks were laid down by currents flowing in that direction. The question arises of how the direction of stream flow reversed after the end of the late Paleozoic mountain building.

Geologists and geographers have tried to answer this question for a century. The key to solving this problem comes from our knowledge of plate tectonics, and probably involves the pulling apart of North America and Africa that took place during the Mesozoic. We now know that when plates move apart, the crust near their margins usually subsides. This sinking may explain how formerly west-flowing streams reversed their direction of flow. Before the subsidence of the eastern margin of North America, the height of land that formed the southeast-northwest divide probably lay along the crest of the Paleozoic Appalachians near the present-day coastline. As the continental margin continued to sink, however, the divide moved farther and farther to the northwest. The northwestern part of the Appalachian region, which originally was lower, gradually became higher than the southeastern part. This southeastern slope made it possible for streams in the Appalachians to flow to the Atlantic (Judson, 1975).

Another event that took place during the later Mesozoic was the submergence of the Atlantic and Gulf continental margins. A look at a geologic map of the Southeastern United States shows that the southwestward trend of the Appalachians is truncated by Cretaceous sediments in western Alabama. Buried Appalachian structures continue beneath the Gulf Coastal Plain sediments as far as Oklahoma. The Cretaceous sediments also extend long distances inland from the present coastline from Alabama to North Carolina. Furthermore, it is very likely that the boundary between the Piedmont and the Coastal Plain (the Fall Line, so named because of the numerous waterfalls that occur along this boundary) has retreated a great distance seaward from its original position, and that the inland incursion of the Cretaceous seas was much greater than marked by todays Fall Line.

(Table:Watershed Number)

The Cenozoic Era extends from 65 million years ago until the present. At the beginning of the era, submergence by the sea was still pronounced, and early Cenozoic sediments occur almost as far inland as the late Cretaceous sediments. From North Carolina northward, the most inland Coastal Plain sediments are Tertiary, not Cretaceous. This occurrence probably does not indicate that the Tertiary sea extended farther inland than the Cretaceous sea, but that Cenozoic uplift in this area has been more rapid than farther south, so that the Cretaceous sediments have been completely stripped by erosion.

(Table:Geologic Time Scale)

Recent stratigraphic evidence provides additional support for the presence of a late Cretaceous and early Tertiary sea far inland from the present Fall Line. Prowell and Christopher (2000), for example, report that Cretaceous marine deposits occur at elevations of 300 m above present sea level in south-central Tennessee. From this conditioning, they infer that most of the Cretaceous and early Cenozoic strata that once covered the Piedmont have been stripped by late Cenozoic erosion. In addition, they report that remnants of late Cretaceous and early Cenozoic beds are preserved at elevations of up to 685 m in numerous fault-bounded sediment traps as far inland as central Tennessee and western Virginia. Assuming latest Cretaceous or earliest Cenozoic deposits in the traps, this elevation translates to an uplift rate of greater than 10 m per million years.

Exceptin the earliest part of the era, erosion has been the dominant activity in the Appalachians during the Cenozoic. The history of a time interval dominated by erosion is much harder to unravel than that of an interval with extensive deposition, simply because erosion leaves behind little evidence. Thus, we know much less about geologic events in the Cenozoic than we do in, say, the Paleozoic. And yet, the modern Appalachian landscape owes its appearance almost entirely to Cenozoic processes. We know that the present Appalachian Mountains are not simply the worn-down remnants of their predecessors. The ancient mountains probably are completely gone. Our knowledge of erosion rates supports such an interpretation. Modern studies show that the Appalachians are being lowered by erosion at a rate of roughly 30 m per million years (Hack 1980; Matmon and others 2001). Let us suppose that this rate has remained the same since the rise of the original Appalachians about 300 million years ago during the late Paleozoic. Thus, 30 x 300 or 9,000 m of erosion have taken place. (In fact, the actual amount of erosion is probably much more than this, for high mountains erode at a much faster rate than do low ones). Even if we suppose that the highest peaks of the Paleozoic Appalachians were 5,000 m in altitude, higher than the highest peaks in todays Alps, the mountains would have worn away long ago had there not been more recent geological uplift were involved. In fact, the mountain landscape we see today, as opposed to the rocks themselves, are unlikely to be any older than Cenozoic. 

The Cenozoic Period produced two dramatic geological events with major implications for the landscape of the Southern Appalachian Mountains:

• Crustal Uplifting: at least part of the uplift responsible for our modern mountains probably can be attributed to isostatic adjustment in response to erosion.
• The Ice Ages: although ice sheets never covered the Southern Appalachians, the effects of cold climate on this region were strong.

At least part of the uplift responsible for our modern mountains probably can be attributed to isostatic adjustment in response to erosion. Isostasy refers to the idea that the heights of continents and ocean floors are controlled by the densities of the rocks underlying them. The best way to visualize this is to think of the lighter continental crust floating on top of the underlying heavier rock, just as a wood block floats on water. Suppose an 8 inchthick wood block with a density half that of water is placed in a tub of water. The result is that 4inches will be under water and 4inches will protrude above the water. Now slice off a 2 inchslab parallel to the water surface -- this is analogous to erosion of crustal material by erosion. Note that although we have removed 2inches from the block, the elevation above water level has not been lowered by 2 inches, for now the block floats with 3inches below the water and 3inches above. Thus, even though we have eroded 2 inches, the elevation is reduced by only 1 inch. Now slice off another 2 inchslab. Again, we have eroded 2 inches, but the elevation is reduced only 1 inch, for the block now floats with 2inches below the water and 2inches above. Thus, to reduce the original 4-inch-high surface to sea level, we have to erode 8 inches, not 4 inches. Now, suppose the density of the wood block was not 0.5 that of water, but 0.8. In this case, every time the surface of the block is lowered by 1 inch, isostatic adjustment will push up the surface by 0.8 inch. The ratio of the density of the light crustal material to the underlying heavier rocks is just about 0.8. Thus, for example, if a 1000-foot mountain were to be worn down to sea level, a subsequent rise of the surface to an altitude of 800feet due to isostatic adjustment would be expected.

Sedimentary accumulation rates

On the other hand, work by Ahnert (1970b) on the effect of relief on denudation rate suggests that isostasy alone is not enough to explain present-day relief in the Appalachians. Ahnert estimated that if the only uplift is isostatic, the mean relief of an area will probably be reduced to 10 percent of its original relief in 30 million years. In many areas the relief of the present Appalachians exceeds 300 m. If only isostatic uplift is assumed, this means that 30million years the relief of these locations was 3000 m, and 60million yearsago was 30,000 m - clearly impossible. This result supports the idea that postorogenic tectonic uplift has been involved, perhaps due to continued forces on the North American plate.

There are other inferred changes in Appalachian topography that cannot be attributed to isostasy. There is indirect evidence that the uplift rate of the Appalachian Mountains has varied greatly during the Cenozoic. This evidence comes from the sediment record left by the eroding Appalachians. Many rivers carry sediment eroded from the Appalachians to the Atlantic Ocean and Atlantic Coastal Plain. These deposits, both onshore and offshore, have now been well studied, so that it is possible to compute the volumes of sediment deposited during different time intervals (Poag and Sevon 1989). The most important factor affecting the amount of sediment deposited seems to be the amount of erosion taking place in the upland source areas at the time.The amountof erosion,in turn, depends largely on the height and steepness of the land surface. When the relief is higher and slopes are steeper, there is more erosion and thus more sediment deposited, whereas the reverse is true whenthe relief is lower and slopes are gentler. By plotting the volume of sediment deposited against time, we have an index of what the topography was like. The results show that very little sediment was deposited during the first 60 million years of the Cenozoic, suggesting a landscape of low relief. We then see a 20-foldincrease in sediment accumulation beginning about 15 million years ago, and culminating in the past million years suggesting a great increase in relief and therefore in uplift rate is suggested. This scenerio also suggests that if we were able to go back in a time machine to the middle Cenozoic, we would probably see much lower mountains than we see today. Exactly what caused such a change in uplift rates is not known.

Maximum ice cover of North America
during Pleistocene.

In addition to crustal uplift, one other dramatic geologic event has had a profound effect on the Appalachian landscape during the Cenozoic: the coming of the ice ages. In the late Tertiary Period, the Earths climate began to cool, and ice sheets formed over Antarctica and Greenland. In the Quaternary Period (the latest 1.8 million years) the cooling increased, and ice sheets began periodically to form in the northern parts of North America. In the United States, glaciers repeatedly have swept southward from northern Canada, at least once reaching as far as northern Kentucky, and then retreated and disappeared. Such episodes of glacial climate are called glaciations, and the relatively warm intervals between glaciations, such as the present (which is still cool enough to maintain the Antarctic and Greenland ice sheets), are called interglaciations.

The latest glaciation, called the Wisconsinan glaciation, ended about 10,000 years ago. At least three, and probably more, glaciations took place before the Wisconsinan. Because later glaciers tend to erode away evidence of previous glaciers, the best evidenceis provided by sediments on the sea floor. Deep sea cores in these sediments show that glaciations and interglaciations have occurred fairly regularly during the Quaternary, with one climatic cycle (one glaciation and one interglaciation) lasting an average of 100,000 years. The climatic cycles appear to be caused, at least in part, by slight periodic variations in the direction and amount of tilt of the Earths axis and the shape of the Earths orbit about the sun.These variationsaffect the distribution of the suns heat on the Earths surface.

Ice sheets never covered the Central or Southern Appalachians, nor were there mountain glaciers. Nevertheless, the effects of glaciations on this region were strong. Based on pollen and other paleovegetation data, some areas had mean annual temperatures as much as 10^o-12^o C cooler than now. As a result, vegetation was greatly different from todays. It wassimilar to that found in present-day Canada. Higher areas were actually above tree line and hadonly tundra-like vegetation (Delcourt and Delcourt, 1981). The intense cold associated with the glacial climates greatly increased the rate of physical weathering processes such as frost wedging. In addition to landforms and deposits, such as sorted patterned ground, that are clearly periglacial in origin, much of the hillslope colluvium and talus in the Appalachians is probably relict from glacial times.

Mean Annual Temperature

The climate of the Southern Appalachians varies considerably with location and elevation. Not only are higher elevations colder,they experience greater cloud cover, relative humidity, and precipitation. The Southern Appalachian climate is produced largely by continental arctic air masses from the north during the winter and maritime tropical air masses from the Gulf of Mexico and Atlantic Ocean during the summer. Based on the Koppen-Geiger system of climate classification (Aguado and Burt, 2000), the Southern Appalachianclimate is classified as Moist Subtropical with a symbol of Cfa (C stands for warm temperate climate, f for sufficient precipitation in all months, and a for warmest monthly mean temperature over 71^o F). The northern area is classified as Moist Continental climate with a symbol of Dfa (D stands for snow climate.) Here, dry continental polar air masses bring cold and dry winters.

Temperature

Temperature varies both with latitude and altitude over the region. The lowest temperatures are on the Allegheny Mountains (AM), and the warmest in the Coastal Plain (CP). The figure shows mean annual temperature for the physiographic provinces of the Southern Appalachians and the surrounding region. The overall trend, of course, is for colder temperatures to the north. However, cold temperatures extend farthest south in the Southern Blue Ridge province, owing to the high elevation of this province. The 39 weather stations in this province have a mean elevation of 698 m, somewhat higher than the mean altitudes for the other provinces. The lowest mean minimum temperature (45.9^o F) occurs in this province. Warmer temperatures extend farther north in the Piedmont province than in the western parts of the Appalachians, owing to lower elevation of the Piedmont.

Precipitation

Mean Annual Precipitation

Many areas in the Southern Appalachians receive large amounts of precipitation. The figure below shows that there is a general increase in precipitation from north to south, owing to the incursion of tropical air masses more frequently into the southern part of the region. In the southern part of the region, precipitation decreases from west to east.The Eastern Piedmont (P) has a modest rain-shadow effect. Aguado and Burt (2000) note that in the southwestern part of the region, moist maritime air masses from the Gulf move ashore, contributing to the development of heavy but brief showers in summer. As the air masses move northward, they gradually lose moisture by precipitation, so that by the time they reach the northern provinces the amount of precipitation is substantially lower than in the southern part of the region.

Superimposed on these general trends are small areas of high precipitation, particularly in the Southern Blue Ridge (SBR). The highest amounts of precipitation, nearly 125 inches per year, occur in the region near the border of Georgia and the Carolinas. This small area is so rainy that some have called it the only temperate rainforest in the U.S. east of the Mississippi (McCrone et al. 1982). Cloud cover and fog frequently occur throughout the Southern Appalachians, because the humidity is high. Heavy snowfalls occur in higher elevations; Mt. Mitchell received over 100 inches of snowfall one year (Redington 1978). Three weather stations in the Southern Blue Ridge Province have mean annual precipitation values greater than 80 inches. Two other high-precipitation areas occur along the western edge of the Cumberland Plateau (CPT) and may represent an orographic effect produced when Gulf air masses encounter the modest (about 300 m) but abrupt rise in altitude along the western Cumberland Escarpment.

Geologically, the Appalachian Mountains are the oldest on the continent. Formed more than 200 million years ago, the rocks of these mountains show the effects of folding, faulting, and metamorphosis of Precambrian and Paleozoic rock beds. Because of this geologic disturbance, Precambrian sediments were not only thrust upward and outward, they were also transformed into a number of metamorphic rocks, including slate, schist, and gneiss.

Regolith is a layer of loose, heterogeneous material covering solid rock. Different regolith characteristics exist in the different provinces of the Southern Appalachian region. Regolith weathers into soil. The most common soil type of the Southern Appalachiansis what scientists call inceptisol, an acidic, shallow soil group developed primarily on shale and sandstone beds.

• Piedmont Province
  • Regolith: Most of the regolith in the Piedmont Province is saprolite, which is formed from decomposed rock. However, there are also substantial areas of colluvium,and other transported regolith.
  • Soil: The dominant soil order in the Piedmont is the Ultisol, comprised mainly of the great group Hapludults.
• Blue Ridge Province
  • Regolith: Although thick saprolite occurs in the Blue Ridge,it is not as prominent as in the Piedmont Province, both because it tends to be thinner and because surfaces in the Blue Ridge are commonly covered by colluvium.
  • Soil: The dominant soil order in the Blue Ridge Province is the Inceptisol. This order consists of relatively young soils that lack horizons of illuvial clay.
  • Mass Wasting and Foot-Slope Deposits: The most common mass-wasting process in the Blue Ridge is probably downslope movement of colluvium and residuum induced by windthrow of trees.
• Ridge and Valley Province
  • Regolith: The flanks of sandstone-capped ridges in this province generally are covered with bouldery colluvium, whereas valley floors underlain by limestone typically are covered with thick clayey residium called terra rossa. Valley floors underlain by shale show only thin residium.
  • Soil: The sandstone ridges are dominated by inceptisols whereas the valleys show mainly inceptisols.
  • Mass Wasting and Periglacial Features: mass wasting is most prominent on sandstone ridges. The boulder colluvium on the slopes generally is quite stable, but at rare intervals may be carried downslope by debris slides set off by intense rainfalls. There is evidence that this colluvium was somewhat less stable during Pleistocene cold periods, when frost creep and solifluction were much more pronounced.
  • Karst Landscapes: The Ridge and Valley, particularly the Great Valley, is one of the major karst regions of the United States. Many areas show sinkholes, sinking streams, and caves. Many famous commercial caverns occur in the Shenandoah Valley of Virginia, for example
• Appalachian Plateau Province
  • Regolith: The Appalachian Plateau is underlain mainly by sandstone conglomerate, and shale, and residuum on these clastic rocks tends to be thin. Where hills are capped with sandstone or conglomerate, hillslopes generally are covered with boulder colluvium.
  • Soil: Soils are mainly Ultisols (Hapludults, Fragiudults, and Ochraquults) and Inceptisols (chiefly Dystrochrepts). At higher elevations limited areas of Spodosols have developed over quartz-sandstone parent materials.
  • Mass Wasting: Compared to other Appalachian provinces, the Appalachian Plateau has the greatest abundance of conspicuous slope failures. Most failures are earthflows and slump-earth flows, which generally occur in shales and mudstones.
  • Karst Landscapes: Because little limestone occurs in this province, karst features are rare. Interestingly, however, near the escarpments of the Cumberland Plateau, where sandstone overlies limestone, some of the largest caverns in the U.S. occur.

The Appalachian Highland is one of eight major physiographic divisions of the United States. The part of this division considered here includes, from southeast to northwest, the Piedmont, Blue Ridge, Ridge and Valley, and the Appalachian Plateau Provinces. The Blue Ridge is separated into the southern and northern sections. The Ridge and Valley is separated into the southern and middle sections. The Appalachian Plateau is separated into the Cumberland and Kanawha sections. Of these, the Blue Ridge contains the highest topography, and the Appalachian Plateau the second highest. The Ridge and Valley is somewhat lower, and the Piedmont is by far the lowest.

Physiographic provinces

The Piedmont Province is a dissected plateau whose inner boundary is the Blue Ridge Province. The outer boundary is the Coastal Plain. The general slope is from the mountains toward the Coastal Plain. The landscape is characterized by hilly relief. Elevations range from a few tens of meters near the Coastal Plain to as much as 600 m near the Blue Ridge.

The Blue Ridge Province is divided into two subprovinces, the Northern Blue Ridge and the Southern Blue Ridge. The Northern Blue Ridge lies north of the Roanoke River and is a narrow range of high mountains that is 395 km long but nowhere exceeds 22 km in width. In its narrowest part it is a single ridge that stands about 365 m above the Great Valley of the Ridge and Valley Province and about 610 m above the Piedmont Lowlands on the east. It is underlain by a sequence of Precambrian and Cambrian rocks that form the northwest limb of the Blue Ridge anticlinorium (Espenshade, 1970). This sequence consists largely of resistant rocks. Only three rock units support the crest of the range: (1) a complex assemblage of medium to coarse granitoid rocks, of which hypersthene granodiorite (Pedlar Formation) is the most resistant; (2) a metavolcanic unit, the Catoctin Formation; and (3) a thick series of quartzite, arkose, and phyllite called the Chilhowee Group ofearly Cambrian in age. The topography of the Northern Blue Ridge is largely due to rock resistance and width of outcrop, although the average altitude of the mountains north of the Potomac River is little more than half that of its southeastern part, despite similar lithology. This decline may be due simply to less uplift in the northern region (Hack, 1982). The Southern Blue Ridge extends from the Roanoke River southwestward into north Georgia.

The Ridge and Valley Province extends from north-central Alabama to beyond the late-Wisconsinan glacial border in Pennsylvania. It is underlain by Paleozoic sedimentary rocks that have been folded and thrust from the southeast. Tight folds characterize the northern part of the province, whereas stacking of thrust sheets characterizes the southern part. The southeastern border of the province is a broad, linear lowland called the Great Valley, but most of the province consists of alternating ridges and valleys. Elevations generally range from 300 to 900 m,but extremes are 120 to 1,300 m (Fenneman, 1938).

Geologic Cross Section

The contrast in bedrock resistance to erosion is greater in the Ridge and Valley than in any other province, with some sandstone and conglomerate units, for example, being many times more resistant than the abundant shale and carbonate rocks. Differential erosion, in which resistant rocks come to form ridges and mountain peaks while easily eroded rocks form valleys,has beenvery prominent in shaping the landscape. Thus, lithology and structure are more dominant in determining the topography than in other province. Certain resistant units repeat themselves and are widespread ridge makers. To the north, these include Pottsville Sandstone of Pennsylvanian age, Pocono Sandstone of Mississippian age, and Tuscarora Sandstone of Silurian age. To the south, such units include Pottsville, Mississippian Fort Payne chert, and Silurian Clinch (equivalent to Tuscarora).

The Appalachian Plateau Province extends from Alabama to beyond the glacial border in Ohio and Pennsylvania, bordering the Ridge and Valley. It differs from the other provinces in several ways:

1. Rocks are dominantly clastic, to include conglomerates, sandstones, and shales, with some interbedded coal. Limestones are uncommon.
2. Strata are mainly Mississippian and Pennsylvanian in age,but some northern areas are underlain by the Dunkard Series of Permian age. Thus, they are generally younger than those of other Appalachian provinces, except for the Mesozoic rocks of the Piedmont rift basins.
3. Rocks have undergone little deformation relative to the other Appalachian provinces; exceptionsare a few gentle folds and thrust faults adjacent to the Ridge and Valley.
4. The Appalachian Plateau is bounded on all sides by outfacing escarpments, reflecting the regional synclinal structure of the Plateau.
5. Altitudes in the Plateau nearly everywhere are higher than those in adjacent provinces.
6. Most of the province, with the exception of that part in Tennessee and Alabama, is highly dissected, and has a higher average slope than any other province. The topography north of Tennessee is a "plateau" only in the sense that the hilltops are concordant and suggest a former flat surface. Near the eastern margin, the plateau is so dissected that the topography commonly is referred to as "mountains" (Thornbury, 1965).

Major streams of the Appalachian Highlands

The hydrology of the Southern Appalachians is largely the story of the regions numerous rivers. Waters draining from the western side of the Appalachians eventually reach the Gulf of Mexico, while drainages on the eastern side end up in the Atlantic Ocean. Major Gulf drainages of the region drain to the Ohio River (New-Kanawha, Tennessee, and Cumberland river drainages) or to the Alabama-Apalachicola Rivers (Coosa-Tallapoosa, Chattahoochee river drainages). Atlantic slope drainages include those to the Chesapeake Bay (Potomac, Rapidan-Rappahannock, and James River drainages) and through the Carolinas (Roanoke, PeeDee, Santee-Cooper, and Savannah River drainages). The U.S. Geological Survey has developed a nationwide system of delineating drainages as hydrologic units that are commonly used to summarize information about watersheds.

Major rivers include the Tennessee, French Broad, Cumberland, Hiwassee, and Holston rivers.

Streams have influenced the topography differently in each province:

• Piedmont Province: In the foothill zone of the Piedmont of North Carolina and Virginia, northeast-flowing tributaries to the southeast-flowing master streams are long and subparallel, whereas opposing tributaries are short and irregular in direction. Small streams flow on saprolite, whereas larger streams flow on bedrock. Soil erosion in the Piedmont is among the severest in the nation.
• Blue Ridge Province: Streams in this province have etched out nonresistent rocks and shear zones to form trench valleys and intermountain basins.
• Ridge and Valley Province: Etching of nonresistant rock by streams has had a much stronger effect on topography here than in the Blue Ridge, owing to the much greater difference in the erodibility of bedrock in this Province. The New River cuts directly across the ridges of this Province, following a direction of flow it has had for hundreds of millions of years.
• Appalachian Plateau Province: The stream drainage pattern in this province generally is dendritic (i.e., random), owing to the subtety of bedrock structures here. However, bedrock control of drainage by fractures and folds occur in some places.

The Appalachian Plateau Province extends from Alabama to

Physiographic provinces

1. Most rocks are clastic (made up of bits of older rocks). They include conglomerates, sandstones, and shales, with some interbedded coal. Limestones are uncommon.
2. Strata are mainly Mississippian (354-323 million years BP) and Pennsylvanian (323-290 million years BP) in age, although some northern areas are underlain by the Dunkard Series of Permian age (290 - 248 million years BP)(BROKEN-LINK Table: Geologic Time Scale). Thus, they are generally younger than those of other Appalachian Provinces, except for the Mesozoic rocks of the Piedmont rift basins.
3. Rocks have undergone little deformation relative to the other Appalachian provinces. There are a few gentle folds and thrust faults adjacent to the Ridge and Valley.
4. The Appalachian Plateau is bounded on all sides by outfacing escarpments.  Overall, the Plateau has a synclinal (troughlike) structure.
5. Altitudes nearly everywhere on the Plateau are higher than those in adjacent provinces.
6. Most of the province, with the exception of that part in Tennessee and Alabama, is highly dissected, andits average slope is higher than any other province. The topography north of Tennessee is a "plateau" only in the sense that the hilltopshave similar elevations, suggesting aformer flat surface. Near the eastern margin, the plateau is so dissected that the topography commonly is referred to as "mountains" (Thornbury, 1965).

• Topography: The Appalachian Plateau Province in the Southern Appalachians has four sections: the Allegheny Mountains, the Allegheny Plateau, the Cumberland Mountains, and the Cumberland Plateau.
• Regolith: Generally, residuum on top of the sandstone in the Appalachian PlateauProvince is quite thin, often less than a meter thick, and overlies hard rock.
• Soil: Soils in the Appalachian Plateau Province are mainly Ultisols (Hapludults, Fragiudults, and Ochraquults) and Inceptisols (chiefly Dystrochrepts).
• Mass Wasting:Among other Appalachian provinces, the Appalachian Plateau has the greatest abundance of conspicuous slope failures.
• Karst Landscape: The near-surface rocks in this province being mainly clastics, karst topography is not widely distributed. However, cave entrances along the escarpments, owing to the cropping out of carbonate units are common.
• Streams: The drainage pattern of the Cumberland Plateau is heavily dendritic ( i.e. randomly branched). Various other types of patterns occur in some places, and commonly either modify or markedly modify the general pattern.
  

Soils are mainly Ultisols (Hapludults, Fragiudults, and Ochraquults) and Inceptisols (chiefly Dystrochrepts). However, the northwestern part of the province has extensive Alfisols(Hapludalfs and Fragiudalfs) due to lower mean annual precipitation (Buol, 1973). At the higher elevations, on stable upland surfaces, limited areas of Spodosols have developed, especially over quartz-sandstone parent materials that support coniferous forest covers.

Earth Flow Terrain

Among Appalachian provinces, the Appalachian Plateau has the greatest abundance of conspicuous slope failures. Here, such failures have ahigh frequency, low magnitude compared to thethose typical of the Blue Ridge and Ridge and Valley provinces. Most slope failures on the Appalachian Plateau are earthflows and slump-earth flows, but earth slumps, debris slides, debris flows, topples and rockfalls are also common. Failuresare most abundantin the region underlain by subhorizontal cyclothemic sedimentary rocks (shale, mudstone, claystone, siltstone, sandstone, and coal) of Pennsylvanian to Permian age.

Slump Earth Flow

Most slope failures on the Plateau occur in colluvium and weathered fine-grained rocks. Different parts of the Plateau are characterized by distinct kinds of slope failures. For example, southeastern Ohio, central and western West Virginia, and northeastern Kentucky commonly have slow-moving earth flows in addition to slump-earthflows and slumps. Large parts of eastern Kentucky and southwestern West Virginia are characterized by debris slides and flows because of steep slopes and large amounts of coarse clastic rock material.

Rock type and structure are important determinants of failure mechanisms, sizes, and rates. Several argillaceous rocks of the Appalachian Plateau are particularly weak and prone to failure. For example, the red mudstones of the Conemaugh and Monongahela formations and the Permian Dunkard Group account for nearly 95 percent of slope failures mapped in eastern Ohio, and for the majority of failures in West Virginia. Instability of redbeds stems from their fine particle size, their tendency to contain swelling clays, and high-angle slickensided surfaces that reduce rock strength and enhance permeability and weathering. Gray and green shales and underclays in the Pennsylvanian-Permian rocks are also relatively weak.

The drainage pattern of the Cumberland Plateau is grossly dendritic (heavily branched) but, various other patterns occur.The latterinclude angulate, rectangular, trellis, radial, and annular patterns, which reflect joint sets, small and large folds, and broad, inconspicuous domes. Linear drainage lines are also locally common.

(Mayfield 1981)reported that mean annual floods of Cumberland Plateau streams are much higher per unit area thanthose ofother Tennessee streams. He attributed this pattern to the low permeability of Plateau bedrock and the high permeability of the thin soils andwhich allow rapid throughflow to stream channels. Base flows are correspondingly low, (and streams arevery likely to run dry in the summer). Streams with highest flood peaks drain areas underlainwith conglomeratie bedrock.

The course of the Tennessee River on the Cumberland Plateau is striking. After flowing in valleys from Virginia to almost the Tennessee-Georgia border, it abruptly cuts westward across the anticlinal Walden Ridge, producing the Tennessee River gorge. After cutting through the ridge, the Tennessee enters the Sequatchie Valley and follows it for about 120 km before abruptly turning northwest again into the Cumberland Plateau, and thence into the Interior Low Plateau, where it eventually turns north and joins the Ohio River. Geomorphologists have argued for more than a century about the possibility that the Tennessee once continued its southwestwardflow fromthe Ridge and Valley province all the way to the Gulf of Mexico, or perhaps that it continued itsflow down the Sequatchie Valley to the Gulf. No definitive evidence has been uncovered, however.

Karst topography, which is characterized by limestone rocks and caves,is not widely distributed. However, near the escarpments of the Cumberland Plateau, evidence of solution of carbonates beneath clastic rocks becomes apparent. In a few places, deep sinkholes have formed with walls of clastic rock, apparently resulting from collapse of underlying voids formed bydissolving of the underlying carbonates. Even more common are cave entrances along the escarpments, owing to the cropping out of carbonate units. These entrances may be abundant, even though sinkholes in the same area may be rare (for example see Shofer and others 2001). Crawford (1984) has propounded a model for retreat of the escarpments in which conduit caves form by subterranean invasion of surface streams resulting from faster chemical erosion of underlying carbonates. As these caves enlarge, the escarpment is eroded from within and retreats.

Residuum

Residuum on the southern part of the Cumberland Plateau, where Pennsylvanian Pottsville Sandstone forms the caprock,varies greatly from place to place. Generally, residuum on top of the sandstone is quite thin, often less than a meter, and overlies hard rock. In some locations, however, perhaps owing to weaker cement, the sandstone is decomposed to a depth of many feet, forming an equivolumetric residuum analogous to saprolite on crystalline rocks. In the Cumberland Mountains and the Allegheny Mountains, residuum is generally formed from sandstone and is thin.On the Unglaciated Allegheny Plateau, large areas of shale outcrops occur, and shale residuum is common. Some shales, particularly in parts of Kentucky and West Virginia, are high in swelling clay and are highly prone to landsliding (see mass wasting).

Colluvium

Schematic diagram showing
development of colluvium on
benched slopes in Appalachian
Plateau

In those parts of the Plateau where sandstone caps interfluves, abundant boulder colluvium occurs on escarpments and the walls of gorges. Thicknesses mayreach 10 m on footslopes. The clasts in the colluvium are chiefly sandstone and the fines often include large amounts of material derived from shales that underlie the sandstone cap rocks. In other parts of the Plateau where shales are dominant, fine-grained colluvium is the rule, much of it prone to earthflows. Colluvium generated from shale residuum generally has mechanical properties very similar to those of the residuum.The figureillustrates how colluvium develops on the benched hillslopes typical of this province. Colluvium tends to be generated by weathering higher on the slope, and then to accumulate farther downslope on benches and in shallow downslope-trending swales. Thickness may be as great as 6 ft. Contemporary failure rates indicate that this colluvium is being produced by present-day weathering and slope failure (Jacobson, 1985).

Other colluvial deposits, however, appear to be relics, perhaps from the last interval of glacial climates. In shale-dominated landscapes of the Appalachian Plateau small streamless hollows to be filled with remnant colluvium as thick as 45 ft. This colluvium does not appear to be moving now, and may have been placed by solifluction during the ice age. These deposits are often dissected by more recent drainage.

Physiographic provinces

The portion of the Appalachian Plateauin the Southern Appalachians can be subdivided into four sections:

1. The Allegheny Mountains Section is at the northeastern margin of the Plateau. It differs from the Unglaciated Allegheny Plateau to the west in that dissection here is so advanced that the topography no longer resembles a plateau, even a dissected one. It also differs in that mild folding and erosion on anticlines and synclines have produced a topography with linear ridges. The Allegheny Front Escarpment lies along the eastern margin of this section, rising 300 m above the valley floors of the adjacent Ridge and Valley Province.
2. The Unglaciated Allegheny Plateau Section (also referred to as the Kanawha Appalachian Plateau) is the dissected middle portion of the Plateau. Its stratigraphy differs from that of the Allegheny Mountains in that its more abundant shalesresult in slopes that tend to be somewhat smoother than those that occur where sandstone is more common. Altitudes are lowest on the western side of the section in Ohio and Kentucky, where they average 365 to 425 m. From here, they increase eastward and northward, exceeding 1,220 m in West Virginia. Here, the New River Gorge, with the river level lying 600 m below the plateau surface, the most spectacular gorge in the Eastern United States.

Elevation Map of Appalachian Plateau Province
3. The Cumberland Mountain Section represents the southern counterpart of the Allegheny Mountains Section. It occupies a strip about 240 km long and 40 km wide in Virginia, Kentucky, and Tennessee. Its geology is dominated by the Cumberland thrust block, which is 200 km long and 40 km wide, and lies about equally in the States of Virginia, Kentucky, and Tennessee. The block is bounded by four faults: a thrust fault (Pine Mountain) on the northwest, another thrust fault (Hunter Valley-Wallen) on the southeast, and two tear faults on the southwest and northeast. The Cumberland thrust block is divided lengthwise into the Middlesboro syncline on the northwest and the Powell Valley anticline on the southeast; the former is in the Appalachian Plateau and the latter is in the Ridge and Valley Province. The Cumberland Mountain Section is higher than the adjacent Cumberland Plateau because the thrust brought resistant rock (Pottsville) to the surface at a relatively high elevation. An anomalous topographic feature in the Middlesboro syncline is the Middlesboro topographic basin, which has been recognized as the product of a meteorite impact.
   
   Another topographic feature of this section is Cumberland Gap, at the intersection of Virginia, Tennessee, and Kentucky. The wind gap is 180 m deep in the otherwise even-crested Cumberland Mountain. One interpretation is that this wind gap was once a water gap, with drainage through it to the south (Thornbury, 1965).
4. The Cumberland Plateau Section is in a sense the southern counterpart of the Unglaciated Allegheny Plateau Section, but it is much less dissected, and over much of its area, particularly in the southern part, is a true plateau. This difference probably stems from a higher percentage of resistant rocks. The Cumberland Plateau is separated from the Ridge and Valley Province by the eastern Cumberland escarpment, and from the Interior Low Plateau by the western Cumberland escarpment. The eastern escarpment, owing to a fairly steep southeasterly dip of the rocks, is relatively linear. Because of its near-horizontal dip the western escarpment is quite irregular. The deep canyons that penetrate the plateau, particularly on its western side are, locally called "gulfs". From Tennessee to central Alabama the anticline is asymmetrical. It is being overturned to the west and broken by a thrust fault over much of its length. It is included in the Appalachian Plateau rather than the Ridge and Valley because it is separated from the latter by Walden Ridge, part of the Plateau.
   

The Blue Ridge province is divided into two subprovinces, the

Physiographic provinces

Northern Blue Ridge and the Southern Blue Ridge. The Northern Blue Ridge lies north of the Roanoke River and is a narrow range of high mountains that is 395 km long but nowhere exceeds 22 km in width. In its narrowest part it is a single ridge that stands about 365 m above the Great Valley of the Ridge and Valley Province and about 610 m above the Piedmont Lowlands on the east. It is underlain by a sequence of Precambrian and Cambrian rocks that form the northwest limb of the Blue Ridge anticlinorium (Espenshade, 1970). This sequence consists largely of resistant rocks. Only three rock units support the crest of the range: (1) a complex assemblage of medium to coarse granitoid rocks, of which hypersthene granodiorite (Pedlar Formation) is the most resistant; (2) a metavolcanic unit, the Catoctin Formation; and (3) a thick series of quartzite, arkose, and phyllite called the Chilhowee Group, which is early Cambrian in age. The topography of the Northern Blue Ridge is largely due to rock resistance and width of outcrop lithology, howeverthe average altitude of the mountains north of the Potomac River is little more than half that of its southeastern part. Despite similar lithology. This decline may be due simply to less uplift in that region (Hack, 1982).

The remaining discussion in this section willcover only the Southern Blue Ridge Province.

• Topography: The Southern Blue Ridge Province extends from the Roanoke River southwestward into north Georgia.
• Regolith: Although thick saprolite occurs in the Blue Ridge, it generally is not as prominent as in the Piedmont Province, both because it tends to be thinner than in the Piedmont and because surfaces in the Blue Ridge are commonly covered by colluvium.
• Mass Wasting: The most common mass-wasting process in the Blue Ridge is probably downslope movement of colluvium and residuum induced by wind throw of trees.
• Soil: The dominant soil order in the Blue Ridge Province is the Inceptisol. This order consists of relatively young soils that lack horizonswhere illuvial clay has accumulated.
• Streams: Because of the high relief, streams in the Blue Ridge tend to have steep slopes. The erosive power provided by such slopes, together with the presence of generally hard bedrock, have produced many gorges.

Debris Flow Chute

The most common mass-wasting process in the Blue Ridge is probably downslope movement of colluvium and residuum induced by windthrow of trees. Slopes are steep and heavily forested. Although disturbed material may only move a few feet in an event, the process is widespread and continual, and so may accomplish more erosion than any other mass-wasting process.

Among rapid mass-wasting processes, debris flows appear to be by far the most common in the Blue Ridge. They seem to occur much more frequently there than in other Appalachian provinces. This abundance may stem in part from the greater permeability of regolith derived from crystalline rocks on steep slopes, relative to the regolith in other provinces. In contrast to the fine-grained colluvium derived from shales that is common on the Appalachian Plateau, for example, this colluvium may be very insensitive to the prolonged, slow rainfall that commonly sets off landslides on the Plateau. Blue Ridge colluvium issensitive to rainfall that is intense enough to infiltrate the soil. The large number of debris slides and flows in the Blue Ridge may reflect the intense rains thatoccur in the Province. The susceptibility of crystalline rocks to saprolitization, which provides an abundant source of hillslope debris for slides, may be another contributing factor. Recurrence intervals for flows at a given location probably range from hundreds to thousands of years. Debris flows usually start as slides that move down "chutes"into river valleys. Typical chute lengths are 50-300 m, with widths of 8-24 m. Thickness of slide masses ranges from 1 to 6 m. Slides commonly occur in troughlike depressions down hollows.here, convergence of surface and subsurface drainage produces high pore pressure that lowers shear strength and makes slope failure more likely. Commonly, only a small part of the material sliding down the hill is deposited at the base of the chute. The greater part travels down the valley as a debris flow or is washed away by subsequent flood waters. Where the chute emerges onto a broad valley, however, debris fans may result. Such fans maycontain boulders6-10 feetin diameter.

debris-flow fan

Large areas of bouldery colluvium occur along the bases of mountains in many parts of the Blue Ridge. The origin of these unsorted, unstratified deposits has been attributed to solifluction in ice-age climates. The similarity of the colluvium to the material found in the debris fans, however, suggests that a large part of the colluvium was probably placed by debris slides and flows during intense rainstorms.

Debris Flow Fans

The most studied surface deposits in the Blue Ridge Province are along mountain footslopes. Theyoccur either as a continuous apron along the base of the mountains or, more commonly, as alluvial fans in gently sloping embayments of the mountain fronts known in some places as "coves". The fans range in area from several acres to several square miles. Larger fans average 15 to 20 m in thickness, and seldom exceed 30 m. Some of the fan material is alluvium, particularly in the distal part of large fans,