Pre-Visit
Activities : Sculpting South Carolina
Background
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Key
Points
Detailed
Information Communities
are defined by the group of organisms that share an environment.
The environment shared by the community can be as small
as a rotten log or as large as a continent. Communities
only contain biotic (living) things but they are
heavily determined by the abiotic (nonliving) things
around them. Topography, climate, soil types, water quality
and many other factors can all determine what type of
community develops in that environment. South
Carolina is divided into five separate geographic regions,
each with its own unique topography. These regions are
the Mountains, the Piedmont, the Sandhills, the Coastal
Plain and the Coast. Though some animals can be found
in all five regions, each region contains unique communities
determined by the physical features of the region. For
example, the American alligator, found throughout the
Coastal Plain of South Carolina, is not found in the Mountain
region. This animal is adapted for living in large pools
of standing water, such as swamps and ponds. Because of
the sharp relief in the Mountains, water in most places
is always flowing and a swamp habitat cannot exist. Also,
the climate is often too cool for the cold-blooded alligator.
Conversely, the trout that are abundant in the cool, shallow,
fast-moving streams of the Mountains are not able to survive
in the warm, slow-moving, murky waters of the blackwater
swamps of the Coastal Plain. Spartina grass, which dominates
the saltmarsh because of its tolerance to saltwater, cannot
compete in freshwater habitats with other plants and so
is not found out of the brackish waters of the Coast habitat.
In all these cases, the abiotic factors of the regions
determine which organisms can live there and thus what
communities develop there. Below
are excerpts from the excellent book South Carolina:
The Making of a Landscape by Charles F. Kovacik and
John J. Winberry. In these excerpts you can find just
about everything you could possibly want to know about
the abiotic factors found in each region of South Carolina
as well as much about the biotic communities that develop
there. From:
Kovacik, C. and J. Winberry. South Carolina the Making
of a Landscape, pp. 13-48. University of South Carolina
Press, (1987). South
Carolina extends 225 mi (360 km) north to south and 285
mi (459 km) east to west. With a 31,113-sq-mi
(80, 583-sq-km) area, it is the smallest of the Deep South
states (the others are Virginia, North Carolina, Georgia,
Alabama, Mississippi, and Louisiana) and ranks only fortieth
in size among the 50 states of the Union. Its small area
is deceptive because South Carolina extends literally
from the mountains to the sea, and its physical geography
varies considerably in form and origin. In this and the
next chapter, we will focus on that diversity as we look
at the state’s landforms, climate, soils, and vegetation. Landform
Regions Blue
Ridge Mountains The rocks
that form the Blue Ridge are predominantly crystalline schists
and gneisses. These metamorphic rocks were formed hundreds
of millions of years ago by the subjection of igneous and
sedimentary rocks to the tremendous heat and pressure associated
with mountain building. Most are very resistant to erosion,
and this accounts for the steep slopes and narrow stream valleys
that form the area’s rugged topography. South
Carolina’s mountains certainly are not as impressive as those
in Alaska and western North America, which soar to altitudes
of 15,000 to 20,000 ft (4,572 to 6,096 m) with steep walls
and angular peaks. Not only are they lower, but they appear
more rounded in form and worn down. One reason for this is
that the Rockies, Sierra Nevadas, and Cascades were uplifted
only about 100 million years ago, whereas the Blue Ridge was
formed more than 350 million years ago. As a result, the forces
of erosion have been at work much longer in the Blue Ridge,
and the effect is very evident. Another factor relates to
climate. Moderate temperatures and greater precipitation in
the eastern part of the country have hastened weathering and
erosion that have tended to round off the mountains by a process
called "creep," the gradual movement of material
downhill. Piedmont The
Piedmont and Blue Ridge have a complex geologic history.
The basement rock of both regions is an estimated 1 billion
to 1.3 billion years old. Current explanations for the
formation of the Blue Ridge and Piedmont rely on concepts
of continental drift and global tectonics, and these new
theories have invalidated many of the traditional interpretations
of mountain building. The rock types are primarily metamorphic,
mainly schists, gneisses, and slates, with some granite
igneous rocks where intrusive activity took place. Metamorphism,
the tremendous heat and pressure that transformed sedimentary
and igneous rocks into the crystalline schists and gneisses
that characterize the Blue Ridge and Piedmont today,
occurred a number of times as a result of major continental
movements. During
the late Precambrian, some 600 million years ago, what
is now the Piedmont existed as a continental fragment,
an island off the coast of the proto-North American continent.
But about 470 million years ago this island joined North
America in a collision that began the formation of the
Blue Ridge Mountains. Metamorphism recurred when the proto-North
American continent, whose leading edge was the Piedmont,
continued to drift eastward and collided with northwest
Africa to form the massive ancient continent of Pangaea
about 350 million years ago. The continents began to separate
some 225 million years ago, and present-day North America
began to take shape as the landmass drifted westward and
northward to its present location. Another
process going on about the same time, which complicated
matters, was intrusive activity. Magma, the molten material
below the earth’s crust, can move toward the surface of
the earth in response to pressure and heat. In the South
Carolina Piedmont, it did not reach the surface but instead
moved between large and small cracks and joints in the
existing stata and filled large cavity areas, where it
eventually cooled to form isolated granitic plutons that
are the foci of the state’s granite quaries. These forces
of metamorphism and intrusion soon settled down, and running
water became the major agent of earth sculpture. Streams
have flowed across the region for millions of years, removing
material and cutting into the land to create the forms
we see today. Although
both the Blue Ridge and Piedmont have a similar geologic
history and are underlain by basically the same rock types,
the two are differentiated by topography, elevation, and
relief. The Blue Ridge is characteristically rugged with
steep-sided, almost V-shaped stream valleys separated
by narrow ridge tops. Streams are short and fast flowing,
with clear water, many rapids and waterfalls and few tributaries.
The
Piedmont, on the other hand, has a more rolling, hilly
topography. Its river valleys, although quite
steep walled in some cases, usually are sloped more gently
and are much wider. Piedmont rivers are long, have many
tributaries, and their waters are discolored by a heavy
sediment load. The valleys are separated by broad upland
areas, or interfluves, whose elevations do not vary significantly
within local areas and whose relief is much less than
that of the mountains. A typical Piedmont landscape may
be seen along U.S. route 321 north from Columbia and along
U.S. Route 21 north of Ridgeway. In addition, many road
cuts reveal the process of soil formation. One
interesting feature found in the Piedmont landscape is
the monadnock, or inselberg. Looking like a small isolated
mountain that stands above the surrounding uplands, a
monadnock is a residual feature that is formed because
the rock of the monadnock is more resistant to erosion
than the rock surrounding it; monadnocks frequently are
of granite. Perhaps the most well known is Stone Mountain,
Georgia, but the best examples in South Carolina are Paris
Mountain and Glassy Mountain near Greenville, King’s Mountain
east of Blacksburg, and Table Rock Mountain north of Pickens. Most monadnocks in South Carolina occur within
20 mi (32 km) of the Blue Ridge and all are within 100
mi (161 km). Some were probably spurs or extensions of
the main ridge that were separated from it by stream erosion;
the common rock material and similar trend of structure
support such an interpretation. Other monadnocks are of
granitic rocks and sometimes quartzite that formed beneath
the surface of the original landscape. As the overlying
material eroded, these structures were exposed. Their
more-resistant composition retarded erosion, and they
became prominent as the surrounding land surface was worn
down more rapidly. Commonly, erosion of these features
is in the form of exfoliation, and slabs of granite are
scattered on their lower slopes. Sandhills The
Sandhills overlap what is called the Fall Line, which
runs northeast-southwest through the Midlands and separates
the Piedmont and Coastal Plain. Along the Fall Line the
resistant crystalline rocks of the Piedmont abut the more
easily eroded sedimentary rocks of the Coastal Plain.
This difference in resistance to erosion results in rock
outcrops and many rapids that may extend more than a mile
(1.6 km) along some river course. The exact position of
the Fall Line is difficult to define because some rivers
have cut through the sedimentary into the underlying crystalline
rock, and rapids can shift locations during periods of
high and low water. Many geographers, therefore, feel
that the Fall Line is a misnomer and prefer Fall Zone
as a more accurate term. We
usually associate sand with ocean beaches, but the Atlantic
is over 100 mi (161 km) away from the Sandhills. Millions
of years ago, however, this was not the case. As late
as the Eocene, about 55 million years ago, the sea covered
a large portion of eastern and southern South Carolina,
and its shoreline corresponded to the present-day Sandhills.
Marine sediments were laid down beneath the ocean to form
the near-horizontal strata of sedimentary rocks that today
constitute the Coastal Plain. The
weathering and erosion of the Piedmont and the Blue Ridge
provided the clays and sand that were carried by rivers
and deposited at their mouths. The ocean waves reworked
these materials to form beaches and sand dunes along this
ancient coastline, just as the oceans are forming shore-zone
features along South Carolina’s present-day coast. The
sea began retreating about 40 million years ago to approximately
its present location. Examples of old dunal features may
be seen along State Route 261 south of Wedgefield and
north of Pinewood in the Manchester State Forest. In several
areas the road cuts through the top of old beach ridges;
along both sides of the road, these ridges appear in profile
as a series of small hills. Coastal
Plain The
Coast Plain has a geologic history that is much less complicated
than that of the Blue Ridge and Piedmont. The sedimentary
rocks that underlie it are made up of muds, silts, sands,
and other substances of marine origin. After deposition,
these materials were consolidated by compaction and cementation
to form shales, sandstones, conglomerates, and coquinas.
Over the tens of millions of years during which Coastal
Plain sedimentary rocks were laid down, they formed a
series of horizontal layers. Because the underlying crystalline
basement structure slopes at a steep angle toward the
coast, the sedimentary layer is only a few feet thick
at the Fall Zone, but attains a thickness of about 3,500
ft (1,067 m) at the coastline. The oldest surface rocks
in the Coastal Plain are found nearest to the Piedmont
margin, and the youngest occur adjacent to the coast. This
landform region can be divided into the Inner Coastal
Plain and the Outer Coastal Plain. The topography of the
Inner Coastal Plain is rolling and hilly and is very difficult,
in most cases, to differentiate from the topography of
the Sandhills and the lower Piedmont. Elevations
range from about 300 ft (91m) near the Sandhills to 220
ft (67 m) at the Citronelle Escarpment (Orangeburg Scarp).
Some 20 to 30 million years ago, this terrace marked a
temporary shoreline as the ocean gradually retreated to
its position. Southeast of the escarpment lies the Outer
Coastal Plain, whose topography is flatter and almost
featureless. The land slopes almost imperceptibly towards
sea level at the coast in a series of 10 broken terraces
formed by marine and fluvial processes. Among the sediments
that formed beneath this ancient ocean are the phosphate
beds that extend through the Outer Coastal Plain. Formed
by insoluble phosphate material and marine fossils, these
deposits became the focus of the state’s phosphate industry
after the War Between the States and continued to be mined
into the early twentieth century. Despite
its relative flatness, the Outer Coastal Plain is not without
features. The sea withdrew initially from the Sandhills
and then from the Citronelle Escarpment, but during the
2-million-year Pleistocene Epoch sea level rose and fell
in response to advances and retreats of the glaciers.
The glaciers themselves did not reach into South Carolina,
extending only about as far south as the Ohio River, but
they did affect the state’s physical geography. As they
formed and grew, these continental sheets of ice locked
up great quantities of water, and sea level fell as much
as 450 ft (137 m) below what it is today, exposing South
Carolina’s continental shelf up to 50 mi (80 km) beyond
the present-day coastline. When the glaciers melted, water
was returned to the ocean, and sea level was even higher
than it presently stands, reaching perhaps as far as 60
mi (97 km) inland of the modern coastline. This advance
and retreat of the ocean across the Coastal Plain formed
a number of temporary shorelines, which persist today
as terraces. Beside
the terraces, various other coastal features were formed
as the ocean moved inland and then stabilized with each
retreat of the glaciers. But as the glaciers renewed their
growth, the sea withdrew once more; and the former shorelines
and their beach ridges, ocean terraces, and deltas were
abandoned far inland. Some of these remnant features have
diverted rivers and streams from a straight course to
the sea. The abrupt northeastward turn of the Black River
is due to old beach ridges, whereas the sharp southward
bend in the Edisto River at Givhan’s Ferry apparently
results from its following an old distributary channel
in an ancient delta formation. In
addition to their common shape, the bays’ axes regularly
parallel each other; in South Carolina they all are oriented
in a northwest-southeast direction. A sandy ridge may
encircle a bay but commonly forms only the southeastern
rim. These peculiar characteristics have led to considerable
speculation about the bay’s origin. Several theories focus
on two major ideas: Either some single catastrophic event
occurred that formed the bays, or the bays are the result
of ongoing processes that are observable today. The most
popular of the catastrophic theories is that the depressions
actually are meteorite scars, left by a huge meteor that,
just prior to striking the earth, broke apart into hundreds
of thousands of pieces that dug depressions into the Coastal
Plain surface. Pieces of a meteor hitting the earth from
a northwesterly direction could explain the oblong shape
and parallel arrangement of the bays. It is an interesting
idea, but no meteor remains have been found near the bays,
and measurement of the magnetism that normally is associated
with such remains has given ambiguous results. A
second theory is based on studies of similarly shaped
lakes in other parts of the world and on laboratory models.
It argues that the peculiar shape of the bays results
from prevailing winds that cause basins to form ovals
whose axes are perpendicular to the wind direction. South
Carolina’s southwesterly winds would, therefore, form
bays with northwest-southeast axes. The buildup of sand
on the southeastern rim would result from the very strong
northwesterly winds associated with infrequent but intense
winter storms. Needless to say, a fully accepted explanation
for the origin of Carolina bays has not yet come along. Although
seismic activity characterizes almost the entire state,
the most sever episode occurred in the Coastal Plain-the
famous Charleston earthquake of August 31, 1886, which
probably ranked a 10 on the Mercalli 12-point scale of
earthquake intensity. The epicenter of the Charleston
quake lay between the city and Summerville, about 20 mi
(32 km) to the northwest. The shocks lasted more than
four days, caused damage estimated at about $23 million,
and left 60 dead. Tremors were felt as far west as the
Mississippi River. Many rural people who experienced the
quake developed a folk calendar around its occurrence,
referring to events as so many years before or after the
"Shake." Some
300 aftershocks were recorded during the 35 years after
1886, and mild earth tremors continue to characterize
the Piedmont. Over the last decade, seismic activity again
has occurred in the Coastal Plain. Studies have indicated
the existence of a major South Carolina-Georgia seismic
zone that runs northwest-southeast for more than 300 mi
(483 km) across the entire state. Among the faults that
form it is the northeast- southwest trending Woodstock
Fault near Charleston. No other earthquake in the state
has equaled the severity of the one at Charleston, and
few seismologists predict a recurrence any time soon.
Nevertheless, the history of the Charleston episode has
resulted in the classification of eastern South Carolina
as a major earthquake risk area. Old Charleston houses
bear scars of the experience. After the earthquake, long
rods were inserted between the opposite walls of a house
to brace them and were held in place by plates placed
on the outside of the walls. The plates are visible on
these houses today. A
feel for the Coastal Plain topography may be acquired
along any highway toward or along the coast. A fine overview
of the Outer Coastal Plan may be had from U.S. Route 378,
east of Shaw Air Force Base, just outside Sumter. Here,
from the Citronelle Escarpment, the broad, flat Outer
Coastal Plain stretches off to the coast. The rock outcrops
and rapids marking the Fall Zone are evident on the Broad
and Saluda rivers Columbia. An excellent example of a
Carolina bay is Woods Bay State Park, just north of Turbeville
in Clarendon County. Other bays, both cleared and uncleared,
are found in its vicinity. Coast The
Santee delta forms the second subdivision of the Coastal
Zone. It is about 20 mi (32 km) wide and is the largest
deltaic complex on the east coast. It is a cuspate, or
pointed, delta, but is has suffered severe erosion over
the last 40 years, retreating almost 900 ft (274 m) at
certain locations. This is largely because of the decreased
sediment load in the Santee River that has resulted from
the completion of Lakes Marion and Moultrie in 1942 and
the diversion of the Santee’s waters into the Cooper River
and Charleston Harbor, as well as the creation of other
reservoirs on the Piedmont tributaries of the Santee system.
As a stream enters one of these lakes, the velocity of
its flow drops sharply, and this reduces its ability to
carry sediment. The reservoirs, therefore, accumulate
much of the alluvial material that otherwise would have
been deposited on the coast. South
of the Santee delta lies the Sea Island complex that extends
for more than 100 mi (160 km) to the Savannah River and
into Georgia. There is considerable diversity among these
islands in size, origin, and development. Some, such as
Kiawah, Fripp, and Hilton Head, have been developed commercially,
whereas others, including Bull, Hunting, and Daufuskie,
remain in a more pristine state. North of the Edisto River,
extensive marsh areas separate the islands from the mainland,
but toward the south the islands are separated from the
mainland and from each other by embayments, such as Port
Royal Sound and St. Helena Sound; numerous tidal inlets;
and extensive interior waterways. The
Sea Island province comprises two types of islands: erosion
remnant islands and active barrier islands. For example,
St. Helena Island, off Beaufort, is inland from the ocean
and is classified as an erosion remnant. This means that
it was at once time part of the mainland. But as seal
level declined during the glacial advances of the Pleistocene
Epoch, streams began cutting down behind it to from river
valleys. As the ocean returned at the end of the Ice Age,
about 10,000 years, these river valleys were flooded,
and St. Helena and similar areas became islands. Hunting
and Fripp are right on the ocean and are referred to as
barrier or beach ridge islands. They are anchored by beach
ridges and sand dune complexes, and, in contrast to the
erosion remnant islands, they are dynamic and constantly
changing. The origin of barrier islands has been much
debated. The classic theory explains their formation from
offshore sandbars built up by wave action, but a new theory
based on emergence and submergence of the coast during
the Pleistocene Epoch has been offered. As sea level declined
during the glacial period and the ocean retreated from
the coast, dunes were built along the new coastline, and
the old dunes were left inland. But as the ocean returned
and inundated the former dune ridges, parts of them remained
above water to become the cores of coastal islands. Wind
and wave action built additional sand dunes on them, and
the barrier islands developed. These
islands are still subject to active modification by marine
processes. Waves and tidal action constantly alter their
beaches; storms bring marked changes, and the prevailing
currents slowly wash material away and transform their
shapes. Generally,
the northern ends of the islands experience erosion, whereas
deposition occurs on the southern ends. This erosion is
a natural process that will continue to occur, but people
seem unaware of this as they vigorously but ineffectively
try to arrest the changes with jetties, groins, seawalls,
and beach nourishment programs. A very limited success
sometimes is realized, but it must be emphasized that
the coast is naturally a dynamic area and that barrier
islands are always subject to change. The
Barrier Islands Act, initiated by the federal government
in 1983, removed undeveloped barrier islands from federal
flood insurance programs and ended subsidies for the construction
of roads and sewer systems on them. The act affected 13
locations in the Sea Islands of South Carolina (Waites
Island complex, Litchfield Beach, Pawley’s Inlet, Debidue
Beach, Dewees Island, Morris Island complex, Bird Key
complex, Captain Sam’s Inlet, Edistor complex, Otter Island,
Harbor Island, St. Phillips Island, and Daufuskie Island)
and will make their development more difficult. Though
opposed initially by some groups, this action is seen
now as logical recognition of the peculiarities of barrier
islands and their susceptibility to sudden and pronounced
changes. The Sea Island landscape may be seen along various
coast roads, especially U.S. Route 21 north and south
of Beaufort and U.S. Route 278 approaching Hilton Head
Island. A spectacular view of a barrier island may be
had from atop the old lighthouse in the Hunting Island
State Park. Rivers
and Streams South
Carolina is drained by three major river systems, the
Pee Dee, the Santee, and the Savannah, as well as a number
of smaller streams. These generally follow the
topographic slope of land from northwest to southeast
across the state. The headwaters of the major rivers form
on the slopes of the Blue Ridge in North Carolina, east
of the Appalachian Divide. Smaller rivers and streams,
such as the Combahee, Edisto, and Ashley, form at the
edge of the Sandhills are situated entirely within the
state. In contrast to the large river systems draining
the Piedmont, whose waters are colored yellow and red
by heavy loads of silt and clay, streams originating in
the Coastal Plain are called "black-water rivers."
They transport very little sediment, and their dark color
comes from a high tannic-acid content resulting from the
decomposition of swamp hardwoods and their leaves. A characteristic
black-water river is the Black River that heads in Lee
County and flows through Williamsburg and Georgetown counties. We
have already discussed the characteristics of streams
in the Blue Ridge and Piedmont. Rivers in the Coastal
Plain typically meander and form wide, flat floodplains.
As a meander grows it develops an increasingly narrow
neck of land that the river will cut through during periods
of high water. This forms a new channel, and the old channel
becomes a remnant lake known as a cut-off, or oxbow, lake.
This process allows the widening of the floodplain as
new channels form to cut more deeply into the adjacent
bluffs. A good example of a meander and cut-off lake is
Bates Old River, in the Congaree floodplain, which may
be seen from the U.S. Highway 601 causeway, just south
of Wateree Store. Large
rivers with considerable flow and carrying a quantity
of sediment, such as the Santee, usually form deltas through
the buildup of alluvial material at their mouths. On the
other hand, smaller rivers carry little sediment and have
less potential for delta formation; estuaries or deep
embayments usually develop where they enter the ocean.
Examples of these include Charleston Harbor, St. Helena
Sound, and the Port Royal Sound, all of which form the
mouths of black-water rivers. Of
South Carolina’s three major river systems, the largest
is the Santee. It and its tributaries in the Piedmont
and Blue Ridge drain nearly 40 percent of the state’s
total area. The Great Pee Dee River winds 197 mi (317
km) from the North Carolina line to the Atlantic Ocean,
and its system drains the eastern quarter of the state.
The Savannah River drains about 15 percent of South Carolina’s
total area. The larger part of its basin is in Georgia;
South Carolina’s portion is about 260 mi (418 km) long
but is only 15 to 60 mi (24 to 97 km) wide. A number of
smaller rivers, including the Ashley, Edisto, and Combahee,
form a fourth drainage basin south of the Santee system.
Lying totally within South Carolina and originating at
the edge of the Sandhills, these rivers together drain
about 20 percent of the state’s area. Lakes
and Waterways These
reservoirs were constructed primarily to produce hydroelectric
power, but in one notable instance a successful project
created a serious problem. In the 1930’s construction
began on the two earth-fill dams that formed the 155-sg-mi
(401-sq-km) Lake Marion on the Santee River and the 95-sq-mi
(246-sq-km) Lake Moultrie on the Cooper River. A 7.5-mi-long
(12-km) diversion canal connected the lakes and effectively
directed much of the Santee River’s waters through Lake
Moultrie into the Cooper River. As a result, the flow
in the Cooper River was increased from about 100 to over
15,000 cu ft per sec (from 3 to 425 cu m/sec). This allowed
electric power generation for the Outer Coastal Plain,
but Charleston Harbor, important for shipping and as major
naval base began to experience silting and shoaling, and
the alluvium had to be removed expensive dredging. The
Corps of Engineers determined that this resulted almost
exclusively from the increased flow of fresh water into
the harbor. The fresh water did not mix well with the
salt water and gave rise to upstream density currents
that blocked the movement of sediments out of the harbor
and caused shoaling. To remedy this situation, the Corps
projected a rediversion of the flow from the Cooper River
back into the Santee. This was accomplished by at 12-mi-long
(19-km) rediversion canal from Lake Moultrie, completed
in 1985, that is supposed to return about 80 percent of
the presently diverted flow back into the Santee. Experiences
such as this make us acutely aware of the interrelatedness
of our environment, and we now realize that one action
may affect a number of unintended and unwelcome results.
In an attempt to anticipate such new problems, the National
Ecosystems Team of the U.S. Fish and Wildlife Service
is now studying the potential impact of this rediversion
project on the Santee delta and the adjoining Coastal
Zone. The
waterways of South Carolina offer one of the best examples
of human modification of natural systems. Vegetation and
erosion are subtle indicators of this impact, but the
numerous vast lakes are highly visible. As we consider
the physical setting, we must realize that human activity
remains one of its most important shapers. Climate,
Soils, and Vegetation Climate Precipitation The
convectional rainfall process develops through as a succession
of stages. To begin with, the warm, moist air of a tropical
mass dominates South Carolina’s atmosphere during the
summer. At the same time, the land surface receives intense
solar radiation. As the summer day wears on, the temperature
of the earth’s surface rises, and it begins to warm the
layers of air just above it. This causes convection currents
in the lower atmosphere, and as these updrafts continue
and intensify, the moisture-laden air is lifted to an
elevation at which it cools to the point of condensation.
Cumulus clouds then develop, and continued convectional
uplifts and further cooling create the familiar threatening
thunderhead clouds. The sky grows dark and precipitation
soon follows. Summer weather forecasts usually include
a chance of showers because the conditions necessary for
the development of these convectional systems, their intensity,
and geographical location make them difficult to predict. A
very different precipitation process occurs during the
winter. Called frontal precipitation, it is related to
the movement of warm and cold air masses. In contrast
to the summer thunderstorm, frontal precipitation can
include snow or sleet but usually is a drizzle or a steady
rain that may last for hours. It normally involves no
thunder or lightning and, in the case of cold fronts,
is associated with a sharp drop in temperature. This type
of precipitation may be related to either warm or cold
fronts. Typically, however, frontal precipitation occurs
when a mass of cold air overtakes a warm air mass. Being
denser, the cold air wedges itself beneath the warm air.
As the warm air is forced to rise, it cools, and rainfall
or snowfall results. Because fronts move at different
speeds and air masses vary in intensity, it is difficult
to generalize about the time necessary for this sequence
of events to unfold. Normally, it involved a day or more.
The typical scenario for a cold front starts with the
presence of warmer, moist air, cloudy or partly cloudy
skies, and generally southerly winds. When the front approaches,
the sky becomes grayer as clouds build up and precipitation
begins. As the hours of rain continue, temperatures drop
sharply. Once the cold air mass following the front establishes
itself, the sky clears, cold temperatures prevail, and
northerly winds dominate. Seasonal
Climatic Differences South
Carolina can be affected by warm, moist air from the Gulf
of Mexico, but winter normally is typified by the presence
of cold, dry continental air masses. December, January,
and February, therefore, are the coldest months of the
year. Two to five very cold outbreaks of polar air occur
each year, and they substantially lower temperatures for
several years. The full thrust of most cold fronts is
weakened or deflected by the Blue Ridge Mountains, and
southerly winds often bring in warmer maritime air from
the Caribbean and South Atlantic. Mild winter days are
not common and occasionally can be truly hot. Columbia,
for instance, recorded 84° F (29° C) in January
1970 and again in February 1973. Coastal temperatures
are moderated by the Atlantic Ocean and especially the
warm Gulf Stream, whereas the higher elevations of the
upper Piedmont and Blue Ridge experience significantly
colder temperatures. Snowfall
is rare in the Outer Coastal Plain, occurs at least once
in 9 of 11 winters in Columbia, and is more common in
the upper Piedmont and Blue Ridge. February is statistically
the snow month, and the state’s record snowfall occurred
in February 1973. This once-in-a-century phenomenon
paralyzed South Carolina, but even light snowfalls cause
snarled traffic, closed schools and offices, and a general
holiday spirit. The true scourge of winter, however, is
the ice storm, which causes serious traffic hazards, fallen
trees, power outages, and often severe discomfort to many
South Carolinians. March,
April and May represent a transition from winter temperatures
and precipitation to those of summer. The frequency of
cold fronts declines during the spring as continental
air masses are replaced by warmer maritime air, and more
convectional precipitation occurs. Despite a general warming,
temperatures can vary considerably from year to year.
Columbia recorded 90° F (32° C) in March 1974
and 18° F (-8° C) in March 1975. Spring marks
the beginning of the growing season, or frost-free period,
which is the number of days between the last killing frost
of spring and the first killing frost of fall. The average
length of the growing season varies from just over 290
days, immediately adjacent to the coast in the Sea Islands
near Beaufort and Charleston, to less than 200 days in
the Blue Ridge near Pickens and Walhalla. The
average last spring frost occurs about February 19 in
the Sea Islands and along the coast, during the last week
of March near Columbia, and in last April in the mountains.
This two-month difference between the average last spring
frost on the coast and in the mountains is related to
the moderating effect of the Atlantic Ocean and Gulf Stream
on the immediate coastal area as well as to the higher
elevations of the upper Piedmont and Blue Ridge. Tornadoes
form during all seasons of the year and at all hours of
the day, but about one-third of the annual total is recorded
in April and May. Conditions favorable to the formation
of tornadoes occur when the atmosphere consists of sharp
temperature contrasts between layers of air. These can
develop rapidly when a mass of cold air approaches during
the late afternoon. At that time, surface heating from
solar radiation is at its peak and the lower layers of
air at their warmest. This causes an intense low pressure
to develop, and violent winds, blowing in a counterclockwise
direction, are drawn into it. Tornadoes can be very destructive
and are always dangerous. A series of tornadoes that followed
two separate paths, one across the upper Piedmont from
Anderson to York counties and the other through the Midlands
from Aiken to Florence counties, left 77 people dead and
800 injured on April 30, 1924. Another serious incident
involved 8 or 9 separate tornadoes that touched down in
McCormick, Abbeville, Newberry, Fairfield, and Marlboro
counties in the early evening of March 28, 1984. Twenty-one
people died and 448 were injured, and property damage
was estimated in excess of $100 million. South Carolina
averages about 10 tornadoes a year and has the highest
tornado frequency of any South Atlantic coast state. Summer’s
hot and humid weather prevails from June through August,
and the heat is relatively unbroken. In contrast to winter
patterns, temperatures are about the same across much
of the state, although Blue Ridge locations are noticeably
cooler because of higher elevations (Map 3.4). Strong
solar heating causes daytime temperatures to rise, whereas
nights tend to be humid and warm. The single most important
factor influencing South Carolina’s summer weather is
the Bermuda High, and extremely large high-pressure cell
centered over the Atlantic. The clockwise circulation
around the Bermuda High causes a prevailing southerly
flow of warm and humid maritime tropical air from the
Gulf of Mexico and South Atlantic Ocean into the state
during the summer months. Normally, this steady supply
of moist air, coupled with strong solar heating of the
land surface, provides ideal conditions for the convectional
precipitation. Frequent thunderstorms during these three
months account for 33 percent of the state’s annual rainfall,
making summer the wettest season of the year. The
Bermuda High, however, frequently stalls or becomes stationary
off the coast and tends to block or divert frontal systems
before the reach South Carolina. Because of this and the
presence of the Blue Ridge Mountains, few cold fronts
pass through the state during the summer, and there is
little relief from the high temperatures and humidity.
Furthermore, the stable subsiding air of the Bermuda High
can become so intense that it prevents the convectional
process necessary for cloud development and thunderstorm
activity. When this occurs, host, sunny days prevail,
drought threatens, and the stagnant air exacerbates atmospheric
pollution problems. Sometimes these dry conditions last
for weeks or even months. July is usually Columbia’s wettest
month with a mean of 5.65 in (14.35 cm) of precipitation,
but in 1973 only 0.57 in. (1.45 cm) was recorded. The
sea breeze plays an important role on the coast during
the summer months. During the day, the land absorbs solar
radiation very rapidly, and convection currents begin
to form. The ocean waters, however, maintain a more constant
temperature than does the land surface. The warm air over
the land rises, creating a zone of low pressure, and the
relatively cooler and denser air above the ocean flows
onshore to take its place. This results in a refreshingly
cool breeze off the ocean during late summer afternoons
and evenings. Also, during last summer afternoons while
cumulonimbus clouds, large and fluffy but with a menacing
dark underline, form inland, the sky above the ocean remains
clear. Rain often will fall inland but usually does not
occur on or near the coast, where convectional activity
is suppressed by the cooler, more stable air coming onshore
from the ocean as a result of the sea-breeze effect. Between
September and November, temperatures slowly become cooler,
and the high summer humidity diminishes. Drier continental
air masses become more frequent, and the continued presence
of the Bermuda high also contributes atmospheric stability.
As a result, South Carolina receives only about 20 percent
of its annual precipitation in the fall; October and November
are statistically the two driest months of the year. Nearly
one-half of all fall days are warm and sunny with bright
blue skies, whereas nights are cool to cold. Fall
also marks the end of the growing season. The first freeze
comes earliest in the mountains and latest along the coast.
On the average, it occurs in Walhalla toward the end of
October, in Greenville in early November, and at Charleston
during the first week in December. Because of the drainage
of cold air along the river valleys from the upper Piedmont,
the initial freeze occurs in Columbia as early as the
first week of November. Cool to cold overnight temperatures
result from the nocturnal cooling of the earth’s surface.
Because there is little cloud cover, the earth rapidly
loses the heat it absorbed during the day, and surface
temperatures drop quickly at night. This
rapid nocturnal cooling and the stagnant circulation associated
with the Bermuda High frequently create temperature inversion
that cause fog during the night and early morning. A temperature
inversion occurs when the normal lapse rate-that is, the
pattern of progressively cooler air temperatures with
increasing altitude-is replaced by a situation in which
cooler air is trapped beneath a layer of warmer air. Temperature
inversions often occur on clear, still nights when heat
reradiated from the earth’s surface during the day had
warmed the atmosphere. The cool surface at night chills
the lower layers of the atmosphere, and as the air is
cooled, its water vapor begins to condense and form fog.
The fog typically "burns off" during the morning
as solar radiation heats the earth’s surface. When the
lower layers of air are warmed, normal lapse rate conditions
are reestablished. Similar
to such inversions, but lasting for days in some instances,
are stagnant air conditions related to very stable high-pressure
systems. These are associated during the late fall with
cool air masses that settle over the state. The results
are much like the situations during the summer and early
fall when a stalled Bermuda High dominates the region.
The high pressures, like the Bermuda High, tend to block
advancing frontal systems and can also limit convectional
activity. Skies are clear, and the weather is generally
pleasant. The stable atmospheric conditions that cause
this ideal weather also create a serious potential for
air pollution. Stable air provides little opportunity
for the dispersal of pollutants and traps them over their
point of origin. The frequency of such atmospheric conditions
in Piedmont South Carolina is among the highest of any
region in the eastern part of the country and makes air
pollution a potentially dangerous situation. Special concern
must be given, therefore, to the types of industries that
locate in the Midlands and Piedmont, and awareness of
this potential pollution problem should be an integral
part of any development plan. A
very dangerous climate phenomenon for coastal South Carolina
is the hurricane. Hurricanes are most common in late summer
or early fall and pose the greatest threat in September.
A large tropical storm with surface winds of at least
74 mi per/hr (119 km per hr), a hurricane develops out of
an "easterly wave," a line of low pressure that
moves with the prevailing easterly winds flowing across
the warm tropical waters of the Atlantic and Caribbean.
As the storm forms out of one of these atmospheric disturbances,
its winds converge in a spiraling counterclockwise fashion
around a developing center of low pressure and reach speeds
of up to 200 mi per hr (322 km per hr). These high winds
and great quantities of rainfall can range up to about
400 mi (644 km) in diameter, but at the center of this
intense low pressure is the "eye," an area of
relative calm between 10 and 15 mi (16 o 24 km) in diameter. Part
of the damage along the coast is caused by high winds,
but most death and destruction result from the storm surge,
which raises tides 8 to 15 ft (2 to 5 m) above normal
levels and carries them towards shore at speeds of 50
to 50 mi per hr (80 to 97 km per hr). Tornadoes sometimes
develop out of this system, and torrential rains always
accompany it. The high wind speeds diminish rapidly as
the storm moves inland, but heavy rainfall continues.
The greatest amount of precipitation recorded in a 24-hour
period in South Carolina was associated with the passage
of a hurricane. Soils Soil
Characteristics Texture
is one of the most important characteristics of soils.
It determines the rate at which water drains through particular
soil and the amount of water that it can hold for use
by plants during dry periods. Texture is dependent on
the sizes of particles that make up the soil’s mineral
matter. Normally, these range from sands-the largest particles-through
silts to clays, which are finest particles. Sands allow
water to drain through quickly and provide little moisture
storage, whereas clays, with minimal space between particles,
permit little water to drain through and exhibit maximum
retention. Between these extremes are various combinations
such as sandy clays, silty clays, and loams. Loams provide
ideal textures for cultivation and are made up of 20 percent
or less clay, 30 to 50 percent silt, and the remainder
sand. They are easily cultivated and are characteristically
neither too dry nor too wet for plant growth. Regional
Soil Types Piedmont
soils are dominantly Ultisols, but there are scattered
occurrences of Alfisols, especially in Fairfield, Chester,
and Greenwood counties. The Alfisols also have clayey
subsoils but are brownish to reddish in color and normally
have higher concentrations of calcium, magnesium, potassium,
and other minerals. The topography of the Piedmont provides
for good surface drainage, but internal soil drainage
is relatively poor because the Ultisols and Alfisols are
compact and clayey in texture. As a result, rainfall does
not readily percolate through the soil, and runoff potential
is considerable, creating a high risk of erosion. Overall
suitability for row crops is ranked fair to poor. The
Alfisols are considered adequate for field crops in some
areas, such as broad, relatively flat interfluves of northern
Fairfield, Chester, and Newberry counties. Most of the
Piedmont, however, is devoted to pasture of forest. The
soils of the Sandhills are classified as Entisols, and
their sandy parent material extends down to depths of
80 in. (203 cm). The rolling uplands of the Sandhills
allow good surface drainage; and, as soil texture is mostly
sandy with some areas of loam, internal drainage is rapid
and even excessive. Sandhills soils are generally low
in plant nutrients and organic material because the soil
texture allows rapid leaching. Agriculture in the region
never has been especially prosperous, and most of the
soils have little potential for row crops. Although traditionally
used for woodland, Sandhills soils, with proper management,
can support the successful cultivation of vegetable crops
and peaches. Ultisols
also characterize the Inner Coast Plain, but here their
texture tends to be loamy with good surface and internal
drainage. Well over half the Inner Coastal Plain is forested,
but the good physical qualities of its soils contribute
to its being the state’s major agricultural zone. The
Ultisols in the Outer Coastal Plain, however, suffer from
poor surface drainage, and the high water table has resulted
in the formation of a gley horizon beneath the surface.
This heavy, claylike layer causes poor internal drainage
because it hampers percolation. Although these soils have
good agricultural potential, their wetness discourages
such use. They are excellent for forest, and slash pines
are planted through much of the Outer Coastal Plain. A
band of Entisols extends across Colleton and into Hampton
County. Remnant of the advance and retreat of the ocean
during the Pleistocene Epoch, the parent material of these
soils comprises sandy and loamy Coastal Plain sediments.
Forests occupy a good portion of the area, but truck crops
and especially watermelons are grown successfully in Hampton
County. In
the Coastal Zone, a strip of land, as narrow as 3 mi (5
km) in the Myrtle Beach area and gradually widening to
more than 25 mi (40 km) near Beaufort, consists of soils
developed on former tidal marshes, beach ridges, and dunes.
These include Entisols along the coast and a band of Alfisols
just inland. North of Charleston, poor drainage generally
leaves the area unsuitable for row crops, and forests
have been planted widely. South of Charleston, though,
certain areas have loamy, better-drained soils. Good management
practices, including artificial drainage systems, have
allowed profitable truck farming to develop. The
major rivers flowing across the Coastal Plain are bordered
by wide floodplains that have agricultural potential.
Classified generally as Inceptisols, these soils are rich
in alluvial material. They are usually loamy but also
can be clayey, depending upon the nature of the riverine
sediments. In either case, they are high in plant nutrients
and organic matter, but both surface drainage and internal
drainage is good or the land has been drained artificially,
the soils are suitable for row crops ad may be very productive.
Such areas in the Outer Coastal Plain and in the Coastal
Zone were the focus of the prosperous Carolina rice industry
during the colonial and antebellum eras. In most cases,
however, extensive floodplain forests, like the Congaree
Swamp, predominate. Vegetation Mountains The
vegetation of the Blue Ridge was classified originally
as an oak-chestnut forest, and species of these trees
dominated the native stands. But in the early twentieth
century a fungus called the oriental Chestnut Blight reached
the United States and ravaged the American chestnut trees
(Castanea dentate) in the eastern part of the country.
Today, dead trunks and rotting stumps are all that are
left of these once mighty trees. As the chestnut tree
disappeared from the mountains, oaks, especially the chestnut
oak (Quercus prinus), and the tulip popular (Liriodendron
tulipifera) competed to replace it on the topmost
canopy of the forests. Other
trees with northern associations include the hemlock (Tsuga
canadensis), white pine (Pinus strobes), beech
(Fagus grandifolia), and yellow birch (Betula
alleghaniensis). Shrubs like the flame azalea (Rhododendron
calendulaceum), pink azalea (R. nidiflorum), and rhododendron
(R. maximum) constitute the understory and give the mountains
a yellow, pink, and white brilliance in late spring and
summer (Fig 3.4). Near the streams, the vegetation complex
is adapted to a wetter habitat and includes such trees
as the alder (Alnus serrulata), cottonwood (Populus
deltoids), and sycamore (Platanus occidentalis),
all of which are found also along rivers in the Piedmont. Piedmont As
late as 1945, over 2 million acres (810,000 ha) of the
piedmont were in crop-land. The 1950s saw a sharp decline
in this acreage, and fewer than 700,000 acres (283, 500
ha) were planted by the mid-1970s. As these lands were
abandoned, a succession of vegetational changes began.
This succession expectedly would lead through various
stages to a mature oak-hickory forest like that which
existed before the initial clearing. Biogeographers refer
to this vegetation assemblage as a "climax forest,"
and it includes the trees and plants that normally occur
under the prevalent conditions of climate, soil, topography,
etc. Successions vary in length, but more than a century
is necessary before a mature climax-forest stage can be
reached in the Piedmont. The
Piedmont landscape today comprises fields and woods at
different stages of this succession. Because most land
has been taken out of cultivation only within the last
40 years, the climax forest has been reached in a very
few areas. After a field is abandoned, it becomes an ecologic
vacuum. Taking advantage of the open field and abundant
sunlight, plants such as dog fennel (Eupatorium compositifolium)
and rabbit tobacco (Gnaphalium obtusifolium) become
the initial occupants. They create an ecologic setting
that allows the grasses, and specifically broomsedge (Andropogon
virginicus), to establish themselves. A few pine seedlings
also appear along with red cedar (Juniperus virginiana)
and wild cheery (Prunus serotina). After about
35 years, pines are the principal trees, but beneath them
grow the seedlings of the hardwoods. The oaks (Quercus
spp), hickories (Carya spp), dogwoods (Cornus
florida), and red maples (Acer rubrum) slowly
begin to dominate the forest floor. This is the stage
that has been reached by most fields taken out of cultivation
and not replanted by timber companies or pulp and paper
companies. Both
the hardwoods and pines will reach maturity within about
70 to 75 years after a field’s abandonment. The tops of
the pines will rise above the forest, but few pine seedlings
will be found on the forest floor. They need the sun that
has been blocked out by the hardwoods’ leafy canopy, and
either the seeds cannot germinate or the pines do not
survive the seedling stage. A century after the field’s
abandonment, the pines will begin to die off, and the
forest will be dominated by an oak-hickory canopy with
an understory of dogwood, red maple, and sourwood (Oxydendrum
arboreum). Only in areas of poorer lands or where
the forest canopy is opened by lightning, fire, or some
other destructive event would we find pines. Two
plants of special interest in the Piedmont are the loblolly
pine (Pinus taeda) and the kudzu vine (Pueraria
lobata). Both occur throughout the area today and
contribute to the Piedmont’s characteristic floral landscape.
Interestingly, though, neither is native to the immediate
area. The loblolly pine was called "old field pine"
because of is widespread presence in the succession stage
of abandoned agricultural fields. Today, it is the most
common tree in the Piedmont, and it has been and is being
planted widely by paper companies and state foresters.
The loblolly pine was not mentioned by eighteenth- and
early-nineteenth-century travelers and botanists who journeyed
through the Piedmont (they noted the short-leaf pine as
the native pine). It therefore must have been introduced
from the Coastal Plan sometime during the nineteenth century. A
bit more is known about the kudzu vine. This plant is
native to Japan but was introduced into the United States
during the last decades of the nineteenth century. Known
initially as the "porch vine," it was used as
a garden ornamental and also was grown on the sides of
porches to provide shade during the summer.
The 1930s and 1940s saw its widespread use for erosion
control and soil restoration. South Carolina agricultural
agents especially encouraged the planting of kudzu, and
perhaps 50,000 acres (20,250 ha) of the vine were growing
across the state by 1950. The plant lost its popularity
during the 1960s and thereafter was considered a weed.
Kudzu’s tendency to climb trees and seemingly smother
them made it undesirable as forestry became an increasingly
important economic activity. The plant still is widespread,
covers acres of land and trees, and creates eerie scenes
of long, hanging vines. But probably fewer than 10,000
acres (4,040 ha) of it remain in the state today, and none
is being planted. Sandhills |
South
Carolina’s Blue Ridge Mountains are a small portion of the Appalachian
Mountain system. Situated in the extreme northern parts of Oconee,
Pickens, and Greenville counties, these 600 sq mi (1,554 sq
km) of rugged terrain constitute only about 2 percent of the
state’s surface area. With elevations ranging from 1,400 to
over 3,500 ft (427 to 1,067 m), the Blue Ridge provides the
greatest relief and steepest slopes in the state. The highest
peaks include Sassafras Mountain, at 3,554 ft (1,083 m) the
highest point in the state, and Pinnacle Mountain, 3,425 ft
(1,044 m), the highest mountain totally within the state. Even
though elevations in South Carolina do not approach Mount Mitchell’s
6,684 ft (2,037 m) in the Blue Ridge of North Carolina, the
area is described accurately as rugged and truly mountainous.
The best views of this region are along State Route 11 between
I-26 and the Walhalla area, along U.S. Route 25 north from Route
11 toward Hendersonville, North Carolina, and along U.S. 276
between Cleveland and Caesars Head.
The
Piedmont (from a French word meaning "foot of the mountains")
consists of a 100-mi-wide (161-km) belt between the Blue Ridge
and the Sandhills. It covers some 10, 500 sq mi (27, 195 sq
km) within South Carolina, one-third of the state’s total area.
Elevations range from about 300 ft (91 m) at the Sandhills margin
to 1,200 ft (366 m) toward the northwest near the Blue Ridge,
which is separated from the Piedmont by a northeast-southwest
trending fault line called the Brevard Zone. The land surface
varies from gently rolling in its southeastern part to extremely
hilly toward the northwest.
Distinctive
among landform features of the Coastal Plain province are the
Carolina bays. Perhaps one-half million of these strangely regular
features occur in the Coastal Plain from Maryland to Florida.
Confusion exists as to the origin of their name, which does
not refer, as is commonly thought, to the embayments of water
that often form their centers but, in fact, derives from the
bay trees that characterize the vegetation found on their edges.
Oval or elliptically shaped depressions, Carolina bays are identified
easily on a topographic map because of their distinctive shapes,
but in the field they look like isolated swamps with standing
water and buttressed trees. For a long time, bays were uncultivated
and bypassed by settlement, but the rich organic soils that
underlie them have enticed farmers to drain and convert many
of the bays to agriculture. They range in size from 4 or 5 acres
(1.6 to 2 ha) to the thousands of acres that make up big Swamp
in Manchester State Forest in Sumter County.
South
Carolina’s coastline is about 185 mi (298 km) long. The Coastal
Zone extends some 10 mi (16 km) into the interior to encompass
about 1.2. million acres (486,000 ha) of land and water. South
Carolina’s coast may be seen as a transition from North Carolina’s
strand to Georgia’s Sea Islands and can be divided into three
zones. The first is the 60-mile-long (96 km) arcuate strand
that extends, almost unbroken by tidal inlets, from the North
Carolina boundary to the area of Winyah Bay. The relatively
stable strand is built on a 100,000-year-old barrier sand formation
and is paralleled by the Waccamaw River, which flows southward
just inland from it. This section of South Carolina’s coast
is called the Grand Strand and today is the focus of the state’s
major recreational development that includes large hotels, motels,
and resort condominiums. Despite the shoreline’s stability,
erosion does occur along its beaches and especially endangers
the hotels that are built near the water’s edge. A series of
storms in the winter of 1982-1983 caused considerable erosion,
and hundreds of sandbags were used to protect these structures.
In the spring of 1986 Myrtle Beach began a beach nourishment
program and trucked sand from inland relict dunes to replenish
the resort’s beaches.