||Engineering Aspects of Karst
Background and Characteristics
New England States
Appalachian Plateau's Province
Southeastern United States
Ohio, Indiana, and Kentucky
Ozark Plateau Province
Oklahoma and Texas
Montana, Idaho, and Wyoming
Notes About the Map Layer
||Background and Characteristics
Distinctive surficial and subterranean features developed by solution
of carbonate and other rocks and characterized by closed depressions,
sinking streams, and cavern openings are commonly referred to as
karst. The term was used first to describe the region of Carso
in northeastern Italy and western Slovenia, where solution landscape
was studied in the 19th century. Originally the term defined surface
features derived by solution of carbonate rocks, but subsequent
use has broadened the definition to include sulfates, halides,
and other soluble rocks. The term has been expanded also to cover
interrelated forms derived by solution on the surface in the subsurface.
A further expansion of the concept of karst was the introduction
of the term "pseudokarst" to designate karstlike terrain
produced by processes other than the dissolution of rocks (Burger
and Dubertret, 1975). When used in its broadest sense, the
term encompasses many surface and subsurface conditions that give
rise to problems in engineering geology. Most of these problems
pertain to subterranean karst and pseudokarst features that affect
foundations, tunnels, reservoir tightness, and diversion of surface
drainage. Environmental aspects of karst lead to additional problems
in engineering geology, especially in site selection. Subterranean
openings may be the habitat of unique and, in some cases, endangered
fauna. The openings are also conduits for water and refuse disposal
from the surface or, in caves, for pollutants that can be carried
for great distances. Many caves contain features of beauty and
scientific interest that can be important esthetic factors in site
selection for structures, transportation routes, and impoundments.
Carbonate dissolution process and karst formation.
Credit: U.S. Geological Survey
study of karst in the United States started with W. M. Davis' (1930)
theory on the origin of caves by deep-seated solution. Bretz (1942)
obtained data, from studies in flat-lying carbonate rocks in the
Midwestern States that supported Davis' theory. After World War
II, studies of karst in the United States became widespread beginning
with investigations in the Appalachian Mountains. Based on these
studies, many of which were in areas of folded rock, older theories
were modified with emphasis on maximum solution activity in a zone
directly beneath a uniform water table (Davies,
1960). Since 1948, the exploration of caves and studies of
landforms in carbonate terrains have produced a vast amount of
data on karst. Reports of these explorations and studies have been
primary sources in compiling this map on the subterranean aspects
of engineering geology of karst and pseudokarst. In addition, published
logs of borings were used. Much of the information on the Eastern
United States, principally for the Appalachian Mountains and Plateau,
is from field observations.
Subterranean openings in karst range in size from minute voids
to large caverns. Most of the openings are formed by solution processes
along fractures, joints, and bedding planes. Caves and related
solution features are common in most carbonate and gypsum terrains
in the United States, except in the area formerly covered by Pleistocene
ice sheets (Davies and LeGrand, 1972).
The southward advance of these ice sheets covered New England,
New York, northeastern and northwestern Pennsylvania, most of
the States bordering the Great Lakes, and much of the area north
of the Missouri River. Karst features in the formerly glaciated
area are covered by glacial drift, and most caves and fissure openings
have been eroded away or filled. The caves and open fissures that
remain generally have less than 1,000 ft (300 m) each of passages
large enough to be traversed by humans.
South of the formerly glaciated area, caves, open joints, fissures,
and other subterranean karst features are present in most soluble
rocks. In general, both the number and size of solution features
increase inversely with latitude. In addition, the number and size
also vary according to the age and structure of the soluble rock
in which solution features develop. Solution features in folded
rocks are subordinate to those in nondeformed rocks; those in rocks
older than Mississippian are subordinate to those in Mississippian
and younger rocks. These are broad generalizations, and local exceptions
exist. However, these generalizations can be used as a hasty estimate
of karst conditions.
Cave Passages and Shafts
The natural entrance to Carlsbad Cavern, New
Photo by Peter Jones, National Park Service
Most caves consist of a series of passages on one level. Some
caves have multiple levels of passages that extend vertically as
much as 300 ft (90 m). The levels are generally connected by shafts
or large galleries. Most passages are less than 10 ft (3 m) high
and less than 10 ft (3 m) wide. Maximum size of passages is about
100 ft (30 m) in height and width. In many caves, passages expand
into galleries or rooms that are 30 to 200 ft (9 to 60 m) long
and wide and up to 150 ft (45 m) high. The largest known solution
opening in the United States is in Carlsbad Caverns, New Mexico,
where a T-shaped room is 1,800 ft (550 m) long in one section,
1,100 ft (330 m) long in the other section, 255 ft (77 m) high,
and up to 300 ft (90 m) wide.
Texas Toothpick in the Lower Cave area
of Carlsbad Cavern, New Mexico.
Photo by Peter Jones, National Park ServiceShafts are present in multiple-level caves and in some single-level
caves. The deepest shafts are about 1,000 ft (300 m) deep, but
in most caves they are less than 300 ft (90 m) deep. Most shafts
are 30 ft (10 m) or less wide. In multiple-level caves, shafts
connect levels; in other caves, the shafts are pits with no apparent
connection at the base. Shafts are irregular in shape; some resemble
funnels, and others are shaped like cylinders. Dome pits are cylindrical
shafts that develop upward from a passage towards the surface of
the Earth. Dome pits are up to 50 ft (15 m) wide and extend upward
for as much as 150 ft (45 m). Their walls are uniform. Dome pits
are capped by a cover of carbonate rocks 10 to 50 ft (3 to 15 m)
thick. In many domes, the caps have collapsed and left vertical-sided
Virginia, West Virginia, Kentucky, Tennessee, Alabama, Missouri,
Texas, and New Mexico contain hundreds of caves, each of which
has over a mile of passages. At least one cavern system in each
of these States has 10 to more than 100 mi (16 to 160 km) of passages.
The largest known system is Flint Ridge-Mammoth Cave in Kentucky
(Brucker, 1979), with over 200 mi (320
km) of passageways in an area of 362 mi (902 km).
Solution Tubes and Fissures
Solution tubes with openings as much as 1 ft (0.3 m) wide and
irregular alignment occupy portions of the carbonate bedrock. In
some cases, the tubes connect with caves. However, the tubes generally
lack the systematic patterns that are common in development of
cavern passages. These tubes apparently predate cavern development.
Although most tubes are seldom longer than a few hundred feet,
they are interconnected and commonly act as conduits for subsurface
drainage. During freezing weather, water from tubes can cause large
buildups of ice where excavations intersect the tubes. At other
times, the tubes lead to flooding of excavations and leaks in reservoirs
and contribute to weakening of retaining walls.
Fissures (also referred to as open joints) up to 1 ft (0.3 m)
wide result from limited solution along joints, fractures, and
bedding planes. Fissures occur in various attitudes from vertical
to gently inclined and generally are in repetitive geometrical
patterns or sets. Fissures form systems that may extend for several
thousand feet horizontally and over 300 ft (90 m) vertically. Some
fissures or parts of fissures are filled with consolidated clay-silt
and clay-gravel that seal them. The seals, however, are altered
in contact with water and can be removed by running water. Fissures
are commonly conduits for subterranean streams. In addition, they
can cause serious engineering problems, such as reservoir leakage
and instability of cuts, bridge abutments, piers, and dam foundations
The depth to which solution openings occur depends on relief in
an area, thickness of soluble rock, and geologic structure. The
configuration and depth of the water table, in some cases, are
controlling factors. Ground water in karst terrain generally is
found in existing openings that extend tens to hundreds of feet
below the water table. In the mountainous areas of the Western
United States, the known vertical extent of solution openings is
as much as 1,100 ft (330 m). In the Eastern United States, where
relief is less, the vertical extent is generally less than 400
ft (120 m), with a maximum of 650 ft (200 m). Beneath many broad
river valleys, solution features in carbonate rocks are present
to a depth of about 100 ft (30 m) in both the Eastern and Western
Surface subsidence (sinkhole development) occurs most commonly
in areas where ground-water conditions are altered by excessive
pumping or by diversion of surface drainage. Subsidence generally
involves weathered bedrock and soil that bridge caverns, subterranean
galleries, and dome pits. The collapse is caused by loss of support
resulting from the reduction of hydrostatic pressure of ground
water, by sapping, and by piping. Most subsidence forms shallow,
steep-sided depressions up to 100 ft (30 m) wide and up to 20 ft
(6 m) deep. However, in Florida and central Alabama, recent subsidence
has resulted in nearly vertical sided sinkholes up to 425 ft (130
m) wide and 150 ft (45 m) deep.
An aerial view of a large sinkhole in Florida.
Credit: U.S. Geological Survey
of local subsidence caused by mining operations and regional subsidence
caused by withdrawal of ground water and petroleum in thick, unconsolidated
sediments have not been included in the map layer of subterranean
aspects of engineering geology of karst and pseudokarst because
natural processes are involved only in a subordinate way in development
of these phenomena. The problems of these types of subsidence are
complex, and the areas involved are so extensive that they are
best treated as subjects for another map.
Solution and collapse features of karst
Credit: U.S. Geological Survey
||New England States
New England States, solution terrain is confined to crystalline
limestones and marbles mainly in northeastern Maine, western Vermont,
and western Massachusetts. Solution features in these areas are
primarily narrow fissures generally less than 200 ft (60 m) long
and less than 30 ft (10 m) deep. A few small caves are known in
western Vermont and in the Berkshire Mountains of western Massachusetts.
In eastern Vermont and much of Maine, carbonate rocks high in silica
and other impurities' are commonly, yet incorrectly, referred to
as limestone. Solution features are generally absent in these rocks.
In the Appalachian Highlands, three major groups of carbonate
rocks are in the karst regions. The Great Valley, in the eastern
part of the Highlands, from southeastern New York to central Alabama,
is a lowland up to 26 mi (42 km) wide eroded across dolomite, limestone,
and shale of Cambrian and Ordovician age. Regionally, and to some
extend reflecting differences in degree of karst development, the
Great Valley is designated from north to south as the Kittatinny,
Lehigh, Lebanon, Cumberland, Hagerstown, Shenandoah, and Tennessee
Valleys. All types of solution features are present in the Great
Valley, with small caves and fissures in southeastern New York
and like features increasing in size and numbers southward. From
central Virginia southward, large caves with over 1 mi (1.6 km)
of passages in each are common, and fissures extend hundreds of
feet in length and over 100 ft (30 m) in depth. The major geologic
units involved in karst development in the Great Valley are the
Elbrook (Cambrian), Conococheague (Cambrian-Ordovician), Beekmantown
(Ordovician), and their equivalents. All are folded with steep
dips, and overturning is common along the east half of the lowland.
Faults are numerous and some major fault zones extend over 200
mi (320 km). Active subsidence is prevalent throughout the Great
Valley and is a result primarily of alteration of the water table.
Generally, the subsidence involves the opening of shallow fissures
and shafts up to 10 ft (3 m) in diameter in farmland through removal
of soil and thin rock cover over fissures, shallow cavern passages,
and small dome pits. More extensive subsidence is in progress in
the vicinity of Allentown and Harrisburg, Pennsylvania, where numerous
subsidence depressions up to 100 ft (30 m) in diameter have developed.
In Staunton, Virginia, active subsidence from collapse of rocks
and soil covering shallow caves and fissures was recorded as early
as 1911. Subsidence in the Staunton area resulted from large-scale
piping of sinkhole soils by leakage from settling basins and from
drawdown of the water table. In central Alabama, steep-sided, water-filled
sinks, up to 425 ft (130 m) wide and 150 ft (45 m) deep, have formed
recently by collapse of weathered limestone and thick soils covering
Karst map within the Great Valley area
In the area west of the Great Valley, a sequence of limestones
in the Upper Silurian (Tonoloway) and the Lower Devonian (Helderberg
Group) forms subordinate ridges in southeastern New York, central
Pennsylvania, eastern West Virginia, and western Virginia. The
rock is folded, and dips are steep. Karst features include fissures
extending several hundred feet vertically and caves with up to
1 mi (1.6 km) of large passageways. Subsidence is uncommon, but
the fissures and caves have caused problems in foundations and
abutments of dams, in cuts because of unstable wedges, and in tunnels
that encounter earth fills in solution cavities.
Along the western edge of the Valley and Ridge province of the
Appalachian Highlands, several large basinlike lowlands underlain
by Cambrian and Ordovician carbonate rocks occur. The lowlands
are eroded across large anticlines with steep dips on the flanks
and moderate to steep plunges along the axes of the anticlines.
In the Nittany and Kishacoquillas Valleys of Pennsylvania, and
some smaller valleys designated as "coves," numerous
caves occur, each with passageways 1,000 to 5,000 ft (300 to 1,500
m) long. The passages generally are 100 ft (30 m) or less below
the surface. Many act as subterranean feeders that carry runoff
from adjacent ridges to a few points of resurgence. The resurgent
points are large springs with a daily flow of up to 1 million gallons
or more (4 million or more). Fissures are present but seldom exceed
200 ft (60 m) in depth. Subsidence is not common, but deep cuts
and excavations are subject to uncontrollable flooding if major
subterranean conduits are encountered. In Germany Valley, West
Virginia, solution features, primarily multiple-level caves and
fissures, extend to depths of 350 ft (105 m) or more. Drainage
of most of this valley is by way of one large spring. Subsidence
from collapse of sinkholes is common, and potential for subsidence
exists over numerous dome pits above caves.
||Appalachian Plateau's Province
Plateau's province and adjacent parts of the Interior Plains in
West Virginia, Kentucky, Tennessee, northern Alabama, and southern
Indiana contain the most intensely developed karst areas in the
United States. The karstic carbonate rocks are Mississippian in
age and include the Greenbrier limestone (West Virginia) and the
Golconda, Ste. Genevieve. St. Louis, and Warsaw limestones and
their equivalents elsewhere. Caves generally contain 3,000 ft (900
m) or more of passageways. Multiple-level caves are not common,
but some large cave systems, such as Flint Ridge-Mammoth Cave in
Kentucky and Organ Cave in West Virginia, have a multitude of complex
passageways at various elevations that extend in aggregate from
30 to over 200 miles (48 to over 320 km). Dome pits, common in
many caves, are areas of potential collapse. Many of the caves
are large subterranean drainage ways that receive streams flowing
from adjacent highlands. Cuts and excavations intersecting these
caves are subject to inundation from over 1 million cubic ft (40,000
m 3) of water stored in the subterranean reservoirs. Large sinkholes,
up to 1 mi (1.6 km) wide and several hundred feet deep, are so
numerous that the rims of many sinkholes intersect the rims of
their neighbors. Suitable foundations for large structures are
difficult to site. Deep cuts, mines, tunnels, and excavations commonly
encounter deeply weathered rock and large volumes of weak soil
filling cavern passages and fissures. Seasonal flooding is common
from snowmelt and from heavy rainfall that exceeds the infiltration
capacity of sinkholes and the capacity of subterranean channels
to carry the runoff. Subsidence in most of the area is not extensive
except above the dome pits and along karst valleys in southern
Indiana and in the Mammoth Cave plateau in Kentucky.
||Southeastern United States
In the Southeastern United States, karst is extensive on the Coastal
Plain in southern Alabama, Georgia, and Florida. The limestones
in the karst area are primarily the Ocala Limestone and Jackson
Formation of Eocene age and their equivalents. In the Dougherty
Plain of southeastern Alabama and southern Georgia, the limestone
has been weathered deeply, and in the southern part of the plain
the limestone is covered by a residuum of sandy clay. In the northern
part of the plain, only small areas of the limestone remain within
the residuum. Subsidence occurs as broad, slowly developing, shallow
sinkholes in the residuum. In Florida, subsidence is more extensive.
In the northern half of the State, the limestone is covered by
younger sand deposits that are locally over 100 ft (30 m) thick.
In Polk County , subsidence has resulted in vertical-sided sinkholes
up to 150 ft (45 m) deep and 425 ft (130 m) wide. The subsidence
has engulfed several houses and resulted in large property losses
to homeowners. The subsidence is related to alteration of ground-water
levels in caverns and to collapse of the weathered carbonate rock
that supports the surface deposits.
Mining exposed this typical karst limestone
surface, which is riddled with dissolution cavities.
Photo by Willam A. Wisner
carbonate rocks of the Selma Group are extensive in central and
western Alabama and northeastern Mississippi. These rocks show
little alteration by solution, and open fissures, open joints,
and caves are generally not present.
||Ohio, Indiana, and Kentucky
The Silurian limestones and dolomites (Niagaran) of northwestern
Ohio and adjacent Indiana are buried beneath glacial drift. Only
in northwestern Ohio, where the glacial deposits are less than
20 ft (6 m) thick, are there karst features large enough to cause
problems in engineering geology. Caves, each generally with less
than 1,000 ft (300 m) of passages, are present but not numerous.
Fissures less than 100 ft (30 m) wide extend for hundreds of feet.
Small areas of subsidence have been attributed to alteration of
the water table by pumping processes in quarries several miles
from the site of subsidence. Because of the flat terrain, excavations
and cuts seldom are deep enough to encounter major karst features.
In the vicinity of Sandusky, Ohio, and on some of the nearby islands
in Lake Erie, beds of calcium sulfate expand and change because
of weathering and may cause local problems in heaving.
Broad anticlines with gentle dips bring Ordovician limestones
and dolomite to the surface in southwestern Ohio and north-central
Kentucky. Small caves and numerous joint-controlled fissures occur.
Subsidence is not common or extensive, but the fissures and caves
that result contain a large volume of water that may flood excavations.
Ordovician and Silurian carbonate rocks also are brought to the
surface in a broad anticline in central Tennessee around Nashville.
Karst conditions are similar to those in north-central Kentucky.
In the Lower Peninsula of Michigan, carbonate rocks are extensive
but are buried deeply beneath glacial deposits. Silurian limestones
along Lake Huron between Alpena and the Straits of Mackinac contain
several large sinkholes up to 1 mi (1.6 km) long and 200 ft (60
m) deep. The sinkholes are interconnected by an extensive fissure
system. Normally, the sinkholes are filled with water, but, over
time, plugs in the fissure system fail and the lakes drain through
the subterranean openings. Subsidence generally does not occur
in the Lower Peninsula.
Ordovician limestones cover the south half of the Upper Peninsula
of Michigan and extend through eastern and southern Wisconsin,
eastern Iowa, and parts of southeastern Minnesota. Karstic features
are poorly developed and consist of simple caves, each with less
than 1,000 ft (300 m) of passageways and less than 50 ft (15 m)
of vertical extent. Fissures developed along joint lines are in
about the same size range as the caves. In the vicinity of Dubuque,
Iowa, and extending into adjacent Wisconsin and Illinois, fissures
several hundred feet long and more than 300 ft (90 m) deep have
been encountered in lead-zinc mines. The fissures possibly are
relict from older buried karst. Subsidence from karst features
is rare, although subsidence over mines is extensive.
||Ozark Plateau Province
Jam Up Cave, Missouri - located on the
Jack Forks River. The entrance
is about 80 feet high and 100 feet wide. Much of the cave is
filled with water, and there is a small underground waterfall.The
Ozark Plateau province and adjacent plains in Missouri and northern
Arkansas have extensive karst areas. The Ozarks are a large regional
structural dome with steep dips along the southern flank. The
dome brings Cambrian and Ordovician limestones and dolomites
to the surface. North and west of the dome are plains underlain
by Mississippian carbonate rocks (Warsaw, St Louis, Ste. Genevieve,
and equivalents). Within the Ozarks, caves, each with passages
1,000 ft (300 m) or more long, are common. The passages in most
caves extend to a depth of less than 100 ft (30 m). Pits, formed
by collapse into cavern shafts and dome pits, are common, and,
in southern Missouri, active subsidence is extensive. Most of
the pits are water filled. Fissures over 1,000 ft (300 m) long
and more than 300 ft (90 m) deep are present in much of the area.
Similar fissures are numerous in the lead-zinc mining region
in southwestern Missouri and adjacent Oklahoma and Arkansas.
Throughout the Ozarks, the caves and fissures give rise to serious
problems in foundations and abutments of dams and with reservoir
tightness, stability of bridge piers, and stability of cut slopes.
The presence of large quantities of subterranean water is a problem
in deep foundations.
Round Spring, Missouri flows into an almost
perfectly circular cavern that has collapsed, and from there
it travels through a natural tunnel before it emerges into the
The Niobrara Formation (Upper Cretaceous) and its equivalents
are the most widespread carbonate rocks in western Kansas, eastern
Nebraska, and southeastern South Dakota. The Niobrara is generally
covered by more than 50 ft (15 m) of younger sediments. Small fissures,
less than 1,000 ft (300 m) long and up to 100 ft (30 m) deep, are
present, but they are not common and are generally irregularly
spaced with 1,000 ft (300 m) or more of solid rock between fissures.
Salt beds in south-central and southwestern Kansas form karst
areas. Fissures are extensive, with openings more than 1,000 ft
(300 m) long and over 300 ft (90 m) deep. Throughout the saline
rock, recent subsidence has resulted from natural causes, as well
as from alteration of the water table by solution mining and open
In western South Dakota and adjacent parts of Wyoming and Montana,
Paleozoic and Cretaceous carbonate rocks, arched steeply upwards,
encircle the structural dome that forms the Black Hills. Caves
and open fissures are common in the Paleozoic carbonate rocks.
A few caves contain many miles of passages but most of the cave
passages and fissures in the Black Hills area only extend up to
3,000 ft (900 m) in length and are generally less than 150 ft (45
m) in depth. Closely spaced solution joints also are prevalent.
Karst map within the Black Hills area
of western South Dakota and adjacent parts of Wyoming and Montana.
||Oklahoma and Texas
In western Oklahoma and in the eastern part of the Texas Panhandle,
extensive areas of karstic gypsum occur. Small open fissures up
to 50 ft (15 m) deep and 1,000 ft (300 m) long are present. Passages
in caves in gypsum are generally of similar length and depth.
The Edwards Limestone (Cretaceous) in west-central Texas forms
an extensive plateau. Large caves and fissures are present to a
depth of 600 ft (180 m), and both fissure systems and passages
of single caves commonly extend for more than 1 mi (1.6 km). Both
the caves and fissures contain large quantities of water in their
carbonate rocks in central and southern New Mexico contain numerous
well-developed karst features. Caves are generally very large and
contain miles of passages with a vertical extent of 1,000 ft (300
m) or more. Fissures are of similar size and are interconnected,
forming networks that extend for several miles. Closely spaced
open joints, enlarged by solution, and numerous small, near-surface
solution tubes cause extensive trouble in reservoir tightness throughout
this karst area.
and central Arizona, the Kaibab Limestone (Lower Permian) and its
equivalents are karstic. North of the Grand Canyon, subterranean
openings are primarily widely spaced fissures up to 1,000 ft (300
m) long and 250 ft (75 m) or more deep. South of the Grand Canyon,
the fissures are more closely spaced and a few shallow caves are
present. East of Flagstaff, there is an area of open fissures.
These fissures are over 300 ft (90 m) deep, up to 1,000 ft (300
m) long, and up to 3 ft (1 m) wide. They cut the Coconino Sandstone,
as well as the Kaibab Limestone (Colton,
||Montana, Idaho, and Wyoming
Limestone (Mississippian) lies under karst areas in western Montana
and adjacent parts of Idaho and Wyoming. Passages in a single cave
are commonly up to 2 mi (3.2 km) long. Open fissures up to 1,000
ft (300 m) long and shallow, open joint systems are also common.
Fissures and cavern passages extend as much as 1,000 ft (300 m)
deep. Large quantities of water are present in the lower parts
of the fissures and in some of the deeper cavern passages. Relict
karst features, developed during times of disconformity at the
end of the Mississippian, are common in the Madison Limestone.
Most of the relict features are solution tubes, caves, and small
fissures that have been filled with younger deposits that are now
lithified. Because of differences in materials, residual openings,
and secondary solution, these features can give rise to foundation
problems and leakage.
features in Alaska are not well known. Most of these features are
shallow, swalelike depressions developed in a thin cover of residual
soil and glacial till that lies over intensely folded limestone.
A few cave openings are in limestone bluffs, but most cave entrances
are hidden by a cover of spalled rock fragments. Streams crossing
limestone terrains commonly disappear into the soil mantle and
resurge at contact with insoluble rocks bordering the limestone.
No subsidence features have been reported in Alaska.
Pseudokarst conditions in the United States develop in areas of
thick, unconsolidated sediments and are primary features in basalt
lava. In addition, in Mississippi and Alabama, numerous subsidence
features occur in unconsolidated silt, sand and gravel of the Coastal
Plain; these subsidence features are analogous to karst features.
The subsidence occurs as numerous shallow depressions that are
generally less than 50 ft (15 m) deep and up to 1 mi (1.6 km) or
more wide. The depressions occur in Miocene and Pliocene sediments
800 to 1,000 ft (240 to 300 m) or more thick. Oligocene carbonate
rocks are present beneath these sediments. The origin of the depressions
is not understood. The depressions appear to be associated with
poorly drained areas such as flat lowlands and elevated, dissected,
higher erosion surfaces. The depressions apparently are confined
to flat surfaces and are not present on slopes that bound the flat
surfaces. Excavations in the depressions probably would encounter
weak and unstable soil and would be subject to flooding.
The High Plains of western Texas and adjacent States contain
numerous depressions, some of which are as much as 3 mi (4.8 km)
long and up to 1 mi (1.6 km) wide. They vary from "buffalo
wallows," 3 to 10 ft (1 to 3 m) deep, to steep-sided features
as much as 250 ft (75 m) deep. The depressions are aligned along
a series of major joints and apparently formed by piping and removal
of fine-grained material along joint planes at depths greater than
250 ft (75 m). Deep excavations in the depressions encounter weak,
unstable soils and are subject to flooding from ground water during
occasional periods of high rainfall.
Sunshine Lava Tube, California gets its
name from several breakdown areas where sunlight can stream into
the passage. The abundance of moisture supports mosses and other
plants that adapt to the cooler conditions in these natural skylight
Pseudokarst features in late Cenozoic basalt lava fields are extensive
in some regions of the west. The largest regions with this type
of pseudokarst are in the Snake River area of Idaho, in part of
the Columbia Basalt Plateau in Washington and Oregon, and in the
lava fields of northeastern California. Smaller areas are in New
Mexico, Arizona, Utah, Nevada, southern California and on the Seward
Peninsula in Alaska. The pseudokarst features include lava tubes,
fissures, open sinkholes, and caves formed by extrusion of the
still-liquid portion of the lava. Subsurface solution of the bedrock
and subsequent collapse are not involved in the formation of these
features. Lava tubes, in the form of tunnels, are up to 20 ft (6
m) in diameter, and some extend for several miles. Fissures are
common but seldom extend for more
Note the pear-shaped character of this passage
in Sunshine Lava Tube, California. A congealed lava flow covers
the center of the passage. The dark areas along the side are pathways
coated with smaller cinders for easier walking within the caves. than
1,000 ft (300 m). The fissures and lava tubes, in contrast to solution
features, are not in geometrical sets but are generally parallel
and extend in the direction of the flow of the lava. Fissures and
lava tubes are generally near-surface features, but some are as
much as 250 ft (75 m) deep. "Sinkholes" in
lava generally lack the symmetry of those developed in solution
terrain. The lava sinks are commonly less than 100 ft (30 m) wide,
but a few large sinks, notably in the Snake River area of Idaho,
are as much as 1 mi (1.6 km) or more wide. Most of the lava sinks
are irregular in shape and generally are shallow features (less
than 30 ft (10 m) deep), although some are 150 ft (45 m) or more
deep. Many of the sinks have near-vertical sides or overhangs.
Lava pseudokarst features present problems in foundations, abutments,
and reservoir tightness. In addition, the tubes and related permeable
lava often contain large quantities of water that may lead to flooding
and slope-stability problems in cuts and excavations.
||Notes About the Map Layer
Although surface features of karst terrain (primarily sinkholes,
solution valleys, and solution sculptured rock ledges) are significant
in engineering geology, they have not been included in the map
layer because of the additional complexity that would occur in
classification and portrayal.
The small scale of the map layer and the limited data on openings,
other than caves, in soluble rocks restrict the use of the map
layer to the most general types of planning and as a guide to areas
where subterranean karst and pseudokarst features occur. The map
layer cannot be used either for specific site selection or as a
substitute for field examination in planning and site development.
and gratitude are extended to Allen W. Hatheway, Cambridge, Massachusetts,
for information and guidance on pseudokarst in lava, to the thousands
of members of the National Speleological Society whose papers on
caves and karst areas they explored are the basic sources used
in compilation of this map, and to members of the U.S. Geological
Survey and various State Geological Surveys for information they
contributed and for technical review and advice on this map layer
Bretz, J. H., 1942, Vadose and phreatic features of limestone
caverns. Journal of Geology, v 50, no. 6, pt2 , p. 675-811.
Brucker, Roger, 1979, New Kentucky Junction. Proctor-Mammoth
Link Puts System over 200 miles, National Speleological Society
News, v 37, no. 10. October, p. 231-236.
Burger, A., and Dubertret, L., 1975, Hydrogeology of Karstic
terrain: Paris, International Association of Hydrogeologists, p.
Colton, S., 1938, Exploration of limestone solution cracks: Museum
of Northern Arizona, Museum Notes, v. 10, no. 10, p. 29-30.
Davies, W. E.. 1960, Origin of caves in folded limestone (Appalachian
Mountains) in Moore, G W., ed.. Origin of limestone caves;
a symposium with discussion: National Speleological Society, Bulletin,
v. 22, pt. 1, p. 5-18.
Davies, W E., and LeGrand, H. E., 1972, Karst of the United States; in Herak,
M. and Stringfield, V. T.. eds., Karst; important karst regions
of the northern hemisphere. New York Elsevier Publishing Co., p.
Davis, W. M.. 1930, Origin of limestone caverns: Geological Society
of America Bulletin, v. 41, no.3, p, 475-628.
The following publications have not been cited in the text but
are works that cover the subject of karst in great detail.
Ford, T. D., and Cullingford, C. H, D., eds., 1976, The science
of speleology: London, Academic Press, 593 p.
Jakucs, Laszlo, 1977, Morphogenetics of karst regions: New York,
Halstead Press, 284 p.
Jennings, J. N.. 1971, Karst: Cambridge, M.I.T. Press, 252 p.
Sweeting, M M.. 1972, Karst landforms: London, MacMillan, 362
Sweeting, M. M.. ed.. 1981, Karst geomorphology: Benchmark Papers
in Geology, v. 59, Stroudsburg, Hutchinson Ross Publishing, 427
from Davies, W.E., Simpson, J.H., Ohlmacher, G.C., Kirk, W.S.,
and Newton, E.G., 1984, Engineering Aspects of Karst Map: U.S.
Geological Survey, National Atlas of the United States of America®,
scale 1:7,500,000, Stock Number 101408.