Karst of the Silurian-Devonian Carbonates in Eastern New York State,
with emphasis on the Cobleskill Plateau
Arthur N. Palmer and Paul A. Rubin
April 2007
Introduction to Karst
Karst is a landscape in which the landforms are produced mainly by dissolution of bedrock, most
typically limestone. Nearly all of the karst in eastern New York State is hosted by carbonate
rocks of the Silurian-Devonian Helderberg Group and the Devonian Onondaga Group.
Approximately 40-50 meters of the Helderberg Group, and less than 30 meters of the Onondaga
Group, are pure enough to contain well-developed karst features. Because they are bounded by
less-resistant strata these carbonate units form prominent structural benches in which sinkholes,
sinking streams, caves, and large springs are common. Karst researchers associated with the
National Speleological Society have documented well-developed cave systems, sinkholes,
disappearing streams, and springs throughout the eastern New York State carbonate belt.
Mapped caves range in length from very short to many kilometers (e.g., Surprise Cave in
Wurtsboro: 3 km; Pompey’s Cave south of Kingston: 1 km; Onesquethaw-Jordans in Feura
Bush: 1.7 km; Skull Cave in Knox: 7 km; McFail’s Cave near Cobleskill: 11.4 km). These caves
range in depth to 96 meters. It is only recently that some significant New York State karst areas
have been identified and described (e.g., the 5.1 km Barrack Zourie Cave System in 1995). The
largest structural bench of carbonate rocks in the region is the Cobleskill Plateau, which is the
site for several of the stops on the HMPGA field trip, including the Howes Cave Quarry (Figure
1).
Karst Geomorphology
Nearly all of the water in a karst area drains underground through solution conduits. The largest
of these include caves such as Howe Caverns. On this field trip we will examine the geologic
controls and flow dynamics that have produced karst aquifers throughout eastern New York
State. Water sinks into carbonate rocks in several ways: through sinkholes and fissures, as
sinking streams that drain from less-soluble rocks, or as diffuse infiltration through soil. Water
from these sources generally converges as tributaries to form branching cave patterns. Stream
caves of this type are more or less the underground equivalent of surface streams. Water emerges
at springs, which are relatively few in comparison to the number of groundwater recharge points.
Caves form along those underground paths that have the greatest discharge. At first the water
follows the network of narrow joints, faults, and bedding-plane partings in the rock. Intergranular
(matrix) pores are insignificant, at least in the well-indurated Paleozoic rocks of this region. As
these openings grow, the discharge increases until nearly all of the water in the catchment area
follows underground paths. Those paths that acquire the greatest discharge grow fastest. The size
of a cave ultimately depends on three factors: rate of discharge, solutional aggressiveness, and
time.
Caves that are fed by sinking streams and large individual or groups of sinkholes tend to be
large, because of the considerable supply of water. The water sinks quickly and remains
undersaturated with calcite for long distances through the ground. Diffuse seepage through
narrow fissures and pores reaches calcite saturation after only a short distance and is rarely
sufficient to form caves, or even minor solution conduits. When this water drips into open-air
caves, some of the carbon dioxide picked up in the soil is released into the caves and the capacity
of the water to hold dissolved calcite is reduced enough to precipitate that mineral as cave
“formations,” more properly called speleothems.
As caves grow, subsidence of soil into them forms sinkholes, which focus increasing amounts of
water underground. Caves and surface depressions therefore grow simultaneously and
interdependently. The presence of sinkholes in the sediment covered glaciated karst of New York
State is a clear indication that conduits below are integrated into an active karst system. Vadose
water (in the unsaturated zone) moves down the steepest available paths, which are generally
vertical fissures along joints, or inclined passages along bedding-plane partings (Figure 2). As
the vertical fissures enlarge, they may widen into nearly cylindrical shafts. In New York State
the largest shafts are up to 30 meters deep and 5-8 meters in diameter. One of the largest in the
region is the 32-meter-high Great Rotunda in Howe Caverns (located along a special off-trail
tour). The prominent jointing in the massive Coeymans Limestone produces many shaft
entrances to caves. Inclined vadose paths deepen into canyon-like passages as their streams
entrench into the floors. The largest canyon passages in the region are about 15 meters high and
up to 3 meters wide. The Winding Way in Howe Caverns is a good example of a narrow but high
canyon. These passages tend to follow the dip of the strata, with occasional offsets along
intersecting joints and faults. The typical vadose flow path therefore consists of alternate shafts
and canyons that form a step-like pattern.
When streams reach the water table, the water no longer has an inherent tendency to follow the
steepest available paths. Instead, the water follows those paths that are hydraulically most
efficient. This water tends to have a strong horizontal component, although it can loop down
below the water table where suitable wide fractures are available. As these phreatic paths grow,
they form tube-like passages whose cross sections in gently dipping limestone are typically
elongate either vertically (along fractures) or horizontally (along bedding-plane partings). The
most typical trend for a phreatic passage is roughly parallel to the local strike of the beds, which
is crudely the line of intersection between the dipping strata and the low-gradient water table
(typical of highly permeable limestones). However, great deviations from this trend are possible.
These phreatic passages tend to enlarge all around their perimeters, rather than just downward, so
they account for most of the largest caves, such as the main tour route of Howe Caverns. In this
region tubular passages have maximum diameters of about 12 meters.
The maximum rate of cave enlargement by subsurface streams is about 0.01 centimeters/year,
but this rate is rarely achieved because the groundwater in most caves is already well on its way
to calcite saturation. Chemical measurements in caves of the region suggest a total age of at least
500,000 years. Uranium-thorium dating of calcite speleothems in some high-level caves exceeds
the 350,000 year limit of the method.
Therefore, the development of caves operates on a time scale longer than that of glacial episodes.
Melt water from glaciers has probably enlarged some existing caves, and in places has even
formed small caves, but most New York caves are adjusted to the long-term erosional
development of their host region, rather than to glaciation. A major effect of glaciation is
blockage of groundwater recharge points and springs, so that underground stream diversions are
common. Most caves in the region have survived glaciation with very little impact.
The most important aspects of karst landscapes are hidden. For example, glacial sediments often
mask karst features that would be visible in non-glaciated regions. Only about 10 % of sinkholes
in a typical American karst are shown on topographic maps. This is also true where there is a
cover of glacial sediment, which tends to mask subsidence features. Many significant karst areas,
some with major cave rivers flowing beneath them, exhibit little or no surficial evidence of karst.
People unfamiliar with karst terrains have been known to incorrectly characterize areas where
there are no sinkholes shown on topographic maps as being non-karst.
Karst Hydrology
The field of karst hydrology has evolved far beyond the early landform-based geomorphic
models proposed by Lobeck in 1939 that attempted to describe karst development from the
standpoint of stages of landform maturity and the presence or absence of diagnostic surface
features. Modern karst researchers agree that the most important criterion for identifying a karst
area is the way groundwater behaves. If surface streams are pirated underground through closed
depressions, there must be a hydraulically efficient karst aquifer regardless of the presence or
absence of surficial karst features. Similarly, abrupt variations in discharge at springs and in
caves provide irrefutable evidence for karst aquifers. Figure 3 depicts a typical flashy response in
Howe Caverns, where flood pulses occasionally require the cave to be closed to tourists. The
quantity of water that moves through caves is highly variable and is dependent on the amount
and intensity of precipitation, snowmelt, soil-moisture conditions, and temperature, as well as on
the size of the recharge area. The water flow in Howe Caverns, for example, has been measured
between 0.025 cfs (11 gpm) at low flow and 170 cfs (3/14/07) at moderately high flow. At times
the discharge is even greater.
An important aspect of karst is its effect on water supply and contaminant transport. Water in
solution conduits can travel up to several kilometers per day, and contaminants can move at the
same rate. This poses serious problems when monitoring for water quality. Contaminants enter
the ground easily through sinkholes and sinking streams, and filtering is virtually non-existent.
Even small solution conduits can transmit groundwater and contaminants hundreds of times
faster than the typical unenlarged fissure network. For these reasons it is widely thought that
nearly all groundwater in karst is susceptible to contamination.
This is often not the case, however. The great majority of the groundwater volume in karst is
contained in narrow fissures with slow, laminar flow. Caves transmit most of the groundwater
discharge, but they typically represent about 2-5% of the total porosity. Most water wells
encounter only the slow laminar flow. This water is generally tributary to the major turbulentflow conduits, in the same manner that groundwater seepage in a typical aquifer is tributary to
surface streams. For this reason, many wells in limestone are no more susceptible to
contamination than wells in any other kind of fractured bedrock. Those that encounter conduits,
or which are exposed to backflooding from conduits during high flow, do have a serious
potential for contamination. Solutionally widened surface fissures may also deliver potentially
contaminated water rapidly downward into wells.
Most of the discharge at a karst spring is delivered by turbulent-flow conduits. Cave water moves
rapidly as turbulent flow, at rates that approximate those in surface streams (for example, 5.3
km/hr [3.3 mph] measured in Howe Caverns on 3/14/07). Karst springs are therefore highly
susceptible to contamination and should never be used for water supply unless development in
the catchment area is minimal, and substantial treatment is provided.
Karst of the Cobleskill Plateau
The rich geomorphic history of the karst region maybe reconstructed by examining both in-cave
and surface features. Howe Caverns and McFail’s Cave faithfully record geologic events that are
not preserved on the surface, many of which are only now being unraveled.
Important aspects of the geomorphic history of a region can be inferred from the geometry of
cave passages, long after much of the surrounding landscape has been altered by stream erosion
and glaciation. For example, it is possible that detailed surveys will reveal that caves in the
Cobleskill Plateau (e.g., parts of Secret and McFail’s-Howe) may be part of a single system that
was once integrated and is now segmented into local drainage areas. The caves apparently
developed in response to entrenchment of Cobleskill Creek, which deepened its channel
progressively westward, allowing underground drainage to join it in sequence from east to west.
Therefore, many or all of the phreatic conduits in the Cobleskill Plateau may by hydrologically
connected by vadose conduits of decreasing age to the west (Figure 1). At the very least, three or
more significant changes in regional base level are documented by relict phreatic tubes.
Because of the predominant down-dip pattern of vadose canyons and the roughly strike-oriented
trend of many phreatic tubes, a common cave pattern consists of a trellis-like arrangement of
vadose infeeders to the main phreatic trunk passages. This branchwork pattern is typical in the
Cobleskill Plateau, and Howe Caverns is a good example. Steep hydraulic gradients present
during the phreatic development of Howe Caverns resulted in the formation of anastomotic or
braided conduits near and along the Lake of Venus (Figure 4). Most of the main passage in
Howe Caverns, including anastomotic sections, were formed in the thinly bedded and faulted
upper and middle Manlius Formation (Figures 5, 6, 7). Certain other caves in the region are
perched on insoluble strata and consist entirely of dip-oriented vadose canyons that feed contact
springs in the valley walls.
Much of the karst hydrology of the Cobleskill Plateau (Figure 1), as well as of other karst
systems of America, has been delineated through tracer tests. Experienced karst hydrologists
follow ASTM Standard procedures (ASTM D 5717–95) to determine groundwater flow
direction, velocity, and destination, as well as to assess contaminant risks. Characterization of the
conduit portions of karst aquifers cannot be made on the basis of a few randomly placed wells.
The Howes Cave Quarry exhibits a number of karst features that further our understanding of the
local karst geology (Figure 8). Research in Howe Caverns is only now working out the
geomorphic history of the cave and its surroundings. Evidence of sediment infilling is found in
Howe Caverns, in other area caves, as surficial deposits, and here in the cliff face relict conduits.
Figure 9 shows two relict conduits that were once part of the furthest downstream end of Howe
Caverns. These are exposed in a northwest-facing wall of the quarry. The sediments in the lower
of the two conduits are depicted. The sequence here is a clay-rich pebble till overlain by finely
laminated lacustrine deposits. The pebbles are composed mainly of chert. The pebbles at this site
match those in upstream Howe Caverns, as well as in an exposed and deroofed conduit in the
quarry floor. Some are highly weathered and others are polished as if they had come from a rock
tumbler. The high percentage of chert and general lack of glacial erratics indicates a local, subglacial, source derived from the Kalkberg and New Scotland Formations. The lacustrine deposits
are interpreted as stemming from deposition in Glacial Lake Schoharie.
The intimate contact between the pebble till and lacustrine deposits is deceiving here. At
different times, Howe Caverns was largely filled with both of these deposits and subsequently reexcavated. Many hundreds of thousands of years and numerous geologic events occurred
between the deposition of these sediments.
Guenther Resurgence Cave is depicted in Figure 10. This outstanding find by Ben Guenther is
believed to be the original outlet of Howe Caverns when it first formed and intersected the
ancestral level of the Cobleskill Creek. Reference to published geomorphic-based denudation
rates indicates the time required to incise the regional base level to where it is now is on the
order of 1 to 2 million years. Upstream from the Howes Cave Quarry, this phreatic tube is next
seen in Howe Caverns at the Bridal Altar. Close examination of the cliff face near Guenther
Resurgence Cave indicates that several other outlet points may also have conducted water at the
same time – perhaps as a downstream continuation of an upper anastomotic maze seen in the
Bridal Altar area. If this turns out to be true, then the cross-sectional outlet configuration would
look similar to that portrayed in yellow on Figure 4. Much of the Howes Cave Quarry material
presented here stems from ongoing collaborative work between the Cave House Museum and
Howe Caverns.
One of the most exciting aspects of working out the karst hydrology and geomorphic history of
an area is the ability to picture what the earth was like long ago. Figure 11 depicts a GIS-based
reconstruction of the shoreline of Glacial Lake Schoharie in the Howes Cave area when the lake
surface was at about 1,170 feet msl. This is about 30 meters above the floor of the Howe Caverns
visitor center. The reconstruction depicts a number of local hills that were once islands.
Comparison with Karst in the folded Appalachians of the Hudson Valley
While cave development in the broad Cobleskill Plateau occurs in gently dipping carbonates, it is
important to recognize that some portions of eastern New York State have well-developed karst
in moderate to steeply dipping carbonate beds. Caves formed in steeply dipping strata are
sometimes laterally bounded by non-carbonates, which structurally control the direction of
groundwater flow. For example, carbonate strata in the Hudson Valley fold-thrust belt (HVB) are
sometimes situated on and along ridges. Cave surveyors have mapped caves as long as 3 km in
this NYS setting. Another example of a karst groundwater flow system has been identified and
described in the Kingston area (Figure 12). There, a large drainage basin funnels surface runoff
into the Lost Lake quarry pond where it enters steeply dipping, strike-oriented, carbonate beds
bounded by non-carbonate units (all within the HVB belt).
Surface water entering Lost Lake (Figure 12) flows over both carbonate and clastic sedimentary
rocks and is ultimately pirated into the karst aquifer. Like the variable discharge discussed above
in the Howe Caverns cave system, the flow into Lost Lake is also highly variable. Flow
measurements made in the aftermath of an October 2005 storm revealed that, at times, as much
as 15 cfs flows into Lost Lake and into the underlying karst aquifer. During periods of high
runoff, the water level of Lost Lake rises up to 0.75 meters and returns to its former level over a
short period of time, thus documenting that surface water must be shunted through the karst
aquifer. If this were not the case, the huge closed basin would fill up and overflow. The rapid
release of Lost Lake water can only be accounted for via discharge through a karst aquifer. The
more common lake level, like that in many mines and natural lakes drained by karst conduits, is
controlled by a combination of a natural or anthropogenically created threshold spill level and
the hydraulic efficiency of drainage conduits.
The short response time between rainfall and water-level rises in caves or mines is evidence for
efficient groundwater flow through conduits. Figure 13 shows flashy rises in water level in a
large flooded portion of the Kingston-Delaware Mine in response to heavy rain on a thick snow
pack (see Figure 12 for location). No surface streams flow into this mine, which shows that water
must be derived from an up-gradient karst aquifer with a large catchment area. As also shown on
the Howe Caverns hydrograph, water levels in the Kingston-Delaware mine decline over time,
indicating that there must be a release of groundwater through either natural or anthropogenic
conduits. Lost Lake is a likely source of this water, as it is hydrologically upgradient and along
the strike of the bedrock.
Nearby historic room-and-pillar mines, like that beneath the Howes Cave Quarry (11.4 acres),
often serve to enhance and integrate groundwater flow through one or more natural, pre-existing,
karstic flow routes. This may be the case in part of the Lost Lake karst aquifer. Insight into the
massive quantities of karstic groundwater encountered during historic mining operations is
gleaned from old lawsuits describing damage to round-the-clock pumping apparatus by
competing mining interests. Mines in the Kingston-Rosendale area, for example, have intersected
karst features including the underside of sinkholes, caves, and cave streams. Some of the mines
were excavated to depths of over 100 meters, are areally extensive, and contain large
groundwater reserves. Some are already being used to provide water supplies.
Sound land use planning in karst terrains requires protection of both groundwater and receptor
surface water quality (e.g. streams, wetlands, springs, wells). This is accomplished using tracer
tests to resolve groundwater flow paths down gradient of stream insurgence points, such as the
stream flowing into Lost Lake.
The lesson here is that New York, like many regions of the world, contains many areas that show
little or no surficial evidence for karst, but which are clearly drained by karst aquifers. The
problems of water supply, water quality, and land subsidence are still severe in these regions.
The fact that the presence of karst aquifers is widely ignored in these areas makes it all the more
likely that karst-related problems will complicate the management of land use and water supply.