The largest known cave in Ohio is Ohio Caverns, just east-southeast of the town of West Liberty, northern margin of Champaign County, western Ohio, USA.
The cave is developed in an NNW-SSE elongated knob of Columbus Limestone (Eifelian Stage, lower Middle Devonian) that is capped by a little Ohio Shale (Upper Devonian). Western Ohio generally has Silurian-aged surface bedrock. However, the Bellefontaine area of western Ohio has an “island” of Devonian-aged surface bedrock. This is the Bellefontaine Outlier, the highest point in all of Ohio. The Columbus Limestone knob at Ohio Caverns is near the southern margin of the Bellefontaine Outlier.
Above: Looking S at northern edge of Columbus Limestone knob, southern Bellefontaine Outlier. Ohio Caverns is developed near the crest of knob on the eastern side of the road (left side in this picture), behind the tall tree at left.
Above: Looking NNE down the northern margin of Columbus Limestone knob. Ohio Caverns is developed in the subsurface of the area behind the photographer here. The hills in the distance are part of the central Bellefontaine Outlier.
Above: Looking ~SE. Ohio Caverns occurs directly below the land surface here. The small whitish building behind the two tall trees is the cave exit house.
The Columbus Limestone outcrops in a north-south trending belt from southern Ohio to central Ohio to the Lake Erie islands. Like all limestones, it is prone to dissolution by acidic fluids & cave development. Not all areas with limestone bedrock will have significant cave development, however.
Above: Columbus Limestone along walls of Ohio Caverns, near the modern entrance.
Many of the walls of Ohio Caverns have readily observable Columbus Limestone bedding. In places, the limestones are coated & obscured by secondary cave mineral deposits. The Columbus Limestone here has the same general lithology & appearance as surface outcrops in central & northern Ohio. The formation consists of light brownish-gray, fine-grained limestones to fossiliferous packstones with several well-developed stylolite horizons & chert nodule horizons.
Above: Wall & ceiling of Ohio Caverns showing bedding nature of the Columbus Limestone. The subrounded to eye-shaped structures along the wall are chert nodules.
Above: The jagged dark line is a stylolite developed in the Columbus Limestone & exposed along a wall in Ohio Caverns. Stylolites are moderately common in limestone successions. They form by limestone dissolution from significant tectonic and/or burial pressure.
Above: The cave ceiling here is a stylolite surface. Stylolites represent surfaces of weakness. At Ohio Caverns, stylolites often define the upper separation planes for collapsed limestone blocks.
Above & below: Blocks of cherty limestone that have collapsed from the ceiling of Ohio Caverns.
Chert nodule horizons are moderately common in Columbus Limestone outcrops of central Ohio. They are also common along the walls of Ohio Caverns. They often protrude from the cave walls. This is a result of differential weathering & differential erosion. The chert nodules are hard (H = 7 on the Mohs Hardness Scale) and not easily prone to natural acid dissolution. The surrounding limestone/calcite matrix is relatively soft (H = 3 on the Mohs Hardness Scale) & readily dissolves in carbonic acid & organic acids in downward percolating groundwater.
Above & below: a fossiliferous chert nodule with an obvious strophomenid brachiopod shell cross-section & a large solitary rugose coral.
Ohio Caverns does not have a very long cave system. Most of the passages are canyon passages, which are taller than they are wide, and keyhole passages, which have a keyhole-shaped cross-section shape. The canyon passages at Ohio Caverns tend to follow straight lines, due to limestone dissolution along planar subvertical joints.
Above: Canyon passage in Ohio Caverns.
Above: Keyhole passage at Ohio Caverns with multicolored staining on the walls & ceiling plus minor speleothem.
Keyhole passages have an upper tubular passage modified by canyon passage downcutting below. The keyhole passage shown above has sediment filling the lower, narrow parts.
Above & below: Keyhole passages at Ohio Caverns
Above & below: Dripping & standing water can be observed in many of the passages at Ohio Caverns, which is still an actively-forming cave.
Much of the passage system in Ohio Caverns was filled with muddy sediments when first discovered in the late 1890s. Some of the smaller side passages still have muddy sediment fills.
Stalactites are mineral icicles hanging down from cave ceilings. They are one of many varieties of speleothem, the general term for all secondary cave mineral deposits. Speleothem that forms by dripping water is called dripstone. Stalactites and their equivalents on cave floors - stalagmites - are the most common & easily recognizable forms of dripstone.
Most stalactites at Ohio Caverns are composed of the mineral calcite (CaCO3 - calcium carbonate), as many of the world’s stalactites are. The rock making up these calcite structures is a calcitic, crystalline-textured, chemical sedimentary rock called travertine. Some people call travertine a “chemical limestone”, but that’s a terrible term. Travertine isn’t limestone - it has the chemistry and mineralogy of limestone, but it’s not limestone. It’s travertine.
Stalactites form as a result of downward-percolating groundwater dripping from the ceilings of subterranean cavities (see photos below). Groundwater tends to partially dissolve limestone bedrock, which is composed of calcite. This happens because groundwater is slightly acidic - it contains some carbonic acid & organic acids. The carbonic acid in groundwater is acquired as water percolates through soils & fractures & pores in bedrock, where the partial pressure of carbon dioxide gas is higher than it is at the surface. A higher partial pressure of carbon dioxide gas results in a rightward shift of the following equation:
H2O (water) + CO2 (carbon dioxide gas) ¬¾® H2CO3 (carbonic acid)
So, groundwater becomes slightly acidic. It dissolves acid-soluble minerals, such as calcite (see equation below).
CaCO3 (calcite) + H2CO3 ¬¾® Ca+2 (calcium ion) + 2HCO3- (bicarbonate ion)
Once downward percolating groundwater reaches the ceiling of a subterranean cavity, the water encounters air with a lower partial pressure of carbon dioxide gas. The two chemical equations given above then shift to the left, and calcite precipitates. Most people think that the calcite precipitates as water evaporates. Well, most caves are quite humid (cave air is close to being water saturated), so the water isn’t evaporating. The calcite in stalactites & other speleothems gets precipitated as a result of a CO2 partial pressure change.
Crystal King Stalactite, the largest known in Ohio Caverns. It’s just shy of being five feet long. It is composed of nice, white travertine.
Stalagmites are dripstones that form on cave floors. Many stalactite-stalagmite pairs are asymmetrical in size (i.e., large/long stalactite on the ceiling with a small stalagmite on the floor or a small stalactite on the ceiling with a large/tall stalagmite on the floor). Slowly dripping water results in large/long stalactites on the cave ceiling and small stalagmites on the cave floor. Quickly dripping water results in small stalactites and large/tall stalagmites.
Soda straws are narrow, cylindrical stalactites. Ohio Caverns has some well developed soda straws, although many are broken. Some of them are thicker than typical soda straws, and are slightly tapering, rather than cylindrical.
Above: a long soda straw with a stalactite at its distal (bottom) end.
Columns are dripstone speleothems that form when stalactite-stalagmite pairs become physically joined by calcite precipitation. They vary considerably in height and width.
Above: Soda straw column in Ohio Caverns having an irregular width.
Above: Nice soda straw column in Ohio Caverns.
Above: An odd column that is barely connected to the cave ceiling.
Above: Lateral & bottom views of a suspended column. This is a column that appears to be floating in air - it’s just attached at the ceiling. This is not a completely natural feature. The base of this column represents the original floor of the cave. This passage was partially filled with mud, which has since been dug out in the process of making Ohio Caverns a tourist cave. Additional suspended columns are shown below.
LOTS OF DRIPSTONE
Helictites are twisted, contorted speleothems growing from cave walls & ceilings that appear to defy gravity. They do not form by dripping water, as stalactites & stalagmites do, nor by flowing water, as flowstones do. Helictites form principally as a result of water moving by hydrostatic pressure & capillarity (= seeping water). Hydrostatic pressure pushes water from pores in a cave wall, and a CO2 partial pressure change results in calcite precipitation. A small calcite protrusion is now present on a cave wall. Capillary action draws additional water sideways through the protrusion, and more calcite precipitation occurs. The spiralling, twisting, and bifurcation seen in many helictites is caused by rotation of calcite crystallographic axes during precipitation events and by the presence of impurities in the precipitated material.
The three pics shown below have nice soda straws & helictites on the ceiling of a room in Ohio Caverns. These are composed of calcite. Many of the helictites here started forming at the distal tips of soda straws. Some have grown upward & attached to the ceiling, apparently in defiance of gravity!
Draperies are planar to subplanar to wrinkled speleothem curtains hanging from the ceilings or inclined walls of caves. They form by calcite precipitation as individual water drops run down inclined surfaces. In many caves, draperies have reddish-brown & whitish color bands parallel to the lower surface. Such strutures are appropriately called “cave bacon” or bacon draperies.
Some info. provided by Hill & Forti (1997 - Cave Minerals of the World, Second Edition).