With the Tufa Caves of Van Hornesville, what you see is what you get: quirky, mossy, storybook ambience

tufa bedrock

The Enterprise — Mike Nardacci
A weathered section of tufa bedrock shows some of the many arches and overhangs.

Situated in the picturesque village of Vanhornesville west of Albany is a display of unique geologic features called “tufa caves” that — along with the village itself — are likely unknown to most people in the upstate area.

Located to the north of Route 20, Vanhornesville is accessible by State Highway 80, about a relaxed 90-minute drive from Albany, passing through farmland and woods as the roads traverse gentle hills.  There are no signs along the way to announce the caves and only a couple of small ones within the village itself to point the way to the Outdoor Learning Center of the Owen D. Young Central School District, the preserve in which the caves have formed.

When most people think of caves, they are undoubtedly thinking of what geologists call “solutional caves,” such as the nearby commercialized Howe Caverns and Secret Caverns and the many wild caves that underlie the Helderberg and Cobleskill plateaus west of Albany.

Solutional caves are the product of the dissolving of carbonate bedrock such as limestone or marble by mild natural acids, most commonly carbonic acid. This acid forms when falling rain picks up carbon dioxide in the atmosphere or when pooled surface water absorbs the gas from decaying plant material.

It is an extraordinarily slow process and great solutional caves such as Mammoth Cave in Kentucky can take millions of years to form.

Other common cave types are fracture caves, caused by the gradual enlargement through erosion and weathering of natural joints in cliff faces; lava caves such as those in Hawaii formed by erupting volcanoes; and what are called “talus caves,” which are essentially enterable spaces between massive boulders that accumulate at the base of a cliff as a result of landslides. These caves are often scorned by sport cavers as “just a pile of rocks,” though geologists find they often contain complex and unique geologic features.

But tufa caves are relatively uncommon and are rarely very extensive, measured in feet rather than miles, unlike solutional caves that can extend for hundreds of miles. Nonetheless, like the tufa caves of Vanhornesville, they have their own attractions, one of which is that many of them require no special equipment to explore beyond a flashlight, and some are shallow enough that even that is unnecessary, though a helmet is recommended if an explorer wants to avoid bumping one’s head.

And the very process by which tufa caves are made is of interest, for, unlike solutional and fracture caves that form in pre-existing bedrock, tufa caves develop from the chemical deposition of rock from flowing mineral-saturated water.

Anyone who has visited a commercial cave has learned the mnemonic regarding the calcite formations that appear there: stalactites — there is a “c” for “ceiling,” and stalagmites — there is a “g” for “ground,” indicating the places where they form.

It is an oversimplification to say that they form from “dripping water,” though that is certainly more accurate than the explanations of the ancient Greeks and Romans who believed that they were some bizarre form of life and were literally “growing” in the cave environment.

But in fact what appears to be pure water dripping from the cave ceiling is a solution of calcium bicarbonate containing dissolved carbon dioxide that stays in solution as long as that liquid is within the confines of narrow fissures through which it is being pulled downward through the bedrock by gravity. 

When the droplets emerge into the cave environment, the decrease in pressure causes the solution to “de-gas” — similar to what happens when the top is removed from a carbonated beverage — releasing the carbon dioxide and depositing a minute amount of calcium carbonate on the ceiling or on the floor.

The agitation of that liquid as it flows down the cave wall or splashes onto the floor can also cause it to de-gas, much as shaking a carbonated beverage may cause the carbon dioxide to de-gas forcefully. Over long periods of time, the result will be the growth of stalactites, stalagmites, flowstone cascades, and other cave formations.

But under certain conditions, the stream in a karst aquifer — a technical name for a solutional cave with flowing water — may itself contain large amounts of dissolved calcium carbonate and is either super-saturated or under sufficient pressure that the “degassing” process does not occur until the stream emerges from the bedrock and flows over the surface.

At that point, the deposition of calcium carbonate — calcite — will occur as the pressure is released or the saturated water mixes with plain H20 and anything in the stream’s path may become thickly coated with these deposits which are known as “tufa.” The resultant rock tends to be relatively soft and crumbly and porous and often has the appearance of petrified shaving cream, sometimes containing mineral-coated sticks and twigs and leaf impressions.

Along the section of Route 146 that runs parallel to the base of Barton Hill near Gallupville there are a number of streams resurging from small caves at the base of the cliff and in times of low flow those streams will deposit tufa, which may appear as a white coating on rocks in the streambed or form pebbles and cobbles containing sticks and twigs and leaf impressions.

A more dramatic example of this deposition can be seen on the north side of Route 443 between Gallupville and Shutters Corners. An extensive section of the hillside is covered with conglomerate — a naturally-cemented mass of rock fragments.

Here, long ago, tufa springs emerging from the cliff above cemented extensive deposits of glacial debris — or “drift” — and formed the conglomerate. These mineral springs eventually sealed themselves up and no longer flow. Today the conglomerate is fracturing and weathering away and may eventually cause a landslide onto Route 443.

The caves at Vanhornesville have formed a series of tufa deposits in a narrow valley that contains the Otsquago Creek. Saturated with calcium carbonate, the stream’s headwaters emerge from a series of springs and deposit the mineral.

At some point in the past, undoubtedly due to the melting of the glaciers at the end of the ice age, the stream carried a far greater volume of mineral-saturated water than it does today, resulting in the massive outcrops of tufa with their irregular, intricate openings: overhangs and tunnels and arches.

But unlike solutional caves, which can take millions of years to develop, these tufa caves are relatively young in geologic terms and are certainly post-glacial. Given the relative softness of tufa, the grinding effect of the continental glacier advancing over the landscape would have ground them away — although there might well have been an earlier series of caves that the glacier destroyed.

The porosity of the tufa allows it to hold water and makes it a perfect environment for moisture-loving plants. The walls and nooks and crannies of the Vanhornesville caves thus are covered with mosses, lichens, various types of ferns, and rare wildflowers in spring.

Though the entrances to the numerous little caves appear mysteriously alluring, upon entering one, the visitor quickly understands the adage, “What you see is what you get,” and there is no danger of getting lost in an underground labyrinth.

But to hike in and around the caves with their quirky, mossy, storybook ambience is to experience a unique example of what nature can create with time and some simple chemistry.

rr12159
Online
Joined: 05/12/2020 - 21:21
Enjoyed this!

A great article Mike. In addition to everything else I learned I now know the proper name for the formation at Howes caverns that includes the stream.

Hope all is well.

Richard Rubin