To me, the rocks that rim Dolly Sods have been sculpted into exquisite forms that resemble everything from humans and animals to abstract art. In a pamphlet about Dolly Sods published by the West Virginia University Extension Service, Norma Jean Venable wrote: “The boulders at Bear Rocks project from the stony earth as if placed by the hands of some ancient race of neolithic people.” This apparent element of intention or art in the rocks of Dolly Sods is intriguing and has led me to explain their origin in geologic terms.
Among the interesting shapes at Bear Rocks are rounded, often water-filled, depressions of varying diameters and depths carved into the stone. These depressions are called weathering pits or gnammas (nam uhs), the latter a term borrowed from the Aborigines of Australia, who depend on the water trapped in natural rock bowls for survival.
A Large Gnamma at Dolly Sods
Gnammas are formed by a geologic process called differential weathering. For example, should just a slight rock weakness cause a small depression to form on a horizontal rock surface, water, seeking the lowest spot, will preferentially flow into it. Should the temperature drop below freezing, the water will turn to ice, expand, and break up the rock particles next to it, thus making the small depression just a little larger. The enlarged depression will attract more water, which, when turned to ice, will further expand the hole. In this way the process feeds on itself, and after repeated cycles of freezing and thawing, what was once a small depression will have grown into a full-fledged gnamma.
A Large Gnamma at Dolly Sods
Gnammas deepen and expand outward, which eventually limits their growth. If the outer circle of a gnamma reaches the edge of a boulder or rock outcrop, the bowl will be partially breached. Further expansion carves a larger breach in the side of the bowl. Eventually the bowl is destroyed leaving, U shaped openings and rounded columns.
Breached Gnammas
Geologic studies show that gnammas can take thousands to tens of thousands of years to form. A study of gnammas in Portugal by David Dominguez Villar and others showed that, in general, the relative age of gnammas was best indicated not by width or even volume but by depth ratios. Without getting more technical, we can say that generally, the deeper the gnamma, the older it is.
Indeed, time is another key factor in nature's sculpting of rocks. Dr. Greg Hancock, professor of geology at the College of William & Mary, has studied the age of the outcrops on the east and west rims of Dolly Sods. He found that these rocks have been exposed at the surface for 60,000 to 240,000 years. That means that differential weathering has been gradually picking away at them for tens and even hundreds of millennia.
Above all, time is a fine hand. Over millennia, every subtle weakness in the rock, each small variation in rock composition, and even the slightest difference in natural openings are delicately but persistently magnified and accentuated. In the hands of time, weathering is a powerful tool, having carved the rocks of Dolly Sods into the intricate forms we see today.
Gnamma at Bear Rocks
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