A reconnaissance study of tafoni development, exfoliation, and granular disintegration of natural and artificial rock surfaces in the coastal and lowland regions of Tamil Nadu, Southern India

Weathering of native charnockites and sandstones of coastal Tamil Nadu occurs by granular disintegration, exfoliation, and tafoni development. This is the first report of tafoni in India. Mafic minerals begin to deteriorate near the coast within a dozen years, leaving irregular differential weathering pits. Colonial tombstones of charnockite, 200 to 400 years old, are covered with small round pits that are interpreted as incipient tafoni. Ancient Hindu and Jain temples, about a thousand years old have pits that are similar in size and shape. Ancient charnockite megaliths, that are about 3,000 years old, have weathering pits that are an up to 20 cm across, and several centimeters deep. Inselberg surfaces that are a few million years old have tafoni in which a person can walk upright. The frequency distributions of depths, widths and volumes of these pits, from the smallest to the largest, are heteroskedastic and lognormal.The megaliths do not have small pits such as the colonial tombstones and ancient temples. The inselbergs do not have pits such as those on the megaliths. We believe that at the same time as the pits are enlarging, the surfaces are exfoliating, that removes the smaller pits. But the small pits do not reform on the old surfaces. This strongly suggests that something is preventing the development of new pits that might be used to conserve ancient stone monuments.