Sinkholes developed in sandstone

Caves and closed depressions developed in carbonate rocks are defining features of karst terranes. With the increasing recognition that significant caves can develop in quartz (siliciclastic) sandstones, it is natural that we should start to examine their surficial counterparts, sinkholes. A review of the literature shows rather limited attention given to these features. In the glaciated region of northeast Ohio (USA) colleagues and I have examined numerous sinkholes in sandstones, with a variety of morphologies. The most commonly found type is cover subsidence sinkholes, where thin overlying regolith (usually till) has sagged into escarpment-parallel widened fractures. The most significant of these is an entrance to Little Mountain Caverns, 8 m deep, where a volume of rock circa 67 cubic meters has been removed along fractures, while the surrounding rock remains intact. Mechanical as well as chemical processes are in effect here. In the Precambrian Hinckley Sandstone of Minnesota (USA) hundreds of small sinkholes are found and are linked with rapid groundwater flow. Several large collapses, apparently related to underlying carbonate dissolution, and found in the desert environment of Arizona (USA). In high rainfall tropical situations, such as the Cerro Sarisariñama tepui of Venezuela, large collapse sinkholes (up to 300 m depth) are found. These are developed in a quartzite. Swallet cave entrances are found in other locations, such as the Aonda Cave system on Auyán tepui. There, researchers have noted that the greatest shafts are found at the margins of the plateau, a situation that is attributed to stress relief fracturing. The occurrence of sinkholes in quartz rocks is not limited to tropical environments, though. All of these cases emphasize that “karst-like” processes may, and do, operate in rocks that we normally consider to be poorly soluble. As a consequence, rapid groundwater movement and its environmental ramifications, as well as the potential for collapses, must be considered in a variety of environments. Great landscape age, high water volumes, and high hydraulic gradients all seem to possibly contribute to the formation of these features