DISTRIBUTION AND MORPHOLOGY OF SINKHOLES TRIGGERED BY FLOODING FOLLOWING TROPICAL STORM ALBERTO AT ALBANY, GEORGIA, USA

Flooding of the Flint River in July 1994 triggered the collapse of at least 312 sinkholes in the karstic Dougherty Blain at Albany, Georgia. We examined the distribution and morphology of these new sinkholes to evaluate the mode of formation, to characterize early stages of the e volution of sinkhole form, and to estimate the lowering of the surface associated with the development of new sinkholes. Eighty-eight percen t of sinkholes occur inside the limits of flooding, especially in area s of sandy overburden, and they often follow joint-controlled linear t rends. Sinkhole dimensions are log-normally distributed with median va lues of circumference = 5.7 m, length = 1.8 m, width = 1.6 m, and dept h = 0.7 m; asymmetry (L:W) = 1.2. Cross-sectional forms range from nar row cylinders to large bowls, with many sinkholes having undercut side s. Flooding triggered the formation of sinkholes by saturating and liq uefying overburden, which caused soil arches to collapse and flow into cavities in bedrock. The prevalence of sinkholes near the periphery o f flooding suggests that drainage and loss of buoyant support as flood waters subsided may also have contributed to failure. A volume ratio index is used to quantify the three dimensional geometric form of sink holes. Initially, small cylindrical shafts open over a bedrock joint, followed by progressive slumping that leads to widening and increases in volume to a final bowl form. Estimates of the aggregate volume of o verburden transported underground in flooded areas range from 7,990 to 11,130 m(3). Averaged over flooded areas, this accounts for 0.26 to 0 .37 mm/km(2) lowering of the surface. Based on a 500 year recurrence i nterval for the flood event, values for lowering of the surface range from 0.52 to 0.74 mm per 1,000 years. These values are an order of mag nitude less than estimates of carbonate dissolution and suggest that t ransport of overburden underground is limited by triggering events.