SUBGLACIAL KARST DEVELOPMENT IN EAST-CENTRAL NEW YORK STATE

Conduit geometry, wall scallops, and surface topography provide evidence that much of Clarksville Cave in Albany County, NY developed in a subglacial setting toward the end of two or more glacial periods. This interpretation is confirmed by Beta Analytic Accelerator Mass Spectrometry (AMS) radiocarbon dating of charcoal located within a 2.7 cm thick silty clay loam layer situated above two in-cave debris flows. The AMS date of > 43,500 years BP exceeds the dating method limit, likely placing charcoal influx into the cave during late Marine Isotope Stage 6 or early MIS 5e (~ 140 ka to 110 ka; Sangamonian interglacial) coincident with a fire in newly developed upland forest. Cosmogenic radionuclide dating of sediment may further elucidate the Quaternary chronology of the region.

The potential catchment area required to develop large-diameter vadose infeeder conduits and a large phreatic conduit in the cave is not available from the present-day watershed. Seasonal variation in the quantity of warm-based subglacial meltwater, over tens of thousands of years, has resulted in alternating vadose and epiphreatic conditions developed behind a hydraulically inefficient or occluded outlet (not multiple phreatic conduits graded to changing base levels). At a second conduit constriction at a three-chert bed sequence (~ 75 cm thick), downward flow of high velocity meltwater has resulted in floodwater passage development elevationally above most of the cave (Pixie Passages).

A number of lines of evidence support substantial subglacial cave development from the influx of glacial meltwater. Factors supporting this interpretation include 1) numerous high-volume water and sediment inflow locations that have no relation to the surrounding hydrologic setting, 2) master phreatic conduit dimensions too large to have solely formed from existing watershed inflow (~ 9 m²), 3) small wavelength scallops on infeeder canyon walls that document high-velocity inflow (e.g., 1 m/sec), 4) sediment profiles that extend far upgradient within infeeder conduits that are unrelated to the surrounding hydrologic setting, and 5) doubling of pre-Wisconsinan phreatic discharge along the master conduit resulting from subglacial infeeder inflows (~ 0.18 m³/sec to 0.33 m³/sec as determined by analysis of scallop wavelengths and conduit dimensions).