Cold-Air Trap Temperature Records Support Simple High-Density Air-Flow Mechanisms at an Appalachian Limestone Cave Entrance Sinkhole

Many Appalachian caves act as cold-air traps, widely open systems chilled by high-density cold air during chilly weather that evolve into density-stratified, nearly closed systems in warm weather. Like algific talus slopes, rock cities, and other cold-air traps in the region, these caves appear to function in accordance with a simple natural refrigeration model popularized by Balch (1900), in which circulation is dominated by static, thermally stratified conditions intermittently disrupted by sinking cold air. Crowder Cave, in Monroe County, West Virginia, hosts two separate cold-air traps in chambers contiguous to an entrance pit, a ~12,000 m3 sinkhole lined with 6 to 18 m high limestone cliffs. The sinkhole and both cave chambers appear poorly connected to surface or subsurface streams. Davies (1958) reported historical accounts of seasonal ice in the small room as late as July, but our ongoing hourly temperature monitoring indicates ice regularly has disappeared by late April in five of the last six years. The entrance pit functions as a relatively open cold-air trap system with a mean annual temperature of ~7°C, well below mean annual surface temperatures of ~10°C recorded at nearby weather stations. In summer, both cave chambers are virtually closed systems with very gradual increases (<0.1 to 0.2 C°/day) in temperature; neither experienced a temperature reading greater than 9.2°C during our monitoring. In stark contrast, both chambers commonly experience brief winter episodes of rapidly plunging (4 to 8 C°/day) temperatures, reaching as low as -13 to -15° C. Icicles, columns, frozen lenses, and other ice accumulations have been observed in the small ~350 m3 chamber at the northeast end of the cave, where mean temperature has been ~2.7° C. Ice stalagmites and various other ice forms have been seen on the floor of the large ~12,000 m3 chamber on the south end of the pit, where the mean temperature has been ~3.5° C. Entrance pit temperatures respond very quickly when atmospheric conditions are appreciably colder than pre-existing air in Crowder Cave; temperatures in the two adjacent chambers seldom lag more than 1-3 hours behind. Despite similar timing, the amplitude of temperature response in the large chamber is considerably less than the small chamber, presumably because of a 35-fold difference in chamber volume. The amplitude of temperature change decreases and mean temperature increases with distance from the mouth of the large chamber. More characteristic of typical cave conditions, temperatures near the end of a narrow 85 m long side passage varied little (9.8° to 10.6° C) during the last 4.5 years. Crowder Cave data show the interplay between density-driven cold air flow, karst topography, and cave geometry lead to wide variability in winter conditions that may give rise to very different bat hibernacula conditions in a single cave. The ecological significance of cold air traps associated with sinkholes may be profound, both as climate change indicators and for a potential role they may play in the course of the ongoing white-nose syndrome (Pseudogymnoascus destructans) epidemic. Conference Topic: Investigation, Monitoring, and Remediation in Karst