DYNAMICS OF COLD-AIR FLOW FROM TALUS AT THE ICE MOUNTAIN ECOLOGICAL REFUGIUM, WEST VIRGINIA, USA
Terrain conductivity and VLF surveys indicate the talus is exceptionally thick (8 to 20 m) compared to others in the region. Talus boulders are derived from upper Helderberg and Oriskany sandstone atop Ice Mountain, but are underlain by Devonian Millboro Shale. All cold-air vents occur on a fluvially truncated convex toe-slope, a morphology contrasting concave toe-slopes typical of most Appalachian talus. Upper and middle talus surfaces are open with little impedance of air flow except spotty vegetation cover. Vegetation and soil cover is more continuous along the convex toe-slope, restricting basal drainage of cold dense air to the small vents, which have a cumulative opening area of only 5 to 20 sq. m.
One year of hourly and bi-hourly temperature measurements indicates that cold-air vents are fed by high-density cold air trapped within the thick boulder accumulation. Mean vent temperatures (3 degrees C) are 7 degrees colder than mean air temperatures on the upper talus. Vent air warms very gradually at the onset of spring. In contrast, cold nights in late summer to mid-winter produced sudden vent temperature drops of 5 degrees or more in an hour, suggesting complete exchange of air whenever the air is colder and denser above the talus than within. Air temps rise within a day of exchange events, but typically stabilize 1 or 2 degrees less than pre-exchange temperatures.
Ice and snow may accumulate deep within the talus during winter months, but year-round ice persistence is not essential to summer cold-air flow. Winter-ice accumulations at two instrumented vents melted during late April 2004.