CHARACTERIZATION AND IDENTIFICATION OF ALGIFIC TALUS SLOPES WITHIN THE VALLEY AND RIDGE PHYSIOGRAPHIC PROVINCE OF PENNSYLVANIA USING LIDAR

Attributes of well-documented extant algific (cold-air producing) talus slopes have been complied to determine if any salient characteristics associated with these landforms might lead to an identification process through remotely sensed data. Data collected for this research will be analyzed using digital elevation models (DEM) produced from LiDAR obtained from the Pennsylvania Department of Conservation and Natural Resources’ PAMAP program.

There are currently three known algific talus slopes in Pennsylvania: Trough Creek Ice Mine, Colerain Ice Cave, and Delaware Water Gap Cold Air Cave. Trough Creek Ice Mine in Trough Creek State Park and Colerain Ice Cave in Rothrock State Forest are both located in unglaciated Huntingdon County in south-central Pennsylvania. The Delaware Water Gap site is located in an area in Northampton County that was covered during a pre-Illinoian glaciation. Periglacial landforms, including talus, abound in mountains south of the Wisconsin glacial limit. These three algific talus slopes produce cold air and form ice at the toe of the slope. During colder months and seasonal cold snaps, cold air sinks through voids surrounding the talus boulders and becomes trapped due to density stratification, a process known as Balch refrigeration. The cold air slowly exits through small vents at the bottom of the talus slope where it comes into contact with relatively humid air that condenses and freezes, further sealing cold air in the talus. This process has a cyclic annual pattern and can produce unique biological diversity supported by airflow that may average 8-10 degrees C colder than annual mean ambient temperatures on adjacent slopes.

Identification of previous unknown algific talus slopes will be attempted with DEMs, processed using ArcGIS. Various DEM derivatives , including slope, curvature, roughness, and aspect, will be processed using a binary system relating to the similar characteristics seen in the three documented Pennsylvania algific talus slopes. Due to the unique microclimate these landforms produce, discovery of more algific talus sites has the potential to greatly enhance our knowledge of the extent of ecological refugia that have survived climatic alteration since the Pleistocene, and may play a key role in future species survival.