GEOGRAPHIC DISTRIBUTION OF APPALACHIAN BOULDER FIELDS AND THEIR RELATION TO CLIMATE

Boulder fields, also called scree or talus slopes, are common features of the Appalachian mountain range. Explanations for the origins of boulder fields have focused on the role of freeze-thaw cycles associated with past periglacial environments. Here we present evidence that suggests a more complicated interpretation than a single-factor cause. We constructed a database of geographic occurrences of boulder fields in the Mid-Atlantic and Northeast regions of the U.S. using a combination of Google Earth and Terraserver true-color and infrared images. To narrow the search field, we counted boulder fields within 8-km swaths along transects at 1-degree intervals. Average transect length was ~300 km, and each transect overlapped the entire valley and ridge province as well as portions of the coastal plain to the east and the Allegheny plateau to the west. For each boulder field, we collected information on location, elevation, whether fields occurred singly or in clusters, and the position of the field on the ridge (summit or side).

If boulder fields are entirely controlled by climate, then we would expect them to occur at similar elevations regardless of slope. All identified boulder fields were found within the mountainous valley and ridge province and none within the relatively flat-lying Allegheny Plateau region, despite the fact that elevations were similar between the two regions. Our data also displayed a clear inverse relationship of latitude with the average boulder field elevation. However, this pattern was paralleled by the maximum elevation of the mountain range at each transect latitude. Our results suggest that these formations are not solely a function of climate (or past climate).