COMPARISON OF PERIGLACIAL BLOCK FIELDS AND TALUS SLOPES IN SOUTH CENTRAL PENNSYLVANIA AND NORTHERN MARYLAND

Relict periglacial boulder fields, or block fields, are scattered across south-central Pennsylvania and northern Maryland. A combination of digital analyses using Google Earth Pro and fieldwork were used to investigate block fields at different scales. At least 29 block fields were identified on Google Earth Pro. Polygons were created by tracing the outline of each block field using the polygon tool, and area was calculated. The distance to the former ice margin of the Laurentide Ice Sheet was approximated by measuring from the centroid of each block field polygon to the ice margin. Preliminary results show no statistically significant relationship between block field area and latitude (p = 0.31). Fieldwork focused on two block fields, which were compared with fieldwork conducted on two talus slopes. The block fields studied were Raven Rock Hollow in Maryland and River of Rocks at Hawk Mountain in Pennsylvania, and the talus slopes were located at Catoctin Mountain, Maryland and Waggoner's Gap, Pennsylvania. The length, orientation and dip of each rock were measured across transects perpendicular to the long axis of each block field or talus slope. Rocks less than 30 cm and that were easily moved due to small size were excluded from the analyses to minimize the impact of human disturbance. Boulders at Hawk Mountain and Raven rock have an average long axis length of 1.49 m and 1.4 m, while boulders on the talus slopes were significantly smaller, 0.7 m and 0.86 m (p < 0.001). The dip or inclination of the block fields and talus slopes is also significantly different (p < 0.001) with block fields exhibiting a higher angle than the talus slopes. These differences illustrate the impact that different geomorphic processes have on formation of block fields compared to talus slopes. Additional analyses are in progress.