APPLICATION OF GIS TO INVESTIGATE SPATIAL STATISTICS AND MORPHOMETRICS OF CLASTS AT HICKORY RUN BOULDER FIELD, PENNSYLVANIA

Hickory Run Boulder Field, located in Carbon County, Pennsylvania, is a 5.7-hectare felsenmeer of which over 500,000 boulders are visible at the surface. Recent investigations employing radio-controlled aircraft to collect low-altitude, high-resolution aerial photographs revealed arrangements of boulders similar to patterned ground produced by cryoturbation. For this study, we orthorectified these images into a Geographic Information System (GIS) to record boulder location, size, orientation and shape and to evaluate spatial relationships.

Over 12,000 boulders were digitized into a database using ArcGIS 9.31. Boulder length followed a log-normal distribution with a geometric mean and variance of 0.51 and 0.08 m, respectively. Boulders were not randomly oriented and displayed a preferential orientation of 58/238 degrees. Aspect ratio (length/width) followed a log-normal distribution with a geometric mean of 1.95 and a variance of 0.53. However, small (<0.1 m length) clasts were rounder (aspect ratio close to 1) than larger boulders. An average nearest-neighbor (cluster) analysis using ArcGIS Spatial Statistics Analyst revealed that the boulders are not randomly located (p < 0.0001), supporting previous observations that boulders are arranged in patterns. Rendering boulder centroids with Spatial Analyst produced a map of boulder density that clearly shows 60/240 degree-trending, linear features and boulder clusters spaced 3 to 7 m apart. We conclude that the geostatistical tools provided with ArcGIS provide a useful means for describing, interpreting, and visualizing boulders at Hickory Run, and will provide a means for comparing boulder patterns with patterned ground generated in contemporary periglacial environments.