Boulder orientation, shape, and age along a transect of the Hickory Run Boulder Field, Pennsylvania
Date
2013
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
The boulder field at Hickory Run State Park in Pennsylvania is the largest such feature in the eastern United States and has been designated a National Natural Landmark. It has generated considerable interest among Quaternary scientists, and many college and university earth science field trips visit the boulder field each year. Beginning with H.T.U. Smith’s pioneering study in the early 1950s, most scientists have regarded the field as a relict of different frozen ground and freeze-thaw processes due to the close proximity of the Laurentide Ice Sheet during the late Pleistocene. Although the boulder field is included in many regional studies, relatively little quantitative data regarding its sedimentary properties have been published to date. This thesis describes a quantitative study of boulder orientation, shape, and relative age collected from 14 samples along a central parallel transect extending over the boulder field’s length. The first two rounds of field sampling used traditional field instruments including a Brunton compass, inclinometer, tape measure, and Schmidt hammer to collect data on boulder orientation, plunge, shape, size, and hardness. A third round of field sampling used ground-based Light Detection and Ranging (LIDAR) to obtain detailed topographic data from three 10 m by 10 m plots along the study transect. The LIDAR data were filtered and used to construct elevation, slope, and aspect models for comparison with the aforementioned manually collected field data. The LIDAR data provides a quantifiably more useful dataset than traditional field methods using a Brunton compass, and the resultant Digital Elevation Models (DEMs) are a robust and data-rich approach to evaluating boulder fabric. The results of this thesis suggest a spatial trend in boulder roundness and a-axis length along an east-west trend of the boulder field. Conversely, no spatial trends were identified in the orientation, plunge, sphericity, flatness, and size data. The implications of spatial trends in sedimentary characteristics are discussed relative to four possible formation processes of the Hickory Run Boulder Field.