IMAGING THE 3-D ARCHITECTURE OF A PRAIRIE ESKER WITH GROUND-PENETRATING RADAR: IMPLICATIONS FOR INFERRING DEGLACIAL ENVIRONMENTS

Very little is known about the internal architecture and depositional environment of prairie eskers. The Clear Lake Esker is the largest esker in southern Alberta extending over 35 km. This esker is located within a tunnel channel, exiting into a shallow glacial lake basin downflow. It has a number of morphological elements that are suggestive of a complex depositional landform. For example, the hummocky crestline of the esker may record primary macroforms or post-depositional modification.

Two study areas were chosen to represent the morphological and, presumably, architectural variability along the landform. At the first site, the esker crest was sharp, undulatory and continuous. At the second site, broad, plateau-like segments separated by troughs characterize the esker. Detailed transverse and longitudinal ground-penetrating radar (GPR) surveys were conducted at these two locations to image the internal architecture of the deposit and to establish its stratigraphic context.

The GPR imaged through the 8-13 m thick esker revealing the 3-D architecture. The geometry of the reflections indicates a complex depositional landform that lies directly on bedrock. The GPR profiles revealed that the landform shape is almost completely the result of primary deposition. The undulating crestline is the surface expression of internal structures including pseudoanticlinal and lateral accreting macroforms. Post-depositional faulting, due to loss of lateral ice support, was not indicated in the profiles. Minor aeolian erosion and deposition was evident in the near-surface. The information gained from the GPR surveys has helped reveal the relationship between the late-glacial hydrology and resulting landforms.