USING NEAR-SURFACE GEOPHYSICAL TECHNIQUES TO INVESTIGATE HOLOCENE SEDIMENTATION IN BEAVER MEADOWS, ROCKY MOUNTAIN NATIONAL PARK

Investigations that analyze sediment packages and the processes associated with their deposition are integral for identifying the historic range of variablity at a site. Near-surface geophysical techniques make it possible to infer sediment packages within the Holocene which are not exposed at the surface. This study uses ground penetrating radar (GPR), near-surface seismic refraction and augering to determine the depth of sediment, to characterize the stratigraphy of the valley fill, and to obtain a preliminary grasp on the impact of Holocene beaver activity in Beaver Meadows, Rocky Mountain National Park. Approximately 5 km of GPR data and 1 km of seismic data were collected along with hand-auger cores from 23 sites. Analysis of the data suggests that the valley fill not associated with glacial deposition is less than 7 m thick in the middle of the valley. The name "Beaver Meadows", a high abundance of fine sediment including silts and clays within the valley, and historical records of beavers all suggest that Holocene beaver activity played a large role in sediment accumulation, despite the lack of visible relict beaver dams containing wood. The use of GPR has proved to be valuable in identifying areas of sedimentation associated with ponding. Although some of the ponded fine sediments could be associated with a period in which the valley was dammed immediately following glacial retreat, analysis of the distribution of ponded sediments within the GPR data, along with slight topographical features resembling buried beaver dams, seems to suggest that beaver activity substantially impacted the site.