CHARACTERIZATION OF DRUMLIN DEPOSITS AND AQUIFERS USING GEOPHYSICAL METHODS: EXAMPLES FROM THE CENTRAL NEW YORK DRUMLIN FIELD

Central NY drumlins dominate the landscape and they vary in shape, size and orientation. There are few places where the internal structure of the drumlins can be observed directly. During this long-term investigation, a number of drumlins have been observed using geophysical methods such as GPR, ER, EM and magnetics in an attempt to characterize the nature and variability of the deposits, the distribution of groundwater and the interaction of the groundwater with surface water. High-resolution and regional (km scale) ER data was collected for three drumlins. The regional data crosses the axis of each drumlin revealing the base of each drumlin with the bedrock base in addition to large internal anomalies most likely associated with variation in gravel and clay content. The high-resolution data was collected along the flank of each drumlin to examine the upper most 10 meters of the subsurface. Serial ER surveys show complex distribution of high and low anomalies, and specifically reveal aquifers confirmed by tracing low anomalies to springs on the drumlin flank, or in some cases small ponds that were dug when the region was heavily farmed. 3D models showing the distribution of these low anomalies (aquifers) were constructed and they look like small braided stream channels and are interpreted to represent post-drumlin reworking during the retreat of the lake that occurred in this region during the late Pleistocene. GPR data was collected on the flank of two drumlins, and the data shows apparent channel forms in the same places of isolated small ER anomalies occur. Two drumlins were mapped using a high-resolution magnetic gradiometer. The magnetic survey produced maps showing apparent variation in near surface deposit with some anomalies correlating directly with the ER anomalies discovered during the high-resolution surveys. Variation in magnetic anomalies are 10’s of nT, and are interpreted to reflect the amount of sand, clay and gneissic materials in the subsurface. Finally, EM surveys were run on the flank of one drumlin where ER and GPR surveys were run. Conductivity variability is consistent with ER observations. The intent of this presentation is to show results from 4 commonly used geophysical methods to assess which combinations of these methods might be best for understanding internal variation of the drumlins studied.