ELECTRICAL RESISTIVITY TOMOGRAPHY TO IMAGE CHANGES IN A GLACIATED AND FRACTURED BEDROCK HILLSIDE

Understanding how the critical zone influences the hydrologic cycle is crucial to mitigating the effects of climate change in New England. Several sites across the United States are currently being studied under the rubric of Critical Zone Observatory. None of these observatories are in the New England region, and importantly, continental glaciers did not impact these sites. In New England, the influence and impact of continental glaciers is pervasive. The collected geophysical data will investigate the critical zone at the MacLeish Field Station in Whately, MA, a site covered by glacial material. The goal of critical zone studies is to understand the structure and evolution of the critical zone and the transport of solutes and sediments within the critical zone. We also need to measure the changes in soil water, surface and groundwater storage, and changes in measured solute and sediment as a function of depth and watershed location.

I collected two, perpendicular electrical resistivity (ERT) profiles on eight occasions between May and November to characterize the subsurface at the MacLeish Field Station. Assuming that the geologic materials of the near surface are constant at these short geologic time scales, changes in the geophysical response can be correlated to changes in water content of the critical zone. These changes are small. Time lapse imaging makes these changes more apparent. The MacLeish Field Station also has a meteorological station, soil moisture data, and two observation wells with ongoing water level measurements. I will compare these ERT data with this other hydrological information. This study correlates geophysical changes with changes in the other data sets. This comparison will help determine rates of aquifer recharge from precipitation into the glacial till and fractured bedrock aquifer. The field work will also establish a base line for any later studies.