Testing the instability hypothesis of drumlin formation using GPR
Multiple lines of Ground Penetrating Radar (GPR) data were collected across drumlins in the upper Eden Valley Cumbria with the specific aims of determining the architecture of the drumlins and inter-drumlin “flats” and characterising the drumlin-substrate interface. The project was, for the most part, a proof of concept to demonstrate the utility of the technique for the investigation pf drumlin genesis. GPR lines were acquired using the Sensors and Software pulseEKKO 100 system using the 100 MHz, 50 MHz and 25 MHz antennae. Some repeat lines were acquired in order to determine the antennae which provided the best results. Site selection was made on presence of nearby bedrock outcrops, suggesting a shallow drumlinised diamict-bedrock contact with a clearly traceable horizon and a permeable lithology (limestone). Despite the clayey sediment and unfavourable weather conditions, a considerable penetration depth down to ~12 metres was achieved using the 50 MHz antennae, with a separation of 1 m, trace interval of 1 m and 128-fold vertical stack. Results indicate that the drumlinised diamict is in direct, contact with the bedrock. While the internal drumlin geometry is generally chaotic on the stoss side, evidence of down-flow dipping reflectors was found in the lee side. The inter-drumlin flats comprise ~4 metres of infilled sediment that masks part of the original drumlin profile. This study indicates that GPR can be successfully deployed for the study of subglacial bedform geometry and sedimentary architecture.