Erosion of ejecta at meteor crater: constraints from ground penetrating radar

Ground penetrating radar (GPR) provides a rapid, non-destructive means for investigating the shallow subsurface around a variety of terrestrial landforms also found on other planets. Impact craters represent one of the most ubiquitous planetary features and GPR data at Meteor Crater, Arizona, delineate stratigraphic relationships between the ejecta and associated alluvial deposits in the shallowest 1-3 m ~f the subsurface. Analyses of these data indicate that the continuous ejecta remain better preserved than was defined previously via surficial mapping. Radar penetrates a thin veneer of alluvium and colluvium that masks the actual distribution. Returns from uniform, finegrained alluvium filling regional drainages blocked by the crater confirm their generally low transport capacity through time. GPR data and sampling further reveal that some subtle ridges extending from the crater are not the result of debris flow deposition of eroded ejecta. Instead these ridges are formed by preserved ejecta deposits draping pre-impacttopography. Collectively, these results establish that the continuous crater ejecta are in a surprisingly pristine state of preservation in contrast with visual inspection. More generally, this study demonstrates the high potential of GPR in future planetary applications. Ease of miniaturization makes GPR ideally suited for planetary rover missions to the terrestrial planets and Galilean satellites where it could help resolve a range of questions relating to their histories of surface processes.