Impact into the Earth's ocean floor: preliminary experiments, a planetary model, and possibilities for detection.

It is estimated that 5+ or -2 Copernican-scale (= or >100km diameter) craters have formed in the present ocean floor. Atmospheric breakup of impacting bodies limits significant interaction with the present sea floor to c600+ or -200 cratering events. While none have been identified to date, impact processes and plate tectonics are sufficiently understood to rectify this situation. A preliminary set of impact experiments was carried out, using standard 22-caliber ammunition (383 m/s velocity) and dense saturated sand as a target medium. Water-table level was the primary variable. Although the results cannot be directly scaled to large events, the experiments exhibit phenomenology expected of actual craters in the ocean floor: steep, mixed ejecta plume, gravitational adjustment of the crater to form a shallow basin, and extensive reworking of ejecta and rim and floor materials by violent collapse of the transient water cavity.-from Author