Asteroid Impacts, 2001
The majority of asteroid impacts occur in the ocean with no record. Eugene Shoemaker of the U.S. Geological Survey estimated that every year a so-called impact event of the size of a nuclear bomb occurs, mostly without damage and noticeable only as a thunderclap and flash. A huge, 30km diameter undersea impact crater has been discovered in the Indian Ocean east of Madagascar. It must have caused a mega tsunami about 5,000 years ago.