Dr. Dallas Abbott
Earth Institute Contact: Dr. Dallas Abbott
Because the maximum size of earthquakes saturates at a magnitude of ~9.8, the largest tsunamis are produced by impact events. Also, the initial wave height from earthquake-generated tsunamis is limited by the vertical slip along a fault scarp: typically <100 meters. In contrast, a bolide hitting the deep ocean produces a tsunami with an initial height equal to the bolide diameter. We have assembled data from chevrons (inferred megatsunami deposits in a V shape with a back azimuth that points towards the tsunami source) and seafloor bathymetry suggesting that there were >14 submarine impacts from bolides that were 500 meters or more in diameter during Holocene time. Because some infer that chevrons are aeolian, this conclusion is controversial. We have found impact ejecta (impact spherules, impact glass, and shocked quartz) around one set of craters in the Gulf of Carpentaria in Northern Australia. However, the chevrons in the Gulf of Carpentaria are found only on the western side of the Gulf due to erasure in the east by fluvial deposition. Thus, we cannot use multiple orientations of the Carpentaria chevrons to make a strong case for their origin from a megatsunami. In contrast, there are 3 sets of prominent chevrons in the Caribbean with differing orientations that cannot be attributed to a regional wind pattern (Fig. 1A). The three sets of chevrons point to an area with one prominent, round topographic low. This topographic low is the Quetzalcoatl crater candidate (Fig.1B).