Figure 4

Megatsunami simulations of impacts into the northern ocean (120 m deep). (a–c) Simulation frames showing an impact into the weaker ground (supplementary movies 2 & 3). An asteroid 3 km in diameter (impact velocity: 10.6 km/s; density: 2.63 g/cc) is required to form Pohl. Details on the strength models are given in the supplementary material. The lack of residual strength results in the formation of a large Worthington³¹ central jet of pulverized rock and the generation of transient oscillations, pushing the crater rim to about twice the diameter of the initial transient crater. The pulverized rock "waves" spilling over the incipient rim (b,c) trigger a megatsunami (c), and the collapsing ejecta curtain (b) generates debris-laden water. (a'–c') Simulation frames showing an impact into the stronger ground, in which a 0.01 MPa residual strength of pulverized rock inhibits the development of a central jet of pulverized rock and transient oscillations (supplementary movies 5 & 6). The final crater extends slightly beyond the initial transient crater as the base of the ejecta curtain (lip) collapses to form the peak ring. Consequently, in this case, a 9 km asteroid (impact velocity: 10.6 km/s; density: 2.63 g/cc) is required to form Pohl. In this scenario, the collapse of the incipient peak ring on the surrounding ocean drove the megatsunami. In addition to the ejecta fallout, we consider that both the collapse of the central jet and rim materials could have contributed to the megatsunami's densification. (d,e) 1-D GEOCLAW simulation using the shallow water solver for long-range propagation, onshore run-up, and an idealized bathymetry from Pohl crater to the V1L site. Panel (d) shows the megatsunami transfer of the megatsunami from the impact simulation into weaker ground to the shallow water solver. Panel (e) to the shallow water solver, which shows that the megatsunami initially reached ~ 500 m in height and propagated to ~ 250 m above sea level, overrunning the V1L site. Figure 5 shows 2-D simulations for both megatsunamis accounting for varying topography. Profile and horizontal velocity data is available in the supplementary material.