Numerical modeling of impact-induced modifications of the deep-sea floor

The mechanics of oceanic impact events differ in several respects from the process that accompanies the strike of an asteroid on land. In order to explore the cratering process on a water-covered target, a series of 2D hydrocode simulations for impact velocities of 10, 15, 20 and 30 km/s and water depth/diameter ratios between 5 and 7 have been carried out. In particular, these simulations were aimed to examine the effects of the asteroid on the deep-sea floor. The interaction of the impacting body and the water column causes loss of the bodyʹs kinetic energy both through oceanic drag and through mass loss due to hydrodynamic heating, prior to hitting the ocean bottom. Regardless of whether the impactor actually hits the ocean floor, the shock wave generated in the water column by the impact of the body on the water surface will leave behind unique traces in the marine sediments. For example an asteroid of 1 km in diameter arriving at the ocean surface with a velocity of 20 km/s induces a shock pressure of 6 GPa in the oceanic crust at a water depth of 5 km. The passage of the shock wave along the water–ocean bottom interface causes significant disturbance in the sediment layer. Moreover, the collapse of the transient cavity that results from the passage of the projectile through the water column causes a strong surge of water that generates a displacement and redeposition of sediments on the ocean floor. In order to examine sediment transport processes, we introduce computationally a large amount of massless particles within the projectile and the target material, and follow the movement of each individual particle. Tracer particles represent only forced material movement and do not account for any frictional forces. Thus, comparisions with real sediment disturbances may be qualitative only. For an impact velocity of 20 km/s and a water depth/diameter ratio of 5, this procedure reveals significant particle movements within a distance of 15 km from the center of the impact. ly known deep-sea impact structure so far, the Eltanin impact in the Bellingshausen Sea, Antarctica, is characterized by a zone of chaotically mixed sediments that most probably originated from impact-induced turbulent water currents. Based on the present observations, which do not allow the identification of an impact structure at the ocean bottom, our model yields estimates of a projectile diameter of 1 km and an impact velocity of 20 km/s.