MECHANISM OF CRATER FORMATION IN METEORITE IMPACTS

Abstract

Laboratory experiments provide a method of studying the dynamics of mechanical phenomena in meteorite impacts, as well as their residual effects. We made a study of this in experiments with explosives, simulating a high-velocity impact in which the meteorite is entirely vaporized and its kinetic energy is converted to the energy of the compressed gases. We decided to work with colophony, which, like most rocks, experiences brittle fracture. The cratering process in a meteorite impact or a contact explosion at the surface of a dense medium subject to brittle failure consists of two stages. In the first, the fragmented material flows outward from the center of the explosion, material is ejected from the epicentral zone, and an intermediate crater whose volume is considerably greater than that of the explosive charge is formed. In the second stage, the fragmented medium flows back toward its original position, undergoing considerable decompaction, which causes an inflow of material into the crater from below and a considerable decrease in its volume. This reverse flow results from the elastic energy stored in the medium and occurs as the pressure generated by the explosion declines. In large-scale meteorite impacts, when the effect of the unconsolidated surface layer is minor, crater formation proceeds in the crystalline rocks beneath the surface, and the reverse flow becomes significant. This is clearly manifested by the presence of central hillocks in large meteorite craters. It has been found that the formation of the central hillock is a dynamic process, as in our experiment.