EJECTA FLOW PHENOMENA IN IMPACT CRATERING

Large meteorite impacts distribute spherules and other impactites as layers over areas much larger than the crater itself. Usually crater formation is analized numerically with methods for elastic-plastic flow. The long-distance mode of transport has been much debated but less investigated. To study these long-term ejecta flows, an Eulerian-Lagrangian algorithm for multiphase flow is used, coupling Lagrangian particulate phases to a higher-order Godunov method for the gas. A variable particle size such can easily be taken into account. Other technical aspects of the computer code such as the parallelization will be demonstrated.

A substantial part of the initial kinetic energy remains as that of disperse solid and liquid droplet phases commonly called ejecta moving through the atmosphere. The ejecta flow also entrains gases of atmospheric and impact origin. Here the modeling effort is concentrated on realistic heat transfer, including real-gas effects and a drag function valid under a wide range of flow conditions. Simulation examples are provided for impact events from the size of the Ries crater to that of Chicxulub or Sudbury. During the propagation of the ejecta curtain the flow changes from a laminar ballistic for the solid phase to a highly turbulent one. Secondary phenomena arise such as hot buoyant clouds of dust and gas after the passage of the main ejecta curtain. Similarity and dissimilarity to volcanic plumes will be discussed. Depending on the spatial scale of the impact and the size of particles, temperatures in secondary plumes may still exceed the melting point of silicates.