On modelling the distribution of volcanic ash fallout
by
Robert McKibbin
Massey University

Volcanic eruptions are physical mechanisms for converting high levels of internal energy and work potential contained in magma to mechanical and potential energy and noise. As magma moves up to the surface of the Earth, the lowering of pressure causes fluids contained within the molten material to expand violently, breaking up the flowing rock into a continuous size distribution of particles which cool and solidify. Upwardly-moving buoyant gases carry the rock fragments to heights which depend on their size. Subsequent movement of the particles is controlled by a balance of gravitational forces, lift caused by movement of the gas and air which constitutes the volcanic plume, and wind.

This talk describes a model which might be used for predicting the fallout distribution of heavier-than-air particles after release at high levels in the atmosphere and subsequent dispersion by wind. The effect of the size distribution of the particles on the deposition patterns is taken into account. Qualitative comparisons are made with measured thickness distributions of tephra deposits from some NZ eruptive events.

Date received: October 11, 2000