Chapter 33 - Tephra Dispersal and Sedimentation

Abstract

Explosive volcanic eruptions inject variable amounts of particles of variable size, shape, and composition (i.e., tephra) into the atmosphere. Tephra dispersal and sedimentation mostly depends on particle characteristics, atmospheric conditions, and plume dynamics, with the potential of affecting the environment and society at multiple scales. In particular, thinning trends of tephra deposits mostly depend on particle Reynolds number, which defines different fallout regimes. Nonetheless, particle–particle interactions (e.g., particle aggregation) and gravitational instabilities can strongly affect the particle residence time in the atmosphere promoting premature fallout of the finest fraction (<100 μm). Several analytical and numerical models have been developed to describe both particle transport and settling with the intent of better understanding dispersal dynamics, quantifying the associated hazards, and determining the main eruption source parameters by solving inverse problems. A full characterization of tephra dispersal and sedimentation can only be achieved through a critical synergy of multiple approaches.