How Much Ash is Premature Fallout Due to Hail Formation?

Abstract

Ash aggregation coupled with hail formation in the plume was physically and experimentally proved to occur during explosive eruptions. The ice-ash interaction process plays an important role in ash dispersal and deposit, but the precise extent of this impact remains a subject of uncertainty. Here, we quantitatively illuminate the influences of hailstone-involved aggregation from a geological record. The buried X72 pyroclastic deposits in the Junggar Basin, NW China, exhibit various aggregates, notably voided accretionary pellets (VAP). Observations from seismic, logging, and core data and aerodynamic modeling reveal that VAPs are a product of ice-involved aggregation, leading to a 3-6 fold increase in terminal fall velocity and the removal of 66 % of the erupted mass out of the atmosphere. This underscores the need for the inclusion of aggregation facilitated by hailstone formation in ash dispersion forecasting and volcaniclastic stratigraphy.

Keywords: ash aggregation, hailstone formation, ash aggregates, premature sedimentation, explosive eruption