Explosive Volcanic Eruptions on Ice

: Dynamics and Hazards of Pyroclast-Ice Interactions

Abstract

Many stratovolcanoes globally are glacier-clad and mantled by seasonal snow cover. When these volcanoes explosively erupt onto frozen substrates, a complex hazard cascade is initiated by pyroclast-ice interactions, where melt and steam are incorporated into the granular layer, potentially causing the dynamic transformation to ice-melt lahar. Pyroclastic density currents (PDCs) and ice-melt lahars are extremely hazardous volcanic flows, yet the fundamental physics underpinning the dynamics of these flows on ice are poorly understood. To develop our ability to model the dynamics and assess the hazards from pyroclast-ice interactions, the effects of ice, melt, and steam must be quantified. Laboratory experiments were used improve our understanding of these hazards and how they evolve over ice. Static particle-ice interaction experiments, analogous to static emplacement of tephra and ballistics on ice, were used to quantify the rate of heat transfer, melt and steam generation. Comparison of the experimental results with a new 1D model shows that heat transfer to the ice was dominated by conduction. Dynamic granular flow experiments over ice, analogous to PDCs on ice, were used to infer frictional conditions and identify the role of melt and steam on flow mobility. An eruption and lahar event at Ruapehu Volcano was used as a case-study to demonstrate one example of how the experiment methods could be applied to explosive volcanic eruptions on ice. Key outcomes, significantly advancing our previous understanding and capabilities, were that melt generated from pyroclast-ice interactions can be quantified, therefore ice-melt lahar model source conditions can be set using
informed values. Steady-state flows developed over ice under a range of conditions allowing for a simple frictional closure to be applied in models for PDC dynamics on ice. Finally, the fundamental nature of the research allows for the methods to be applied to any explosive glacier-clad volcano.

Date of Award	23 Jan 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jeremy C Phillips (Supervisor), Alison C Rust (Supervisor) & Geoff Kilgour (Supervisor)