The Dynamics of Short-Duration, Unsteady Volcanic Eruptions

Arizona State University, Scottsdale AZ

Investigators

Abstract

Approximately 30 of the more than 550 historically active volcanoes in the world are adequately monitored despite the threats they pose to encroaching human populations. Better predictions of volcanic eruption timing and scale are critical for reducing risk to these vulnerable populations. To that end, scientists are attempting to identify currently unrecognized patterns in explosive eruption dynamics and subsequently build reliable predictive models. Computer models of large, sustained (Plinian) eruptions, like the eruption of Mt. St. Helens on May 18, 1980, or the June 12, 1991 eruption of Pinatubo volcano in the Philippines, form the basis of our current understanding. However, despite the fact that pulsating or unsteady source properties are thought to have significant impact on eruption behavior, such models are necessarily simplified by time-averaging key source properties such as density and velocity. In response to this apparent disconnect, this research aims to establish robust relationships between unsteady source conditions and explosive eruption dynamics. The study will focus on small, short-lived, highly unsteady (vulcanian) eruptions, which occur much more frequently than Plinian eruptions, and are thus a valuable and accessible source of data for enhancing general understanding of eruption dynamics and improving models. Collapsing eruption columns and resulting pyroclastic flows (avalanches of hot gas, blocks and ash) are one of the deadliest phenomena produced in explosive volcanic eruptions. The complexity and danger presented by volcanic eruptions motivates the laboratory investigations that will take place with the aim to define the transition between stable, rising eruption columns and unstable, pyroclastic-flow-producing columns in terms of the unsteady forces driving the eruption. Of particular interest is how variations in the initial buoyancy and momentum forces influence changes in the ash and velocity distribution of these flows. The team will also test the effectiveness of existing mathematical models of eruptions in capturing the behavior of simple laboratory experiments. Simultaneously, they will assess whether the same models are valid representations of real volcanic eruptions. The ultimate goal of the project is to establish theoretical understanding of a wide-range of flows generated by impulsive, unsteady sources, including large-scale explosive volcanic eruptions, industrial explosions, contaminant plumes, forest fires and many other phenomena.