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.
The overarching goal of this project was to understand the dynamics of jets and plumes generated by unsteady sources. Examples of such flows include industrial exhaust and explosions, weapons detonations, undersea volcanic eruptions called black smokers, and this project’s main target, short-lived explosive volcanic eruptions. Short-lived explosive volcanic eruptions are some of the most common types of volcanic activity on Earth; they occur frequently, sometimes daily, at several volcanoes around the world, including Santiaguito in Guatemala (Image 1), Semeru in Indonesia, Sakurajima in Japan, and several volcanoes in Alaska. This type of eruption poses significant threat to local populations and their infrastructure, including agricultural fields, and has the potential to disrupt global air traffic, possibly resulting in big economic consequences. The scientific findings of this primarily experimental project provide an entirely new model to describe the dynamics of short-lived volcanic jets and plumes. A key result is that the experiments demonstrate that a highly-unsteady vent flux has significant impact on overall rise dynamics of volcanic jets and plumes, and that these dynamics are fundamentally different from that predicted by steady flow theory, which in the past has been commonly used to model all explosive volcanic eruptions (Image 2). The new model provides a more appropriate method for predicting the final rise height and corresponding ash dissemination. We can also use the new theory to effectively interpret simple video observations of these explosions in order to estimate mass eruption rate and total mass erupted, which is otherwise nearly impossible to measure in real-time. Also, our laboratory data is one of the best data sets (and the only one of its kind) suitable for validating complex predictive computer models of explosive volcanic eruptions. These scientific outcomes can be enumerated as follows: 1) Short-lived volcanic jets produced by unsteady vent flux evolve in a sequence of stages that correlate in time with variations in vent flow rate. The different stages can be recognized by different plume morphologies (plume shapes) representing the development of different flow structures. In other words, variable discharge rates have significant effects on turbulent jet dynamics, and those effects may have bearing on whether or not the jet rises buoyantly or collapses to form dangerous ground-hugging currents called pyroclastic flows. 2) Quantitative experimental data has been used to develop a basic scaling law, linking vent flux to observable and measureable eruption characteristics such as rise rate. This scaling law has been successfully applied to video observations of volcanic jets to estimate important parameters at real volcanoes, such as the amount of magma erupted in a single eruptive burst. 3) This project is the first to demonstrate that these flows have an internal velocity structure that is different from that of steady volcanic jets. This different velocity structure has direct implications for understanding the ash carrying capacity of these volcanic jets, and is therefore important to predicting the trajectory of volcanic ash in the atmosphere and its final destination (Image 3). 4) These experimental results are now in the early stages of being incorporated into sophisticated models that predict the height and path of explosive volcanic eruptions. In the long-term, merging these experimental results and numerical models will improve real-time prediction of volcanic hazards. The laboratory experiments that formed a large part of this project have had significant impact on the development of several students and post-docs in the School of Earth and Space Exploration (SESE) at Arizona State University (ASU). Several post-docs, three undergraduate students, and several PhD students have been trained in some aspect of the experiments or outgrowths of those experiments; this training has enhanced their research skillsets and positively impacted their career paths. The experiments have also enhanced the learning experience for many classroom students at ASU. The experiments have greatly enhanced the research capacity of ASU’s experimental volcanology lab, and as a result the lab is quickly becoming a resource for several other departments on ASU's campus, as well as becoming a draw for volcanologists from other institutions. The laboratory experiments supported by this grant have figured prominently in large ASU outreach activities. The two biggest of these are Earth and Space Exploration Day, which attracts more than 1000 young school students each year, and Night of the Open Door, which had more than 10,000 members of the public in attendance this year. Both of these events attract K-12 teachers who often adapt our demonstrations to their classrooms.
