Understanding the forces controlling basaltic explosive eruptions is of fundamental importance in order to improve understanding of the range of behaviors of our most frequently active volcanoes and to assess hazards of future explosive events. The summit of Kîlauea is the site of large and growing volcano-tourism (e.g., 5000 visitors/day at the overlook at Jaggar Museum), and there is a public need both for better knowledge of the volcanoes' behavior and improved forecasting of the likely course of future eruptions. Although not its usual style, explosive eruptions have punctuated Kîlauea's history, with five moderately large events since 1500 CE.
The study quantifies and models the dominant factors that determine explosive eruptive behavior at Kilauea volcano, through a study of the eruptive products from three plume-forming and fountaining eruptions. The events are episode 1 of the highest historical fountaining eruption at Kîlauea, the 1959 Kîlauea Iki eruption, a much earlier powerful fountaining eruption in 1480 CE and a powerful; plume-forming eruption in 1635 CE.
The novelty of the approach lies in using new 'rate-meters' to estimate likely durations of magma ascent beneath the volcano to arrive at the influence of this residence time on the ultimate 'fate' of the magma. The investigators will study microtextures (vesicles and microlites), volatiles in melt inclusions, and embayments in eruptive products.
In addition to direct support for 3 graduate students and undergraduate students, results will contribute to educational outreach efforts anchored on development of volcanology classes at University of Hawaii, Columbia University and Rice University. The proposal involves exchange of material and ideas between five institutions to the benefit of young researchers, and undergraduate and graduate classes. Our results will be widely disseminated via the Internet using linked web sites hosted by Hawaiian Volcano Observatory and NSF-funded institutions.
The volcanoes of Hawaii are generally thought to erupt peacefully, but this has not always been true. Several hundred years ago (c. 1635), Kilauea delivered an explosive subplinian eruption, which, if it had occurred today, would likely shut down airspace over a substantial part of the Pacific. This project studied the deposits of that eruption, and contrasted them with those from two other, less vigorous eruptions (including the 1959 Kilauea Iki fire fountain that created a lava lake; see Contrasting Eruptions image). Two major hypotheses were assessed for the causes of these different eruptive behaviors: 1) that the concentration of volatile species differs between eruptions, with higher CO2 and H2O driving more explosive eruptions, and 2) that the magma ascent rate differs between eruptions, with faster ascent leading to larger number of smaller bubbles that cause explosive magma fragmentation. Field work led to collection of volcanic rock samples, and the work in the laboratory isolated tiny bits of magma (now glass) trapped inside crystals (see Melt Inclusion Image). Ion microprobe analysis of these inclusions demonstrated that all three eruptions derive from magmas with similar initial volatile contents. Moreover, the most explosive eruption appears to have lower H2O and CO2 prior to eruption, just the opposite of what would be expected for the first hypothesis. Instead, there is clear evidence for variable magma ascent rates prior to eruption, based on a novel method that uses zonation profiles of H2O and CO2 in crystal melt tubes. Magma that fed the weaker fountain eruptions ascended up to four times more slowly than that for the violent subplinian eruption. This directly supports the second hypothesis, and the results can be tested with geophysical observations and used as input for bubbly-melt-flow conduit models. The ascent rates deternined here indicate magma movement on the timescales of minutes to hours from kilometers depth prior to large fountains and more explosive eruptions. Such rapid run-ups to eruptions challenge most existing techniques for volcano monitoring and informing the public. Results of this work have been disseminated to the science community in the form of conference presentations and publications, and to the public through lectures and interviews with the media. This project has supported the development of a postdoctoral scientist at Columbia University, David Ferguson, who has recently moved to Harvard University, and is well-poised for a successful career in igneous petrology and volcanology.
