Continuous SO2 Emission Rate Measurements at Kilauea: Capturing Transitory Events

Kilauea is one of the better studied volcanoes on Earth, and regular SO2 flux measurements over the past 26 years have, along with concurrent geophysical measurements, improved our understanding of eruptive processes. In particular, the temporal pattern of summit SO2 release has served to test the model of Kilauea's summit reservoir as a way station for magma bound for the east rift eruption site. East rift SO2 emissions, on the other hand, are now regularly used to track the overall lava effusion rate. These gas-based eruption rate data confirm concurrent geophysical measurements made by Very Low Frequency (VLF) profiling of master lava tubes. Although data from weekly SO2 measurements clearly track eruptive changes over weeks to months, much of Kilauea's activity varies on a shorter timescale-minutes to days. In order to capture these transients, including complex deflation-inflation events, effusive bursts, and gas pistoning, high sampling rates are required, comparable to those of geophysical instruments. Preliminary results from a continuously recording, fixed-view spectrometer indicated that Kilauea was likely a good location for implementing continuous SO2 emission-rate monitoring. Accordingly, we are now field testing a telemetered scanning spectrometer system that incorporates characteristics from instruments employed at Soufriere Hills Volcano, Stromboli, and Mount Etna, as well as some novel features to improve data quality. The Kilauea SO2 monitoring system is comprised of a pair of Ocean Optics miniature-UV spectrometers interfaced with scanning assemblies, and is linked to the observatory via spread spectrum radio. The temperature-controlled spectrometers undergo in-situ calibration by periodic, automatic insertion of SO2 calibration cells. One goal of this system is to provide emission rates every few minutes throughout the day. The SO2 data are ingested directly into the observatory data stream for near real-time visualization, along with other concurrent geochemical and geophysical data and observations.