Episodic outgassing and lava level fluctuations at Kilauea Volcano’s summit lava lake in Halema`uma`u Crater

Kilauea’s ongoing summit eruption began in March 2008 and has been characterized by a lava lake deep within an enlarging pit in Halema‘uma‘u Crater. The level of lava in the lake has exhibited cyclic rise and fall behavior, accompanied by episodic seismic and infrasonic tremor. From 2010 on, this episodic behavior has involved the lake abruptly switching between “spattering” and “non-spattering” regimes. Spattering phases consist of spattering and passive outgassing from the lake, as well as elevated tremor and a vigorous gas plume. Non-spattering phases are associated only with passive outgassing from the lake, with unusually low tremor and a weak gas plume. Non-spattering phases usually last several hours and often correspond with the lava lake level abruptly rising, in some cases up to 20 m. We consider these episodic lava level fluctuations a type of “gas pistoning”, and focus on events in 2010 and 2013-2014.

We interpret the gas pistoning to be driven by shallow gas accumulation near the top of the lava lake, based on long-term multidisciplinary monitoring including seismicity, infrasound, gas emission and geochemistry, lake level and surface motion, and robust visual and time-lapse camera observations which comprise a comprehensive characterization of gas pistoning at Kilauea. Competing models for gas pistoning, such as deeply sourced gas slugs, or dynamic pressure balances, are not consistent with the gas geochemistry or other observations at Halema‘uma‘u. The observed spattering regime represents significant decoupling of gas bubbles in the lake, while the non-spattering regime represents gas bubbles largely coupled, and downwelling, with the circulating lava. Gas pistons reflect a slight imbalance in gas influx/outflux at the lake surface during the non-spattering phases, associated with gas accumulating beneath the lake surface. These data illustrate the complex and episodic nature of gas emission from a lava lake. Unlike other lava lakes which have cyclic behavior that is thought to be controlled by deeply sourced processes external to the lake itself, the lake at Halema`uma`u Crater provides an example of lava lake fluctuations driven by cycles of activity that are shallowly rooted.