Shallowly driven fluctuations in lava lake outgassing (gas pistoning), Kīlauea Volcano

Abstract

Lava lakes provide ideal venues for directly observing and understanding the nature of outgassing in basaltic magmatic systems. Kīlauea Volcano's summit lava lake has persisted for several years, during which seismic and infrasonic tremor amplitudes have exhibited episodic behavior associated with a rise and fall of the lava surface ("gas pistoning"). Since 2010, the outgassing regime of the lake has been tied to the presence or absence of gas pistoning. During normal behavior (no gas pistoning), the lake is in a "spattering" regime, consisting of higher tremor amplitudes and gas emissions. In comparison, gas piston events are associated with an abrupt rise in lava level (up to 20 m), during which the lake enters a "non-spattering" regime with greatly decreased tremor and gas emissions. We study this episodic behavior using longterm multidisciplinary monitoring of the lake, including seismicity, infrasound, gas emission and geochemistry, and time-lapse camera observations. The non-spattering regime (i.e. rise phase of a gas piston cycle) reflects gas bubbles accumulating near the top of the lake, perhaps as a shallow foam, while spattering regimes represent more efficient decoupling of gas from the lake. We speculate that the gas pistoning might be controlled by time-varying porosity and/or permeability in the upper portions of the lava lake, which may modulate foam formation and collapse. Competing models for gas pistoning, such as deeply sourced gas slugs, or dynamic pressure balances, are not consistent with our observations. Unlike other lava lakes which have cyclic behavior that is thought to be controlled by deeply sourced processes, external to the lake itself, we show an example of lava lake fluctuations driven by cycles of activity at shallow depth 3 and close to the lake's surface. These observations highlight the complex and unsteady nature of outgassing from basaltic magmatic systems.

Degassing dynamics of basaltic lava lake at a top-ranking volatile emitter: Ambrym volcano, Vanuatu arc

“…It is also supported by theoretical 23 modelling (Witham and Llewellin, 2006) and cyclic crystal zonation in erupted solid products 24 (Moussallam et al, 2015). However, separate bubble flow is another mechanism able to carry 25 heat and gas to a lava lake (Bouche et al, 2013) and to control its level oscillations through 26 bubble accumulation at its top (Patrick et al, 2016). Variations in magma-gas supply rates, 27 degassing modes and the style of convection actually determine a wide range in lava lake 28 behaviour, from vigorous bubbling and overturn to quieter degassing and resurfacing, 29 interrupted or not by recurrent gas outbursts (e.g.…”

“…At Erebus, passive degassing with relatively constant composition was 390 found to prevail between the explosive bursting of deeper-derived large gas bubbles or slugs 391 happening every ~10 mn Ilanka et al, 2015), while at Kilauea ~30 392 mn long cycles of low passive degassing and lava lake upheaval, controlled by shallow 393 bubble accumulation (gas pistoning), were observed to alternate with intervals of spattering 394 and increased H 2 O-SO 2 -rich gas release after a sudden drop in lake level (Patrick et al, 2016 classical (in situ) methods. Ambrym basaltic gas is markedly richer in water and halogens 411 than hot spot or rift basaltic gases from Kilauea and Erta'Ale lava lakes, respectively, whilst 412 being poorer in CO 2 than magmatic gases from Nyiragongo and Erebus alkaline lakes.…”

“…Variations in magma-gas supply rates, 27 degassing modes and the style of convection actually determine a wide range in lava lake 28 behaviour, from vigorous bubbling and overturn to quieter degassing and resurfacing, 29 interrupted or not by recurrent gas outbursts (e.g. Le Guern et al, 1979;Tazieff, 1994;30 Oppenheimer et al, 200430 Oppenheimer et al, , 2009, and to cyclic upheaval and drain back due to gas-piston 31 effects (Edmonds and Gerlach, 2007;Patrick et al, 2016). 32…”

Automated tracking of lava lake level using thermal images at Kīlauea Volcano, Hawai’i

“…The spike itself is an artifact, in which spattering along the north margin of the lake causes the algorithm to incorrectly detect a rise in the entire lake. However, the drop in lava level following the spike is real, and presumably due to release of a large volume of gas during the intense spattering phase (Patrick et al 2016). This characteristic lava level signal -a spike followed by sharp drop -is diagnostic of intense spattering episodes, which are often triggered by small rockfalls into the lake.…”

“…In general, short-term changes (e.g. seconds to hours) are normally attributable to shallow gas-related processes, such as rockfall-triggered spattering ) and "gas pistoning" (Swanson et al 1979;Patrick et al , 2014Patrick et al , 2016Nadeau et al 2015). Two episodes of intense spattering occurred on April 10-11, 2014, during deflation and lava level drop (Fig.…”