Abstract
Erebus volcano, Antarctica, exhibits periodical surface fluctuations of both geochemical and physical nature. Modeling the physics driving the lake oscillation is a challenge, even with a relatively simple theoretical framework. We present a quantitative analysis that aims to reconcile both lake level and gas geochemical cycles. Our model is based on the assumption that the periodicity is caused by the regular release of magma batches and/or core annular flow that have a fixed volume of melt and ascend and degas in equilibrium. Results suggest that cycles are not caused by the mixing between magma residing in the lake and a deep magma but by two distinct deep sources that rise separately. These sources of bubbly magma come from at most 2–3km depth and rise buoyantly. Individual batches detach from the rising magmas at depths of 20–250m. The two batch types can coexist in a single conduit up to a depth of ~30m, above which they rise alternately to release respectively 19 and 23kg/s of gas at the lake surface every 10min. The temperature of the descending flow is between 890 and 950°C, which is roughly 100°C colder than the ascending currents. Batch pairs have shapes likely constrained by the conduit width. Regardless of their shapes, the pairs reach very high porosities near the surface and have diameters of 4–14m that are consistent with video observations showing spreading waves at the lake surface. The alternating arrival of these large batches suggests a lava lake mostly filled with gas-rich magma.
Highlights
The lava lake in the summit crater of Erebus volcano, Antarctica, has sourced a persistent gas plume for at least several decades
We present lake elevation changes derived from infrared data collected at the end of 2009, which complement Terrestrial Laser Scanning (TLS) data from 2009–2010 (Jones et al, 2015) and 2012 (Peters et al, 2014b), and which we use to constrain the physical modeling of the shallow part of the Erebus magmatic system
The lake level oscillations are on the order of 1 to 1.5 m amplitude with periods increasing by a factor of 2.2 to 3 between 2004 and 2009, while the area of the lake decreased by a factor of ~3 (Peters et al, 2014a)
Summary
The lava lake in the summit crater of Erebus volcano, Antarctica, has sourced a persistent gas plume for at least several decades This overall longevity is accompanied by a series of cyclical processes that persist. These include cyclic change in the level of the lava lake These periodic variations are remarkably in phase with changes in the respective proportions of different gases in the plume, variation of the heat loss and gas temperature at the surface of the lake, and changes of the surface velocity of the magma (Oppenheimer et al, 2009; Alletti et al, 2014; Peters et al, 2014a,b; Jones et al, 2015). Those changes have been associated with secular change in lake level (Jones et al, 2015) but do not affect the 10–20 min period oscillations (Peters et al, 2014a)
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