A model of the geochemical and physical fluctuations of the lava lake at Erebus volcano, Antarctica

AbstractErebus 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