Abstract
We report here on the chemical signature of degassing at Erebus lava lake associated with intermittent explosions and the return to passive conditions. Explosions caused by bubble bursts were frequent during the 2013 field season, providing the first opportunity to observe such activity since 2005–06. Several of the explosions were captured by multiple instruments including an open-path Fourier transform infrared spectrometer. Explosive bubble bursts and other transient degassing events are associated with gas compositions that are distinct from the usual range of passive degassing compositions. We set out to compare the chemical signature of explosive degassing during the 2005–06 and 2013 episodes, and to characterise the chemistry of gases emitted during the period of lake refilling after explosions. We found little change in the explosive gas chemistry between 2005–06 and 2013, suggesting reactivation of a common mechanism of gas segregation. Bubbles can be distinguished by their size and composition, the ranges of which are likely modified during ascent by gas–melt interaction and adiabatic expansion. The proportions of water, SO2, and HCl in the emitted gas plume increase during the refill of the lake after explosions, as the lake is recharged by a combination of magma that has already partially degassed, and that vesiculates rapidly in response to the drop in magmastatic pressure at the lake.
Highlights
Explosions at the surface of the Erebus lava lake, Antarctica, occur sporadically and range considerably in magnitude
The smallest bubbles are associated with minor seismic signals, and changes in gas ratios are minor, so similar events may exist in Fourier Transform infrared (FTIR) and infrared data without being identified here. (iv) Small bubbles (n = 4) and other degassing events (n = 7)
Small bubbles are often difficult to detect in FTIR data, as the associated changes in gas ratios can be within the normal range of gas ratios measured during passive degassing
Summary
Explosions at the surface of the Erebus lava lake, Antarctica, occur sporadically and range considerably in magnitude. They result from gas bubbles or slugs bursting at the surface of the lava lake. These vary from small (a few metres in diameter) bubbles that rupture without generating bombs, to overpressured bubbles that expand to the lake diameter prior to rupture, sometimes ejecting bombs a few hundred metres over the summit crater rim. The frequency of explosions is variable – smaller events are commonly observed, whereas the large, lake evacuating events occur in episodes of several months’ duration, during which there can be several explosions per day. Explosions were captured regularly by thermal infrared cameras and seismometers, and in the 2005 season the physical parameters of these explosions were studied by Gerst [12] and
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