Hydrothermal alteration of andesitic lava domes can lead to explosive volcanic behaviour


Different stages in a volcanic process. Photo.
Figure. Photographs from Merapi volcano (Indonesia) outlining the process described in the study. Left: Volcanic gases can escape (outgas) and the pressure within and beneath the dome does not increase. Middle: Hydrothermal alteration reduces the permeability of the dome and effectively shuts off outgassing, resulting pressure buildup beneath the dome. Right: This gas overpressure drives fragmentation and explosive behaviour. The explosion provides new outgassing pathways and the clock is reset.

Volcanoes that extrude lava domes – mounds of blocky lava that form as high-viscosity magma slowly extrudes from the top of a volcanic conduit – are among the most hazardous on Earth.

 As magma rises to the surface, volatiles trapped in the magma – such as carbon dioxide and water – exsolve to form gas that can, eventually, travel independently throughout the volcanic system. If this gas cannot reach the surface through a permeable network, however, pressure can build up below the dome, priming the volcanic system for explosive behaviour. Explosions at dome-forming volcanoes are common and often unpredictable, suggesting that there is a mechanism that not only reduces permeability sufficiently to promote explosive behaviour, but can also rapidly repeat the feat following an explosive event. Heap et al. (2019), published in Nature Communications, shows that the permeability of a lava dome can be reduced sufficiently by hydrothermal alteration, common to dome-forming volcanoes worldwide, to provide the gas overpressures necessary to fragment rock and magma and promote explosive behaviour. The study highlights that hydrothermal alteration, which can develop over months to years, could therefore be driving the erratic explosive behaviour commonly observed at dome-forming volcanoes. The authors of the study conclude that mapping the extent and evolution of hydrothermal alteration at active lava domes emerges as an important tool to help anticipate explosions at otherwise unpredictable dome-forming volcanoes.

Heap, M. J., Troll, V. R., Kushnir, A. R. L., Gilg, H. A., Collinson, A. S. D., Deegan, F. M., … Walter, T. R. (2019). Hydrothermal alteration of andesitic lava domes can lead to explosive volcanic behaviour. Nature Communications, 10(1), 5063. https://doi.org/10.1038/s41467-019-13102-8

Published in Nature Communications (predicted publication date: 07/11/2019)

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