Cyclical Volcanoes

Hello readers, and welcome to another edition of From Physics to English!
Today we’re focusing on volcanoes–more specifically, Erebus volcano in Antarctica. An active volcano on Ross Island, Erebus is an oft studied volcano that still leaves us with questions. The volcano has been noted to have fairly cyclic cycles in the behavior of its lava lake and outgassing (the gasses in the magma being released into the air). These things have been noted, and of course an obvious question is whether the cycles are related. However, getting measurements of all of these at the same time to compare them is difficult.
An image of Erebus volcano. The main photo is a true-color image: the inset is thermal, showing the heat of the volcano in an otherwise icy landscape. Image credit: NASA EO-1 Team, NASA Earth Observatory
An image of Erebus volcano. The main photo is a true-color image: the inset is thermal, showing the heat of the volcano in an otherwise icy landscape. Image credit: NASA EO-1 Team, NASA Earth Observatory
The team of scientists who worked on today’s featured article, however, got instruments running at the same time, observing different features of Erebus. Measured items included amount of sulfur dioxide, gas composition, and the elevation and surface speed of the lava lake (a lava lake is exactly what it sounds like). The volcano was observed in December of 2012 and 2013. The resulting article was published in 2014 in the American Geophysical Union’s Geochemistry, Geophysics, Geosystems, entitled “Correlation of cycles in Lava Lake motion and degassing at Erebus Volcano, Antarctica” by the authors Nial Peters, Clive Oppenheimer, Drea Rae Killingsworth, Jed Frechette, and Philip Kyle.
The authors used the average surface speed of the lava lake (speed of the lava at the lake’s surface) to show the cyclic patterns, at it is easier to see in this data. They also used the ratio of carbon dioxide to another chemical compound, OCS. The ratio of CO2/OCS and the surface speed are alarmingly similar. An explosion that occurred while data was being collected did not seem to affect this similarity. Agreement with the amount of sulfur dioxide being released was not as striking, but measuring the sulfur dioxide has inherent difficulties; turbulent motion and possible inconsistencies in how long it takes the gas to rise to the level of the instrument in use.
The elevation and surface speed of the lava lake were also notably similar; again, and explosion only ‘paused’ this while the lava lake refilled. The surface speed peaked after the surface elevation, by a one to three minute delay; the other cycles line up much more precisely. The CO2/OCS ratio is highest with the highest lake motion. Considering the complexity of the system, the evenness and longevity of the cycles is remarkable.
The exact causes of these cycles are not quite known. The CO2/OCS ratio can be affected by things such as temperature and pressure, and I’ve already mentioned that the amount of sulfur dioxide is not a simple measurement. One idea is that the behavior, especially that of the lava lake, is connected to the density difference in gas-rich magma and magma that has been degassed. Cyclic degassing has also been observed at Mt. Etna in Sicily, so further studies there may help shed some more light.

 

Bibliography
Earth Observatory. Volcanic Activity on Mt. ErebusNational Aeronatics and Space Administration. 6 Feb. 2009. Web.
The location of the image used in today’s article.
Judson, Olivia. Antartica’s Mount Erebus. National Geographic, July 2012. Web.
While I did not technically use any information from this article, this is a (slightly long) but very interesting read about looking for life (yes, life!) at Erebus and what it’s like going to Antartica. It also starts with a fantastic image of the volcano.
Marshak, Stephen. Earth: Portrait of a Planet. 3rd ed. W.W. Norton & Company. Print
My geology textbook, used as a reference for volcanoes in general.
Peters, N., C. Oppenheimer, D. R. Killingsworth, J. Frechette, and P. Kyle (2014), Correlation of cycles in Lava Lake motion and degassing at Erebus Volcano, Antarctica, Geochem. Geophys. Geosyst., 15, 3244–3257, doi:10.1002/2014GC005399.
Today’s main article.

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