Plumbing Masaya's lava lake

by Mary Caperton Morton
Tuesday, July 3, 2018

In recent years, volcanic activity at Nicaragua’s Masaya Volcano has been relatively benign, with small eruptive episodes occasionally producing a lava lake in a summit crater that has become one of the country’s top tourist attractions. But Masaya’s explosive eruptive history suggests that the volcano could someday threaten the surrounding towns and the capital city of Managua, 20 kilometers to the north. Two new studies explored novel ways to monitor activity at the volcano and have revealed new information about Masaya’s multiple magma chambers.

Masaya’s last major eruption occurred in 1772, but the volcano frequently experiences minor eruptions. “Masaya is part of a big caldera system that is surrounded by about 2 million people who are potentially at risk from a large eruption,” says Christelle Wauthier, a geophysicist at Penn State University and co-author of one of the new studies, published in Geophysical Research Letters.

To improve monitoring and better understand how magma moves through the system, Wauthier and her graduate student, Kirsten Stephens, used satellite-based Interferometric Synthetic-Aperture Radar (InSAR) to track ground deformation at Masaya over a 10-month period from November 2015 to September 2016. They detected 8 centimeters of ground swelling north of the summit crater in the weeks leading up to the Dec. 11, 2015, formation of a lava lake, likely due to magma intruding into a spherical magma chamber 3 kilometers north of the summit and about 3 kilometers below the surface.

In addition to establishing the timing of the deformation relative to the formation of the lava lake, “these data pretty nicely constrain the magma chamber’s location in the center of the old caldera system, offset from the summit where the lava lake is located,” Wauthier says. This offset is an important consideration when monitoring activity at the volcano, she says. “A lot of studies tend to focus on the lava lake at the summit, but if you were only looking at the active vent, you would miss most of the inflation.”

Wauthier’s findings are corroborated by a second, independent study of continuous gas measurements collected at the lava lake over a three-year period spanning the December 2015 formation of the lava lake. “We were very lucky to be able to follow the entire transition from quiescence to pre-eruptive degassing to degassing during the formation of the active lava lake,” says lead author Alessandro Auippa of the University of Palermo in Italy.

Auippa’s team recorded steady degassing for several months in late 2015, punctuated by a peak in the weeks leading up to the formation of the lake, which was still present as of June 2018. These observations can be explained by a pulse of gas-rich magma entering the volcano’s plumbing system about two weeks prior to the formation of the lava lake, Auippa and his colleagues wrote in Geochemistry, Geophysics, Geosystems.

The lava lake is likely fed by a smaller, shallower magma reservoir at a depth of about 1 kilometer below the summit. “The magma in this chamber is very rich in gases and the bubbles seem to control the level and activity of the lava lake,” Auippa says. “Wauthier’s study tells us that this shallower reservoir is probably fed by the deeper reservoir and that the lava lake is formed when the magma is transferred toward the surface, but we still don’t know how they are connected.”

Combining InSAR satellite data and gas measurements provides a clearer picture of the sequence and timing of events taking place in the interior of the volcano leading up to the formation of the lava lake, says Hazel Rymer, a geophysicist at the Open University in England, who was not involved in the new research. “The advantage of the InSAR data is that you can look at a very large area — the whole of the volcanic system and its surroundings — over a longer period of time.”

Previous studies using GPS or gravity measurements to study ground deformation were only able to measure ground deformation at a few positions, and gravity readings were taken only on an annual basis. “Combining all these monitoring methods helps us pin­point the magmatic processes that are driving Masaya’s volcanic activity,” Rymer says. “There’s still a lot to learn about Masaya, but the more ways we look at it, the clearer it becomes.”

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