Earthquakes and Fumaroles as Unrest Hits Peru’s Sabancaya

The strong, persistent fumarolic activity at the summit of Sabancaya in Peru, seen on February 26, 2013. Image: Ingemmet

Over the past few days, the Peruvian Geologic Survey (Ingemmet) has noted a sharp increase in seismicity underneath one of the more active volcanoes in the southern part of the country: Sabancaya. Over 500 earthquakes were recorded under the volcano between February 22-23 and with an accompanying increase in fumarole emissions (steam and volcanic gases) from the summit (see above), Ingemmet chose to raise the alert status at Sabancaya to Orange. The fumarolic activity at the summit is especially notable the new steam/gas plume reached over 100 meters over the volcano (although this can also be mitigated by weather conditions) — and closely followed the onset of the new seismicity.

Interestingly, before this new seismic swarm and fumarolic activity began, I noted on Twitter an interesting sequence of earthquakes near Sabancaya. On February 22, three M4.9-5.3 earthquakes struck within 2 hours of each other ~30-40 km to the northeast of the volcano (see below). All these earthquakes were fairly shallow (10-18 km) — in fact, much shallow than much of the historic seismicity in the area. I noted the earthquakes because of their location between Sabancaya and another large Peruvian volcano, El Misti. Now, this is where we have to worry about chickens and eggs — there is no evidence for a connect between these earthquakes and the new unrest at Sabancaya. [SPECULATION] However, it does leave open the potential that (a) the earthquakes could have triggered this new unrest or (b) the earthquakes are part of the new unrest. Under option (a), these earthquakes might not have been directly related to magmatic activity/movement, but their proximity to Sabancaya disturbed the magmatic or hydrothermal system at the volcano. Under option (b), these earthquakes could be the intrusion of a new batch of magmatic itself — however, their distance from Sabancaya seems a little far for that to be the case. My [wild] hunch here might be that the three earthquakes might have “jostled” the hydrothermal system at Sabancaya, producing an increase in hydrothermal flow leading to more intense fumaroles and resulting in an earthquake swarm as the hydrothermal system re-establishes itself. Now, this is not to say that magma movement under the volcano isn’t a potential cause as well — as Ingemmet collects more data, such as the types/amounts of volcanic gases in the fumaroles and can survey the volcano looking for deformation, their geologists can then make a more definitive statement about the nature of the unrest at Sabancaya. Jersy Mariño Salaza from Ingemmet did, however, mention that this unrest is similar to the unrest prior to the volcano’s eruptions in the late 1980s and early 1990s.

A Google Earth image showing the location of the three M4.9-5.3 earthquakes on February 22, 2013, along with Sabancaya (to the west), El Misti (to the southeast) and the city of Arequipa (to the south). Image: Google Earth/USGS

The last eruption at Sabancaya was back in 2003 — one of the handful of VEI 2 and 3 eruptions that have occurred at the volcano since it began erupting again after almost 200 years of quiet. Sabancaya is the younger half of the Ampato-Sabancaya complex. Much like many Andean volcanoes, the largest threats from Sabancaya is going to be explosive eruptions that produce pyroclastic flows — but lahars and other debris flows moving upwards of 30 km down channels on the volcano into the surroundings are also significant hazards. The 1991 eruption of Sabancaya did produce a number of lahars and landslides that resulted in 20 casualties. Over 15,000 people live in villages surrounding the volcano and 250 families living in Maca might need to be evacuated if the unrest continues as they live only ~13 km / 8 miles from the volcano. The nearest large city in Arequipa (population of nearly 1 million), located 75 km / 46 miles to the southeast.

Erik Klemetti is an assistant professor of Geosciences at Denison University. His passion in geology is volcanoes, and he has studied them all over the world. You can follow Erik on Twitter, where you'll get volcano news and the occasional baseball comment.

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source by wired.com