On May 25th 2022, an earthquake swarm began underneath a little known volcanic complex
on the border of Colombia and Ecuador.
By 6 days later, more than 400 daily volcano tectonic earthquakes were occurring at the
Chiles-Cerro Negro complex, and this figure is still continuing to increase.
These quakes were centered on the southern flank of the Chiles stratovolcano which has
not produced an eruption in 160,000 years.
Specifically, these quakes were centered adjacent to a series of hot springs within a volcanic
crater, hinting that if an eruption was to eventually occur, this spot would represent
the most likely site.
The several thousand volcano tectonic earthquakes which have occurred so far are caused by rock
fractures related to the internal pressure of the volcano.
Magma moves at depth, pressure builds in a specific spot, and is subsequently released
by an earthquake.
Despite this rapid increase in seismicity, the alert level of this volcanic complex remains
at yellow.
Although notable, the ongoing earthquake swarm is so far less energetic than two other quake
swarms in 2013 and 2018.
These quakes are largely centered at 4 to 6 kilometers depth while an underlying body
of magma is known to exist at 13 kilometers depth.
The Chiles Cerro Negro volcano is located on the border of Colombia and Ecuador, where
it is 25 kilometers west of the city of Tulcan.
As the name of the complex implies, this system consists of two highly eroded stratovolcanoes
which contain collapse scars due to hydrothermal alteration; Cerro Negro de Mayasquer to the
west, and Volcan Chiles to the east.
The first of the two volcanoes to form was Cerro Negro de Mayasquer, which erupted an
explosive mixture of andesite and dacite lava flows interspersed with large volumes of ash.
This eruptive activity lasted from 1.4 million years ago until around 200,000 years ago,
constructing a very large volcanic cone.
Subsequently, Volcan Chiles became active around 510,000 years ago, constructing a large
stratovolcano out of eruptions which were surprisingly ash poor, consisting mainly of
voluminous lobes of andesite and dacite lava.
Although it last eruption was dated to 160,000 years ago, there is a large dacite lava lobe
on its eastern flank which appears to be far younger due to its morphology and lack of
erosional features.
Despite a young looking ash deposit on Chiles, and potentially unreliable reports of a phreatic
eruption here in 1936, I do not think that this volcano has erupted in many tens of thousands
of years.
Regardless of whether this volcano has erupted in that timespan, it continues to produce
heated acidic hot springs, fumaroles, earthquakes, and release of sulfur dioxide gas.
Clearly, there is a large body of magma at depth, but we do not know the size of this
magma chamber.
I suspect that a truly massive magma reservoir is present, perhaps on the order of at least
several dozen cubic kilometers of material.
I am basing this assumption on the number of earthquakes alongside the amount and area
of magmatic uplift this complex has produced in the last decade.
It bears a clear resemblance to large volume silicic systems such as the Campi Flegrei
supervolcano in Italy and the Clear Lake volcano in California, and this is truly worrying.
Although not always true, generally speaking the longer a volcano goes without erupting
and the larger a magma chamber it has, the more voluminous and destructive its eventual
eruptions are.
What is most worrying relates to the nature of ongoing magmatic uplift.
Between 2014 and 2019, a large swath of ground with two clear epicenters was uplifted by
7.5 centimeters near the hot springs where the current earthquake swarms are and 10 centimeters
at a location 9 kilometers to the southeast.
This uplift is incredibly broad, suggesting that whatever magmatic system is feeding this
complex spans an area of as much as 350 square kilometers.
Due to the lack of verifiable information on this volcano, I cannot truly say what the
odds of a new volcanic eruption are.
With this being said, if an eruption was to occur, it would most likely begin on Cerro
Negro's southern flank and be highly explosive, resulting in pyroclastic flows which could
reach up to 13 kilometers distant along with damaging lahars along riverbeds which could
severely damage 3 nearby cities.
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