Since May 25th of 2022, an increase in so called volcano tectonic earthquakes has occurred
underneath the Chiles-Cerro Negro volcanic complex on the border of Colombia and Ecuador.
Then, beginning on July 14th, the abundance of a different type of earthquake called a
long period quake also began to greatly increase.
For context, while volcano tectonic earthquakes typically occur due to magma exerting pressure
on overlying rock or faults which causes it to slip or crack, long period quakes have
a more direct implication.
Long period quakes only occur due to the movement of heated fluids through cracks in the ground,
which can either signal the movement of magma or hydrothermal fluids.
Regardless of which is the case, it is almost certain that magma is on the move at depth.
This is supported by the fact that the ground just south-southeast of the Chiles stratovolcano
is being pushed upwards by what is likely magma at a rate of 10.6 centimeters a year.
This is quite significant compared to other episodes where lesser rates of volcanic uplift
were detected, while also being unusual considering that Chiles has not reportedly produced an
eruption in 160,000 years.
Then, on July 25th, a moderately large earthquake occurred south of the volcanic complex.
Registering in as a magnitude 5.6, it was felt over a wide area.
This earthquake was triggered not directly by the movement of magma, but rather residual
stress on a lengthy fault line as the ground to the north of it was uplifted.
The uplift eventually created a threshold of stress on the fault which was then released,
generating an earthquake.
This larger earthquake subsequently triggered an increase in earthquakes at the two locations
south-southeast of the Chiles peak, and as of today a total of 17,738 earthquakes have
occurred since the period of volcanic unrest began.
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.
This volcanic complex has been erupting intermittently since 1.4 million years ago, although there
hasn't been a confirmed eruption in the last 10,000 years at either volcanic cone.
With this being said, the volcano was reported to have produced an eruption in 1936.
Yet, this report might be inaccurate as it may have actually meant that an eruption occurred
at a separate volcano, Reventador.
Despite the apparent lack of recent eruptions, this complex is still quite geothermally active.
It continues to produce heated acidic hot springs, fumaroles, and earthquakes.
These features are owed in part to a magma chamber known to exist at around 13 kilometers
in depth.
The presence and movement of magma within this magma chamber is responsible whether
directly or indirectly for the majority of regional earthquakes.
Based on the current distribution of quake activity, I believe a second shallower magma
chamber exists.
While the main deeper magma chamber is the source of 7 to 14 kilometer deep earthquakes
to the south-southeast, quakes closer to the Chiles stratovolcano occurred at between 1
and 6 kilometers in depth.
The slight gap between these two figures might represent the pathway or conduits magma takes
towards the shallower magma chamber from the deeper one.
So, what does all of this mean?
Although magma is most likely on the move and has reached depths far shallower than
during previous unrest episodes, it is unlikely to produce a magmatic eruption anytime soon.
However, an increased level of hydrogen sulfide gas has been measured at several hot springs.
For now, all hot springs adjacent to the volcano should be completely avoided.
While unlikely, the chance of a phreatic eruption has also increased, and will continue to increase
while magma gets shallower and shallower.
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