Beginning on March 30th of 2023, a rapid increase in the number of daily seismic events occurred
at an active volcano which partially straddles the border of Chile and Argentina.
Known as Laguna del Maule, although this volcano has not erupted in around 1600 years, it has
the potential to produce large volume and sometimes explosive rhyolitic eruptions, as
shown by the 6 rhyolite lava flows it has produced via distinct eruptions in the last
10,000 years.
Unlike less silica rich lava such as basalt, rhyolite is incredibly viscous, which during
eruptions can prevent large volumes of gas from escaping.
This gas then during an eruption builds up in pressure, eventually triggering a powerful
explosion with this process repeating several times during an eruptive sequence which also
builds a tall lava dome.
In other words, Laguna del Maule is one of the few volcanoes which could theoretically
produce a VEI 5 or VEI 6 explosive eruption on the order of Mount Saint Helens in 1980
or Mount Pinatubo in 1991 respectively, at least given our current understanding of this
volcanic complex.
Supporting this fact is that underneath a section of the lake Laguna del Maule is a
magma chamber and magma reservoir which altogether actively holds more than 100 cubic kilometers
of magma, although the vast majority of this is solidified aka not easily eruptible at
the present.
However, near the top of this magma chamber is rhyolite magma which is more than 70% melt.
This is far more than the minimum of 35 percent to 50 percent melt often thought is needed
for a volcano to be considered capable of erupting.
However, this fact alone does not guarantee that it will erupt anytime soon.
The ongoing earthquake swarm at Laguna del Maule is somewhat unusual as it has been occurring
for far longer than is normal.
While previous earthquake swarms have only lasted for less than 6 hours, the ongoing
swarm has lasted for more than 80 hours.
This marks the more than 2,000 earthquakes which have thus far occurred in the swarm
as the longest swarm to occur since the seismic network was put in place, with it also being
one of the most energetic.
These quakes were almost universally what are referred to as "volcano-tectonic" earthquakes.
Per a direct quote from the U.S. Geological Survey, "Volcano-tectonic (VT) earthquakes
represent brittle failure of rock, the same process that occurs along purely "tectonic"
faults such as the San Andreas Fault.
At volcanoes, VT events can occur due to "normal" tectonic forces, changing stresses caused
by moving magma, and movement of fluids through pre-existing cracks."
In my opinion, the recent volcano tectonic earthquakes at Laguna del Maule are probably
directly or indirectly related to a combination of changes in its hydrothermal system and
the intrusion of magma at perhaps depths of at shallow as 3000 meters.
In my opinion, I think that the ongoing magmatic uplift which is indeed occurring and is centered
in the southwest section of the lake right next to the volcano's last eruption in around
400 CE places additional strain on adjacent fault lines which are commonplace in this
complex.
These faults then slip due to the built up strain, generating an earthquake.
Because of all of this activity, the alert level of Laguna del Maule was raised from
green to yellow on April 3rd of 2023 by Sernageomin.
However, the center of where the majority of earthquakes in the current swarm are located
is centered 7 kilometers southwest of where the uplift center is at a depth of 4.5 to
8 kilometers.
Above these quakes on the surface at the approximate or within the vicinity of the coordinates
labeled on screen, fairly large quantities of carbon dioxide gas are venting onto the
surface.
While this venting has been occurring since at least 2012, you must stay at least a 2,000
meter radius away.
As a whole, Laguna del Maule is experiencing one of the highest rates of uplift on the
planet, as sections of it are being pushed upwards by as much as 20 centimeters or 8
inches a year, only falling behind the rate Iwo Jima and Askja is undergoing at the present.
Laguna del Maule appears to have undergone dozens of cycles of uplift in the last 10,000
years such as what is currently ongoing, meaning that in the long term it is not all that unusual,
with the vast majority of instances not resulting in a volcanic eruption.
Thus, while an eruption could theoretically result from the current unrest, I find this
possibility to be unlikely.
Thus, on my 0 to 10 opinion based volcanic unrest scale I am placing Laguna del Maule
at a 3.
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