Within the nation of Colombia, one of its most active volcanoes erupted 24 times from
1816 to 1977.
However, since then the Purace volcano has not produced a single eruption, representing
its longest period of inactivity since thorough record keeping began in 1816.
With this being said, there is now a chance that this eruption drought might soon end,
as on March 30th, 2022, the volcano's alert level was raised from green to yellow.
This change was made in response to an ever-increasing number of earthquakes beneath the volcanic
complex, which were caused by both the movement of magma and hydrothermal fluids heated by
molten rock.
As a result, the government has now recommended that people should not climb or hike on its
edifice due to the threat of large explosions which could occur with little or no warning.
So, if an eruption was to occur, what areas would be placed at risk?
Is there a threat of long distance lahars, such as what occurred at Nevado del Ruiz in
1985?
This video will answer these two questions and discuss the ongoing seismic unrest.
The towering Purace volcano is located in southwest Colombia, where it is centered 28
kilometers east southeast of the city of Popayan.
This volcano is very tall, often having snow on its summit and standing at 4,650 meters
or 15,256 feet above sea level.
It is a bit of a geologic oddity, as the complex consists of an andesite stratovolcano built
on top of an extinct dacite shield volcano.
The dacite magma the prior volcano produced travelled unusually long distances, and these
lobes of solidified lava can still be seen today.
The active stratovolcano consists of a chain of more than a dozen vents aligned in a northwest
facing orientation.
These volcanic craters each measure up to 500 meters in diameter, and are largely aligned
with the mostly hidden Coconucos Fault.
In historic times, frequent explosive eruptions have expanded the largest of these vents,
with several eruptive episodes even adding smaller craters within the summit complex.
Underlying this volcano is inferred to be an unusually large magma chamber, as the entire
complex has been defined as an unusually productive geothermal energy area.
Sulfur crystals are even mined from an area near its summit due to the abundant fumaroles
which are present.
Although we are not truly sure how old the Purace volcano is, its size and height suggest
that it could be well over a million years in age.
Its eruptions have been defined by moderately sized explosive vulcanian style activity,
which produce pyroclastic flows that travel several kilometers and generate small to medium
sized lahars.
As for ashfall, the last eruption in 1977 caused a dusting to several centimeters of
material to fall up to 7 kilometers from the volcano's summit.
Although the latest activity is concerning, as it represents the volcano's most activity
in 40 years, there is not any sign that an eruption will cause a Nevado del Ruiz sized
disaster.
Unlike Nevado del Ruiz, this volcano does not have thick glaciers on its summit.
Given the latest satellite footage available of the complex, it does also not have much
snow on its summit.
The lack of ice which could rapidly melt is important, as it lowers the amount of material
a potential lahar could contain.
Thus, if an unexpected volcanic eruption was to occur, the resulting lahars would be small
and only cause damage to low lying areas such as streams and on the sides of river channels.
At the present, an imminent volcanic eruption seems unlikely, although one could technically
occur.
With this being said, the volcano's overall seismic activity is continuing to increase,
meaning that it may very well erupt in the next several months.
I have outlined a series of risk zones around the volcano, where red indicates areas lava
flows and bombs of lava can occur, orange indicates the outer radius of where large
pyroclastic flows and destructive lahars occur, and yellow indicates areas where small scale
river flooding or a few centimeters of ash could occur during an eruption.
Thanks for watching.
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