Although generally not as well known as in neighboring Chile, the nation of Argentina
also contains dozens of potentially active volcanoes including ones which have produced
catastrophically large eruptions in the last several million years.
For example, in 2260 BCE, the Cerro Blanco volcano explosively erupted, causing pyroclastic
flows to scorch the landscape in a 40 kilometer radius and ejecting more than 100 cubic kilometers
of volcanic rock.
This eruption formed a large depression in the ground referred to as a caldera which
measured 7 kilometers wide.
Although this eruption was voluminous it was not completely unexpected as the same caldera
had another similarly sized older caldera right next to it.
However, this is not the only active volcano which contains a similarly large caldera.
More than 1,000 kilometers to the south and partially straddling the border with Chile
is the Copahue volcano which lies within an unusually large depression visible from satellite.
To the east of the volcano, the walls of the massive 22 kilometer long and 16 kilometer
wide Caviahue caldera are quite prominent.
However, this is not the only large and geologically recent caldera which the Copahue volcano lies
within.
The majority of Copahue's modern edifice is also situated above a 10 by 10 kilometer wide
caldera which is younger than the aforementioned caldera.
Both of these calderas formed in large volume explosive eruptions which will be discussed
in this video.
Although this complex has been erupting for millions of years, the root cause of volcanism
has remained the same.
Offshore of Chile, the Nazca plate is colliding with and subducting underneath the South American
Plate.
The melted material from this collision then migrates upwards until it erupts onto the
surface, forming a chain of volcanoes.
In this part of the continent there is a large lineament which stretches between the Callaqui
and Copahue volcanoes.
Both of these volcanoes formed on the lineament as it represented a path of least resistance
for magma to easily intrude into.
Although the exact age of when this complex began first erupting is unclear, it may have
began producing volcanic eruptions as early as 4.3 million years ago.
As lava erupted onto the surface, it created a series of explosions due to the interaction
with present groundwater.
Into these craters soon erupted lobes of basaltic andesite lava which expanded outwards and
eventually covered the craters.
As frequent eruptions occurred, one vent became dominant, forming a fissure like stratovolcano
which resembled Hekla in Iceland.
Over time, the erupted magma became compositionally more and more silica and alkali rich, changing
from basaltic andesite to andesite, to finally trachyte.
On the surface this caused eruptions to become more explosive and ash dominated, while also
producing shorter and taller flows of lava via lava domes instead of longer lava lobes.
As a large magma chamber or complex of magma chambers slowly grew underground to a volume
of more than 100 cubic kilometers of material, an immense amount of pressure started to build.
This pressure was eventually released via a cataclysmic eruption 2.02 million years
ago of a size comparable to Cerro Blanco's massive eruption.
This caused a plume of ash to shoot more than 45 kilometers or 148,000 feet into the atmosphere.
As a section of the eruption column collapsed downwards, it created pyroclastic flows which
swept across the landscape, destroying everything in a 50 kilometer radius.
Then, due to the large amount of erupted material, the magma chamber was partially drained.
This caused rock overlying it to collapse downwards, forming a massive caldera.
The modern Copahue volcano would later begin to form around 1.2 million years ago, and
for similar reasons would also collapse in a large eruption.
That eruption occurred 500,000 years ago, perhaps even breaking through a substantial
ice sheet which once again coated the landscape in a 30 kilometer radius in superheated ash
and pyroclastic deposits.
As the volcano collapsed, another caldera formed.
The modern Copahue volcano has since grown out of this caldera and luckily its eruptions
since have for the most part been relatively small.
Thanks for watching!
If you would like to request a specific topic, please leave a comment below.
Additionally, I would like to thank my new patron Paweł Zuzelski for supporting this
channel!