When people hear the term supervolcano, they tend to think of Yellowstone in Wyoming, or
Toba in Indonesia.
However, these are not the only supervolcanoes on the planet.
As, within southwestern New Mexico is an ancient cluster of supervolcanoes which formed when
this part of North America was more volcanically active than modern day Indonesia.
These numerous volcanoes produced eruptions so large that they caused significant chunks
of overlying rock to collapse downwards and fill the empty space in a previously full
large volume magma chamber, creating features known as calderas.
One of these larger calderas measures 34.2 miles long and 15.5 miles wide, having formed
in a cataclysmic volcanic eruption which was larger than what the Yellowstone volcano produced
in its last true supereruption 631,000 years ago.
This is the story of the Emory Caldera and the adjacent geologic formation it created
which is now protected via the City of Rocks State Park.
The ancient Emory caldera can be found approximately 40 miles north of the city of Deming, where
the small town of Kingston along with Hillsboro peak are located within the now no longer
exposed ancient caldera.
Despite being located 27 miles to the southwest of where the eruption originated, in the City
of Rocks State Park it left behind a more than 30 foot thick layer of volcanic rock.
This largely consisted of ashfall but also pyroclastic flow deposits which over time
were preferentially eroded in some spots, forming pillars of ignimbrite which now seemingly
stick out of the ground.
The reason this supervolcano formed and erupted somewhat relates to why the Rocky Mountains
exist.
Several tens of millions of years ago, the Farallon tectonic plate began subducting underneath
the North American Plate.
This started to occur at a very shallow angle, causing strain to occur as the bottom of the
North American Plate was being pulled in the opposite direction as the top of the same
plate.
This process caused an extreme amount of compression, causing the uplift and formation of the Rocky
Mountains.
However, several million years later, something changed.
The Farallon tectonic plate suddenly snapped downwards at a much steeper angle in a process
called slab rollback.
This caused magma to rush upwards to fill the empty space previously occupied by the
tectonic plate.
Large volumes of magma than creeped through the crust, and erupted onto the surface through
incredibly large volume explosive eruptions which was referred to as the Mid-Tertiary
Ignimbrite Flare-Up.
Around 36 million years ago, one section of crust underneath southwestern New Mexico built
up a large magma chamber.
This chamber eventually expanded in size to contain several thousand cubic kilometers
of magma.
At first, this chamber was incapable of producing an eruption but as time progressed became
a greater percentage of liquid magma.
Eventually a threshold was passed which allowed for a release in pressure to occur, triggering
a catastrophic volcanic eruption.
The size of this eruption was unimaginably large, as it was equivalent in size to 1,000
simultaneous eruptions of Mount Saint Helens in 1980.
As a plume of ash traveled more than 50 kilometers into the atmosphere, pyroclastic flows raced
across the surrounding landscape.
Due to how energetic the eruption was, these kilometer high pyroclastic flows even traveled
up mountains.
Although we aren't sure of the full extent of the eruption, these pyroclastic flows likely
traveled up to 120 kilometers or 75 miles away, resulting in an extreme level of destruction.
Ash from this eruption then fell over the entirety of what is now the lower 48 U.S.
states.
Then, due to the extremely high volume of material erupted, totalling about 1,300 cubic
kilometers of volcanic rock, a massive section of the volcano collapsed downwards to fill
the nearly empty magma chamber.
This formed a massive 55 by 25 kilometer wide caldera in an event which was 30% larger than
Yellowstone's last true supereruption 631,000 years ago.
In total, the thickest layers of ash and pyroclastic deposits produced by the eruption may have
been as much as 470 meters or 1,542 feet thick.
This supervolcano did not produce another caldera forming eruption afterwards, although
it may have produced smaller lava dome forming eruptions before becoming permanantly extinct
34 million years ago.
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