What you are looking at is an impressive 3,000 foot or 914 meter long explosion crater located
in eastern Arizona.
It is 1970 feet wide and 350 feet deep, and might be at first thought to be an impact
crater or have originated from weapons testing.
However, neither of these is the case as this massive crater is completely volcanic in origin.
As we zoom out, you can see other nearby volcanic vents known as cinder cones which have largely
eroded over hundreds of thousands of years.
This area during the last 2 million years was the site of the 3rd largest known volcanic
field in the United States in what is called the Springerville Volcanic Field.
From 2.1 to 0.3 million years ago, this volcanic complex produced cinder cones, lava domes,
and maars during intermittent eruptions about once every 4,400 years.
This built a series of 405 vents, one of which is the aforementioned explosion crater called
Cerro Hueco.
To understand how this explosion crater formed we must first understand why the surrounding
volcanic field exists in the first place.
The Springerville volcanic field exists along a northeast trending chain of young volcanic
fields in both Arizona and New Mexico which include the active Zuni Bandera field and
the Valles Caldera supervolcano.
This trend represents a 1.7 billion year old scar in the Earth's crust, as it was once
the site of a subduction zone where one tectonic plate was subducted underneath another.
In the more than 1 billion years since, this scar known as the Jemez lineament has remained
as a weak point in the crust, offering a path of least resistance for any magma deep in
the crust to travel upwards and erupt onto the surface.
Approximately 570,000 years ago, the planet was in the warming phase of the still ongoing
glacial cycle of the much broader ice age.
Arizona at the time was the site of 5 active volcanic fields which were spread across the
modern border of Mexico all the way to the Grand Canyon.
Each of these volcanic fields primarily consisted of a feature known as cinder cones.
Cinder cones are a medium sized volcanic cone which are typically 300 to 1,000 feet in height
which form through intermittent ejections of ash and lava, much like seen during the
2021 eruption at La Palma in the Canary Islands.
Since the supply of magma to the Springerville volcanic field was intermittent, each new
eruption occurred at a new location which built a brand new cinder cone.
One such eruption occurred 570,000 years ago, sending fountains of lava to a height of several
hundred feet and throwing bombs of lava in a large radius.
Since this specific vent began due to an underlying dike intrusion of magma, the cinder cone it
produced developed into an irregular profile.
It had two centers which partially overlapped each other; one to the east and one to the
west.
After the eastern cinder cone reached a height of 600 feet, the seasons changed, likely bringing
about monsoon rains.
These rains added to the existing water table underground which in part was located right
beneath the cinder cones.
Since nearby magma was still present, the associated heat began causing the groundwater
to rapidly increase in temperature.
Eventually, the water flashed to steam which caused an immense amount of pressure to build.
This pressure was owed to the fact that steam takes up more space than the same mass of
liquid water.
Eventually, this pressure became too great and a powerful explosion occurred in what
is known as a phreatic eruption.
Large boulders of rock were thrown in a several mile radius, and a plume of ash rose more
than 15,000 feet into the atmosphere.
Simultaneously, pyroclastic flows raced across the landscape, burning all nearby vegetation.
Once the plume of ash which drifted to the northeast cleared, what remained was a 3,000
foot wide explosion crater termed a maar.
In total, this eruption was about 5% the size of the 1980 eruption of Mount Saint Helens,
and would have been assigned a volcanic explosivity index of a 3.
Other maars can be found throughout the Springerville volcanic field, but none are quite as deep
or spectacular as the Cerro Hueco crater.
Thanks for watching.
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