What you are looking at is a large and deep depression in the desert of southern New Mexico.
If you look around this feature, known as the Kilbourne Hole, you will find many dark
colored rocks which distinguish this feature as not being a sinkhole or a nuclear test
crater.
Instead, these rocks are volcanic in origin, and this fact is supported by the adjacent
eroded dark black lava flows from the Aden Crater shield volcano.
The fascinating Kilbourne Crater is also volcanic in origin, as it is in fact a type of volcanic
explosion crater referred to as a "maar".
It measures an impressive 12,580 feet long, 9,000 feet wide, and 440 feet deep.
And, within this crater are numerous pieces of Earth's mantle.
What I am referring to are green and greenish yellow crystals known as olivine, with the
gem variety of this mineral being known as peridot.
The Kilbourne Hole is located in far southern New Mexico where it is 25 miles south-southwest
of the city of Las Cruces. 25 miles SSW of Las Cruces.
The Kilbourne Hole is not simply an isolated feature as to its south are three other maars
while an additional 3 more maars are to its southwest.
All of these vents are part of the same volcanic complex, which when combined with the numerous
cinder cone vents and the Aden Crater shield volcano is known as the Potrillo Volcanic
Field.
While this volcanic field has not produced an eruption in more than 10,000 years, it
likely will erupt again at some point in the future perhaps distant future and thus could
best be classified as dormant.
Just like the more than 300 cubic kilometer body of magma more than 10 miles deep in the
crust and the potentially active Carrizozo volcano to the north-northeast, the Potrillo
volcanic fields exists due to a rift zone in the crust known as the Rio Grande rift.
Here, in parts of New Mexico and Colorado, the crust is very slowly spreading apart to
the east and west.
This spreading causes material in the mantle to more easily permeate through the crust,
occasionally reaching the surface and forming a chain of infrequently erupting volcanoes.
By the time the story of the Kilbourne Hole began, the Potrillo volcanic field had been
erupting intermittently for approximately 1 million years.
Approximately 24,000 years ago, a body of magma originating from the mantle began intruding
into the crust via an already established path of least resistance.
Along the way, this magma carried with it pieces from the mantle which included numerous
olivine crystals.
While this intrusion was ongoing, it likely created a series of small to moderate magnitude
earthquakes which continually got shallower and shallower.
Finally, the intruding batch of magma reached the underlying water table present in this
section of New Mexico during the ice age.
Due to the intense heat generated by the magma, it caused the large body of overlying groundwater
to quickly flash to steam.
Since the same mass of steam takes up vastly more volume than the water it once was, it
caused an immense amount of pressure to build.
Eventually, this pressure reaches a breaking point, causing a powerful explosion to shoot
upwards with an energy release equivalent to the detonation of more than a megaton of
TNT.
As a several thousand foot wide patch of ground exploded, a plinian eruption column shot more
than 82,000 feet or 25 kilometers into the sky.
Part of the eruption column then collapsed downwards, creating incinerating pyroclastic
flows which swept across the ice age era landscape at a speed of more than 200 miles per hour
and travelling up to 8 miles distant.
Then, smaller eruptions began, causing a larger volume of lava rich in olivine crystals to
be deposited onto the crater floor.
As these smaller eruptions continued for several weeks, ash would continue to pile up, which
along with pyroclastic flow deposits would total more than 40 feet thick on the newly
formed crater rim.
It would take perhaps decades for this ash to eventually cool, by which time the extent
of the eruption which occurred had become clear.
In total, at least 0.33 cubic kilometers of volcanic rock had erupted, meaning the eruption
which formed Kilbourne Hole had a volcanic explosivity index rating of a 4 at a very
minimum.
As a final note, I want to mention that collecting any rocks and minerals including olivine/peridot
at the Kilbourne Hole is forbidden as the site is part of a national monument.
Rock samples shown in this video were all presumably photographed on site and not removed
outside of it.
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