Within the state of New Mexico, there are a surprisingly high number of young lava flows
due in part to several active volcanoes being present.
The youngest of these lava flows was emplaced in 1170 BC, when a spatter cone from the Zuni
Bandera volcanic field sent several hundred million tons of lava towards the town of McCartys.
However, not all of the young volcanic features in the state are relatively small.
Overlooking this Zuni Bandera volcanic field to the northeast is a far more impressive
volcano, which measures 12 miles wide and stands at 11,305 feet tall.
What I am referring to is Mount Taylor, which is the name given to an impressive stratovolcano
which erupted on and off for around 2 million years.
Facing towards the southeast, the most prominent feature of Mount Taylor it its 2 mile wide
horseshoe shaped caldera.
Calderas of this shape tend to be formed through highly explosive lateral eruptions to the
side of a volcano, such as during the 1980 eruption of Mount Saint Helens.
While this crater is larger than the Mount Saint Helens Crater, it has a completely different
origin.
After Mount Taylor stopped erupting, the southeastern section of its edifice experienced greatly
accelerated levels of erosion compared to the surrounding volcanic rock.
This was caused by significant levels of hydrothermal alteration, which weakened its edifice thus
making it more prone to erosion.
Subsequent large volume landslides occurred, leading to its modern appearance.
So, how tall did Mount Taylor used to be, and why did it form?
Estimates vary as to how tall Mount Taylor used to be, with figures ranging from 12,000
feet to 14,000 feet.
I am of the opinion that it used to have a summit of around 12,200 feet, based on an
attempted reconstruction of its summit via its topography.
Mount Taylor and its surrounding volcanic field are one of several young volcanic features
within New Mexico which have seemingly formed along a northeastern trending straight line.
This line is called the Jemez Lineament, and represents a regional weak point in the crust
due to the collision of two tectonic plates at this very location 1.7 billion years ago.
Since the crust is thin in the area, magma at depth can easily travel upwards and erupt
onto the surface, thus forming volcanic fields such as Zuni Bandera, Red Hill, and Mount
Taylor.
Mount Taylor began forming 3 million years ago, when a volume of high silica rhyolite
composition magma erupted onto the surface.
As this magma interacted with nearby groundwater, it produced a series of powerful explosions
which carved out a several hundred meter wide crater in the ground.
Then, at the bottom of this crater erupted rhyolite lava.
Since this lava was not able to move very far due to its high viscosity, it formed into
a large dome which continued to expand.
On occasion, parts of this dome would collapse, releasing pyroclastic flows.
Several plinian eruptions occurred which created large craters in the lava dome, thus depositing
a thick layer of ash over the surrounding landscape.
However, at depth, the magma was slowly becoming less silica rich.
By 2.9 million years ago, Mount Taylor was no longer erupting rhyolite but instead trachydacite.
Although the volcano still produced lava domes during eruptions, they were now larger and
less steep.
Then, volcanic activity switched to producing trachyandesite lavas.
During the next 300,000 years, hundreds of eruptions built the bulk of Mount Taylor,
thus covering it in the distinctive gray rock associated with stratovolcanoes.
At its summit was a large volcanic crater formed via explosive eruptions which measured
perhaps half a mile in diameter.
Then, 2.52 million years ago volcanic activity at Mount Taylor's main cone ceased.
Over the next 1 million years, trachybasalt cinder cone forming eruptions occurred around
the flanks of the volcano, depositing thin and lengthy flows of lava.
The last such eruption occurred 1.5 million years ago.
Then, Mount Taylor became extinct.
While this volcano will never erupt again, there is always a possibility that the nearby
Zuni Bandera volcanic field will.
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