One of the most impressive features within Wyoming is a towering volcanic edifice called
Devils Tower.
This ancient mass of rock contains hexagon shaped columns which rise 867 feet above the
surrounding landscape.
Yet, despite how famous this beautiful rock formation is, little was known about how it
formed...until recently.
This video will discuss a new theory on how Devils Tower formed, and mention some nearby
related geologic features.
And yes, Devils Tower is part of an ancient volcano.
Devils Tower is located in the northeast corner of Wyoming, where it is only 28 miles from
the southern border of Montana.
Before Devils Tower was created, the area was covered with a shallow sea during the
Triassic period, approximately 220 million years ago.
Over the course of many subsequent millions of years, this sea repeatedly expanded and
retreated, leaving behind a large volume of sand and other fine particles.
Over this long time period, layers of various sedimentary rocks formed the surrounding landscape.
The red rock type is a variety of sandstone.
The white rock type is limestone, and the tan rock is shale.
By 157 million years ago, a several thousand foot thick grouping of various sedimentary
rocks towered over the surrounding landscape, much like what is seen today in southern Utah.
For some additional context, this sedimentary rock originally towered several hundred feet
above the modern peak of Devils Tower, indicating the vast amount of erosion which has occurred
since then.
Beginning around 50 million years ago, a large volume of magma intruded into this section
of North America, as the slow formation of the Rocky Mountains had given a path for magma
to travel upwards into the crust.
In this section of ancient Wyoming, there was an abundance of groundwater several hundred
feet beneath the surface.
As the magma continued to travel upwards, it began to heat this nearby groundwater,
causing it to flash to steam.
Eventually, the pressure was too much, and the ground exploded upward from a depth of
several hundred feet in what is termed a phreatic eruption.
As boulders of rock were thrown several miles, pyroclastic flows raced across the surrounding
landscape.
By the time this eruption was over, a several thousand foot wide and 800 foot deep crater,
termed a "maar" remained in the landscape.
This crater would eventually become the site of Devils Tower.
Around the same time period, 3.5 miles to the northwest, four similar explosions occurred.
However, these explosions were less energetic, creating a smaller complex of four craters.
Eventually, large volumes of magma emerged at these five distinct craters, which began
slowly to fill the bowl shaped craters.
At Devil's tower, the most extensive volume of magma erupted, creating a very tall edifice.
After the eruption ended, the lava began to cool in an unusual manner.
The lava cooled at the top first, creating a series of hexagon shaped cracks.
These hexagon shaped cracks then propagated downwards, as once the process began, going
further down required less energy.
By the time the cooling had completed, a series of hexagon shaped columns, some of which are
up to 10 feet wide, stood in this vast crater.
These columns were built out of a rock type called phonolite.
Over the following millions of years, the thick sedimentary rocks marking the top of
the crater were easily eroded away, while the layers of phonolite lava were far more
resistant and thus remained in the landscape.
By 5 million years ago, the vast majority of these sedimentary rocks had eroded away,
causing only the center of the respective lava flows to remain.
This formed the modern Devils Tower seen today.
Surrounding the tower you can see large quantities of volcanic rock which have eroded away, as
the entire edifice only became fully exposed quite geologically recently.
Further to the north, the maar complex also was eroded, thus leaving behind four buttes
referred to as the Missouri Buttes.
As a final note, I want to add that the theory of how Devils Tower formed is one of many
plausible explanations.
However, I feel that this theory is the best match given the available evidence.
I hope that you enjoyed this video!
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