On May 2nd, 2015 at 7:30 pm local time, a small earthquake struck just north of Jackson
Mississippi.
Despite only being a magnitude 3.2, the relatively high age of the area's rocks allowed for the
minor ground movement to be felt over an unusually wide area.
Less than an hour later a second earthquake struck, registering in as a magnitude 3.0.
These earthquakes were caused by a near vertical fault line present at a depth of approximately
3 miles.
However, the reason why this fault exists relates to a strange geologic oddity in the
vicinity.
Underneath the center of Jackson is the remains of a once highly active stratovolcano which
erupted during the late Cretaceous period when dinosaurs roamed the Earth.
Thus, Jackson is the only capital city in the United States to be completely built on
top of a volcano, and this is not a mere coincidence.
The large volumes of magma which intruded into the crust uplifted a large section of
overlying ground, creating a series of hills.
The presence of these high points was a deciding factor in Thomas Hinds to select where the
area's new capital city would be located in 1821.
As a whole, the Jackson volcano is highly unusual due to it erupting a rare type of
lava, and is loosely connected to the creation of the island of Bermuda.
The Jackson volcano is centered just east of the Jackson city center where it is located
at depth underneath the Mississippi Coliseum.
There, its now highly eroded highest point is still at a depth of 2,900 feet underneath
the city, meaning that its remains is completely below sea level.
This volcano is linked to a chain of unusual composition volcanoes that stretch from south
central Kansas to eastern Georgia which formed between 100 and 50 million years ago.
All of these volcanoes were caused by the underlying Bermuda hotspot which injected
significant quantities of partially melted material into the crust, of which some molten
rock would eventually erupt onto the surface.
The apparent track is not because the hotspot moved.
Rather, the overlying continental tectonic plate moved to the west while the hotspot
remained nearly stationary.
This plate would eventually move further west, and now the hotspot is centered northeast
of the island of Bermuda.
Due to the unusual nature of this very deep hotspot, it sent up material typically only
found at the depths in the mantle.
This resulted in the formation of highly explosive, diamond bearing kimberlites at more than a
dozen sites in Kansas.
However, not all of the magma this hotspot created was kimberlite, as it also produced
a dark colored type of volcanic rock unusually rich in potassium.
This rock is known as lamproite, which is the variety of rock diamonds are found within
at the Crater of Diamonds site in the state of Arkansas.
Although the rock type of the Jackson volcano is not specified, the existing notes from
an oil logging company are available online, who identified where the volcanic rock was
located.
However, they unfortunately referred to the material as a "dark colored felsic rock" and
"granitoid composition".
The first term is an oxymoron as felsic rocks are generally light in color, and specimens
of the existing rock did not look like granite.
Thus, we are left with the listed mineral abundances in hand samples observed, which
points back to a composition of lamproite.
The initial eruption of this volcano occurred 74 million years ago, where the region was
covered by a shallow inland sea.
Large volumes of lamproite composition magma quickly shot upwards through the crust at
a rate of potentially more than 100 miles per hour.
Propelled by gas, when it reached the seafloor it created a powerful explosion, carving out
a large crater in the ground and scattering large amounts of ash.
However, after this explosive phase ended, nonexplosive lava effusion began.
Over the next several years, dark colored potassium rich magma erupted onto the seafloor,
eventually building above the waterline.
By the end of this eruptive period, a several mile wide stratovolcano was constructed which
likely had an appearance similar to the island of Krakatau.
At some point this volcano produced another major eruption, causing it to fall below sea
level and for coral reefs to form on its former summit.
This material was then buried by a layer of ash.
In the millions of years since, several thousand feet of sedimentary rock has been emplaced
above the volcano, and the majority of ash it once had has long eroded away.
All that remains of this once great volcano is a section of its magma chamber.
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