The term "supervolcano" is used to describe volcanoes which have produced the planet's
largest explosive eruptions, ejecting several hundred to several thousand cubic kilometer
of volcanic rock in a single event.
Some supervolcanoes such as Yellowstone are well known, while others such as the Aira
caldera in Japan are not.
Well, another potentially active supervolcano was discovered in a place few people would
ever expect.
Located just 920 kilometers or 570 miles south of the North Pole, and centered north of the
edge of Siberia, is a massive oval shaped depression which is quite prominent on topographic
maps.
This giant blue hole is not an error in the dataset, as it has been explored by submarine
and confirmed to exist.
It represents the site of a massive supervolcano called Gakkel Ridge, and its massive depression
formed during the world's single largest volcanic eruption in the last 25 million years.
This giant hole in the ground is in fact a caldera that measures 80 kilometers long,
40 kilometers wide, and 1200 meters deep.
It originated in a massive supereruption which occurred 1.09 million years ago at a depth
of 2 kilometers underwater.
This caldera is centered on an unusual location for a highly explosive volcano, as it straddles
what is called a mid ocean ridge.
At mid ocean ridges the crust slowly spreads apart every year, from which shallow magma
in the mantle erupts, forming new oceanic crust.
In this case, the North American Plate to the east is spreading apart from the Eurasian
Plate to the west.
However, possibly due in part to its location near the pole, this oceanic ridge is highly
unusual.
While typical ridges spread apart 3 to 10 centimeters each year, it only moves 6 millimeters
each year.
This marks the Gakkel Ridge as the slowest divergent plate boundary on the planet, which
has allowed large volumes of magma to occasionally build underneath sections of the ridge, leading
to powerful explosive eruptions.
Explosive eruptions are typically absent in this type of geologic setting, as most submarine
volcanoes produce low gas and silica content rock known as "pillow basalt".
Before its powerful supereruption occurred, there was likely a large group of shield or
stratovolcanoes in its place which were aligned along the mid ocean ridge.
Over what was likely a span of several hundred thousand years, numerous eruptions constructed
a volcanic complex which towered 1500 meters or 4900 feet above the ocean floor.
Another weird thing about this supervolcano is its apparent composition.
Almost all supereruptions universally produce rhyodacite or rhyolite lavas, which have an
unusually high silica content, indicating a high viscosity.
In contrast, the ash which was erupted from this volcano appears to have a composition
somewhere in the basalt to basaltic andesite range.
Before the supereruption occurred, volcanic activity either drastically decreased or stopped
altogether, allowing for thousands of cubic kilometers of magma to build underneath the
complex.
Then, 1.09 million years ago, the explosive eruption began.
This eruption likely began from several vents along a northern trending line of activity
matching the plate boundary, which sent a plume of superheated gasses to the surface.
Due to the amount and temperature of material contained in this eruption column, it boiled
overlying water, creating a mushroom shaped eruption cloud which climbed above the surface.
Although this cloud initially had a white color, it soon turned to dark gray.
Millions of tons of material were ejected every second, of which many fine particulates
were carried high into the atmosphere and the surrounding Arctic Ocean.
This material subsequently fell in a 1,000 kilometer radius, coating the seafloor with
a thick layer of ash.
Then, due to the amount of material erupted, the existing volcano completely collapsed
downwards to fill the empty space in the underlying magma chamber, forming a large caldera.
In total, 3,000 cubic kilometers of magma was erupted.
This marks the eruption as one of the 10 largest known single explosive eruptions to ever occur
on the planet, even surpassing the eruption of Toba 75,000 years ago.
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