Lava fountains produced during volcanic eruption are a spectacular sight to behold.
While during the 2021 eruption of the Cumbre Vieja volcano on the island of La Palma lava
fountains reached a height of up to 2,000 feet, and at Mount Etna in Italy, lava fountains
have historically reached as high as 9,850 feet or 3 kilometers into the sky.
Yet, Earth is not the only object in the solar system to produce such impressive lava fountains.
As in fact, an alien like world exists orbiting Jupiter which can also produce 2 kilometer
high lava fountains.
What I am referring to is a hostile moon of Jupiter, unsuitable for life or even human
visitation as we know it; the mostly yellow but also orange and red stained surface of
the moon Io.
Io's yellow color is owed to the sheer abundance of sulfur and sulfur oxide its surface has,
being produced by the more than 150 active volcanoes this strange moon has.
Overall, Io which has a diameter of 2,264 miles, being about 5% wider than Earth's moon
is.
Yet, you would not want to travel there in person as it for all intents and purposes
does not have a notable atmosphere as it is 1/125 millionth that of Earth, has a surface
temperature averaging around -210 degrees Fahrenheit, but most importantly, the planet
experiences 5 times the lethal dose of radiation for a person each day.
This radiation is so severe that it has even darkened surface mineralization near Io's
poles, turning them from primarily yellow to brown or black.
However, I want to note that Io's gravity is approximately 18.3% of Earth, meaning that
an average person could almost jump over the rim of a basketball hoop.
Because of this, and the almost complete lack of air resistance, eruptions on Io produce
volcanic plumes with abundant ash that reach up to 400 kilometers in height, being so high
that some of this material escapes into space before being captured due to the gravitational
pull of Jupiter.
One of these plumes above a massive shield volcano known as Prometheus with a 28 kilometer
wide caldera was recorded in every single image taken of the yellow moon between 1979
and 1997, meaning it could have been continuously erupting material and sending it into space
for at least 18 years straight, perhaps far longer.
During this time, 6,700 square kilometers was covered in a fresh layer of lava, although
volcanic debris fell over a larger radius, forming a wide circle visible from orbit.
This long duration eruption is similar in volume to lower end flood basalts on Earth,
indicating the sheer scope of mere common eruptions on Io.
You might be wondering why eruptions on Io are so explosive, and believe it or not, elemental
sulfur is part of the reason.
On Earth, a type of explosive volcanic eruption known as a phreatic eruption occurs when groundwater
or just standing water above an intruding body of magma is greatly heated.
It then flashes to steam, and since the same mass of steam takes up 1700 times more volume
than the water it once was, it causes an immense amount of pressure to build.
This eventually escapes via the path of least resistance which is almost always upwards,
generating a powerful volcanic explosion.
A similar thing happens on Io, except with elemental sulfur instead of water which has
a low boiling point.
However, this isn't the only reason why eruptions are so explosive.
As, the lower the gravity is on a moon or planet, the more explosive a volcanic eruption
will be.
This is because on Earth, higher gravity limits how much gas could theoretically expand when
it reaches the surface through a volcanic eruption.
Yet, with lower gravity and a near vacuum environment, gasses could expand further than
on Earth by a factor of 10s, 100s, or 1000s of times more, making purely effusive eruptions
incredibly rare on Io.
Additionally, any pyroclastic flows generated by eruptions would travel much further in
the lower gravity environment, and produced flood basalt like lava flows would be on average
thinner but cover a wider area than on Earth.
As for the root cause of volcanoes on Io, it relates to this.
As the moon orbits around Jupiter in a slightly variable orbit, the gravitational pull of
Jupiter and three other large moons pulls on Io at differing intensities.
This causes Io to stretch by as much as 100 meters or 330 feet every day, which creates
an immense amount of friction and then heat in the planet's upper mantle.
This causes rock to melt and generates abundant volcanic eruptions.
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