Many people who live within Africa are familiar with two highly active volcanoes in the region.
These two volcanoes are Nyiragongo and Nyamuragira, which are located north of Lake Kivu and are
both erupting right now.
However, there are several other active volcanoes nearby.
One of these other volcanoes is located on the Congo Rwanda border, 35 kilometers northeast
of the town of Goma.
The volcano I am referring to is called Visoke, which last erupted in 1957.
This video will discuss this volcano, and mention what its future hazards are.
The Visoke stratovolcano is located in this section of Africa due to a rift zone in the
crust.
This rift zone stretches from northern Uganda all the way to northeast Zambia.
There, the crust is slowly being spread apart, thus splitting the large African tectonic
plate.
The splitting of this crust allows magma to travel upwards through the rift zone and erupt
onto the surface through a series of volcanoes.
The Visoke stratovolcano is the middle of three active volcanoes which define the northwest
border of Rwanda, as they define a natural barrier.
All of these volcanoes are hundreds of thousands of years old, and have produced numerous explosive
eruptions.
With this being said, the lavas from Visoke are unusual for the area.
Most of the lavas from nearby volcanoes originate directly from the mantle, and erupt as a highly
fluid low viscosity black rock type called basalt.
However, the eruptions from Visoke produced a different type of higher viscosity lava
called trachyandesite, which is gray in color.
Since this lava has a higher viscosity, it indicates that of the volcanoes in the vacinity,
Visoke could technically produce the largest explosive eruptions.
The most prominent feature on Visoke is a semi circular summit crater which contains
a crater lake.
This crater is 600 meters wide, and more than 100 meters deep.
It represents the main vent of the overall volcano, and due to the level of erosion on
the crater, likely formed 4 to 6,000 years ago.
An eruption large enough to form a 600 meter wide crater likely had a volcanic explosivity
index of 4, and generated medium distance pyroclastic flows which traveled down the
slopes of this tall volcano.
However, what I just said is based on limited data, as this volcano has not been well studied.
The recorded history of this volcano only began in 1800, since when we have had a full
picture of its eruptive history.
In 1891, a large body of magma rose towards the surface.
This magma then heated water in the crater lake, causing part of it to flash to steam
and then subsequently explode in a phreatic eruption.
Then, in 1957, another eruption occurred.
This eruption did not occur from the summit crater but rather an area 11 kilometers to
the north.
Initially, a fountain of lava shot several hundred meters into the sky.
Much of this lava then fell close to two adjacent erupting vents, which built a 40 meter high
cinder cone called Mugogo.
Over the next 42 hours, lava traveled 1500 meters to the northwest before the eruption
ended.
Although no additional eruptive activity has occurred since 1957, there have been changes
in the landscape surrounding this vent, indicating likely undetected changes at depth.
I have identified two vents in the region, which are located along a known fault in the
crust.
These vents seem to emit large volumes of carbon dioxide, as the thick jungle vegetation
is nonexistent within a 40 meter radius.
As such, I suggest that they are both fumaroles, and should be studied further.
If Visoke was to erupt again, in all likelihood it would occur either from the summit crater
or a chain of cinder cones and maar explosion craters which stretch 10 kilometers to the
northeast of the volcano's summit.
Regardless of the eruption type, thousands of people would be put at risk within Rwanda
due to the risk of pyroclastic flows alongside long distance lava flows, which could each
travel up to 5 kilometers away.
Overall, the odds of Visoke erupting in any given year are about 1 in 450.
Using the US Geological Survey's method of rating volcanoes, Visoke would be classified
on the upper end of the moderate threat category.
I hope that you enjoyed this video!
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