Unknown to many, the nation of Kenya contains more than a dozen active volcanoes.
The most recent eruption from one of these volcanoes occurred from the Barrier volcano
in 1921.
However, within the country is a far more impressive volcano, which contains a massive
1800 meter wide and 155 meter deep crater formed by one of its recent eruptions.
This crater marks the summit of the volcano I am referring to, called Longonot.
Longonot last erupted in 1863, and it will certainly erupt again.
This video will discuss this volcano and mention what its future hazards are.
The Longonot stratovolcano is located in southwest Kenya, where it is 60 kilometers northwest
of the nation's capital, Nairobi.
As we zoom in on this volcano, we can see a number of distinguishing features.
These prominent features include two recent lava flows, a summit crater, and several recent
cinder cones...which all indicate a history of highly explosive eruptions.
First off, why does this volcano exist?
In eastern Africa, there are three areas of the crust which are slowly spreading apart,
allowing magma to travel up through these cracks and erupt onto the surface.
One of these areas stretches from SW Ethiopia, through central Kenya, all the way to NE Tanzania.
There, the crust is spreading to the east and west, which over time has caused the creation
of more than a dozen distinct volcanoes in the country.
The Longonot volcano began forming 400,000 years ago, when magma from this rift zone
traveled up through the crust and erupted onto the surface.
This magma erupted in an explosive manner, as it had a high viscosity.
As a result, numerous thick layers of a gray rock type called trachyte piled on top of
one another, thus forming a tall stratovolcano.
By 25,000 years ago, this stratovolcano may have reached a height of 3000 meters.
Eventually, the eruptions at Longonot stopped, as pressure began to build in its underlying
magma chamber.
For some time, this chamber continued to expand in size.
Then, 21,000 years ago, this pressure was released in a catastrophic eruption.
As the top of the volcano exploded, pyroclastic flows raced across the surrounding landscape,
traveling more than 40 kilometers in some directions.
Concurrently, large volumes of ash were ejected high into the atmosphere, causing the overall
magma chamber to drain.
Then, much like a sinkhole, the overlying volcano collapsed downwards to fill the empty
space in the underlying magma chamber.
This collapse created a massive 12 by 8 kilometer wide caldera in an eruption which ejected
more than 100 cubic kilometers of material.
Today, the remnants of this caldera rim are quite prominent, as they form more than 100
meter tall cliffs in several locations surrounding the overall volcano.
Over the next several thousand years, numerous eruptions rebuilt a large section of the volcano.
However, 11,000 years ago, a second large eruption occurred.
This eruption created another smaller caldera, which can be seen to the southwest of the
current summit.
Since then, eruptions mostly filled in the areas emptied of volcanic rock by two major
caldera collapses.
A series of these eruptions created a chain of northward trending cinder cones on the
northern slope of the mountain, and a chain of tuff rings on the southern slope.
Then, in 1500 BC, another major eruption occurred.
At the time, Longonot contained a small summit crater, perhaps 200 meters wide, which was
filled with a crater lake.
As magma pushed upwards towards the surface, it caused this water to flash to steam, eventually
generating a large explosion.
This explosion created a vast 1800 meter wide crater, which has since been filled by lava,
giving it a relatively flat appearance.
The most recent eruption from Longonot occurred in 1863 from the aforementioned chain of volcanic
cones and tuff rings.
There, two lava flows erupted, one to the north and one to the south.
From these vents emerged a significant volume of lava, which set the surrounding landscape
on fire, and traveled approximately 3600 meters.
Since then, no additional eruptions have occurred.
However, we know that Longonot is still active due to the presence of fumaroles in its summit
crater and the detection of a still active magma chamber beneath its summit.
I want to note that much of Longonot's eruptive history in the last 10,000 years remains a
mystery, so we are not truly sure how often this volcano erupts.
Given the current limited evidence, if we were to use the US Geological Survey method
of rating volcanoes, Longonot would be classified as a very high threat volcano.
When this volcano erupts again, it will either produce a relatively peaceful lava flow like
it did in 1863, or a series of violent explosions.
I hope that you enjoyed this video!
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