When people generally think of west central Africa, they tend to think of the mostly dense
rainforest climate and the wildlife which exists there.
Yet, if you are specifically thinking of the nation of Cameroon, another feature should
come to mind; volcanoes.
There, only 22 kilometers inland from the Atlantic Ocean is one of the world's 10 largest
volcanoes.
Known as Mount Cameroon, it towers to a height of 4,095 meters or 13,435 feet, being so tall
that its summit is often above the regional cloud level, and on occasion allows it to
receive some snowfall.
Its landmass covers 1,450 square kilometers, and this volcano is quite active.
Having last erupted in 2012, and with half a million people living on its flanks, this
volcano poses a potentially wide ranging threat due to its historical long reaching lava flows.
For example, in 1999, a flank eruption on the southern portion of Mount Cameroon sent
a lava flow more than 14 kilometers to the south over a timespan of 21 days.
Covering a little more than 8 square kilometers in this timespan, the lava flow in question
stopped only 270 meters short of the coastline.
While this historical eruption did cause property damage, a number of major cities around the
volcano could one day be put at risk such as Buea due to the fairly wide distribution
of lava flows Mount Cameroon has produced which in the last 100 years has gone in almost
every direction.
Additionally, in the event of a future eruption, some populated areas could be at risk due
to carbon dioxide gas emitted by advancing lava flows, as carbon dioxide is heavier than
air and thus could get trapped in areas that are surrounded on all sides by slightly higher
terrain.
The reason why Mount Cameroon exists is somewhat interesting.
Zooming out, you might notice that Mount Cameroon is highly elongated to the northeast and southwest
and quite narrow in a perpendicular direction.
Zooming out further, we can see that this parallels with an extinct secondary peak known
as Little Cameroon but also a series of active and extinct volcanoes that stretch across
other portions of Cameroon, Equitorial Guinea, and Sao Tome and Principe.
Altogether, this 1,800 kilometer long trend is known as the Cameroon Line, and we are
currently unsure why it exists.
Adding to this mystery is the fact a trend of seamounts trends another 1900 kilometers
to the southwest in the exact same orientation, going all the way to Saint Helena.
Thus, since our current science cannot adequately explain why the Cameroon line exists, we simply
call this region a mantle "hot line".
This is meant as a broad catch all term to explain what this might be.
This "hot line" has been the site of volcanic activity for approximately 50 million years,
with no age progression trend in one direction to where volcanism occurred during this timespan.
Volcanism at Mount Cameroon began approximately 3 million years ago, when along several points
a lengthy dike intrusion caused a several kilometer long fissure to erupt onto the surface.
Several hundred foot high lava fountains were generated, which eventually fell back to the
ground, forming long and runny flows of basaltic lava.
This process continued for some time before several vents in the chain became dominant.
After several hundred thousand years of eruptions, Mount Cameroon most likely looked like a shield
volcano albeit without a summit caldera.
You can see this stage of the volcano's lifespan by simply looking at its slopes, as there
is an area where it jumps from a gentler to steeper slope, marking the boundary of more
explosive volcanism.
The more explosive volcanism which produced VEI 1 to VEI 3 eruptions sometimes producing
more viscous trachyte and phonolite lavas, which formed in Mount Cameroon's underlying
magma chamber due to fractional crystallization combined with leaching of silica in the surrounding
crust.
This caused the volcano to build a steeper slope, approaching 45 degrees in some sections.
At a point likely around 100,000 years ago, a 1 mile wide and 3.4 mile long section of
the volcano's western flank collapsed in what was in my opinion a large debris avalanche
event.
Since then, eruptions have on rare occasions occurred away from the volcano such as at
the Debunscha maar, having mostly occurred at cinder cones in mildly explosive strombolian
eruptions in the central north to south line on the volcano.
Since 1800, Mount Cameroon has erupted on average about once every 13 years.
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