In the vast Saharan Desert, one of the many famed locations are a series of oasises where
water seemingly has ponded along with trees and vegetation in one of the world's driest
locations.
What you are generally not expecting to see at an oasis is a potentially active albeit
likely dormant volcano.
Yet, one such location exists in a country typically not associated with volcanoes, Libya.
There, even visible from satellite is a large black patch which heavily contrasts with the
color of the surrounding desert landscape.
Known as Waw an Namus, this unique and isolated volcano at some point produced a catastrophic
eruption which coated the surrounding landscape in ash and led to the formation of a 3.9 kilometer
long, 2.9 kilometer wide, and 140 meter deep caldera.
Since the caldera floor is below the top of the water table, several small lakes formed.
However, due to the remoteness of Waw an Namus, it presents a number of mysteries.
For example, despite the lightly eroded appearance of the black tephra layer which surrounds
the volcano for many miles, the youngest rock on the volcano to be reliably dated was 200,000
years old.
Yet, if we compare it to another widespread volcanic deposit in a similar environment
albeit one that has a little more rainfall, something does not add up.
At the Pinacate volcanic field in Mexico, the El Elegante Crater is dated at 32,000
years old.
Yet, the tephra field at Waw an Namus appears to have experienced a similar or even lesser
amount of erosion.
This suggests that at least one eruption at this volcano possibly could have occurred
as recently as during the last 25,000 years.
Because of this uncertainty, it is difficult to classify this volcano as extinct, dormant,
or active.
It could be any of the 3 categories as more studies are needed on this complex.
However, for the sake of this video we will assume it is dormant, meaning it has not erupted
during the Holocene period but could theoretically erupt again at some point in the future.
The Waw an Namus volcano is located in south central Libya where it is 344 kilometers west-southwest
of the city of Tazirbu.
At great distances to the south are a series of volcanoes in the nation of Chad which likely
owe their origin to an underlying mantle hotspot.
While Waw an Namus might also owe its existance to a hotspot, another distinct possibility
exists.
In the section of Libya where Waw an Namus is located is a feature referred to as the
Sirte Basin.
This basin is slowly spreading apart due to extensional forces to the northeast and southwest.
This has over time created basin and range like topography, potentially allowing for
magma to intrude into the crust and erupt via a path of least resistance.
One of these weak points in the crust appears to be a chain of activity which has resulted
in volcanic features along a southeast trending line which Waw an Namus is a part of, and
even includes features which look somewhat similar to maar explosion craters.
Based on the area the black tephra covered, which totals approximately 237 square kilometers,
it can be assumed that it originated during the caldera forming eruption of this complex.
Whenever this eruption occurred, it likely involved a large quantity of intruding magma
which when it interacted with overlying groundwater generated a powerful explosion.
A plinian eruption then occurred, and as a plume of ash shot high into the atmosphere,
part of the eruption column collapsed downwards and generated long traveling pyroclastic flows
which travelled as much as 13 kilometers distant.
Then, due to the large amount of erupted material, Waw an Namus's underlying magma chamber was
significantly drained.
This caused a large section of overlying rock to collapse downwards to fill the empty space,
forming its modern caldera.
Phreatomagmatic eruptions then commensed, and through semi-continuous explosive activity
built its central tuff cone.
Several maar forming eruptions then occurred to the northwest, which overlayed existing
black tephra deposits.
Although this volcano may never erupt again, if it was to erupt, the most likely sequence
of events would create another maar explosion crater.
Thanks for watching!
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Additionally, I would like to thank Astrid Mühlenberg for becoming a channel member
on youtube of GeologyHub!