In my last article I wrote about the Turkana, volcanism that is part of the Great African Rift. But unbeknownst to most this is just one of several rift systems in Africa that are tearing the continent apart.
In this article we will be making an initial contact with an even larger, younger and far less understood rift system that over time will spell the end of what we know and understand today to be the African continent.
This rift system is so large that we will have to walk through it country by country, but in the end we will see how it is connecting well known large volcanic features at the very outer ends of this huge continent creating the largest continuous volcanic system on earth if you do not count the Mid Atlantic Rift.
Now, how big is big? Well, without going into detail the volcanic rift system starts at Etna and Pantelleria in the north and goes all the way down to the Cameroon Volcanic Line and from the Red Sea in the East all across Northern Africa well past Chad to the West edges of the continent.
As at pretty much every other large rift system it is where two different rifts intersect you get the largest scale volcanism, or were the rift volcanism is affected by a mantleplume. In Libya there is one major triple-junction were the main north to south rift transects a local East to West rift.
But before we start I feel an urge to talk about Wikipedia and not always trusting what it says. Many years ago I walked through Sahara from West to East, and part of my trek went through Libya, and one of my pit stops was at the Waw an Namus oasis that is inside the caldera of the same name. It is by all means one of the most remote places on earth. Back then Qaddafi kept some sort of order in the area, but today it is one of the most dangerous parts of the world. It is suicide to go there. Still Wikipedia states that it is an increasingly popular tourist attraction; I would take that statement with a pinch of salt the size of a mountain.
Local rift volcanism
From the border towards Tunisia there is a Northwest to Southeast trending rift that runs all the way through Egypt into the Red Sea. It follows the same trajectory as the far larger Ti Besti rift that cuts all of North Africa in half.
This local Jifarah-Jabal Nuqay volcanic rift system consists of 4 volcanic centers, from NW to SE these are Jifarah, Jabal as Sawda, Jabal al Haruj and Jabal Nuqay. This local rift transects the major North to South rift at Jabal al Haruj creating a triple junction volcano of prodigious size.
Al Haruj Al Abiyad
Libya has two Holocene volcanoes, one of which is on the local rift. It is the 45 000 square kilometer Al Haruj Al Abiyad flood basalt center. During the last 6 million years it has erupted in an extended series of rifting fissure eruptions with an average length of 60 kilometers per rift event.
The average size of eruptions is roughly twice that of the far more famous Lakí eruption giving an average of 30 cubic kilometers per eruption. Since Al Haruj has been active in the Holocene this makes it likely that the last eruption rivaled the Thjorhsahraun commonly thought of as the largest Holocene flood basalt, but both size and exact age is badly constrained for this eruption and we are not likely to receive good data for the foreseeable future due to regional instability.
The volcanic complex is littered with more than 150 visible cones, dozens of shield volcanoes, rootless lava flows and pit craters and the eruptive styles are similar to the Icelandic large rift eruptions, but with the exception that there is no magma/water or lava/water interaction here leaving the lava highly pristine.
The lavas are mainly alkaline basalts or alkali hawaiinites with a high degree of fluidity. Recent petrochemical analysis gives at hand that there are marked similarities with lavas from Pantelleria and Etna.
Unlike the other 3 volcanic centers on this line Al Haruj is still active and is likely to erupt again over time, but there is insufficient data about average time between eruptions and there is no equipment in the region that monitors the volcano (with the possible exception of oil companies), so we are unlikely to know when an eruption would occur until lava breaches to the surface.
Waw an Namus
To the south of Al Haruj we find the subsidence caldera of Waw an Namus, it is 4 kilometer wide gently sloping caldera that features a central tephra cone of Holocene age and no less than 3 alkali/saline lakes with a high sulphuric content.
The oasis has been used by the caravans going into Central Africa for a very long time and it is a very interesting place to visit, especially if you have been walking through the vastness of the Libyan desert for a couple of weeks.
The oasis is aptly named since Waw an Namus means the Oasis of Mosquito’s, so any visitor needs to go heavy on the chloro-quinine as a countermeasure against getting malaria. Climbing the tephra cone is hard going, but generally well worth the effort. The view is quite stunning and I slept one night on the crater rim watching the stars.
The caldera formed as a large shallow magma reservoir was emptied out about 200 000 years ago in an eruption that created large scale lava flows around the volcano. The young tephra cone was created as alkaline basalts interacted with water inside the caldera and the local region is covered in tephra that is quite visible from space.
The tephra is young, but there is no exact dating. If it had been old it would have been covered by the frequent sand storms in the region.
As volcanoes go, this is about as far away you can come from the beaten track. There are no roads leading here except for the caravan tracks, or if you are walking the traverse desert route that I did. The only good way to go visit would be via helicopter, but the political instability in the region makes this about as hazardous as walking. This is definitely not a tourist attraction volcano.
This article was just a start to what is to come. Next time I will meander off into the far more fertile volcanism of Chad and the Ti Besti rift. What I find so interesting with the volcanism here is that it is so badly studied and poorly understood, even though it may in all fairness be the world’s largest volcanic system.
This series of articles is in part a call for more studies and it is also very hard to write since there is so little material to be had.
Map images above from: “Plio/Pleistocene Flood Basalt Related Scoria and Spatter Cones, Rootless Lava Flows, and Pit Craters, Al Haruj Al Abiyad, Libya” by Németh et al.
Additional sources: “Miocene to recent alkaline volcanism between Al Haruj and Waw an Namous (southern Libya)” by Bardintzeff et al.; “Multiphase Alkaline Basalts of Central Al-Haruj Al-Abyad of Libya: Petrological and Geochemical Aspects” by Abdel-Karim et al.