“What a view!” I yelped before snapping another photo. “Mmm, yes,” murmured Henry who had seen it many times before. While driving from Arusha to Ngorongoro we had topped the escarpment overlooking Lake Manyara (Fig. 1) and been confronted by an eye-grabbing view—steep, two to three thousand ft slopes fronting Lake Manyara and the Maasai Steppe like the ramparts of an immense fortress (Fig. 2). Wow!
However, I would have been even more impressed had I known this was only a small part of one of the geologic wonders of the world, a system of separate but related rift basins, composed of escarpments, and troughs some 30-40 miles wide, stretching 3,700 miles all the way from Turkey to Mozambique (Fig. 3).
And, it’s all caused by the earth’s crust pulling apart. In Eastern Africa, the Somali Tectonic Plate, which lies east of the Eastern or Gregory Rift (Fig. 3) is splitting away from the larger African or Nubian Plate causing huge chunks of land to sink between parallel faults (Fig. 4).
Geologists postulate that elevated heat flow from the earth’s mantle is causing “thermal bulges,” creating the highlands of Kenya and Ethiopia. As they form, these “bulges” stretch and fracture into a series of faults forming rift valleys. Huge chunks of land sinking between parallel fault lines force up molten rock in volcanic eruptions. Consequently, the East African Rift System (EARS), especially the Eastern or Gregory Rift, tends to be geologically active with numerous volcanoes, hot springs, geysers and earthquakes (Figs. 5 & 6).
The geological processes driving the formation of the East African Rift System have greatly benefited the region. For instance, rift basins with steep 2000-3,000 ft (600-900 m) escarpments, solitary volcanoes, including Kilimanjaro and Meru, and 7,000-12,000 ft (2,134-3,658 m) volcanic highlands, provide a scenic and biological diversity that otherwise would not exist (Figs. 6&7). A rough measure of this diversity is the number of Kenyan and Tanzanian national parks (16) found in areas affected by rifting and volcanism.
In addition, highly fertile volcanic soils support dense populations of agriculturists, as on the well-watered slopes of Mt. Kenya and Mt. Kilimanjaro (see Mt. Kilimanjaro post). Livestock productivity of rangelands occurring on volcanic soils is up to twice (or sometime more) of that on soils derived from other geological materials.
Yet another benefit is that steam from hot springs and geysers can be harnessed to create geothermal energy. In 2015, geothermal energy generated nearly half of Kenya’s electricity (Fig. 8). And, it’s green energy, too!
Then, there’s this: The East African Rift System may even have influenced human evolution. Discovery of so many remains of early hominids within the rift (Fig. 9) has led to the idea that the processes of formation of the East African Rift System (uplifts of land thousands of feet in elevation, volcanoes spewing ash into the atmosphere, extensive lava flows . . . ) may have caused frequent alternations between wet and dry periods, thereby influencing the evolution of the human species by forcing our ancestors to adapt by becoming smarter and bipedal.
And, here I’d thought it was all about the scenery.
Dennis — Interesting and well done. I like the format with some asides on the left. Candy
Thanks, Candy.
I learned a lot and Husband Mike will especially enjoy understanding more about the geologic history of that area. He did a day trip to the Oldupai Gorge and was fascinated. This issue must have taken some time to gather the visuals to illustrate your material. Enjoyed it all. Kay
Thanks, Kay. Yes, the blog post did take a while to do, but then, most everything I do these days seems to take an inordinate amount of time.
Great read again. Glad to see you are back working on your blog and book. Such great memories . I will Share .
Sent from my iPhone
>
Thanks. Glad you liked it.
Thanks.
Dennis, i did enjoy your second Ngorongoro Post. I too took numerous pictures of the rift system above Lake Manyara. It is classic! As a Geologist, i must point out that the Great Rift System is in the process of forming at least one other continent, as the Western rift splits Africa. The Rift system actually runs almost the north-south length of the African continent, I, personally, have not worked on it, but it does run from northern Somaliland (the old British Protectorate) south all the way to Mozambique, and also splits into an Eastern and Western Rift in the central part (including Uganda and Kenya). When I worked on evaluating the uranium occurrences in Somalia for the IAEA, the Head of the UN Mission to the Somali Geological Survey was the late Dr. Ray Cannon, who told me he had worked the Rift in Mozambique and Malawi, spent most of his career in Kenya, and was working the northern part in Somalia in 1983. I also joined several geologists from the Malawi Geological Survey on the Zomba Plateau overlooking the Rift Valley in the southern part of Malawi. Real odd-ball rocks down in the Rift that ranges from carbonatites (calcareous lavas) to alkali lavas and intrusives. In 1982, i visited the Western Rift in Uganda (Lake Albert Rift) looking at radioactive hotspots related to petroleum seeps north of Fort Portal. Absolutely beautiful country. Unfortunately, we don’t have any active rift systems in West Africa. Bob – by the way, Stella and I received our second Pfizer vaccinations yesterday (Tuesday, march 2nd).
Glad you liked it, Bob. We get our second dose of shots today.
Mother nature is so stunning!! Thank you for the phenomenal post and lovely photos. It is a joy to learn about this beautiful region 😉
-Tami
Glad you liked it.
Thank you for doing these articles. Your past experiences and knowledge are very much worth sharing and reading about. Hope Debbie and I can do a trip to see it ourselves one day. Glad you are well, healthy and vaccinated!
Anne: thanks for following my posts; I’m pleased you like them. I think that you and Debbie would indeed enjoy visiting East Africa.
So, keep it in mind. Cathy and I are in pretty good shape, all things considered, especially now we’ve have had our shots. How about you?
Nice portrait of the Rift Valley! A tiny correction: in fig 6, the mountain we see beyond Empakaai is Kerimasi, yet another extinct volcano, and Lengai would be out of frame to left.
O.k., thanks for the heads up. I will look at that photo again.
Damn! You’re right: that is Kerimasi. You’d have thought I’d have noticed the dark patch of forest high up on its slope and realized it couldn’t be Olodonio Lengai, which has bare slopes.