Category: Geothermal

ON THE ROAD TO NGORONGORO: PART II

ON THE ROAD TO NGORONGORO: PART II

“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!

Figure 1. Map of the Crater Highlands area. The Great Rift Escarpment passes west of Lake Manyara, east of the Crater Highlands (Loolmalassin Mts., Olmoti Crater etc.) and west of Lake Natron.
Figure 2. View south over Lake Manyara and along the Great Rift Escarpment. The Lake Manyara Hotel swimming pool is in the foreground.

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).

Figure 3. The Great Rift Valley includes the Dead Sea and the Sea of Galilee. In Africa, it cuts through the highlands of Ethiopia before dividing into the Albertine Rift and the Eastern or Gregory Rift. Lake Manyara is in the latter. (Author: Redogeographica. Creative Commons Attribution-Share Alike 4.0 International license.)

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).

Figure 4. Parts of the rift system are not distinct valleys (Graben) but, as at lake Manyara, a single escarpment (Footwall) rising above a shallow depression (Half-Graben). (Author: Aymaith 2. Creative Common Attribution-Share Alike 3.0 Unoported License)

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).

Figure 5. Geyser at Lake Bogoria, Kenya.

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.

Figure 6. Empakaai Crater (Embargi Crater in Fig. 1), an extinct, 10,569 ft. volcano in the Crater Highlands. Beyond, Kerimasi, another inactive volcano, rises from the arid rift floor where dry season dust devils swirl among leafless thorn trees. In contrast, temperatures at Empakaai Crater are lower, rainfall higher, and morning fogs drench evergreen forests and perennial grasslands.
Figure 7. Shallow lakes typical of the Eastern Rift are well known for their flamingoes. Lake Makat, Ngorongoro Crater.

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!

Figure 8. Geothermal power station at Olkaria, near Lake Naivasha, Kenya.

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.

Figure 9. Oldupai Gorge, Ngorongoro Conservation Area, Tanzania. The concrete block marks the site where the remains of an early hominid species, Zinjanthropus boisei (since renamed Paranthropus boisei) were discovered in 1959.