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One of the harshest environments on Earth, the Sahara is most famous for its sprawling sand dune fields.

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AFRICA - Explore the Regions - Ethiopian Highlands

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Home " Plate Tectonics " The East Africa Rift System

East Africa's Great Rift Valley: A Complex Rift System

by James Wood and Alex Guth - Michigan Technological University

Part I. The East African Rift System

The East African Rift System (EARS) is one of the geologic wonders of the world, a place where the earth's tectonic forces are presently trying to create new plates by splitting apart old ones. In simple terms, a rift can be thought of as a fracture in the earth's surface that widens over time, or more technically, as an elongate basin bounded by opposed steeply dipping normal faults.

Geologists are still debating exactly how rifting comes about, but the process is so well displayed in East Africa ( Ethiopia- Kenya- Uganda- Tanzania) that geologists have attached a name to the new plate-to-be; the Nubian Plate makes up most of Africa, while the smaller plate that is pulling away has been named the Somalian Plate (Figure 1). These two plates are moving away from each other and also away from the Arabian plate to the north.

The point where these three plates meet in the Afar region of Ethiopia forms what is called a triple-junction. However, all the rifting in East Africa is not confined to the Horn of Africa; there is a lot of rifting activity further south as well, extending into Kenya and Tanzania and the Great Lakes region of Africa. The purpose of this paper is to discuss the general geology of these rifts and highlight the geologic processes involved in their formation.

What is the East Africa Rift System?

The oldest and best defined rift occurs in the Afar region of Ethiopia and this rift is usually referred to as the Ethiopian Rift. Further to the South a series of rifts occur which include a Western branch, the "Lake Albert Rift" or "Albertine Rift" which contains the East African Great Lakes, and an Eastern branch that roughly bisects Kenya north-to-south on a line slightly west of Nairobi (Figure 2).

These two branches together have been termed the East African Rift (EAR), while parts of the Eastern branch have been variously termed the Kenya Rift or the Gregory Rift (after the geologist who first mapped it in the early 1900's). The two EAR branches are often grouped with the Ethiopian Rift to form the East Africa Rift System (EARS).

The complete rift system therefore extends 1000's of kilometers in Africa alone and several 1000 more if we include the Red Sea and Gulf of Aden as extensions. In addition there are several well-defined but definitely smaller structures, called grabens, that have rift-like character and are clearly associated geologically with the major rifts. Some of these have been given names reflecting this such as the Nyanza Rift in Western Kenya near Lake Victoria. Thus, what people might assume to be a single rift somewhere in East Africa is really a series of distinct rift basins which are all related and produce the distinctive geology and topography of East Africa.

How did these Rifts form?

The exact mechanism of rift formation is an on-going debate among geologists and geophysicists. One popular model for the EARS assumes that elevated heat flow from the mantle (strictly the asthenosphere) is causing a pair of thermal "bulges" in central Kenya and the Afar region of north-central Ethiopia. These bulges can be easily seen as elevated highlands on any topographic map of the area (Figure 1).

As these bulges form, they stretch and fracture the outer brittle crust into a series of normal faults forming the classic horst and graben structure of rift valleys (Figure 3). Most current geological thinking holds that bulges are initiated by mantle plumes under the continent heating the overlying crust and causing it to expand and fracture.

Ideally the dominant fractures created occur in a pattern consisting of three fractures or fracture zones radiating from a point with an angular separation of 120 degrees. The point from which the three branches radiate is called a "triple junction" and is well illustrated in the Afar region of Ethiopia (Figure 4), where two branches are occupied by the Red Sea and Gulf of Aden, and the third rift branch runs to the south through Ethiopia.

The stretching process associated with rift formation is often preceded by huge volcanic eruptions which flow over large areas and are usually preserved/exposed on the flanks of the rift. These eruptions are considered by some geologists to be "flood basalts" - the lava is erupted along fractures (rather than at individual volcanoes) and runs over the land in sheets like water during a flood.

Such eruptions can cover massive areas of land and develop enormous thicknesses (the Deccan Traps of India and the Siberian Traps are examples). If the stretching of the crust continues, it forms a "stretched zone" of thinned crust consisting of a mix of basaltic and continental rocks which eventually drops below sea level, as has happened in the Red Sea and Gulf of Aden. Further stretching leads to the formation of oceanic crust and the birth of a new ocean basin.

Part II. The East African Rift

If the rifting process described occurs in a continental setting, then we have a situation similar to what is now occurring in Kenya where the East African/Gregory Rift is forming. In this case it is referred to as "continental rifting" (for obvious reasons) and provides a glimpse into what may have been the early development of the Ethiopian Rift.

As mentioned in Part I, the rifting of East Africa is complicated by the fact that two branches have developed, one to the west which hosts the African Great Lakes (where the rift filled with water) and another nearly parallel rift about 600 kilometers to the east which nearly bisects Kenya north-to-south before entering Tanzania where it seems to die out (Figure 2).

Lake Victoria sits between these two branches. It is thought that these rifts are generally following old sutures between ancient continental masses that collided billions of years ago to form the African craton and that the split around the Lake Victoria region occurred due to the presence of a small core of ancient metamorphic rock, the Tanzania craton, that was too hard for the rift to tear through. Because the rift could not go straight through this area, it instead diverged around it leading to the two branches that can be seen today.

As is the case in Ethiopia, a hot spot seems to be situated under central Kenya, as evidenced by the elevated topographic dome there (Figure 1). This is almost exactly analogous to the rift Ethiopia, and in fact, some geologists have suggested that the Kenya dome is the same hotspot or plume that gave rise to the initial Ethiopian rifting. Whatever the cause, it is clear that we have two rifts that are separated enough to justify giving them different names, but near enough to suggest that they are genetically related.

Other Points of Interest:

What else can we say about the Ethiopian and Kenya Rifts? Quite a lot actually; even though the Eastern and Western branches were developed by the same processes they have very different characters. The Eastern Branch is characterized by greater volcanic activity while the Western Branch is characterized by much deeper basins that contain large lakes and lots of sediment (including Lakes Tanganyika, the 2nd deepest lake in the world, and Malawi).

Recently, basalt eruptions and active crevice formation have been observed in the Ethiopian Rift which permits us to directly observe the initial formation of ocean basins on land. This is one of the reasons why the East African Rift System is so interesting to scientists. Most rifts in other parts of the world have progressed to the point that they are now either under water or have been filled in with sediments and are thus hard to study directly. The East African Rift System however, is an excellent field laboratory to study a modern, actively developing rift system.

This region is also important for understanding the roots of human evolution. Many hominid fossil finds occur within the rift, and it is currently thought that the rift's evolution may have played an integral role in shaping our development. The structure and evolution of the rift may have made East Africa more sensitive to climate changes which led to many alternations between wet and arid periods. This environmental pressure could have been the drive needed for our ancestors to become bipedal and more brainy as they attempted to adapt to these shifting climates (see Geotimes 2008 articles: Rocking the Cradle of Humanity by Beth Christensen and Mark Maslin, and Tectonic Hypotheses of Human Evolution by M. Royhan Gani and Nahid DS Gani).

Conclusions:

The East African Rift System is a complicated system of rift segments which provide a modern analog to help us understand how continents break apart. It is also a great example of how many natural systems can be intertwined - this unique geological setting may have altered the local climate which may have in turn caused our ancestors to develop the skills necessary to walk upright, develop culture and ponder how such a rift came to be. Just like the Grand Canyon, the East African Rift System should be high on any geologist's list of geologic marvels to visit.

About the authors:

James Wood has a PhD from Johns Hopkins University and is currently Professor of Geology at the Michigan Technological University in Houghton, Michigan where he teaches Earth History, Geochemistry, Remote Mapping and conducts a field course every spring in East Africa. His main research interests are energy deposits, mainly gas and oil, and doing field work in rift valleys.

Alex Guth is currently a PhD candidate at Michigan Tech and is looking at the effects of climate on desert varnish on the exposed flows and alluvium in the East African Rift Valley. She assists Dr. Wood with the geology field camp. Her website can be viewed at: pages.mtu.edu/~alguth/.

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East Africa's Great Rift Valley: A Complex Rift System

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A description of the East Africa Rift System with maps and cross sections.

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Kilimanjaro is the highest mountain in Africa at 19,341 feet (5,895 meters), but it isn't a mountain in a traditional sense. It is a giant stratovolcano that began forming about a million years ago and is composed of many layers of hardened volcanic ash, lava, pumice and tephra - fragmental material that is the fallout from a volcanic eruption.

One of the Seven Summits (the highest peaks on the seven continents), Kilimanjaro is in Tanzania in east Africa.

Credit: Graeme Shannon shutterstock

A number of theories exist about the meaning and origin of the name. One theory is that the name is a mix of the Swahili word Kilima, meaning "mountain," and the KiChagga word Njaro, loosely translated as "whiteness." Another is that Kilimanjaro is the European pronunciation of a KiChagga phrase meaning "we failed to climb it."

One of the Seven Summits (the highest peaks on the seven continents), Kilimanjaro is in Tanzania in east Africa. Kilimanjaro lies within the 292-square-mile (756 square kilometers) Kilimanjaro National Park. Kilimanjaro rises from its base approximately 16,732 feet (5,100 meters) from the plains near the Tanzanian municipality of Moshi, making it the tallest free-standing mountain in the world.

There are three volcanic cones that make up Kilimanjaro: Kibo is the summit; Mawenzi at 16,893 feet (5,149 meters); and Shira at 13,000 feet (3,962 meters). Uhuru Peak is the highest summit on Kibo's crater rim. Uhuru, Swahili for "Freedom," was named in 1961 when Tanganyika gained its independence . Tanganyika later joined with the islands of Zanzibar to form Tanzania.

While the other two volcanic formations are extinct - meaning that they are highly unlikely to erupt again - Kibo (the highest peak) is merely dormant, so there is the possibility that it could erupt. Estimates have the last major eruption dated to 360,000 years ago, but volcanic activity was recorded just 200 years ago.

While Kibo is dormant, gas is emitted into the crater, causing several collapses and landslides, with the most extensive ones creating the area known as the Western Breach.

While the name Kilimanjaro has its origins in the KiChagga word for "white," it is becoming increasingly less so. While it still covered with ice caps and glaciers at higher levels, global warming is quickly changing the climate and scientists expect the famed snows of Kilimanjaro to disappear sometime between 2022 and 2033.

Climbing Kilimanjaro

About 30,000 people climb Kilimanjaro each year and about three-quarters of those reach the summit. It is a relatively safe climb, and most climbers who fail to summit experience altitude-related issues or harsh weather near the peak. Temperatures at the peak can be 0 degrees F (minus 18 C), and if the winds are blowing, the wind chills reach dangerous levels.

The climb can be done any time of year but the rainy winter season make the summer and early fall a popular time to climb.

Kilimanjaro has five climbing routes to the summit: Marangu Route; Machame Route; Rongai Route; Lemosho Route; and Mweka Route. The popular Machame and Lemosho routes are scenic, while the busy Marangu is the easiest until the difficult final ascent to the rim of the crater.

In 1861, the German officer Baron Carl Claus von der Decken and British geologist Richard Thornton made a first attempt to climb Kibo, but had to turn back at 8,200 feet (2,500 meters).

Von der Decken tried a second time the following year, and with Otto Kersten got as far as 14,000 feet (4,280 meters).

In 1887, during his first attempt to climb Kilimanjaro, German geology professor Hans Meyer reached the base of Kibo, but was not properly equipped to handle the deep snow and ice and retreated.

On Oct. 5, 1889, Meyer, Marangu scout Yoanas Kinyala Lauwo and Austrian Ludwig Purtscheller were the first team to reach the summit. They were the first to confirm that Kibo has a crater, which was filled with ice at the time.

Honey badgers and bushbabies

Kilimanjaro encompasses a wide variety of ecosystems, including tropical jungle, savannah, and desert to montane forests, subalpine plants, and the alpine zone above timberline.

Kilimanjaro has a large variety of forest types that harbor 1,200 vascular plant species. Montane Ocotea forests occur on the wet southern slope. Cassipourea and Juniperus forests grow on the dry northern slope. Subalpine Erica forests at 13,451 feet (4,100 meters) represent the highest elevation cloud forests in Africa.

Another feature of the forests of Kilimanjaro is the lack of a bamboo zone, which occurs on all other tall mountains in East Africa with a similarly high rainfall. Because there is no bamboo zone there is a limited supply of food for animals.

However, there are a number of species that thrive in the area. Blue monkeys, which are not actually blue but grey or black with a white throat, gather in the forest zone on the Rongai Route. Olive baboons, civets, leopards, mongooses and bush pigs, which have a distinctive white stripe running along its back from head to tail, are abundant.

There are honey badgers and aardvarks, but visitors rarely get to see these nocturnal creatures. Noisy bushbabies, which are also nocturnal creatures, can be more easily heard more than seen. There are also small-spotted genets with distinctive black-and-white tails, and the loud tree hydraxes that are similar to chipmunks.

- Kim Ann Zimmermann

Related:

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Kim Ann Zimmermann, Live Science Contributor

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Kilimanjaro: Facts About Africa's Highest Peak

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Kilimanjaro is the highest mountain in Africa at 19,341 feet (5,895 meters), but it isn't a mountain in a traditional sense. It is a giant stratovolcano that began forming about a million years ago and is composed of many layers of hardened volcanic ash, lava, pumice and tephra - fragmental material that is the fallout from a volcanic eruption.

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This article was most recently revised and updated by

Libyan Desert, Arabic Al-Ṣaḥrāʾ al-Lībīyah, northeastern portion of the Sahara, extending from eastern Libya through southwestern Egypt into the extreme northwest of Sudan. The desert's bare rocky plateaus and stony or sandy plains are harsh, arid, and inhospitable. The highest point is Mount Al- ʿUwaynāt (6,345 feet [1,934 metres]), located where the three countries meet. The Qattara Depression (Munkhafaḍ al-Qaṭṭārah) of Egypt descends to 436 feet (133 metres) below sea level. The very few inhabitants are mainly concentrated in the Egyptian oases of Siwa, Al-Baḥriyyah, Al-Farāfirah, Al-Dākhilah, and Al-Khārijah and the Libyan oasis of Al-Kufrah. The Egyptian part, known as the Western Desert (Al-Ṣaḥrāʾ al-Gharbiyyah), was a critical area of operations in World War II.

John P. Rafferty.

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Libyan Desert | Location, Weather, & Facts

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Libyan Desert, Arabic Al-Ṣaḥrāʾ al-Lībīyah, northeastern portion of the Sahara, extending from eastern Libya through southwestern Egypt into the extreme northwest of Sudan. The desert's bare rocky plateaus and stony or sandy plains are harsh, arid, and inhospitable. The highest point is Mount Al-ʿUwaynāt (6,345 feet [1,934 metres]), located where the three countries meet.

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The Atlas Mountains

With snow-capped peaks, lush valleys & traditional mud-built Berber villages, the Atlas Mountains offer superb trekking and a wonderful respite from the madness, heat and noise of Marrakech. Read on for our guide to accommodation in the Atlas Mountains, trekking options and weather.

The High Atlas Mountains are the most easily reached section of the Atlas Mountains and arguably the most spectacular, the High Atlas Mountains, are only a 2 hr drive from Marrakech centred around the trail head town of Imlil and peak of Toubkal. This guide is primarily concerned with this area.

The area can be reached in a (long) day trip from Marrakech. However given the 2 hr drive each way, we would rather recommend staying overnight. Multi-day treks are a wonderful way to experience the landscape and traditional Berber culture, or you can simply relax on the rooftop terrace of a charming mountain guesthouse and take in the views over a good book and a few gentle short walks.

Accommodation in the High Atlas Mountains

Since the arrival of the (deservedly) legendary Kasbah Du Toubkal, the Atlas Mountains have built a reputation for indulgent and stylish hotels. Kasbah Bab Ourika stands out for pure indulgence and majestic situation. Douar Samra wins the charm award hands down with a wonderfully earthy rambling village property with a just-so shabby chic. And whilst the Kasbah Du Toubkal is more expensive, the superb terraces, lounges and views pull together to create an superb stay.

Hotels are clustered around three broad areas, the Ourika Valley, Ouirgane and Imlil. The Ourika Valley is closest to Marrakech located in the foothills of the Atlas range. It is an incredibly picturesque valley, but is much more densely populated and heavily frequented by tourist coaches with less good walking options. Generally speaking we don't recommend this area with the exception of Kasbah Bab Ourika, a very high class boutique hotel that occupies a prominent hill in the heart of the valley. The Ouirgane area has a number of good options including the superb Domain Malika. However, if you are trying to avoid the heat of summer and or you are keen on walking then the Imlil area is our favoured choice, the scenery is most dramatic, temperatures are a little cooler and the village is at the heart of a wonderful network of walking trails.

Trekking in the High Atlas Mountains

Basing yourself in a hotel (or even on a day trip from Marrakech) there are several good day walks possible in the Imlil area and the near-bye Ouirgane National Park. The area around Imlil offers walks to neighbouring high passes or up to the shrine on the main trail to Toubkal, whilst Ouirgane and Ourika offer less dramatic more low key scenery and gentler walking. See here for our guide to trekking in the Atlas Mountains with children

A nicely balanced itinerary might include 2 to 3 nights in Douar Samra (or Kasbah Du Toubkal if you can afford it) with one or two day walks and plenty of time to soak up the views from the roof terraces and gardens. It is quite feasible to walk on your own, but trails aren't marked and guides are very good, relatively in-expensive and highly recommended.

A multi-day trek really is the best way to experience the mountains. Most hotels reside in relatively modernised villages, but on a multi-day trek you can explore more traditional mud-built Berber villages, some beautiful valleys and high mountain scenery. All our multi-day treks include a guide, cook (who will prepare a cooked picnic lunch on the trail, dinners and breakfast all from delicious fresh ingredients) and mules to carry your gear.

Two to three day valleys and villages treks are not dis-similar to the concept of a Nepalese tea-house trek. These treks are designed with a lighter itinerary (typically 5-6 hrs max walking per day), stay overnight in traditional village gites and where possible your guide will take you for tea in a village home. These treks avoid the more difficult high passes staying below 3000m, making them perfect for winter and for those whose primary objective is enjoyment rather than testing peaks and passes. We tend to focus most of our valleys treks around the Azzaden and D'knt Valleys as the combination of scenery, varied trails and traditional villages is hard to beat. We have recently discontinued the traverse trek from Imlil to Ourika Valley traverse, because a recent road has been built along most of the route.

Toubkal can be climbed on treks from 2 days up to 6. We don't recommend the 2 day route as it heads up and back down via the same, over-trafficked route. In three days, you can summit Toubkal and enjoy the wonderful scenery of the Azzaden Valley. In four or five days, there is also time to explore the more remote valleys and villages. The 6 day Toubkal Circuit is the ultimate Atlas Mountain trek, taking a broad circle around Toubkal, reaching the remote and striking high alpine areas around Lak D'Ifni.

It is worth noting that you will need a good sleeping bag (it gets cold at night at altitude), waterproofs and good walking shoes or boots if you are planning on going on a multi-day trek.

Accommodation on multi-day treks usually involves some combination of camping, village gites (guesthouses) and mountain huts (where necessary). Gites are traditional village homes that serve as an inn for guests and can be a wonderful cultural experience. Rooms are very simple and there are bare bones shared bathrooms. If you'd rather not experience the shared facilities, then we can offer two to three day treks staying at the Azzaden trekking lodge, a three (en-suite) bedroom village outpost of the Kasbah Du Toubkal in the Azzaden Valley.

Weather in the Atlas Mountains

The Atlas Mountains offer a typically warm, dry and sunny climate that makes them a perfect year-round destination. However trekkers need to be aware of snow and freezing temperatures at high altitudes in winter:

Spring (April - May) & Autumn (Sep - October) are unarguably the optimum time to visit, with perfect temperatures and the added bonus of spring growth and autumn colours.

Summer (July - August): In summer the high Atlas Mountains offer a cool respite from the 40 degrees C plus temperatures in Marrakech. The valleys of the High Atlas around Imlil typically experience temperatures in the range of low 30 degrees C during the height of the day, with the lower altitudes of the Ourika Valley and Ouirgane National Park hotter (often too hot for walking). There is a risk of afternoon thunder storms and heavy rain.

Winter:(November - March): Expect mild day time temperatures (10-20 degrees C), cooler night-time temperatures (down to 5 degrees at Imlil, and well below zero at altitude on Toubkal) with the high passes and peaks thick with snow cover. If you are planning a multi day trek, please note that during these months, crampons and ice axes are required for any treks above 3000m.

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The Atlas Mountains - Guide to Accommodation & Trekking in the Atlas Mountains | Tourdust blog

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The Atlas Mountains With snow-capped peaks, lush valleys & traditional mud-built Berber villages, the Atlas Mountains offer superb trekking and a wonderful respite from the madness, heat and noise of Marrakech. Read on for our guide to accommodation in the Atlas Mountains, trekking options and weather.

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THE AHAGGAR IS a large mountainous plateau region lying on the TROPIC OF CANCER in the north-central SAHARA DESERT. It covers an area of 210,000 square mi (543