The African continent, the second-largest continent on Earth, is currently undergoing a dramatic geological transformation. A giant rift, known as the East African Rift System (EARS), is slowly tearing Africa apart.
The East African Rift System (EARS) or East African Rift (EAR) is an active continental rift zone in East Africa.
This depression is a network of valleys that stretches about 2,175 miles (3,500 kilometers) long, from the Red Sea to Mozambique, according to the Geological Society of London.
The Great Rift Valley offers both insights and intrigue in the world of plate tectonics.
At the heart of this vast depression lies the East African Rift System (EARS), a zone where the African continent is slowly being torn apart.
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East African Rift System Map
It's Finally Happening! Africa Is Splitting Into Two Continents
The Tectonic Plates at Play
In the past, scientists thought that Africa sat upon a single tectonic plate.
Along this colossal tear in eastern Africa, the Somalian tectonic plate is pulling eastward from the larger, older part of the continent, the Nubian tectonic plate, according to NASA's Earth Observatory. (The Somalian plate is also known as the Somali plate, and the Nubian plate is also sometimes called the African plate.)
The Somalian and Nubian plates are also separating from the Arabian plate in the north.
These plates intersect in the Afar region of Ethiopia, creating a Y-shaped rift system, the Geological Society of London noted.
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A narrow zone, the rift is a developing divergent tectonic plate boundary where the African plate is in the process of splitting into two tectonic plates, called the Somali plate and the Nubian plate, at a rate of 6-7 mm (0.24-0.28 in) per year.
The rift system consists of three microplates, the Victoria microplate to the north, and the Rovuma and Lwandle microplates to the south.
The Victoria microplate is rotating anti-clockwise with respect to the African plate.
Southward from the Afar triple junction, the EAR consists of two main branches.
The Eastern Rift Valley (also known as Gregory Rift) includes the Main Ethiopian Rift, runs southward from the Afar triple junction, and continues south as the Kenyan Rift Valley, into northern Tanzania.
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The Formation and Evolution of the Rift
The rifting extended southward over time, reaching northern Kenya by 25 million years ago.
The rift consists of two broadly parallel sets of fractures in Earth's crust.
The eastern rift passes through Ethiopia and Kenya, while the western rift runs in an arc from Uganda to Malawi, the Geological Society of London noted.
The eastern branch is arid, while the western branch lies on the border of the Congolese rainforest, according to NASA's Earth Observatory.
Today, the narrow rift segments of the East African Rift system form zones of localized strain.
These rifts are the result of the actions of numerous normal faults which are typical of all tectonic rift zones.
An artificial rendering of the Albertine Rift, which forms the western branch of the East African Rift.
Periods of extension alternated with relative inactivity.
The first stage of rifting of the EAR was characterized by rift localization and magmatism along the entire rift zone.
Prior to the rift's formation, enormous continental flood basalts erupted, uplifting the Ethiopian, Somali, and East African plateaus.
Over time, many theories have tried to clarify the evolution of the East African Rift.
In 1972 it was proposed that the EAR was not caused by tectonic activity, but rather by differences in crustal density.
The most recent and accepted view is the theory put forth in 2009: that magmatism and plate tectonics have a feedback with one another, controlled by oblique rifting conditions.
According to this theory, lithospheric thinning generates volcanic activity, further increasing magmatic processes such as intrusions and numerous small plumes.
The varying geochemical signatures of a suite of Ethiopian lavas suggest multiple plume sources: at least one of deep mantle origin, and one from within the subcontinental lithosphere.
In accordance, a 2014 study compares the geochemical signature of rare earth isotopes from xenoliths and lava samples collected in the EAR.
Parallel to geological and geophysical measures (e.g. isotope ratios and seismic velocities) it is constructive to test hypotheses on computer based geodynamical models.
The geophysical method of seismic tomography is a suitable tool to investigate Earth's subsurface structures deeper than the crust.
It is an inverse problem technique that models which are the velocities of the inner Earth that reproduce the seismographic data recorded all around the world.
Vs model of lower mantle structures beneath the East African Rift
Volcanic Activity and Seismic Events
The East African Rift Zone includes a number of active and dormant volcanoes, among them: Mount Kilimanjaro, Mount Kenya, Mount Longonot, Menengai Crater, Mount Karisimbi, Mount Nyiragongo, Mount Meru and Mount Elgon, as well as the Crater Highlands in Tanzania.
Notable active examples of EAR volcanism include Erta Ale, Dalaffilla (also called Gabuli, Alu-Dalafilla), and Ol Doinyo Lengai.
Erta Ale is a basaltic shield volcano in the Afar Region of northeastern Ethiopia, active continuously since at least 1967, with a summit lava lake documented since at least 1906.
The 2008 eruption of Dalafilla, its only documented activity since the start of the Holocene, is the largest recorded eruption in Ethiopian history.
Ol Doinyo Lengai is currently the only active natrocarbonatite volcano on Earth.
Its magma contains almost no silica; typical lava flows have viscosities of less than 100 Pa⋅s, comparable to olive oil at 26 °C (79 °F).
The EAR is the largest seismically active rift system on Earth today.
The majority of earthquakes occur near the Afar Depression, with the largest typically occurring along or near major border faults.
Seismic events in the past century are estimated to have reached a maximum moment magnitude of 7.0.
The seismicity trends parallel to the rift system, with a shallow focal depth of 12-15 km (7.5-9.3 mi) beneath the rift axis.
The Role of Mantle Plumes
The volcanic activity and tectonic splitting of the East African Rift Valley is probably driven by activity deep within the Earth, a new study reveals, starting where the core meets the mantle.
Most explanations for the extreme events occurring there are based on mantle material rising from the edge of a mysterious province whose center is under the South Atlantic.
However, alternative scenarios exist, including the possibility of two smaller and probably shallower plumes rather than one big one.
To settle the question of what is driving the EARS, Professor Fin Stuart from the University of Glasgow and colleagues investigated isotope ratios of the noble gases trapped in the magma.
Noble gases can reveal behavior deep in the Earth because in the upper mantle they get opportunities to escape over billions of years, losing lighter isotopes more than heavier ones.
Deeper in the mantle, the ratios are thought to resemble those when the Earth formed.
