East African Rift

Geography glossary

Also called: Great Rift Valley · Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Beyond NCERT

Meaning

The East African Rift (also called the Great Rift Valley) is a system of rift valleys about 6,000 km long. It runs from the Afar region (Ethiopia) through Kenya and Tanzania. Along it, the African plate is slowly splitting into two plates: the Nubian plate in the west and the Somali plate in the east [2].

It is the best example on land of a divergent boundary (a line where two plates pull apart). It shows the first stage of how a new ocean is born.

Explanation

How it forms: cause → process → result

  • Cause: the crust is stretched
  • The Nubian and Somali plates are moving away from each other [2].

  • This pulls the continental crust thin.

  • Process: the crust cracks and a block sinks

  • The stretched crust breaks along long, parallel cracks called faults.
  • The block of land between two faults drops down.

  • The result is a rift valley (a long valley with steep walls on both sides).

  • Result: lakes and volcanoes

  • Water fills the sunken blocks. This makes rift lakes, which are long and deep.
  • Magma (hot melted rock from the mantle) rises through the thin crust and builds volcanoes.

Afar triple junction: where the rift begins

  • A triple junction is a point where three plates meet.
  • At Afar (Ethiopia), three plates are pulling away from one another: the Arabian plate, the Nubian plate and the Somali plate [2].
  • Three arms spread out from this point:
  • Arm 1, Red Sea: formed when spreading separated Arabia from Africa [1].
  • Arm 2, Gulf of Aden: another young ocean opening from the same junction.
  • Arm 3, East African Rift: still a rift on land. No ocean has formed here yet.

Its place in the life story of an ocean

Stage What happens Example
Continental rift Land stretches and cracks. Rift valleys, lakes and volcanoes form East African Rift
Young, narrow ocean Sea water floods the rift. New oceanic crust begins to form Red Sea, Gulf of Aden
Mature ocean A wide ocean with a mid-ocean ridge (an underwater mountain chain where plates part) in the middle Atlantic Ocean, Mid-Atlantic Ridge
  • Future: USGS says the East African Rift Zone may become the earth's next major ocean. If the plates separate fully, the Horn of Africa could become an island [1].

Features it shows

  • Shallow earthquakes, because the crust keeps cracking as it stretches.
  • Basaltic volcanism, meaning volcanoes that erupt runny, dark lava from the mantle.
  • High heat flow close to the surface. This supports geothermal energy (power made from the earth's inner heat) in the Kenyan rift.

Where it occurs

  • Afar region, Ethiopia: the northern end of the rift and the site of the Afar triple junction (Arabian, Nubian and Somali plates) [2].
  • Kenya and Tanzania: the rift runs south through both countries.
  • Rift lakes:
  • Lake Turkana (Kenya)
  • Lake Tanganyika (between Tanzania and DR Congo)

  • Lake Malawi (bordered by Malawi, Mozambique and Tanzania)

  • Rift volcanoes:

  • Kilimanjaro (Tanzania)

  • Nyiragongo (DR Congo)

  • Lake Victoria lies between the arms of the rift. It is not a rift lake.

  • Link to India: in NCERT's description, the western margin of the Indian plate follows the Kirthar Mountains (Pakistan) and the Makran coast. It then joins the spreading site that runs from the Red Sea rift south-eastward along the Chagos Archipelago. So the same divergent system that starts near Afar also borders India's own plate.

Don't confuse with

  • Mid-Atlantic Ridge: this is a divergent boundary under the ocean, and it already makes new oceanic crust, at about 2.5 cm per year [1]. The East African Rift is a divergent boundary on land, where no ocean has formed yet.
  • Red Sea / Gulf of Aden: these are young, narrow oceans that sea water has already flooded. The East African Rift is the earlier stage: it is still a continental rift.
  • San Andreas Fault: this is a transform boundary (plates slide sideways past each other, so crust is neither made nor destroyed). The East African Rift is a divergent boundary, where plates pull apart and crust is created.
  • Lake Victoria: it sits between the rift arms but is not a rift lake. The rift lakes are Tanganyika, Malawi and Turkana.

Prelims Hooks

  • The East African Rift is about 6,000 km long and runs from Afar (Ethiopia) through Kenya and Tanzania.
  • Along it, the African plate splits into the Nubian (west) and Somali (east) plates [2]. Watch for the trap of "Arabian plate": Arabia is the third plate at Afar, not one of the two halves of Africa.
  • Afar triple junction = Arabian + Nubian + Somali plates [2]. Its three arms are the Red Sea, the Gulf of Aden and the East African Rift.
  • Rift lakes are Tanganyika, Malawi and Turkana. Lake Victoria is NOT a rift lake.
  • Rift volcanoes: Kilimanjaro (Tanzania) and Nyiragongo (DR Congo).
  • Ocean-opening stages, from youngest to oldest: East African Rift → Red Sea → Atlantic Ocean.

Mains Points

  • How oceans are born (GS-I):
  • A continent stretches and forms a rift valley (East Africa).
  • Sea water enters and a narrow sea forms (Red Sea, Gulf of Aden).
  • The sea widens into an ocean with a central ridge (Atlantic, about 2.5 cm per year [1]).

  • This chain explains the break-up of Pangaea and why the continents have their present shape. The Horn of Africa may one day become an island [1].

  • Hazards and resources (GS-I / GS-III):

  • Divergent zones such as the East African Rift have shallow earthquakes and basaltic volcanoes such as Nyiragongo. Both are risks for the people living in the rift.

  • The same heat is a resource: geothermal energy is produced in the Kenyan rift and in Iceland.

  • Relevance to India: India's plate is bordered by the divergent ridge system that runs from the Red Sea rift south-eastward along the Chagos Archipelago. Mid-ocean ridges in this system hold hydrothermal sulphide deposits (metal-rich minerals laid down by hot water from vents on the sea floor). These deposits matter for India's deep-sea exploration in the Indian Ocean.

Related concepts

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Sources

  1. 1USGS, "This Dynamic Earth: Understanding plate motions"pubs.usgs.gov · tier 2
  2. 2USGS, "This Dynamic Earth: East Africa"pubs.usgs.gov · tier 2