The Great African Rift Valley A2 unit four case study

The East African Rift Valley

Q1 Tectonics

The Great African Rift Valley is the south branch of the Afar Triangle, the only one remaining which has not yet been filled by the sea. This is therefore an example of continental rifting.

The rift itself was formed by a combination of two key factors:

·         The constructive/divergent plates: African and Arabian.

·         And the magma plume beneath the plates.

The plume pushed up the land creating bulges and cracks allowing flood basalts to rise through fissures and add to the gradient and create long mountain ranges.

As a result of the divergent plates a small section of land in between these plates breaks away and sinks leaving faults which are filled and covered by lava (flood basalts)

Horsts and Grabens are therefore formed (raised land and depressed land)

ß Secondary processes:

·         Shield volcanoes formed in depressions (Grabens) as a result of weak thin crust. Magma pushes easily to the surface, pure, easily eroded shield shaped structures.

·         Composite volcanoes found on raised areas (Horsts) as a result of folding, faults form in the thicker crust, magma pushes to the surface but faces obstruction: higher pressure, explosive pyroclastic flows. ß Steep cone shapes.

·         As a result of volcanoes and faults there is also a minor risk of seismic activity in the area, mostly attached to erupting composite volcanoes.

Examples for each process named in the landscape section below.

Information found from Geology.com and the article ‘East Africa’s Great Rift Valley: A complex rift system.’

Q2 Landscapes

 The Rift Valley stretches over approximately 5000km from Syria to Mozambique. It is a massive horst and graben structure with steep sided sloping mountains surrounding low lying valleys that host lakes, deserts and shield volcanoes. 

The width of the rift varies between 30-100kms and the depth also varies from a few hundred to a few thousand metres.

The rift is 35million years old and is still growing meaning that eventually East Africa including the horn of Africa: Ethiopia, Somalia and Eritrea will break away and form its own continent (the rift being filled by the sea.

Many parts of the rift are already filled by lakes: some freshwater and some salinized. Lake Tanganyika is the 2^nd deepest lake in the world.

Secondary landforms created as a result of the rift include Mt Kenya 5,200m extinct and Mt Kilimanjaro 5,900m dormant, the two tallest mountains (composite volcanoes) in Africa.

Erta Ale is also a volcano in the Rift Valley but instead is a shield volcano that continuously erupts in the Afar depression. Being wide with soft slopes it is only 613m high.

Q3 People

5 scientists were executed on by the Afar Tribe when trying to visit the Erta Ale in January 2012. The tribes are uneducated and difficult to reach, meaning they are vulnerable to tectonic activity.

Human Uses/Benefits:

·         Tourist attraction i.e. beautiful scenery e.g. lakes, mountains, escarpments etc.

·         Lakes in the rift valley provide fish.

·         Lakes in the rift valley provide water for domestic and industrial use and irrigation for agriculture.

·         Rain shadow areas /areas with low rainfall provide pasture for grazing.

·         Lakes are used for navigation.

·         There is forestry on the slopes, so source of timber.

·         Gentle slopes are used for arable farming and settlement.

·         Wildlife conservation

·         Salt-water lakes are used for mining.

·         Production of geothermal electricity from underground.

Challenges:

·         Poor means of transport and communications leaving rural areas without access to services.

·         Shortage of water due to high temperatures, geothermal activity basins.

·         Earth quakes (tremors)

·         Little rainfall /drought in the rain shadows areas.

·         Volcanic eruptions, which destroy property and lives.

·         Poor soils in areas of frequent eruptions.

·         Flooding in depressions.

·         Salty lakes because of high temperatures/high evaporation.

The rift valley lakes are essential to the African economy. Lake Victoria is responsible for a large percentage of the Nile discharge making arid land habitable. Being dependent on primary agricultural and fishing industries, the continent is heavily reliant on the great rift lakes.

Q4 Management

The main management strategies involved in the rift valley are environmental or conservation projects. The WWF is example of this, attempting to protect animal and plant species from over fishing, pollution, drought and fires. Conservation projects also exist in government schemes, private reservations and local farming projects. Conservation is funded by private and public organisations both internally and outside of the continent as the area is of heritage value for the evolution of many species including humanity.