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The Great Rift Valley
In this region the rift valley extends
in a roughly north-south direction
from the Afar depression,
where the rift valley
joins the oceanic domains
of the Red Sea and Gulf of Aden,
to the Zambezi river in
Mozambique.
The rift valleys are enormous fractures affecting the
continental plates that widen progressively with time: they
represent the first stages in the complex process of extension
and rupture of continents and anticipate the development of
new oceanic basins between them. The process is related to
the divergent movements of lithospheric plates above the
underlying asthenosphere in slow convective motion. The rift
valley represents the primary and most superficial response to
this divergence and to the consequent application of tensional
forces to the plates, which is manifested through the
development of normal faults. These represent fractures with
vertical displacement of the Earth's surface that accommodate
the separation of portions of the crust and determine the
collapse of the block in between. Major normal fault systems
thus give rise to the downthrowing of the valley floor with
respect to the surrounding plateaus and form the huge tectonic
escarpments bordering the rift valley. These tectonic
movements give rise to a diffuse seismicity and volcanism,
phenomena that are typically associated with the African rift
valleys.
1 – Great Rift Valley
2 – Red Sea
3 – Atlantic Ocean
NOTE
Divergent boundary (or divergent margin)
two plates are moving in opposite directions as
in a mid-ocean ridge.
Transform boundary (or transform margin)
two plates are sliding past each other as in the
San Andreas fault of California.
Convergent boundaries (or convergent margin)
two plates collide to form mountains or a
subduction zone.
The Great African Rift Valley is the south
branch of the Afar Triangle.
This is therefore an example of
continental rifting.
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 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).
LANDFORMS
Many parts of the rift are already filled by
lakes: some freshwater and some
salinized. Lake Tanganyika is the 2nd
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.
HUMAN USES/BENEFITS
•Tourist attraction i.e. beautiful scenery (lakes, mountains)
•Lakes in the rift valley provide fish.
•Lakes in the rift valley provide water for domestic and industrial use
and irrigation for agriculture.
•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.