Describe the formation of the Rift Valley System

A large geological fracture from north to south in the eastern section of the
African Continent is known (or defined) as the Great East African Rift Valley System.
This system is characterized by Rift-Volcanic of Tertiary period including recent
sediments of Quaternary period
As an outstanding feature that was caused by internal process, the Rift-Valley is a
geological formation and looks like a great crack running through the African Continent,
and being the only one of its kind on dry land, registered as the largest and most
impressive globally. The fracture starts from Turkey in the northern Hemisphere to
Zambezi River delta in the southern Hemisphere with a length of about 6500km long.
The length across the African Continent is about 5600km, starting from the afar
depression in Eritrea to the mouth of River Zambezi in Mozambique.
This Rift Valley System passes through the Dead Sea including the Jordan Valley
in Israel known as the Levantine Rift.
According to Colin Buckle (1978, the eastern part of Africa contains series of Rift
Valley Systems which form a number of interconnected troughs. Within troughs lie most
of East Africa’s Lakes, with an exception of Lake Victoria – a down-warping physical
feature.
In the Rift Valley floor, as well as on either sides there are a number of volcanoes,
although to-day most of them are extinct.
In a number of sources it is indicated that the Rift Valley may be divided as
follows:-
(a) Ethiopian Rift – from the Afar depression to Lake Turkana
(b) Eastern Rift – through Kenya, Tanzania with branches of Lake Eyasi and
Kavirondo Gulf.
(c) Western Rift, - from Lake Mobutu, Lake Tanganyika.
(d) Malawi Rift, including Lake Malawi and Shire Valley.
(e) Urema trough of Mozambique and the Luangwa Valley of Zambia, at times
regarded as a section of number ‘d’ above.
These rift have an average width of about 50km and the average height of the
limiting (or bounding) scarps stands at about 600m.
However, it has been observed that from one part to another usually are large
variations both in the width and the trough’s depth.
For example the Eastern Rift (through Kenya) the width is up to 100m only. The
bounding Aberdare Range, that forms the eastern wall do rise to over 2000m above the
main valley floor.
To the south in northern Tanzania, the rift faulting nearly disappears, where the
scarps do not rise above 100m.
Within the western Rift Valley these contrasts are even bigger, where for example
Mount Ruwenzori, regarded as a block mountain within the rift do rise above 5000m. Far
south the floor of Lake Tanganyika falls (or drops) to about 650m below sea level.
Studies indicate that the nature of the escarpments do vary greatly within the same
zone from each side of the rift to the next.
For instance the Zairian side of Lake Mobutu, the rift is almost twice as high as
the Uganda side. For some sections the edge of the rifts are bounded by a single fault, but
usually there is a system of many faults that produce stepped escarpments at the side.
For example the stepped faulting system has been noticed at the base of the
Kedong Scarp, to the south-west of Nairobi within the Eastern Rift.
On the western side of Lake Malawi Rift, as well occur parallel step faults that
form gentle profile than that of the eastern side (Colin Buckle 1979).
To the north-east side of Lake Malawi, rises steep from that level of the lake
within the scarp of the Livingstone mountains over 2000m above the Lake Surface.
Although the scarps usually rise to favourable heights but they only represent
fraction of the actual depth of the troughs (Colin Buckle, 1979).
Some observations/or study examples indicate the following:
- For millions of years since the rift’s formation there have been in filled by
outpourings of molten rock and immense thicknesses of sediments.
- Depth of infilling are usually more than a single kilometer.
- Huge volcanic rock flows like Mbaruk and the Kirikiti Basalts have filled the
Eastern Rift of Kenya.
- Here the floor is nearly 1800m above sea level around Lake Naivasha.
- Volcanic infilling has appears within the Ethiopian Rift and also within the
Western Rift, north of Lake Kivu.
- Great alluvial sediments are deposited within the troughs.
- Observations indicate that in places the original floor seem to be below sea level.
- Tertiary and Quaternary sediments within Lake Mobutu rift are more than 1500m
in depth.
- Differences in infilling of sediments indicate that some section of the trough floor
may be lower than other sections of the trough.

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Titany answered the question on January 17, 2022 at 11:59