Glaciation in Africa

8/7/2019 Glaciation in Africa

1/6

3RD FEBRUARY, 2010

AMOO K. OBAFEMI 10234452

GLACIATION IN AFRICA

This is a very interesting discussion as it seeks to unite a phenomenon with a phenomenal event.

The continent of Africa undoubtedly has a mlange of historical event, and it is worth noting that

glaciation has its part to play. Before elaborating this relationship; I would like to bring the

concept of glaciation and glaciers to foreplay, so that this discussion can be better appreciated

when it is made composite with the continent of Africa.

Glaciers are huge masses of ice that flow under the influence of gravity, with the exclusion of

icebergs, sea ice or immobile snow fields in mountainous areas. Globally, they cover about 10%

of the earths surface, and hold the largest reservoir of freshwater formed as a result of snow

recrystallization. This is usually achieved by large snow accumulation (about 40m), formation of

ice granules as it thickens and the eventual formation of glacial ice with further melting,

compaction and pressure melting. This mass will then move if the accumulation is greater than

wastage, else it either remains stationary or retreats depending on the factors present. They erode

and transport huge quantities of materials by plucking, abrasion and bulldozing, reshaping

topography to form valley or continental landforms and were known to have once covered larger

areas than they presently do depositing drifts-glacial sediments. It is equally worth noting the

effects of glaciation which includes important climatic changes, changing sea levels as glaciers

can store up to 70million km3

of water, animal and plants migration as climatic zones are shifted,

divert stream drainage patterns and down cutting of streams, depressed continental crust due to

weight of ice followed by eventual rebound and many more; therefore the African continent must

have undergone some or all of this effect.

Even as most of the African glaciers have disappeared; the few left are atop iconic mountainsand are disappearing at amazing paces, while excellent preservation of glacial moraines in other

areas as well as other erosional features has put limits on the spatial extent of the paleoglaciers.

The tectonic setting of the African continent imposes a control on both hydrology and glacier

formation. It lacks continuous mountain chains owing to its passive tectonic margins, and

features a broadly elevated plateau form with relatively high mean elevation ( about 650m above


2/6

Glaciation in Africa

sea level) compared to other continental blocks The continent currently resides in the tropics

which make it impossible for ice to form. However, clues are left behind on which geologists

work to determine areas of glaciation. These includes

y Striated blocks: these forms as a result of the glacier scraping over the bedrock. Asglaciers mover over continents, they collect and deposit a variety of rocks along the way.

Rocks at the bottom of the glacier scrape against the bedrock and leave striations in the

direction of the scraping. This kind of glacial evidence is unique to glacial movement and

provides information such as rate and direction of movement to glaciologists.

y Tillite formations: Tillite forms as a result of the compaction and cementation of glacialtill deposits. Till deposits form when glaciers drop the rocks that they are carrying as they

retreat. Like a bulldozer, glaciers break and shove rock over land as it moves forward.

When warmer temperatures ensue, the glaciers retreat, leaving behind unsorted piles of

rock. These rocks are of different sizes and types - characteristic of a glacier that picks up

everything and anything as it moves forward.

y Meltwater deposits: Meltwater deposits, also referred to as meltwater stream sediments,form as a result of sand and gravel being transported by streams carrying water from a

melting glacier. These sediments can also include a variety of rock type, but are generally

better sorted than till deposits so that the most prominent size of rock is coarse sand and

gravel.

With the above clues, ancient melted African glaciers have been identified as well as existing

ones studied. It has therefore been established that the while glaciation once covered the

continents comparable to todays Antarctica, some parts of it were far more loaded than

others. However; evidence of former glaciation occurs on relatively isolated highlands, from

the Atlas Mountains bordering the Mediterranean in the north, through elevated plateaus and

volcanoes in the East African Rift zone, to the escarpment ofSouth Africa as shown below.


3/6


Fig: map of Africa showing areas of significant glacial fields

In theNorth-African sub region, the Atlas and other groups of mountains have evidence of

glaciation but havent been put up for significant study. It is believed that African ice-sheets

existed 250-300 million years ago as well as in the southern portion, or during the late Paleozoic

era. The ice-sheets extended from Antarctica into the continent as global cooling dominated.

However; the stratigraphic record of this era is incomplete in southern Africa - due to geological

processes, mainly erosion - but in North America, there is evidence of repeated marine invasions.

These sea-level fluctuations can be attributed to a period of cyclical ice build-up and decay of

continental glaciers world-wide during the Pennsylvanian and Permian periods of the Paleozoic.

The cyclical fluctuation of sea-levels worldwide led to the repeated burial and reburial ofPennsylvanian and Permian swamps, which today is the source of large deposits of hydrocarbons

(fossil fuels) in North America. During this same period, the African continent was experiencing

tectonic drifting, causing the land mass to slowly drift northwards away from the cold-weather

influences of Antarctica. Currently, this continental drift is still active, making it unlikely that the

African continent will ever experience a period of glaciation comparable to that of the late


4/6


Paleozoic. The Atlas Mountains of North Africa show evidence of being glaciated, although

there are no radiometric dates from the region (Hughes et al., 2004). They comprise a series of

ranges and plateaus over a 2400 km span from southwestern Morocco through northern Algeria

to northern Tunisia that form a major climate divide between the wet Mediterranean northern

slopes to the dry southern slopes bordering the Sahara Desert.

In the East-Central African subregions, the iconic mountains Kilimanjaro, Rwenzori and

Kenya are brought to limelight because they present the last of African glaciers, which are fast

disappearing. The shrinking ice cap atop the iconic dormant volcano that rises from the

grasslands of Tanzania: Mount Kilimanjaro is Africas most famous glacier, and holds the best

dated sites for quaternary glaciers alongside Mount Kenya. But the sub region also harbors other

pockets of ice, most notably in the Rwenzori Mountains of western Uganda. Rwenzori range is

mostly Precambrian rock that has some evidence of Quaternary uplift post-dating glaciation

In Southern Africa sub region; geomorphic features resembling moraines and protalus ramparts

have been described from the Drakensberg Mountains. The Drakensberg Mountains are part of

the Great Escarpment and feature summits over 3000 m, including the highest point ofSouth

Africa (3482 m). They comprise horizontal sequences of plateau basalts over 1500mthick, and

feature the majority of periglacial and palaeoglacial evidence in South Africa that has been

studied and debated over the past half century (Boelhouwers and Meiklejohn, 2002). While

previously noted as equivocal (Osmaston and Harrison, 2005), multiple arguments based on

geomorphology, sedimentology, topographic analyses and a palaeoclimatic euristic argue

convincingly for small cirque glaciers roughly dated to the Last Glacial Maximum (LGM).

Generally; glaciation during the late Paleozoic as is shown by glacial strata in several major

basins and fault blocks such as the Karroo, Botswana, Orange River, Zambezi, and Congoand

in smaller areas of the Kaokoveld in South West Africa, in southern Madagascar, and in the

Kafue Flats, Zambia. Age of the glaciation ranges from Late Carboniferous to Early Permian but

may have begun in the Early Carboniferous.

Striated floors beneath the glacial rocks indicate that extensive lobes of ice flowed radially

outward from the African interior in Rhodesia and Zambia, suggesting that a continental ice

sheet occupied this region. This is supported by environmentally significant facies relationships

and paleocurrent flow directions. Major ice lobes occupied the Botswana fault block (flowing


5/6


6/6


While ongoing glacier recession is occurring in the context of globally warming temperatures,

detailed studies on Kilimanjaro show that the current negative mass balance is actually strongly

impacted by regional East African aridity (Kaser et al., 2004)accompanying a dislocation of the

upper winds over the Indian ocean (Hastenrath, 2001). The Ruwenzori glaciers fluctuated from

an area of 1,600 acres (650 ha) in 1906 to 870 acres (352 ha) in 1955 to just 366 acres (148 ha)

in 2008, as determined by WWF, the Congolese Institute for Nature Conservation, and the

Uganda Wildlife Authority. At this rate, they will be gone in 30 years.

Fig: ice at 1950 fig: Ice at 2008

The ice fields on Kilimanjaro are substantially higher than the Rwenzori and therefore less prone

to melting, hence shrinking snowcap is likely due to decreasing humidity, not rising

temperatures.

REFERENCES

y Boelhouwers JC, Meiklejohn KI. 2002. Quaternary periglacial and glacialgeomorphology of southern Africa

y Hughes PD, Gibbard PL, Woodward JC. 2004. Quaternary glaciation in the AtlasMountains, North Africa.

y Mark, B. G. and Osmaston, H. A. 2008.Quaternary glaciation in Africa: key chronologiesand climatic implications. J. Quaternary Sci., Vol. 23

y Morrison, D, Mountains on The Moon Glaciers Melting in Africa, NationalGeographic Science Blog

y Skinner, Brian J., Porter, Stephen C, and Park, Jeffrey. Dynamic Earth - An Introductionto Physical Geology. NJ: John Wiley and Sons Inc., 2004.

Documents

Glaciation in Africa