GeographyAfrica
Africa isname ofcontinent representinglargest ofthree great southward projections frommain mass ofearth's surface. It includes within its remarkably regular outline an area, according1911 computations,29,000,000 km2 (11,262,000 square miles), excludingislands.
Separated from Europe byMediterranean Sea, itjoinedAsia at its northeast extremity byIsthmusSuez, 130 km (80 miles) wide. Frommost northerly point, Ras ben Sakka,little westCape Blanc,37 deg. 21' N., tomost southerly point, Cape Agulhas, 34 deg. 51' 15" S., isdistance approximately8,000 km (5,000 miles); from Cape Verde, 17 deg. 33' 22" W.,westernmost point,Ras Hafun, 51 deg. 27' 52" E.,most easterly projection, isdistance (also approximately)7,400 km (4,600 miles). The lengthcoast-line26,000 km (16,100 miles) andabsencedeep indentations ofshoreshown byfact that Europe, which covers only 9,700,000 km2 (3,760,000 square miles), hascoast-line32,000 km (19,800 miles).
The main structural lines ofcontinent show botheast-to-west direction characteristic, at least ineastern hemisphere, ofmore northern parts ofworld, andnorth-to-south direction seen insouthern peninsulas. Africathus composedtwo segments at right angles,northern running from eastwest,southern from northsouth,subordinate lines corresponding inmainthese two directions.
Main Geographical Features
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The mean elevation ofcontinent approximates closely600 m (2,000 ft.), whichroughlyelevationboth NorthSouth America, butconsiderably less than thatAsia, 950 m (3,117 ft.). In contrast withother continents itmarked bycomparatively small area bothvery high andvery low ground, lands under 180 m (600 ft.) occupying an unusually small part ofsurface; while not only arehighest elevations inferiorthoseAsiaSouth America, butarealand over 3,000 m (10,000 ft.)also quite insignificant, being represented almost entirely by individual peaksmountain ranges. Moderately elevated tablelandsthuscharacteristic feature ofcontinent, thoughsurfacethesebroken by higher peaksridges. (So prevalentthese isolated peaksridges thatspecial term [Inselberg-landschaft] has been adoptedGermanydescribe this kindcountry, whichthoughtbegreat partresultwind action.)
Asgeneral rule,higher tablelands lie toeastsouth, whileprogressive diminutionaltitude towardswestnorthobservable. Apart fromlowlands andAtlas range,continent may be divided into two regionshigherlower plateaus,dividing line (somewhat concave tonorth-west) running frommiddle ofRed Seaabout 6 deg. S. onwest coast.
We thus obtainfollowing four main divisions ofcontinent:
(1) The coast plains - often fringed seawards by mangrove swamps - never stretching far fromcoast, except onlower coursesstreams. Recent alluvial flatsfound chiefly indelta ofmore important rivers. Elsewherecoast lowlands merely formlowest steps ofsystemterraces which constitutesascent toinner plateaus.
(2) The Atlas range, which, orographically,distinct fromrest ofcontinent, being unconnectedany other areahigh ground,separated fromrest ofcontinent onsouth bydepresseddesert area (the Sahara),places below sea-level.
(3) The high southerneastern plateaus, rarely falling below 600 m (2000 ft.),havingmean elevationabout 1000 m (3500 ft.)
(4) The northwest African plains, borderedtraversed by bandshigher ground, but generally below 600 m (2000 ft.) This division includesgreat desert ofSahara.
The thirdfourth divisions may be again subdivided. Thushigh plateaus include:
(a) The South African plateau as far as about 12 deg. S., bounded east, westsouth by bandshigh ground which fall steeply tocoasts. On this account South Africa hasgeneral resemblancean inverted saucer. Due southplateau rimformed by three parallel stepslevel ground between them. The largestthese level areas,Great Karroo, isdry, barren region, andlarge tract ofplateau properofstill more arid characteris known asKalahari Desert.
The South African plateauconnected towardsnorth-east(b)East African plateau,probablyslightly greater average elevation,marked by some distinct features. Itformed bywidening out ofeastern axishigh ground, which becomes subdivided intonumberzones running northsouthconsistingturnranges, tablelandsdepressions. The most striking feature isexistencetwo great linesdepression, due largely tosubsidencewhole segments ofearth's crust,lowest partswhichoccupied by vast lakes. Towards the southtwo lines convergegive placeone great valley (occupied by Lake Nyasa),southern partwhichless distinctly dueriftingsubsidence thanrest ofsystem.
Farther northwestern depression, sometimes known asCentral African trough or Albertine rift-valley,occupiedmore than half its length by water, formingfour lakesTanganyika, Kivu, Albert EdwardAlbert,first-named over 400 milesandlongest freshwater lake inworld. Associatedthese great valleys arenumbervolcanic peaks,greatestwhich occur onmeridional line east ofeastern trough. The eastern depression, known asEast African trough or rift-valley, contains much smaller lakes, manythem brackishwithout outlet,only one comparablethose ofwestern trough being Lake Rudolf or Basso Norok.
At no great distance eastthis rift-valleyKilimanjaro -its two peaks KiboMawenzi,former 5889 m (19,321 ft.), andculminating point ofwhole continent -Kenya, 5184 m (17,007 ft.). Hardly less important isRuwenzori range, over 5060 m (16,600 ft.), which lies east ofwestern trough. Other volcanic peaks rise fromfloor ofvalleys, some ofKirunga (Mfumbiro) group, northLake Kivu, being still partially active.
(c) The third division ofhigher regionAfricaformed byEthiopian highlands,rugged massmountains forminglargest continuous areaits altitude inwhole continent, littleits surface falling below 1500 m (5000 ft.), whilesummits reach heights4600 m4900 m (15,00016,000 ft.). This blockcountry lies just west ofline ofgreat East African trough,northern continuationwhich passes along its eastern escarpment asruns upjoinRed Sea. There is, however, incentrecircular basin occupied by Lake Tsana.
Both ineastwest ofcontinentbordering highlandscontinued as stripsplateau parallel tocoast,Ethiopian mountains being continued northwards alongRed Sea coast byseriesridges reachingplacesheight2000 m (7000 ft.). Inwestzonehigh landbroader but somewhat lower. The most mountainous districts lie inland fromhead ofGulfGuinea (Adamawa, etc.), where heights1800 m2400 m (60008000 ft.)reached. Exactly athead ofgulfgreat peak ofCameroon, onlineVolcanic action continued byislands tosouth-west, hasheight4075 m (13,370 ft.), while Clarence Peak,Fernando Po,first oflineislands, risesover 2700 m (9000 ft.). Towardsextreme westFuta Jallon highlands form an important diverging pointrivers, but beyond this, as far asAtlas chain,elevated rim ofcontinentalmost wanting.
The area betweeneastwest coast highlands, which north17 deg. N.mainly desert,divided into separate basins by other bandshigh ground, onewhich runs nearly centrally through North Africa inline corresponding roughly withcurved axis ofcontinent aswhole. The best marked ofbasins so formed (the Congo basin) occupiescircular area bisected byequator, once probablysitean inland sea.
The arid region,Sahara -largest desert inworld, covering 9,000,000 km2 (3,500,000 square miles) - extends fromAtlantic toRed Sea. Though generallyslight elevationcontains mountain rangespeaks rising2400 m (8000 ft.) Bordered N.W. byAtlas range, toN.E.rocky plateau separatesfromMediterranean; this plateau gives place atextreme east todelta ofNile. That river (see below) piercesdesert without modifying its character. The Atlas range,north-westerly part ofcontinent, between its seawardlandward heights encloses elevated steppesplaces 160 km (100 miles) broad. Frominner slopes ofplateau numerous wadis takedirection towardsSahara. The greater partthat now desert region is, indeed, furrowed by old water-channels.
The following table givesapproximate altitudes ofchief mountainslakes ofcontinent:
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The Hydrographic Systems
Fromouter margin ofAfrican plateauslarge numberstreams run toseacomparatively short courses, whilelarger rivers flowlong distances oninterior highlands before breaking throughouter ranges. The main drainage ofcontinenttonorthwest, or towardsbasin ofAtlantic Ocean.
The high lake plateauEast Africa containshead-waters ofNileCongo:formerlongest,latterlargest river ofcontinent. The upper Nile receives its chief supplies frommountainous region adjoiningCentral African trough inneighbourhood ofequator. Thence streams pour east toVictoria Nyanza,largest African lake (covering over 26,000 square m.),westnorth toAlbert EdwardAlbert Nyanzas, tolatterwhicheffluents ofother two lakes add their waters. Issuing from itNile flows north,between 7 deg. 10 deg. N. traversesvast marshy level during which its courseliableblocking by floating vegetation. After receivingBahr-el-Ghazal fromwest andSobat, Blue NileAtbara fromEthiopian highlands (the chief gathering ground offlood-water),crossesgreat desertentersMediterranean byvast delta.
The most remote head-stream ofCongo isChambezi, which flows south-west intomarshy Lake Bangweulu. From this lake issuesCongo, knownits upper course by various names. Flowing first south,afterwards turns north through Lake Mwerudescends toforest-clad basinwest equatorial Africa. Traversing this inmajestic northward curvereceiving vast supplieswater from many great tributaries,finally turns south-westcutsway toAtlantic Ocean throughwestern highlands.
North ofCongo basinseparated frombybroad undulation ofsurface isbasinLake Chad -flat-shored, shallow lake filled principally byShad coming fromsouth-east. Westthis isbasin ofNiger,third riverAfrica, which, though flowing toAtlantic, has its principal source infar west,reversesdirectionflow exhibited byNileCongo. An important branch, however -Benue - comes fromsouth-east. These four river-basins occupygreater part oflower plateausNorthWest Africa,remainder consistingarid regions watered only by intermittent streams which do not reachsea.
Ofremaining rivers ofAtlantic basinOrange, inextreme south, bringsdrainage fromDrakensberg onopposite side ofcontinent, whileKunene, Kwanza, OgoweSanaga drainwest corst highlands ofsouthern limb;Volta, Komoe, Bandama, GambiaSenegalhighlands ofwestern limb. North ofSenegalover 1000 milescoastarid region reaches toAtlantic. Farther north arestreams,comparatively short courses, which reachAtlanticMediterranean fromAtlas mountains.
Ofrivers flowing toIndian Oceanonly one draining any large part ofinterior plateaus isZambezi, whose western branches rise inwest coast highlands. The main stream has its rise11 deg. 21' 3" S. 24 deg. 22' E. at an elevation5000 ft. It flows westsouth forconsiderable distance before turning toeast. Alllargest tributaries, includingShire,outflowLake Nyasa, flow downsouthern slopes ofbandhigh ground which stretches acrossconbnent10 deg. 12 deg. S. Insouth-westZambezi system interlacesthat ofTaukhe (or Tioghe), from whichat times receives surplus water. The rest ofwater ofTaukhe, knownits middle course asOkavango,lost insystemswampssaltpans which formerly centredLake Ngami, now dried up.
Farther southLimpopo drainsportion ofinterior plateau but breaks throughbounding highlands onside ofcontinent nearest its source. The Rovuma, Rufiji, Tana, JubaWebi Shebeli principally drainouter slopes ofEast African highlands,last named losing itself insandsclose proximity tosea. Another large stream,Hawash, rising inEthiopian mountains,lost insaline depression nearGulfAden.
Lastly, betweenbasins ofAtlanticIndian Oceans therean areainland drainage alongcentre ofEast African plateau, directed chiefly intolakes ingreat rift-valley. The largest river isOmo, which, fed byrains ofEthiopian highlands, carries downlarge bodywater into Lake Rudolf. The riversAfricagenerally obstructed either by bars at their mouths or by cataracts at no great distance up-stream. But when these obstacles have been overcomeriverslakes affordnetworknavigable watersvast extent.
The calculation ofareasAfrican drainage systems, made by Dr A. Bludau (Petermanns Mitteilungen, 43, 1897, pp. 184-186) givesfollowing general results:
| Basin ofAtlantic | 4,070,000 square miles |
| Basin ofMediterranean | 1,680,000 square miles |
| Basin ofIndian Ocean | 2,086,000 square miles |
| Inland drainage area | 3,452,000 square miles |
The areasindividual river-basins are:
| Congo (length over 3000 miles) | 1,425,000 square miles |
| Nile (length fully 4000 miles) | 1,082,0004 square miles |
| Niger (length about 2600 miles) | 808,0005 square miles |
| Zambezi (length about 2000 miles) | 513,500 square miles |
| Lake Chad | 394,000 square miles |
| Orange (length about 1300 miles) | 370,505 square miles |
| Orange (actual drainage area) | 172,500 square miles |
The area ofCongo basingreater than thatany other river exceptAmazon, whileAfrican inland drainage areagreater than thatany continent but Asia,whichcorresponding area4,000,000 square miles
The principal African lakes have been mentioned indescription ofEast African plateau, but some ofphenomena connectedthem may be spokenmore particularly here. Asrulelakes which occupy portions ofgreat rift-valleys have steep sides andvery deep. This iscase withtwo largest oftype, TanganyikaNyasa,latterwhich has depths430 fathoms.
Others, however,shallow,hardly, reachsteep sides ofvalleys indry season. SuchLake Rukwa, insubsidiary depression northNyasa,EiassiManyara insystem ofeastern rift-valley. Lakes ofbroad typeof moderate depth,deepest soundingVictoria Nyanza being under 50 fathoms.
BesidesEast African lakesprincipal are: - Lake Chad, innorthern areainland drainage; BangweuluMweru, traversed byhead-stream ofCongo;Leopold II.Ntomba (Mantumba), withingreat bendthat river. All, exceot possibly Mweru,more or less shallow,Chad appearsby drying up. The altitudes ofAfrican lakes have already been stated.
Divergent opinions have been beld as tomodeorigin ofEast African lakes, especially Tanganyika, which some geologists have consideredrepresent an old arm ofsea, dating fromtime whenwhole central Congo basin was under water; others holding thatlake water has accumulated indepression caused by subsidence. The former viewbased onexistence inlakeorganisms ofdecidedly marine type. They includejelly-fish, molluscs, prawns, crabs, etc.
Islands
With one exception - Madagascar -African islandssmall. Madagascar,an area229,820 square miles, is, after New GuineaBorneo,largest island ofworld. It lies offS.E. coast ofcontinent, from which itseparated bydeep Mozambique channel, 250 miles wide at its narrowest point. Madagascarits general structure, asflorafauna, formsconnecting link between Africasouthern Asia. EastMadagascar aresmall islandsMauritiusRéunion. Sokotra lies E.N.E.Cape Guardafui. Offnorth-west coast areCanaryCape Verde archipelagoes. which, like some small islands inGulfGuinea,of volcanic origin.
ClimateHealth
Lying almost entirely withintropics,equallynorthsouth ofequator, Africa does not show excessive variationstemperature.
Great heatexperienced inlower plainsdesert regionsNorth Africa, removed bygreat width ofcontinent frominfluence ofocean,here, too,contrast between daynight,between summerwinter,greatest. (The rarity ofair andgreat radiation duringnight causetemperature inSaharafall occasionallyfreezing point.)
Farther south,heat issome extent modified bymoisture brought fromocean,bygreater elevation oflarge part ofsurface, especiallyEast Africa, whererangetemperaturewider than inCongo basin or onGuinea coast.
Inextreme northsouthclimate iswarm temperate one,northern countries being onwhole hotterdrier than those insouthern zone;south ofcontinent being narrower thannorth,influence ofsurrounding oceanmore felt.
The most important climatic differencesduevariations inamountrainfall. The wide heated plains ofSahara,inlesser degreecorresponding zone ofKalahari insouth, have an exceedingly scanty rainfall,winds which blow over them fromocean losing parttheir moisture aspass overouter highlands,becoming constantly drier owing toheating effects ofburning soil ofinterior; whilescarcitymountain ranges inmore central parts likewise tendsprevent condensation. Ininter-tropical zonesummer precipitation,rainfallgreatest whensunvertical or soon after. Ittherefore greatestall nearequator, wheresuntwice vertical,less indirectionboth tropics.
The rainfall zones are, however, somewhat deflected fromdue west-to-east direction,drier northern conditions extending southwards alongeast coast,those ofsouth northwards alongwest. Withinequatorial zone certain areas, especially onshores ofGulfGuinea and inupper Nile basin, have an intensified rainfall, but this rarely approaches that ofrainiest regions ofworld. The rainiest districtall Africa isstripcoastland westMount Cameroon, where there ismean annual rainfallabout 390 in. as compared withmean458 in. at Cherrapunji,Assam.
The two distinct rainy seasons ofequatorial zone, wheresunvertical at half-yearly intervals, become gradually merged into one indirection oftropics, wheresunoverhead but once. Snow falls on allhigher mountain ranges,onhighestclimatethoroughly Alpine.
The countries borderingSaharamuch exposed tovery dry wind, full of fine particlessand, blowing fromdesert towardssea. KnownEgypt askhamsin, onMediterranean assirocco, itcalled onGuinea coastharmattan. This windnot invariably hot; its great dryness causes so much evaporation that coldnot infrequentlyresult. Similar dry winds blow fromKalahari insouth. Oneastern coastmonsoons ofIndian Oceanregularly felt,onsouth-east hurricanesoccasionally experienced.
Whileclimate ofnorthsouth, especiallysouth,eminently healthy,evenintensely heated Saharasalubrious by reasonits dryness,tropical zone aswhole is,European races,most unhealthy portion ofworld. Thisespeciallycase inlowermoister regions, such aswest coast, where malarial feververy prevalentdeadly;most unfavourable factors being humidityabsenceclimatic variation (daily or seasonal). The higher plateaus, where not only isaverage temperature lower, but such variationsmore extensive,more healthy;in certain localities (e.g. Ethiopia and partsBritish East Africa) Europeans findclimate suitablepermanent residence. On tablelands over 6500 ft. abovesea, frostnot uncommon at night, evenplaces directly underequator.
Initial text from 1911 encyclopedia -- Please update as needed
- See also : Africa
