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CHAPTER THREE:
TOPOGRAPHY OF ETHIOPIA & THE HORN
1. Introduction
2. Physiographic Divisions
• The Western Highlands and Lowlands
• The Southeastern Highlands and Lowlands
• The Rift Valley
3. The Impacts of Relief on Biophysical and Socioeconomic
Conditions

3.1. INTRODUCTION
• The topography of Ethiopia is largely determined by geologic
activities of the Cenozoic Era.
• The shattering of the land b/n parallel fractures on the uplifted
dome shaped mountain & the subsequent lava flow & deposition
result in developing an outward sloping highland area, a great
structural valley & depressions on which later lakes emerge.
• Geomorphic processes brought some modification to this landform.

At the end of this chapter, the learners will be able to:

• explain the physiography of Ethiopia and the Horn as well as its impact on
biophysical & socioeconomic conditions

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GENERAL PHYSIOGRAPHIC CHARACTERISTICS

• The landforms of Ethiopia is characterized by great variety that

include
• flat-topped plateaus
• high & rugged mountains
• deep river gorges
• vast plains
• The variety in topography is accompanied by differences in other
natural features such as soil, climate & wildlife.
• Likewise, the socio-cultural & economic phenomena are also
affected by the topography.

• Altitude ranges from the lowest at Kobar Sink [125mbsl] to the

highest at Mt Ras Dajen [4,620masl].
• Above 1,000m elevation makes more than 50% of the total landmass
• Above 1,500m makes 44% of the country.
• Half of this is above 2000 masl.
• The highland which stretches NE – SW direction is surrounded by
lowlands towards the periphery of the country.

• HLs [rugged mass of mts] are most significant physical features

• Most part of the country is occupied by high plateau & mt ranges
• The largest portion of continuous elevated ground in the continent
• described as Roof of East Africa due to its height & large area.

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• dissected by several rivers & gullies which have deep gorges.

• divided into several regions & mountain systems.
• sources of many rivers & streams that made the country to be
named as the Water Tower of East Africa.
• Elevation of 1,500m is used to classify places into Highland &
Lowland in Ethiopia
Features Highlands:
• Moderate to high amount of rainfall (>600 mm per year).
• Lower mean annual temperature (<200C).
• Favorable climate for biotic life.
• Free from tropical diseases.
• Attractive for human habitation and densely settled.
• Rain-fed agriculture is possible.

• These highlands make up nearly 56% of the area of the Ethiopia.

• This is further subdivided into lower HL (1,000 - 2,000 masl),
which make up 35% & higher HL (>2,000 masl) constituting nearly
22%.
• In contrast to the highlands, the remaining 44% of the Ethiopian
lowlands are characterized by:
• Fewer amounts of rainfall & higher temperature.
• High prevalence of tropical diseases.
• Lower population densities.
• Pastoralist & semi-pastoralist economic life.
• Vast plain lands
• Favorable for irrigation agriculture along the lower river basins.

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3.2. THE PHYSIOGRAPHIC DIVISIONS OF ETHIOPIA

• The three/3/ major physiographic units
1.The Western highlands & lowlands
2.The South-eastern (Eastern) highlands and lowlands
3.The Rift Valley

3.2.1. THE WESTERN HIGHLANDS & LOWLANDS

• It contains all the area west of the Rift Valley.
• It extends from north to south encompassing nearly the whole
western half of Ethiopia.
• It makes up about 44% of the area of the country.
• In the east the western escarpment of the Rift Valley bound it
• whereas westward, the land gradually descends in altitude until it
merges into the western foothills & lowlands, along the Sudan &
South Sudan border.
• This region is further subdivided into four groups of highlands
(76.3%) & four groups of lowlands (23.7%).

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1. THE WESTERN HIGHLANDS

A. The Tigray Plateau
• extends from Tekeze gorge in the S to Mereb River in the N.
• an elongated HL most of which is between 1000 & 2000 masl.
• High mts peaks of this plateau are Mt. Tsibet =3988masl,
Mt Ambalage =3291masl & Mt Assimba =3248masl
• drained by left bank tributaries of Tekeze river.
• Long period of denudation created residual features of granite
hills, rugged topography & Ambas.
• The famous monastery at Debre-Damo, a tableland that can only
be climbed by a rope pulley is also located in this plateau region.

B. North Central Massifs

• The largest in the western highlands.
• Much of its Nn & southern limit follows the Abay & Tekeze gorges
• Abay & Tekeze with their tributaries [that have made maze of
gorges & steep sided river valleys] dissect the land into many
isolated plateau blocks, precipitous tablelands & other rugged
surface forms.
• Much of these plateau & tablelands are capped by basalt of the
Trapean lava
• In its central part, Lake Tana basin is surrounded by plains of
Fogera & Dembia in the N & an upland plain in its south.

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• 58% of the region is at an altitude of more than 2000m, making it,

next to the Shewan Plateau, the second highest topographic
division.
• The region consists of the Gonder, Wello & Gojjam Massifs.
• 19 of the 26 mt peaks having elevation of more than 4,000masl in
Ethiopia, are found in this region. Among these, the most popular
ones include
• Mt Ras Dajen = 4,620masl, Mt Weynobar/Ancua = 4462masl,
• Mt KidusYared =4453masl, & Mt Chuahit = 4437masl in Simen Mt
• Mt Guna =4,231masl in the Debre Tabour Mt System,
• MtAbune Yoseph = 4,260 masl in the Lasta highlands of Wello and
• Mt Birhan =4,154 masl in the Choke Mt System of Gojjam.

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• These mountains have steep cliffs & rugged terrain that provide
scenic views to climbers
• The Mountain systems in Gonder & Gojjam are separated from the
eastern group of mountains in Wello by impenetrable & deep
gorges.
• At one point though, they are connected by Yeju-Wadla Delanta
land bridge (ridge).
• This land bridge has been significant in history.
• It served as a route of penetration by the Turks, Portuguese, &
Italians etc.
• The Woreta-Debre Tabor-Woldya road constructed to link the
northwestern region with Asseb through Woldya & Dessie took
advantage of this land bridge.

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c. The Shewa Plateau/central highlands

• It is bounded by
• the Rift Valley in the east & southeast,
• the Abay gorge in its northern & western limit, and
• the Omo gorge in the south & west.
• It occupies a central geographical position in Ethiopia.
• It is the smallest of the Western highlands accounts only 11%.
• Nearly three-fourth of its area is at an altitude of more than 2000
masl.
• It has the largest proportion of elevated ground.
• It is drained, outward in all directions by the tributaries of Abay,
Omo & Awash.
• It forms a water divide for these three river basins.

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• The tributaries of Abay-Guder, Muger, Jema etc. have cut deep

gorges & steep sided river valleys.
• They have created several tablelands & isolated plateau units in
the north.
• Similarly, the tributaries of Omo & Awash have dissected the other
sides of the plateau.
• Otherwise, this plateau has relatively extensive flat-topped
uplands, giving it the appearance of a true plateau.
• The highest mountain in the Shewan plateau is
• Mt Abuye-Meda 4000 masl in Northern Shewa,
• Mt Guraghe in the south is 3,721 masl.

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d. The Southwestern Highlands

• It consists of the highlands of Wellega, Illuababora, Jimma, Kaffa,
Gamo & Gofa.
• It is separated from the adjacent highlands by Abay & Omo rivers.
• It extends from the Abay gorge in the north to Chew Bahir in the
south.
• It is the 2nd largest in the Western highlands accounting for 22.7%.
• About 70% of its area is lies within 1000-2000m altitude.
• It is the wettest plateau in Ethiopia.
• It is drained by Dabus, Deddessa, Baro, Akobo & the Ghibe/Omo
rivers.
• The most dissected & rugged terrain due to numerous streams.
• Mt Guge 4,200masl is the highest peak in this region.

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THE WESTERN LOWLANDS

• These are the western foothills & border plains that extend from
Western Tigray in the north to southern Gamo-Gofa in the South.
• They make 11% of the area of the physiographic region.
• The general elevation ranges between 500 & 1000 meters above sea
level.
• Their continuity is interrupted by protruding ridges/ part of
Highlands.
• They are further subdivided into four subregions. These are
• Tekeze lowland,
• Abay-Dinder lowland,
• Baro lowland, and
• Ghibe lowland from north to south.

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• With the exception of the Baro lowland, the region is generally

characterized by arid or semi-arid conditions.
• The Ghibe/Omo lowland, which includes the lower Ghibe/Omo
Valley and the northern section of the Turkana basin, is classified
in the Western lowlands from its geographical location.
• But structurally it also belongs to the Rift Valley.
• It is an area, which is both faulted & tectonically depressed.
• In the Western lowlands, there are small but important towns
• Their importance could be related to agriculture, history, or are
simply border towns and frontier ports.
• These are Humera, Metema, Omedla, Kurmuk, Gambella etc.

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3.2.2. THE SOUTHEASTERN HIGHLANDS & LOWLANDS

• 2nd largest in terms of area &accounts for 37% of the area of
Ethiopia
• The highland make up 46% of the region while the rest is lowland.
• They are bounded by:
• eastern escarpment/ fault line of the Rift Valley in the West &
North
• Ogaden Lowland in the east
• Elkerie & Borena Lowlands in the south
• This landmass gradually descends into the southeastern lowlands.
• These are further subdivided into
• two units of highlands and
• two units of extensive lowlands.

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THE SOUTHEASTERN HIGHLAND

A. The Arsi-Bale-Sidama Highland
• found east of the Lakes Region & form the SW part of this region.
• They make up 28.5% of the area of the region & 62% of the south -
Eastern Highlands.
• The Arsi Highland is made up of flat rolling uplands & dissected
mountains.
• The well-known mountains in this area are
• Mt Kaka (4,180 masl),
• Mt Bada (4,139 masl) &
• Mt Chilalo (4,036 masl).
• It is separated from Bale highland by Wabishebelle river.

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• The Bale highland consists of basaltic plateau in the north-central

part & high mountain massif to the south.
• The Afro-Alpine summit of Senetti plateau is found on the latter
group.
• The highest mt peaks in this region are Tulu-Demtu (4,377 masl) &
Mt Batu (4,307 masl).
• Erosion features of Pleistocene glaciation which is modified later
by fluvial processes are seen in the trough-like gorges, hanging
valleys, & depressions.
• The Arsi-Bale Highland is important grain producing area with
high potential.

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• The Sidamo Highland is separated from the Bale Highlands by the

Ghenale river valley.
• They occupy the southwestern corner of this region.
• The prominent feature here is the Jemjem plateau, an important
coffee growing area.
• Rivers Wabishebelle & Ghenale along with their tributaries have
dissected this physiographic region.
• Specially, Weyb River, tributary of Ghenale, has cut an
underground passage (Sof Omar cave) through the Mesozoic
Limestone rocks.
• The cave is found near Bale Mts.
• It is one of the World's most spectacular & extensive underground
caves creating a magnificent view accessible only by an
underground stream.

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B. The Hararghe Plateau

• This plateau is a north-easterly extension of the SE highlands.
• It extends from the Chercher highlands in the SW to Jigjiga in the
east.
• It makes up 38% of the SEn highlands & 17.4% of the whole region.
• It has the smallest proportion of upper highland (>2,000 meters).
• It is a low lying and elongated region.
• Rising sharply from the Rift Valley floor, it immediately but gently
descends east & southeastward.
• The left-bank tributaries of Wabishebelle drain it.
• Much of the Trappean lava is removed & the Mesozoic rocks are
extensively exposed.
• The highest peaks are Mt Garamuleta = 3,381 masl.

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THE SOUTHEASTERN LOWLANDS

• It is located in the southeastern part of the country and they are the
most extensive lowlands in Ethiopia.
• It makes up 54% of the region & around one-fifth of the country.
• It is divided into Wabishebelle plain (60%) & the Ghenale Plain
(40%).
• They include the plains of Ogaden, Elkere, and Borena.
• Southeastward sloping plains characterize these lowlands.
• These extensive plains are interrupted here and there, by low hills,
low ridges, inselbergs and by shallow & broad river valleys &
depressions.
• Because of the harsh climatic conditions, these lowlands are little
used and support very small population.

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3.2.3. THE RIFT VALLEY

• a structural depression bounded by two major & more or less
parallel escarpments formed tectonicaly.
• runs from NE to SW dividing Ethiopian into two i.e. East & West
• covers a length of 1,700 km accounting for 18% of the total area of
Ethiopia.
• made of interconnected grabens & depressions.
• covered with Volcanic rocks, fluvial & lacustrine deposits.
• Full of volcanic domes, hills & cinder cones in many places.
• Altitude ranges from 116mbsl at Dallol to 2000masl in the Lakes
region.
• the most unstable physiographic division of the area.

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subdivided into three subregions

• Afar Triangle/ north
• Main Ethiopian Rift/central
• Chew Bahir Rift/ south

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i. The Afar Triangle [Northern Subdivision ]

• the largest & widest part that makes 54% of the Rift Valley area.
• a triangular-shape valley.
• altitude ranges from 116 mbsl at Kobar Sink to about 900 masl at Awash
• The area is characterized by
• faulted depressions [Dallol/Denakil Depression] & grabens[troughs].
• volcanic mountains.
• bounded by parallel fault lines in west & east. Its floor is made of
• Grabens such as Tendaho volcanic ash & lava deposits
• Lacustrian & fluvial deposits Volcanic mountains such as Mt Fentalle
• A large part of the area is covered by extensive salt plains & lakes (Lake
Assale & Lake Afrera).
• Separated from the Red Sea by a 200 meters high land barrier.

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ii. The Main Ethiopian Rift/Central Rift

• It is the narrow belt of the Rift Valley that extends from Awash
River in the north to Lake Chamo in the south.
• It has an average width of 50-80 km & general elevation of 1,000-
2,000 masl.
• The floor in many places is dotted by cinder cones & volcanic mts.
• The big ones include
• Mount Fentale,
• Boseti-guda (near Adama), Aletu (north of Lake Ziway) and
• Chebi (north of Lake Hawasa).
• The northern section has more of these cinder cones and lava fields.
• There are numerous lakes of enormous aesthetic value.

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iii. The Chew Bahir Rift [Southern subdivision]

• The smallest & the southern part of the Rift Valley.

• also known as the Omo-Ghibe trough.
• Gneissic highlands of Konso & the surrounding highlands separate
it from the Main Rift to the north.
• It is the broad & shallow depression into which the Segen & Woito
streams flows/ empty.
• It consists of an extensive shallow marshy area covered by tall
grasses.
• In the vicinity of Arba Minch, it is split into the Ganjuli & the
Galena Valleys by the Amaro mt range.

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3.3. IMPACTS OF RELIEF

• The highly dissected landscape along with the limited flat surfaces
present influence on various socioeconomic aspects of Ethiopia.
1. Agricultural practices : Relief influences
• farm size & shape, farming techniques, crop production type,
animal husbandry
• In area of rugged terrain the farmlands are small in size,
fragmented, tend to be irregular in shape, difficult for mechanized
farming techniques .
• some corps are well adapted to higher altitudes (barley, wheat) &
others to low altitude (sorghum, maize).
• most equines & sheep are reared in the higher altitudes while
camels & goat are well adapted to lower altitudes

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2. Settlement pattern
• Highlands that are mainly free from tropical diseases are densely
settled.
• Rugged & difficult terrain hinders the development of settlement &
its expansion.
• Highlands are characterized by permanent settlements while
lowlands that are inhabited by pastoralists have temporary
settlements.
3. Transportation & communication
• The highly dissected nature of the landscape /difficult terrain is
• a barrier to the development of surface transportation
• makes infrastructure development & maintenance costly.
• makes rivers less navigable.
• Can block TV & radio communications.

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4. Hydroelectric power potential

• Great difference in altitude coupled with high rainfall created
suitable conditions for very high potential for the production of HE
power in Ethiopia.
5. Socio-cultural feeling
• The rugged terrain as a result of excessive surface dissection
resulted in the long-term isolation of communities.
• People who live in cool higher elevation have been identified as
degegnas [highlanders] & those who live in warm lower elevation as
kollegnas (lowlanders).

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6. Climate
• Altitudinal variation result in d/nt types of climate.
• Highlands with higher amount of rainfall & lower rate of ET tend
to be moisture surplus compared to the moisture deficit lowlands.
7. Soil
• Steep mountain slopes provide low angle of rest, unstable surface
materials and subject to degradation processes and relatively form
shallow and little developed soils.
8. Impacts on natural vegetation
• Relief through its effect on climate & hydrology affect the type of
natural vegetation grown in an area.

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