Ethiopia Mountain

In this generalized soils record only the dominant soil types are indicated. The area percentages given for each soil unit are the percentage of occurrence of the soil type over the country as dominant soil, as well as in association with other soil types.

The nomenclature used is the FAO/UNESCO legend for the soil map of the world 1966 E.C (1974).

A. Orithic Acrisols (4.5 %)
These soils have a distinct argillic B horizon and a low base saturation. The topsoil can have a coarse texture.

Orthic Acrisols occur mainly on sloping terrain. They have limited agricultural potential. The soils are chemically poor; the contents of weatherable minerals is generally low; the PH is less than 5.5. and available P contents are very low.

Physically these soils have few limitations. The rooting depth might be limited by the argillic B horizon, or by rock at shallow depth.

The moisture storage capacity is, depending on the depth of the soil, moderate to good. Only when the topsoil is very sandy do tillage operations create problems like compaction or erosion.

Be. Chromic, Eutric and Calcic Cambisols (7.5%)
These soils have a cambic B horizon and a base saturation of 50 per cent or more. Chromic Cambisols have a strong brown or red colour.

Those with a calcic horizon or with lime accumulation are Calcic Cambisols. The latter mainly occur in limestone areas with limited precipitation.

Most Cambisols have little agricultural value, as they occur dominantly on slopes, are often shallow of have many stones or rock outcrops. Where Cambisols are deep and not stony they are good for agriculture.

Bh. Dystric and Humic Cambisols (2%)
These soils have a low base saturation and a cambic B horizon (Dystric Cambisols) or a deep umbric A horizon. The latter are Humic Cambisols. They mainly occur at high altitude. Dystric Cambisols are found on steep slopes in high rainfall areas.

Their agricultural value is limited, as they occur on slopes, they are shallow and have many stones or rock outcrops.

Bv. Vertic Cambisols and Vertic Luvisols (3%)
These soils are Cambisols and Luvisols with vertic properties. As the Vertisols, these vertic soils have fairly good, but limited agricultural potentialities. Land preparation is difficult, dry soils are hard and wet soils are sticky.

Only during a short period is the moisture condition of the topsoil favourable for tillage practices. Chemically these soils have no limitations.

H. Rendzinas, Haplic and Luvic Phaeozems (4%)
These are soils with a mollic A horizon. Rendzinas and Haplic Phaeozems mainly occur in the highlands, where soil depth is often limited by hard rock at shallow depth.

Rendzinas have only a mollic A horizion resting directly on calcareous rock.
Their agricultural value is limited, because generally they occur on steep slopes, rooting depth is small and there are many stones and rock outcrops. when they are deeper, they are suitable for agriculture.

Luvic Phaeozems have an argillic B horizon. They occur in the Rift Valley. As most of them are sodic, their agricultural value is limited.

I. Lithosols (17%)
These soils are less than 10 cm thick, developed over hard rock. They occur on steep slopes and in area with very limited precipitation. These soils have no agricultural potential.

J. Calcaric and Eutric Flovisols (8.5%)
Fluvisols are young soils developed in recent alluvial deposits of river plains, deltas, former lakes and coastal areas.

Soil conditions are highly variable. In arid regions many soils are saline. Fluvisols with calcareous material are Calcaric Fluvisols, those which are non-calcareous, having a base saturation of 50 per cent or more, are Eutric Fluvisols.

Fluvisols are generally good agricultural soils and often intensively used, although land use has to be adapted to floods, inundations or high groundwater.

L. Chromic and Orthic Luvisols (5%)
Luvisols are soils with an argillic B horizion and a base saturation of 50 per cent or more. Those with a strong brown or red B horizon are Chromic Luvisols.

Most Luvisols have good agricultural potentialities. Base saturation is high and they have weatherable minerals. In soils with a heavy textured B horizon, permeability might be low, and drainage and good root distribution can be hindered.

Nd. Dystric Nitosols (7.5%)
Nitosols are deep, clayey red soils with an argillic B horizon. Dystric Nitosols have a base saturation of less than 50 per cent. They are found on almost flat to sloping terrain in high rainfall areas.

They have rather good potentialities for agriculture. These soils have very good physical properties. They have a uniform profile, are porous, have a stable structure and a deep rooting volume. Their moisture storage capacity is high.

Chemically these soils have some restrictions. The base saturation is rather low, PH’s are less than 5.5 and available P contents are low.

Ne. Eutric Nitosols (5%)
Eutric Nitosols are Nitosols with a base saturation of 50 per cent or more. They are found on almost flat to sloping terrain in the highlands.

They are among the best agricultural soils. Their physical properties are similar to those of the Dystric Nitosols. Chemically these soils are better, although available p contents are low.

Q. Calcic Arenosols (5%)
These are coarse-textured soils. The sub-soil has the characteristics of a cambic B horizon, but does not classify as such, because the soil texture is too coarse. Arenosols are developed on sandstone.

Arenosols have very limited agricultural potentialities. They have a low water retention, are very permeable, have a low natural fertility and a low CEC. Rooting depth is often restricted by limited soil depth.

R. Calcaric and Eutric Regosols (11%)
Regosols are soils without profile development, consisting of loose, non-alluvial soil material.

They occur in areas with little precipitation; or on steep slopes subject to severe erosion. Those with lime accumulation are Calcaric Regosols. Eutric Regosols have a base saturation of 50 per cent or more.

They have limited agricultural value, especially where soil depth is limited. Water retention in Regosols is low.

T. Humic, Mollic and Vitric Andosols (1%)
Andosols occur in volcanic regions. They are formed in volcanic ash material. The ash material being very light, their bulk density is less than .85 g/cm3. Vitric Andosols have more than 60 per cent volcanic glass, they occur in rather arid zones.

Mollic Andosols have a mollic A horizon, Humic Andosols have an umbric A horizon. The latter mainly occur in cool and humid regions, at altitudes.

Most Andosols are good for agriculture. They can absorb much water and are very porous. The CEC is high (35-70/me/100gr soil) and the organic matter content is often high. Some Andosols, especially in the rift valley, have a high sodium content and thus a limited agricultural value.

V. Chromic and Pellic Vertisols (10%)
These are heavy clay soils in flat areas, having a pronounced dry season during which they shrink and have deep cracks in a polygonal pattern.

During the wet season the clay swells and causes pressure in the sub-soil. Pellic Vertisols are dark, usually occupying areas which are water-logged during the rainy season. Chromic Vertisols are brownish and better drained.

Vertisols have fairly good, but limited agricultural potentialities. Land preparation is difficult, dry soils are hard and wet soils are sticky. The moisture condition of the surface layer is only during a short period favourable to prepare land.

Another difficulty is that the permeability of the subsoil is very low. Very often these soils are flooded or have stagnant water during the rainy season.

The soil has a high water retention, but relatively a small amount of water is available for plant growth. Rooting depth might be restricted because of the swelling and shrinking properties of the soil.

Chemically these soils are good. The CEC is very high (often over 70 me/100g soil) and the base saturation is over 50 per cent, mainly with Ca+++ and Mg++ ions.

Free CaCo3 is often present as nodules in the profile. When precipitation is limited, salinity problems might occur. Because of the low permeability and the difficult drainability of the subsoil, it is very difficult to improve such soils.

X. Haplic, Calcic and Luvic Xerosols (5%)
Xerosols are soils in arid and semi-arid regions, with a weakly developed A horizon. Those with an argillic B horizion, mostly at shallow depth, are Luvic xerosols.

Those without a calcic horizon are Haplic Xerosols, those with a calcic horizon are Calcic Xerosols.

The calcic horizon may harden, forming a petrocalcic horizon.
The agricultural value of Xerosols is low, except when they can be irrigated and when physical properties are good for irrigated crops.

Y. Gypsic Yermosols (3%)
The moisture regime of these soils is aridic and they have a weakly developed ochric A horizon.

They consist of highly gypsiferious parent material, and have a gypsic horizon. The gypsic horizon may harden, forming a petrogypasic horizon.
Gypsic Yermosols are not suitable for agriculture in irrigation projects.

Z. Gleyic and Orthic Solonchaks (4.5%)
Solonchaks are highly saline soils containing soluble salts that influence plant growth. These are poor soils because most plants cannot grow at all.

Most solonchaks are Orthic Solonchaks. If they have hydromorphic properties within the first 50 cm, they are called Gleyic Solonchaks.

In saline soils that have a moderate to rapid permeability to a depth of at least 3 m, and that can be drained, the harmful soluble salts can be washed out, and carried away, in drain water. When this is completed, soils may have agricultural potential, although it is necessary to take care that salts do not accumulate in the rooting zone again.

(Source: National Atlas of Ethiopia)

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The basement upon which all younger formations were deposited contains the oldest rocks in the country, the Precambrian, with ages of over 600 million years.

They are exposed in areas where the younger cover rocks have been eroded away; namely, in parts of Harerge, Sidamo, Bale, Ilubabor, Gojam, Welega, Gonder, and Tigray Administrative Regions.

The Precambrian contains a wide variety of sedimentary, volcanic and intrusive rocks which have been metamorphosed to varying degrees.

The basement in the south and west of the country, where granitic rocks and gneisses predominate, has been more strongly metamorphosed than Preecambrian sequences in the north.

Though in many cases strongly folded and foliated, the rocks in the north, which include the youngest formations yet known in the Precambrina, have generally undergone only weak metamorphism, reflecting the relatively low temperatures to which they have been subjected since their deposition.

The Precambrian or basement rocks contain most of the presently known metallic deposits of Ethiopia. In particular, the gold deposits of the northern, western and southern regions all occur in these rocks, where they are associated with fractured quartz reefs or sulphides.

Under favourable conditions, these deposits have given rise to major placer deposits along river beds, as in the Kibre Mengist (Adola) area.

Copper, zinc and lead sulphides have been found in the weakly metamorphosed volcanic facies (greenschists) of these old rocks. Similarly occurrences of potentially exploitable talc and nickel deposits are associated with ultrabasic bodies, and it is in a layered body of this type that platinum mineralisation occurs at Yubdo in Welega Administrative Region.

There are considerable possibilities of finding other economically exploitable deposits of these minerals in the Precambrian series, while major intrusions and dykes contain good potential for other minerals.

Most of these Precambrian rocks are relatively impermeable, and have been subjected to several orogenic episodes since their formation.

These processes, combined with the rifting associated with the development of the Red Sea and the East African-Ethiopian Rift Valley, have resulted in considerable fracturing and shattering. Major water resources are associated with these fracture zones.

At the end of Precambrian times uplift occurred; this being followed by a long period of erosion. Any sediments which were deposited during Palaeozoic interval, which lasted some 375 million years, have been largely removed by erosion.

Some, shales and deposits of glacial origin, were laid down in northern Ethiopia during this period.

Subsidence occurred in the Mesozoic which began some 225 million years ago, and a shallow sea spread initially over the Ogaden and then extended further north and west as the land continued to subside.

New sandstone was deposited on the old land surface. Deposition of mudstone and limestone followed as the depth of water increased. The subdivision of the Mesozoic sequence and younger sediments on the map into approximate age categories is largely based on palaeontological evidence.

In the west of the country, sedimentation ended with the deposition of clay, silt, sand, and conglomerate brought in from the land as the sea receded due to uplift of the land mass. In the southeast, gypsum and anhydrite were precipitated on inter-tidal flats.

In the Ogaden there was a fresh invasion of the sea in late Mesozoic times during which the sequence of sedimentation was repeated, ending again with the precipitation of gypsum and anhydrite.

The same cycle of sedimentation was reported yet again in the Ogaden during the Teritary period. It ended with the deposition of conglomerates.

Mesozoic rocks are considered to have the greatest potential for oil and gas deposits. The presence of such deposits is dependent on the original existence of organic materials mostly of marine origin in sediments which were buried to form the so-called source beds.

In these beds, which may now be represented by shales or stromatoloid reef limestones, the organic material was altered by the pressure of the overlaying sediments and a build-up of heat into oil and gas which migrated into nearby permeable (reservoir) rocks.

The Mesozoic of southern Ethiopia contains few favourable structures for oil, beign only weakly folded; nevertheless, there remains a reasonable possibility of the occurrence of stratigraphic traps.

Outcrops of the Mesozoic in the north and west are considered as less favourable, due to the possible terrestrial nature of the rocks in the north and the probable thinness of the rocks in the west.

The mp emphasizes the necessity for additional studies in these areas.
Metallic minerals have not be discovered to date in the Mesozoic rocks but the occurrences of limestones and saline deposits shown on the map point to the need to prospect these formations further for lead, zinc and silver ores.

Rocks of this age also represent major reserves of glass sands, cement limestones and other industrial minerals.

Extensive fracturing occurred in the early Cenozoic (this interval started 65 million years ago), although major displacement along the fault systems of the Red Sea, Gulf of Aden and East African Rifts did not occur until later in the Teritary.

Faulting was accompanied by widespread volcanic activity which led to the formation of vast quantities of basalt lava over the western half of the country.

This was accompanied by, and alternated with, the eruption of large amounts of ash and coarser fragmental material, forming the Trap Series. Several shield volcanoes, also consisting of alkali basalts and fragmental material, then developed around the eastern edge of the Lake Tana depression and southwest of Goba.

More recent volcanism is associated with the development of the Rift Valley, activity being concentrated within this structure and along the edges of the adjoining plateaux.
Volcanism has persisted to the present in the Afar region conglomerate, sand, clay, and reef limestone which accumulated in the Afar Depression and at the northern which accumulated in the Afar Depression and at the northern and of the main Rift Valley.

Sediments which accumulated in former lakes occur at the south end of the Afar, in the main Rift Valley and in the Omo valley. Undifferentiated Quaternary sediments and superficial deposits occur intermittently along the Sudanese and Kenyan borders.

Oil and gas deposits may be present in some of the Teritary deposits but in general the rocks of Cenozoic age in Ethiopia are of potential economic importance because of their extremely large salt deposits.

These include not only the common rock salt traditionally worked in the Afar region but also deposits of potassium and magnesium salts.

Furthermore, the geothermal activity associated with the many Cenozoic deposits has given rise to metallic mineral occurrences-copper and manganese in particular, concentrated as a result of leaching of the rocks by saline solutions.

Iron ores, and possibly even aluminium ores (bauxite), developed on the volcanics as a result of intense weathering and may prove to be of economic interest
The underground water resources of the Cenozoic are of great importance.

The often lenticular nature of the beds necessitates detailed investigation but, given suitable recharge areas, the deposits can be considered as highly favourable for water exploitation.

(Source: National Atlas of Ethiopia)

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