9 The Land Resources of North East Nigeria A/blume1 The ...

The west and central portions of these plains contain extensive northeast-orientated longitudinal
dunes are are part of the 'Ancient Erg of Hausaland' (Grove, 1958). The Lantewa
Dunefield merges southwards into the Damaturu Plains which are a series of sand plains with
very little relief. The cover of aeolian sand is thinner south of Damaturu and, along the
southern border of these plains, clays and sandstones of the Chad Formation are exposed
beneath the drift. Between Buni and Damboa the plains are underlain by rocks of the Basement
Complex and by Cretaceous sediments. Between Potiskum and Azare aeolian drift sands similar
to those of the Damaturu Plains overlie sandstones of the Kerri Kerri Formation and form the
extensive Potiskum Plain. Apart from occasional flat-topped ironstone-capped hills this
plain has very little variation in relief.
In the northeast the longitudinal dunes of the Lantewa Dunefield are replaced by transverse
northwest-orientated dunes of the Gudumbali Dunefield. These dunes rise as much as 15 m
(50 ft) above the interdune areas. North of Mongonu some of the interdune areas contain
extensive clay flats. The Lantewa and Gudumbali Dunefields are separated by a complex sand
ridge called the Bama Ridge. This Ridge stands as much as 12 m (40 ft) above the surrounding
plains and runs from east of Geidam, through Maiduguri and Bama, to the Cameroon frontier.
It has also been mapped in the Niger and Chad Republics and marks an old shoreline of Lake
Chad. A sand plain lying between the beach ridge and the dunes further east is interpreted
as a former beach when Lake Chad was considerably larger than it is at the present time.
East of the sand plains and dunefields the area is dominated by the Yedseram and El Beid
rivers which flow north from the Mandara Mountains to Lake Chad. The upper reaches of the
El Beid are in Cameroon Republic. In its upper reaches the Yedseram flows over the gently
undulating Uba Plains, which descend gradually from over 600 to 300 m (2 000 - 1 000 ft) east
of Damboa and are more typical of the Basement plains of the southern part of the project
area. North of the boundary between the Basement rocks and the overlying Chad Formation the
Bama Deltaic Complex extends as far north as Dikwa. This Complex consists of extensive clay
and sandy plains with very little relief. South of Bama it contains both the present and
older, more extensive, floodplains of the Yedseram river. North of Bama neither the Yedseram
nor its major tributary, the Ngadda, reach Lake Chad. They disperse between the Bama Ridge
and the present shoreline of the Lake over virtually flat plains. In the Bama Deltaic
Complex these plains consist of a very complex association of deltaic deposits formed when
Lake Chad extended to the Bama Ridge. East of Bama and north of Maiduguri, on the edge of
the Gudumbali Dunefield, these deltaic deposits have partially buried relics of the longitudinal
dunes. North and east of Dikwa this complex of deltaic plains gives way to extensive
flat clay plains - known locally as 'firki'. These are the plains of the Chad Lagoonal
Complex and they owe their form to clays deposited during lagoonal conditions of a more
extensive Lake Chad. The present border of Lake Chad is marked by a series of undulating
sand plains grouped as the Chad Lacustrine Plains. In the north these plains consist of a
series of low sand ridges parallel to the present shoreline; further south small clay
depressions occur within the sand plain and its border with the Chad Lagoonal Complex is
marked by a small but distinct beach ridge.
The Gongola and its tributaries form the major river system in the southern part of the
project area. The Gongola rises on the Jos Plateau from where it flows northeast across the
Bauchi Plains, west of the survey area, and through the Kerri Kerri Plateau as far as Nafada;
it then swings abruptly south and flows through the main Gongola Valley to join the Benue
opposite Numan.
The Gongola Valley is cut mainly in Cretaceous sediments, although Basement rocks are exposed
at Kaltungo and to the east of the Gongola between it and the Biu Plateau. The Valley contains
flat and undulating plains descending gradually from 430 m (1 400 ft) southwest of
Damaturu to 180 m (600 ft) north of Numan where they merge with the plains of the Benue
Valley. The various plains are separated by hill ranges which in some places rise abruptly
to over 300 m (1 000 ft) above the surrounding plains. These ranges are formed on both
sandstones and Basement Complex rocks and there are many prominent single hills formed by
volcanic plugs or cones. In the southern half of the Valley, where the Gongola cuts through
folded Bima Sandstone, these hills form some of the most spectacular scenery in Nigeria.
West of the Gongola Valley the Kerri Kerri Plateau forms extensive rolling upland plains
between 300-600 m (1 000 - 2 000 ft), with occasional upstanding flat-topped ironstone-capped
relic hills. North of the Gongola the Plateau drains to the Gongola itself; to the south
most of the Plateau is drained south by the river Pai to the Benue. The Pai and its major
tributaries have flat-floored incised valleys bounded in most places by steep sides rising to
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