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Nigeria PHYSICAL SETTING
Relief and Main Physical Features
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Figure 8. Topography and Drainage
Much of Nigeria's surface consists of ancient
crystalline
rocks of the African Shield. Having been subject to
weathering
and erosion for long periods, the characteristic landscape
of
this area is extensive level plains interrupted by
occasional
granite mountains. These features form a major landscape
type of
Nigeria and of West Africa as a whole. There are also
smaller
areas of younger granites found, for example, on the Jos
Plateau
(see
fig. 8).
Sedimentary strata dating from various periods overlay
the
older rocks in many areas. The sedimentary areas typically
consist of flat-topped ridges and dissected plateaus and a
characteristic landscape of extensive plains and no major
rocky
outcrops. This landscape is generally true of the basins
of the
Niger and Benue rivers as well as the depressions of the
Chad and
Sokoto basins in the far northeast and northwest of the
country,
respectively. The most dramatic of the sedimentary
landscapes are
in southeastern Nigeria, where thick sedimentary beds from
the
Abakaliki Uplift to the Anambra Basin have been tilted and
eroded. This process has resulted in a rugged scarp land
topography with east-facing cliffs at in the Udi Hills,
north of
Enugu, and in the area around Nanka and Agulu.
Although relatively little of the Nigerian landscape
has been
shaped by volcanic episodes, there are two main areas of
volcanic
rock. They are found on the Biu Plateau in the northeast,
extending into some localized volcanic areas along the
eastern
border with Cameroon, and on the Jos Plateau in the
northern
center of the country.
The elevational pattern of most of Nigeria consists of
a
gradual rise from the coastal plains to the northern
savanna
regions, generally reaching an elevation of 600 to 700
meters.
Higher altitudes, reaching more than 1,200 meters in
elevation,
are found only in isolated areas of the Jos Plateau and in
parts
of the eastern highlands along the Cameroon border. The
coastal
plain extends inland for about ten kilometers and rises to
an
elevation of forty to fifty meters above sea level at its
northern boundary. The eastern and western sections of the
coastal plain are separated by the Niger Delta, which
extends
over an area of about 10,000 square kilometers. Much of
this is
swampland, separated by numerous islands. The coastal
plain
region penetrates inland about seventy-five kilometers in
the
west but extends farther in the east. This region is
gently
undulating with elevation increasing northward and a mean
elevation of about 150 meters above sea level. Much of the
population of southern Nigeria is located in these eastern
and
western coastal plains and in some of the contiguous areas
of the
coast and the lower Niger Basin.
Separating the two segments of the coastal plain and
extending to the northeast and northwest are the broad
river
basins of the Niger and Benue rivers. The upper reaches of
these
rivers form narrow valleys and contain falls and rapids.
Most of
the lower portions, however, are free from rapids and have
extensive floodplains and braided stream channels. To the
north
of the Niger and Benue basins are the broad, stepped
plateau and
granite mountains that characterize much of northern
Nigeria.
Such mountains are also found in the southwest, in the
region
between the western coastal plains and the upper Niger
Basin. The
western wedge between Abeokuta and Ibadan and the Niger
Basin
reaches elevations of 600 meters or more, while the
extensive
northern savanna region, stretching from Kontagora to
Gombe and
east to the border, includes extensive areas with
elevations of
more than 1,200 meters or more at its center. The
mountainous
zone along the middle part of the eastern border, the
Cameroon
Highlands, includes the country's highest point (2,042
meters).
In the far northeast and northwest, elevation falls again
to
below 300 meters in the Chad Basin in the far northeast
and the
Sokoto Basin in the northwest.
Data as of June 1991
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