The Nigerian territory has a rather simple structure; it corresponds to an ancient penepian which has its prominent parts in the central-northern section, where the crystalline, archaeozoic formations of the African base emerge over vast surfaces. These raised areas, which are configured as a sort of not very high plateau, represent the remains of an ancient relief gradually leveled by erosion, which underwent rejuvenation in the Cenozoic era., when the depressions that complete the picture of the Nigerian territory were outlined or defined, as a reflection of the vastest crustal settlement of the African continent. They are: the southern one facing the coast, the one crossed by Niger and that of its tributary Benue, finally the northern one that falls within the internal continental depression of Chad. In these depressed areas the archaeozoic formations are covered by sedimentary layers due to the periodic ingress of the sea: they are particularly represented by deposits from the Cretaceous period in the central sections (depressions of Niger and Benue), from Cenozoic coasts in the southern belt and finally of recent formations in the marginal areas both to the N, in the Chadian basin, and to the S, in the coastal strip. The geographical picture of Nigeria is completed with volcanic formations, whose origin is linked to the same crustal settlements already mentioned, present above all in the central section of the country, where the Jos plateau (or of Bauchi; 1781 m) constitutes the highest part of the Nigerian territory together with the easternmost ridges (Shebshi mountains, 2042 m with Mount Dimlang). From the morphological point of view, Nigeria has typically African characteristics, that is, mature, open profiles, broken here and there by the eminences of ancient residual reliefs, by isolated granite hills, by ancient erosional escarpments. The only bumpy area is the central one between Niger and Benue, the aforementioned Jos plateau, furrowed by the valleys that radiate towards the surrounding depressions. Extremely flat surfaces are found to the N, where there are sandy dunes fixed by vegetation; the territory moves towards the E, where there are hilly areas and plateaus of crystalline rocks and in some cases, as in the plateau of Biu, of basalt rocks. The central-southern section presents reliefs only to the W of the confluence of the Niger and Benue rivers: characteristic granite intumescences give a severe aspect to the landscape. Further to the S, the relief gradually fades towards the coastal strip, 60-70 km deep on average, in which the vast delta surface of Niger stands out (approx. 25,000 km²), which has a front of 350 km and is furrowed by numerous branches of the river, the so-called Oil Rivers, “rivers of oil”, because they cross an area rich in oil palms. Outside the delta, the coastal strip is bordered by lagoons – the largest being that of Lagos – which continue those of the Guinean coast.
According to itypeusa, the hydrography of Nigeria is substantially reducible to Niger and its important tributary, the Benue. The two rivers enter the country, one from the state of Niger, the other from Cameroon, joining Lokoja; from here the Niger turns decisively to the S but despite the considerable volume of its waters, due to the low slope, the continuous accumulation of sand banks means that, after Onitsha, the vast delta begins. The floods correspond to the (summer) rainy season; while the Niger, turning its high course embedded in the crystalline base, is frequently interrupted by rapids and therefore not navigable everywhere, the Benue, with a morphologically more mature profile, is entirely navigable during the period of full. For the rest, Nigeria pays NE to Lake Chad via the Komadugu River, and S directly to the Atlantic Ocean via short streams (Ogun to SW, Cross to SE, etc.).
Vegetable variations adapt to the zonal variations of the climate. Generally speaking, a forest belt with an equatorial climate predominates on the S, characterized by an evergreen forest, shady-loving, rich in species, which in less humid areas brightens up and associates trees with deciduous leaves; in the delta area there is amphibious vegetation and vast formations of mangroves obstruct the river outlets. In the intermediate belt the arborate savannah (or forest-park) prevails, alternating, in the degraded areas, with prairie with tall grasses and with tunnel forest bands along the rivers. In the north the savannah becomes grassy, interrupted by groups of trees typical of the Sudanese region, such as baobabs, acacias, and tamarinds. Finally, the northwestern part of the Sahel it is characterized by a semi-desert vegetation. As for the fauna, large carnivores, antelopes, warthogs, monkeys and birds inhabit the savannahs and scrubland, while elephants, hippos, snakes and crocodiles live in the forests and rivers. Nigeria, like many other states of the African continent, is characterized by an extraordinary biodiversity threatened, however, by the intervention of man who has changed the natural balance. Desertification, deforestation and intensive exploitation of grazing lands are the unfortunate consequences of population growth. Despite the environmental problems, 15.6% of the territory is a protected area, with numerous reserves and 14 national parks, among which the best known is the Yankari National Park.