Landscapes and Landforms of Nigeria

Three major rock types are present in Nigeria: igneous, metamorphic and sedimentary. Igneous and metamorphic rocks constitute the Precambrian Basement Complex which is the oldest, crystalline, solid physical foundation of the country. Sedimentary rocks of the Cretaceous and Cenozoic age fill up the basins, which are depressions within the basement landmass. The Basement Complex and the sedimentary basins are equally dispersed in Nigeria. Quaternary to Recent age alluvial deposits occur along the main river valleys as thin and discontinuous sandy beds to thick sedimentary units up to 15 km wide and 15–30 m thick along the channels of rivers Niger and Benue, as well as along the courses of major ephemeral streams and fadamas, especially in the northern parts of Nigeria. The diverse geology of Nigeria offers opportunities for the exploitation of varied mineral deposits contained in different rock units. Abundant mineral deposits occur in all components of Nigerian geology with mineral deposits of economic significance that include gold, iron ore, cassiterite, columbite, wolframite, pyrochlore, monazite, marble, coal, limestone, clays, barites, lead–zinc, etc. The geological, structural and tectonic settings of different rock units have significant implications on the geomorphological evolution of the landscapes in Nigeria. In addition, a number of the associated geological–geomorphic features and scenery have considerable aesthetic and touristic potential, which in some cases combines with cultural importance.

Nigeria generally has a warm climate all year round, with marked differences between dry and wet seasons. The wet season is normally from April to October, while the dry season is from November to March, although slight alterations have recently been observed in the onset of rains and the interludes between seasons. There are three main climatic regions and types of climate according to Köppen classification. These include the tropical monsoon occurring mostly in the south with rain almost all year round, the dry semi-arid Sahelian climate in the northern parts of the country usually with higher temperatures throughout the year and the savannah climate in the central parts.

Natural vegetation in Nigeria, as elsewhere, is the plant cover that develops with little or no influence or modification by humans and is dominated by native species. Some introduced species, like Gmelina arborea and Tectona grandis, have naturalized and become important components of the local vegetation varieties in the different parts of the country. The wide variation of environmental factors in the country has produced a range of vegetation types, with forests (mangrove forest and rainforest) in the south and savanna vegetation (Guinea, Sudan and Sahel savanna) in the middle and northern parts. Vegetation communities together with the country’s landforms influence considerably the nature, pattern and biophysical processes taking place in the country. Human interference and climate change are posing a serious challenge to the biophysical processes, and there is a need to continue green growth to mitigate human impact on the country’s landscape.

Northern Nigerian lower plains are extensive areas of lower topography situated within the relief region that comprises plains, basins and isolated hills. The region is composed of Sokoto Plain which acted as a watershed for most of the rivers in the sub-region. Among the lower plains of Northern Nigeria, areas around Kano, Kaduna and Zaria are higher than the rest of the region in terms of relief and landscape features, Maisaje hill is the highest at 1593 m above mean sea level. Riruwai Ring Complex with its old tin mining ponds serves as a source to the major rivers in the north-western part of the plain. To the north-east, the lower plain formed features such as sand dunes and isolated hills around Jahun, Katangare, Gudumbali, Bulatura and Lantewa Dunefields. Some of the dunefields are blessed with potash deposits. The major landscape features of the region include inselbergs, lake, dams, rivers, metasediments, sand dunes and isolated hills among others. In the north-east, Gwoza Hills an extension of the Cameroun Mountains appears to be the highest point of the sub-region surrounded by plains, basins, wetlands and the shrinking Lake Chad. The physical nature of lower plains and available water bodies provide a good environment for effective agriculture, fishing and mining among others. For that, it is important to identify, study and describe lower plain regions of Northern Nigeria for understanding the display and interaction between drainage sources, landscape, landform units and development processes.

The Basement Complex rocks of southwestern Nigeria host a variety of residual hills. A distinction can be made among hills based on their parent materials and mode of formation. The hills include mesas, inselbergs, tors, regolith hills (i.e., erosional residuals in regolith), and regolith/forest-covered hills developed in amphibolite and diorite. Most common are inselbergs, which based on size have been classified into whalebacks, turtlebacks, bornhardts, and castle kopjes. They are either symmetrical or perfectly domical—bornhardts, elongated and symmetrical, or elongated and asymmetrical. They occur in clusters and with higher density in granitic plutons, but are scattered in various gneisses. These physical features have become a veritable touristic resource in the area. Good examples include the Idanre hills and the location of Abeokuta around the famous Olumo rock (which is actually a tor) in 1830.

South-east Nigeria is endowed with picturesque massifs, escarpments, residual hills and ridges, some of which are hydrothermally mineralized or contain beds of fossil fuels. In addition, dry valleys, springs, and caves occur. The landscape displays a gradual rise from the south to the Obudu Highland in the north-east, but a similar ascent from the west to the east, towards the maximum elevation in the Obudu Highland, is interrupted by the Nsukka Escarpment and associated hills, which form an elongated north-east to the south-west ridge. The escarpment is a 400-km-long seahorse-shaped structurally monoclinal line of hills, extending from beyond the Nsukka area in the north to Afikpo in the south. It is about 60 km wide in the Nsukka area but tapers to 2 km at Afikpo and has a maximum elevation of 590 m a.s.l. at Ukehe.

The Niger Delta is the largest in Africa and the third-largest in the world, with a total area of 112,106 km². The region has the largest freshwater swamp in Africa and is a biodiversity hot spot because of its rich variety of plant and animal species. This chapter describes geomorphological/geological units, with an emphasis on physiography, land cover characteristics and hydrocarbon pollution. The plains are homo-clinal geomorphic structures that trend westwards and south-westwards. This trend is broken in many places by small hogback ridges and shallow swamp basins, which abut at the coast against the sandy beach-ridge barriers lying between the tidal basins and the open sea. The gently undulating coastal lowland inland from this beach-ridge barrier zone has height ranges between 2.05 and 45 m above sea level. The geomorphological units of the region include the outer barrier island complexes adjoining the Atlantic Ocean, the lower tidal floodplain which consists of estuaries, mangroves, and creeks, and the upper freshwater riverine floodplain, within which seven ecological units are formed.

Lake Chad is the terminus of a vast inland drainage system. It was an inland sea with a basin connected to the sea through the River Mayo Kebbi. With time, fluvial processes cut off the sea by blocking its outlet, thereby turning it into the largest freshwater lake in the world, with a catchment area of 2,537,373 km² some 5000 years ago, ten times its present size. Since then, the water body area has reduced from 400,000 km² to between 1500 and 2000 km². This size reduction has been attributed mainly to anthropogenic activities and climate change. Other factors include a combination of desert winds blowing across portions of the basin that lie in the Sahara Desert and fluvial activities operating in more humid areas that lie within the Savanna belt. Lake Chad Basin has many landforms, including the grotesque-looking rock pedestals of the Ennedi Plateau along its northern boundary in Chad. They also include inselbergs in northern Nigeria, such as the famous Kano Dala Hill, the paleo-dunes that covered northern Jigawa and Yobe states of Nigeria, and the famous Bama Beach Ridge, which essentially forms a depositional ring of sand around the Mega-Chad. Man is a principal player in the Chad scenario; therefore, the study of the basin that is home to over 40 million people must include humans. For this reason, the socioeconomic implications of the dying lake are also briefly reviewed.

The presence of large areas covered by sand dunes on the plains of northern Nigeria has attracted considerable attention over the years due to the unique and spectacular pattern they form on the landscape. The dominantly linear dunes are relict from the Quaternary period when the climate of northern Nigeria was drier. Today, the dunes are found in areas that receive as much as 1000 mm of rainfall per year. The dunes were first recognized on aerial photographs and later using satellite imagery. The history of the dunes has been further deciphered by the application of luminescence techniques to directly date periods of their formation. In recent years, remote sensing technology has enabled better identification of not only the major units but also the main features. Though degraded, the dunes nonetheless form a distinct and prominent feature on the plains. Besides their significance as a major tourist attraction from within and outside the region, the dunes contain fossil biota that has been used to reconstruct past hydrology and vegetation communities as well as serve as information on the paleoclimatology and paleobotany of the region.

The Jos Plateau is situated in the north-central part of Nigeria, with the highest peak at 1829 m. It is surrounded by plains on all sides. The landforms and landscapes of the plateau can be grouped into three physiographic units, namely hills and mountains, dissected terrains and undulating terrain. The Jos Plateau is drained by a radial river network, with numerous waterfalls at topographic escarpments. Regional geology includes two major structural units: an Older Basement Complex and the Younger Granites. The Basement Complex comprises intrusive igneous rocks and structures long exposed by denudation. For the Younger Granites, ring complexes are characteristic, with escarpments and massive outcrops of Jurassic granites. There are over 22 dormant to extinct volcanoes in the Jos Plateau, which occur as four series of volcanic lines named as Ganawuri, Hoss, Panyam (Sura) and Gu (Jiblik). There are two major waterfalls and three minor ones and springs on the Plateau. One of the waterfalls has hydroelectric power stations for electricity generation. Terracing-based farming, animal husbandry, tin mining, lumbering and tourism are common human activities in the plateau area.

The area covered by the Kainji dam, Kainji Lake and Kainji National Park constitutes a distinct landscape within the Nigerian scenery. The dam and lake were created along the River Niger approximately 105 km upstream from Jebba between 1964 and 1968. Though the primary focus of the dam and associated impoundment is hydroelectricity generation, other ancillary purposes are flood control, navigation enhancement, irrigation and fishery development. The lake’s annual hydrograph shows there are two peak inflows: the ‘White’ and ‘Black’ floods, occurring in September and February, respectively. Draw-down occurs from February to June. A National Park was created from two existing game reserves that were contiguous to the impoundment area. Notable geomorphological features, namely corestones, tors, ruwares, and littoral caves and crevices abound in the area. Corestones, tors and ruwares were etched out from crystalline rocks, while the caves and crevices were created by the impact of waves and seiches on headlands and promontories in the lake’s draw-down zone.

The presence of vegetation along a stream has been shown to affect a variety of biotic and abiotic processes, resulting in complex effects on stream structure and water flow dynamics. The magnitude of these effects depends on the type of vegetation, its mechanical properties and density, as well as its spatial distribution. Across rivers draining Nigeria, the riparian composition varies significantly. The southern part of the country presents more luxuriant vegetation along river courses than the northern part. However, biodiversity along river courses in Nigeria presents a scenery that is attractive to view and also serves as economic gains for the local people. River Ogun, an alluvial example that is reported in this study, largely epitomizes the situation of riparian ecosystems in the humid tropics. Typically found along this alluvial stretch are woody plants and light forests which influence riverbank stability. Morphological features like sand bars, cut banks, oxbow lakes and braided channels that have been colonized by riparian species are prominent along the reach. The natural functioning of this riparian ecosystem has over time been disturbed by sand mining, plantation agriculture and arable crop farming.

Quartzitic ridges traverse a large part of southwestern Nigeria, extending through the Oyo, Osun and Ekiti and terminating in some parts of Kwara States. Quartzites are known for their toughness, low porosity and permeability, and hence, they typically support terrain elevations. Quartzite ridges are particularly conspicuous around Ibadan township, around Iseyin and at Olokemeji. Although they occur mainly as ridges and as lines of hills, bedrock outcrops are rare because the ridges are often covered by flaggy debris due to rock weathering. Quartzite ridges are the most impressive and notable landform units in the Ibadan region. The ridges have a general width-to-length ratio of up to 1:20 or more with slope angles ranging between 10 and 21°, generally trending in the NNW-SSE direction. Their original relief has been modified by human impact, both directly due to various constructions and indirectly, leading to gully erosion.

This chapter reviews the geology and landscape of southwestern Nigeria. The basement complex rocks in western Nigeria are sources of minerals and support some tourist attractions. The first section focuses on the geology of southwestern Nigeria, while the subsections on the landscape discuss the evolution of inselbergs and pediments. Two examples of inselbergs, in banded gneiss and granite, are presented as typical tropical landforms existing as isolated hills rising abruptly above the surrounding plains, either in isolation or in clusters. Pediments, which have usually been treated in existing literature as ‘appendages’ of inselbergs and consequently received less attention, are discussed more thoroughly, with the specific focus on the pediment slope profiles at Eruwa that have developed on the undifferentiated schist complex.

The Cross River State in the south-eastern part of Nigeria hosts some remarkable landforms and resultant landscapes that have been created by a series of processes dating from the Precambrian to recent times. The Precambrian basement and associated landforms are well expressed within the Obudu Plateau and the Oban Massif, built primarily of granites and metamorphic rocks, as well as other numerous rock units. These Precambrian geologic domains bear relics of ancient geodynamics and evolutionary land-forming processes with its scenic mountain ranges, deeply incised valleys and cascading waterfalls. Also within the Cross River State are landforms associated with sedimentary rocks, typically exemplified by the karst geomorphology of the Mfamosing Formation with weathering and dissolution structures such as caves, stalactites and stalagmites, pinnacle structures, sinkholes and burrow trails.

Gully erosion occurs in many parts of Nigeria under different geologic, climatic and soil conditions, with varying degrees of severity. However, the South East of Nigeria is the major gully erosion precinct of Nigeria. This chapter describes geomorphological processes leading to gully formation in the study area and highlights various gully erosion hotspots. Major processes that lead to gully formation in the southeast are knick point formation/slumping from surface runoff, swelling and shrinkage of soil, heaving and landslide, lateral bank failure and undercutting. Gullies are formed on the major highland and plateau areas whose precipitous escarpments are formed by sandstone bedrocks (Ajali sandstones and Nanka sands). Gullies on these formations are deep (about 50 m), long (over 1,200 m) and wide (about 30 m) and usually anastomosing, while gullies formed on the lower slopes and plains that are mainly underlain by shale units (Imo, Mamu, Nsukka and Bende-Ameki Formations) are single-channel and moderate in size. Nanka, Ekwulobia, Orlu, Okigwe, Isuikwuato and Bende areas are extensively dissected by these gullies.

Human activity in the coastal zone often results in accelerated coastal erosion or accretion. The coastal zone of Nigeria stretches from the 20 km barrier island ridges, which abut directly with the Atlantic Ocean, through the tidal basins and creeks to the ferruginous sands of the Benin Formation. The 800 km coastline of Nigeria is witnessing accelerated erosion at some sections, while active accretion is dominant at other stretches of the coastline. The Victoria Beach in Lagos, the 50–75 km-long transgressive mud coast between the Benin River mouth and the Lekki-lagoon complex, and the mouths of the major drainage arteries of the coastal landscape are witnessing active coastal erosion. At the other end of the continuum, sections of the arcuate Niger Delta and protected reaches of shoreline are actively accreting. The problem of riverbank erosion at the mouths of the main drainage arteries of Nigeria rises from the impact of breaking swell waves on the unconsolidated materials of the riverbanks.

Coastal landforms have long attracted mankind to exploit and modify the coast. The lagoon system in the Lagos area runs parallel to the sea, with intricate networks of creeks in some places, creating many small and large islands which are together referred to as the Islands of Lagos. The Islands of Lagos are part of the 200 km barrier-lagoon coast of southwest Nigeria and show considerable geodiversity, including beaches, mangroves and sand. The Islands are occupied by the Lagos Megacity—the largest human agglomeration in Sub-Saharan Africa. Large population and heavy industrial facilities including ports and associated infrastructures have made the Islands one of the most stressed. The historical land–water interphase has shifted significantly, and geoheritage sites have been significantly impacted. The Lagos Harbour/Commodore Channel and the Victoria Island Bar Beach have experienced significant alteration in the last hundred years, including the construction of groynes and dredging of the Lagos Harbour entrance, leading to massive erosion and loss of economic assets. A thousand hectare of reclaimed land—the Eko Atlantic City—protected by the Great Lagos Sea Wall has emerged on the Victoria Island coast. Although the nostalgic Lagos Bar Beach may have gone forever, the sea wall is expected to finally stop erosion on the coast. However, the nature of the ultimate impact of the Great Lagos Sea Wall on the entire barrier-lagoon coast in the future is still unknown.

Urban areas are places with a unique combination of natural and human elements. Some, including Abeokuta in southwestern Nigeria, have unique geological features (geoheritage) that are important to modern society because of their scientific, educational and touristic values. In this study, the Olumo rock in the city of Abeokuta in Ogun state—a granite inselberg with a variety of minor granite landforms due to weathering and mass movement—is considered as an important geosite. The Olumo rock attracts tourists from all parts of Nigeria and other countries of the world, generating up to about $18,000 (approximately N 6.3 million) annually for the government. Given the geotourism and economic benefits associated with Olumo rock and its position in the history and development of Abeokuta city and Yoruba people of Egba extraction, the study concludes that the Olumo rock should be duly recognized, conserved and preserved as a vital geosite for sustainable tourism development in Nigeria.