PHYSICAL SETTING

Posted by on 1/29/2003 12:00:04 PM
Post Comment PHYSICAL SETTING Nigeria

Geology: Much of Benue State falls within the Benue Valley/trough which is believed to be structurally developed. During the Tertiary and possibly the interglacial periods of the Quaternary glaciation, the Benue and Niger Valleys, otherwise known as the

Benue Hotels, Markurdi
Benue Hotels, Markurdi

Niger/Benue trough, were transgressed by the waters of the Atlantic Ocean. As a result, marine sediments form the dominant surface geology of much of Benue State.

These sediments have undergone varying degrees of metamorphism. These sedimentary materials are underlain at variable depth by basement complex rocks. In the southern LGAs such as Ado, Ogbadibo and Okpokwu, the metasediments may be more than 20m thick. Benue State geology can, therefore, be broad Meta-sediments occurring in more ths 7.5 per cent of the state, associated with the Benue trough; Basement complex rocks occurring higher ground further away, particular in Kwande and the eastern part of

The meta-sediments are dominantly san stone, but also contain shale, siltstone, limestor and quartzite. On the flood plains of the Benue are Katsina Ala Rivers and other smaller rivers, alluvial deposits, comprising an assortment clays, sand, gravels and pebbles, overlie the met sediments and form the superficial geology.

phonolite, trachyte and various types of pyroclastic materials (e.g. pummic, bomb lapilli) on the surface. In Benue State, these volcanic materials are well represented in Guma LGA around Gbajimba. These volcanoes are thought to be responsible for some economic mineral formations of the area, including the salt springs.

Basement complex rocks comprising ancient igneous and metamorphic rocks, occur mainly in Kwande LGA and the eastern part of Oju LGA. The materials also outcrop in widely scattered locations as upland residuals, such as inselbergs, knolls and ruwares and underlie all of the metasediments.

The basement rocks are dominated by porphyritic granites, migmatites, diorites, pegmatites and gneisses. In much of Benue State, both the tertiary sedimentary rocks and the basement complex have been deeply weathered to produce regolith and saprolite several metres deep. These rocks are rich in solid minerals, such as limestone, baryte, coal, gypsum, salt, shales, silica, sand and kaolin which are currently being mined.

Relief and Drainage:The land is generally lowlying (averaging 100m250m) and gently undulating with occasional inselbergs, knolls, ruwares laterite capped mesas and buttes. It is only at the boundary area with Cameroun Republic in Kwande and

Old Markurdi Bridge (Commissioned in 1932)
Old Markurdi Bridge (Commissioned in 1932)

Oju LGAs that hilly terrain with appreciable local relief is encountered. Here, the terrain is characterised by steep slopes, deep incised valleys and generally rugged relief. Elsewhere, gradients average less than 4.

Such areas are made up o If interfluves, broad open valleys and flood plains , River Benue is the dominant geographical feature in the state. It is one of the few large rivers Nigeria not plagued with water falls and rapids. The KatsinaAla is the largest tributary, while the smaller rivers include Mkomon, Amile, Duru, Loko Konshisha, Kpa, Okpokwu, Mu, Be, Aya, Apa Ogede and Ombi. The flood plains which are char. acterised by extensive swamps and ponds are good for dry season irrigated farming. Elsewhere surface drainage is generally good.

Though Benue State has high drainage density many of the streams are seasonal. Also, the per manent water table in many parts of the state is very low, as a consequence of the thick overlyinc permeable metasediments and the great depth tc which weathering has reached. Hence, there is ar acute water shortage in the dry season in LGAs such as Guma, Okpokwu, Ogbadibo, GwerWes and Oju.

Climate:Benue State has a tropical subhumid climate, with two distinct seasons, namely a we af season and a dry season. The wet season which alasts for seven months, starts from April and ends ir October. There is, however, usually one or more is heavy outofseason rains in January, February o k March from EastWest line squalls. It is this early rainstorm that enables farmers to hoe their farms in preparation for the planting season that starts in March. The annual rainfall total ranges from 1,200mm1,500mm.

Temperatures are generally very high during the day, particularly in March and April. Along the river valleys, these high temperatures plus high relative humidities produce inclement/debilitating weather conditions. Makurdi, the state capital, for example, records average maximum and minimum daily temperatures of 35C and 21 C in summer and 37C and 16C in winter, respectively.

Soils and Soil Erosion: The soils are mainly oxisols and ultisols (tropical ferruginous) which vary over space with respect to texture, drainage, gravel

Benue State University,Markurdi
Benue State University,Markurdi

content, etc. A typical profile is highly weathered with a sandy surface layer overlying a clay mottled subsoil. In the southern part of the state, around Vandeikya, Oju, Obi, Oturkpo, Ogbadibo LGAs, well developed lateritic profiles with pallid zones exist. Deep seated lateritic crusts occur over extensive areas on the plains.

The agronomic significance of this subsoil crust is that it often produces a perched water table which is an important source of capillary water, which keeps the surface moist long after the end of the rainy season. Entisols and inceptisols also occur associated with young soils on hill slopes and recent alluvium on flood plains. Around Gbajimba in Guma LGA, Euthropic Brown Earths occur associated with the volcanic parent materials.

Sheet erosion is the dominant form of water erosion in the State. Deep gullies occur in Ogbadibo LGA and represent a northern extension of the eastern Nigerian, metasedimentary deepgully system. Other gulled areas in the state include Makurdi North Bank area, TseMker and Gbem in Vandeikya LGA, Gbajimba town, stream bank erosion in Gboko town, incised streams on sloppy ground coterminous to AnwaseKyogenAbande ranges in Kwande LGA.

Vegetation:Benue State lies in the southern Guinea Savannah. Persistent clearance of the vegetation has led to the development of regrowth vegetation at various levels of serai development, but more importantly, parklands with grasses ideal for animal grazing during their early growth. These succulent grasses can be cut with machinery, dried and baled for dry season livestock feeding.

Benue Cement Complex,Gboko
Benue Cement Complex,Gboko

The grasses however grow very tall, coarse and tough on maturity. The scattered trees are mainly those of economic value and include locust bean, shear butter, mango, silk cotton, African iron, Isoberlinia, cashew, oil palm, Daniellia Oliveri, gmelina, et cetera. These trees produce valuable fruits, wood and fibre which can be utilized for smallscale cottage industries.

In the southern part of the State, particularly in Oju, Ado, Obi, Ogbadibo and Okpokwu LGAs, the veaetation is mainlv oil calm bush The oil oalm is utilized for its palm oil, palm kernel, palm wine, broom sticks and several other products. Dense forests are few and far apart, except in a few LGAs such as Vandeikya, Kwande and Okpokwu.

Generally, forest vegetation may be grouped into: village forest; gallery forests; and forest reserves. In these forests, typical rain forest trees such as mahogany, Obeche, Iroko, . Afara, etc. occur and are used for timber. Other economic trees in these forests include African . pear, ogbono, bamboo, raffia palm, oil palm, orange and coconut.




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