Geology: Enugu State occupies much of the highlands of Awgu, Udi and Nsukka. The hills are flanked by the rolling lowlands of OjiRiver, Adada and Anambra Basins to the west, and the Ebonyi (Aboine) River Basin to the east. The area contains about nine geological formations.
Caged Lion in Enugu Zoo
From east to west, and in terms of age and sequence of expo sure, the formations are: . The Asu River Group of the Albian (Lower Cretaceous) Age, made up of shales, sandstones and siltstones.
The sediments later became folded, giving rise to the Abakaliki anticlinorium and the related Afikpo synclinorium both within the present Ebonyi State, as well as the syclinal basin lying between the Niger and EzeAku shales formation of the Turonian Age which contains shales, siltstones, of sandstones and limestones.
AwguNdeaboh Shales Formation of the ie ConiacianSantonian Age. Enugu Shales (to the North) and Awgu Sandstones (to the South) along the ie same axis. They were laid in the Campanian substage. Lower Coal Measures Formation (Mamu reFormation) of the Meastrichtian Age.
This is the coalbearing formation. Falsebedded Sandstones Formation si (Ajali Sandstones) also of the e Meastrichtian Age. The body of the sand stone is thick, friable and poorly sorted. Upper Coal Measures Formation (Nsukka is Formation) of the Nadian Age.
The formation consists of coarse sandstones or with shale intercalations and fragments of iron stones and ferruginized shales and nt sandstones. It abounds extensively on ct the UdiNsukka Plateau where differential the erosion has left the resistant portions n standing out as rounded, conical, domey, is cuestalike, elongated and sometimes a flattopped hills, some hundreds of of metres above the general level.
These a Upper Cretaceous Sediments were prob p ably uplifted during the Tertiary formation, giving rise to the EnuguOkigwe escarp ment. is 8 Imo ShaleClay Formation of the of Pleistocene Age. It is about 1,000 metres In thick and overlies the Upper Coal Je Measures conformably. , Alluvium Deposits which belong to the ia Recent Age. In Enugu State, this formation occurs farthest to the northwest, and . belongs to the NigerAnambra flood plain (Ofomata, 1975).
Relief and Drainage: All the formations trend generally north to south, and various prominent ja landforms and related features have been carved iyi out of them. The prominent landforms include the is NsukkaOkigwe cuesta which, in Enugu State,
University of Nigeria, Nsukka
is to made up of two distinctive features the Enugu and Awgu Escarpments and the UdiNsukka Plateau.
The scarpface of the cuesta landforms is formed by resistant sandstones of the Lower Coal Measures, while the less resistant Falsebedded Sandstones , form the gentler upper slopes and the crest. The escarpments are very much indented by deep river to valleys, and intense gullying has taken place at the it headwaters of most of the streams. ie To the west and southwest of the Nsukka Plateau falls gently towards the lowlands along the Niger and Imo rivers. The plateau is very extensive, some 48km wide in
Nsukka area and 16km in Udi and Awgu. Apart from the residual hills, the Plateau is also charac terised by low density of drainage and wide, flat bottom dry valleys. The dry valleys are thought to be former normal river valleys that later got dried up by infiltration into the Falsebedded Sandstones.
Climatic change is another cause of dry valleys but, in the case of progressive migration of the Enugu Escarpment, the alternative cause may be the pro gressive migration of the water table caused by gul lying and ravination. Enugu State is drained by one main river sys tem the Anambra Mamu River System in the west.
The AnambraMamu River drains extensive areas of UzoUwani Local Government Area in the north west and Awgu in southwest. For most of the rainy season the UzoUwani lowlands in particular, are completely covered by floods. The impeded drainage of the soil provides a good environment for specialised agricultural practices, especially rice and yam production, and fish farming.
Soils and Soil Erosion: The soils are made up of shallow and stony lithosols found on the steep slopes of the cuesta and often left uncultivated, the ferrallitic soils, also called Red Earth or Acid Sands, found on the plateau, and the hydromorphic soils of the flood plains.
Soil erosion, both from physical and manmade causes, is rampant in several parts of the state. It shows in rills along roadside embankments, in sheet wash across compounds and farmlands, and in gullying, sometimes very dramatic, along definitive channels and zones.
Coal Mine, Iva valley
The major gullies are concentrated on the edges of the highly friable sandstones which yield easily to erosion and induce gullying even on slopes as low as 5°. About 65 per cent of the entire area of Enugu State is affected by sheet erosion.
Vegetation: The vegetation on the highlands of Awgu and stretching through its rocky promonto ries to link with the undulating hills of Udi, is of the semitropical rainforest type. It is characteristically green and is complemented in the Nsukka area by typical grassy vegetation. Fresh water swamp forests occur in the NigerAnambra Basin.
Climate: The climate is comparatively congenial, and particularly equable in the hilly and ecolog ically transitional region of Nsukka. The mean monthly temperature in the hottest period of February to April is about 33°C and the annual rain fall ranges between 152 to 203cm. The rain is almost entirely seasonal, most of it falling between May and October.
Ecological Problems: There are a number of ecological problems. Apart from soil erosion, there are the hazards of excessive sandiness in the EzeaguUdi corridor, and rainfed massive floods of UzoUwani area. Deforestation constitutes a man made hazard that has adversely affected ecological balance and agricultural prospects in the state