PHYSICAL SETTINGPost Comment PHYSICAL SETTING Nigeria
Geology and Relief: The geology of Yobe principally comprises crystalline and sedimentary rocks, underlain by basement complex rocks. The crystalline rocks are represented by older granites found in pockets of places in the southern part of the state. Another crystalline rock formation of younger age is located in the northwestern tip of the state in the Machina area.
The Emir's Palace, Gashua
The older granite is Pre cambrian in origin consisting of metamorphic struc tures of gneiss and amphibolites. The younger granitic rocks are of Jurassic period, deposited between 195 and 135 million years before the present. The sedimentary rocks that are found in most parts of the state were uncomfortably deposited on the basement crystalline rocks.
In the southern fringe of the state, the sedimentary deposits are made up of the cretaceous Bima, Pindiga, Fika and Gombe formations. The Karekare formation is also found in this part of the state. However, in the greater part of Yobe, alt these sedimentary formations were uncomfortably overlaid by a large expanse of Quaternary Chad formation that stretched into Jigawa and Borno States.
The Biu basalts found in the southern end of the state are believed to have been extruded during the Tertiary/Quaternary periods as lava flows. However, the influence of climatic fluctuations is reflected in the superficial deposits overlaying most of Yobe State. This, for instance, has led to the deposition of series of longitudinal and traverse dunes around Yunusari, Yusufari, Machina, Geidam and Bade local government areas.
The Central Mosque, Gashua
They run in a northeast to southwest direction in response to the prevailing wind direction. Yobe State generally lies between 300m and 600m above sea level, except in the southern part of the state where volcanic rocks occur. The rock formation also contains waterbearing aquifers from which much of the water supply in the state is derived. The River Yobe, from which the state derived its name, is the biggest river in the state. It flows eastwards and drains into Lake Chad. It has a few tributaries, one of the most important being River Alkalam, where the famous yearly Bade fishing and cultural festival takes place.
Climate: The climate of Yobe State is hot and dry for most period, of the year. The mean temperature for most stations in the state is about 37°C. The highest temperature (about 42°C) is normally experienced in April, while minimum temperatures (about 30°C) are usually recorded in December. (lloeje, 1977). The State exhibits a remarkably high annual range of mean monthly temperatures.
For example, Nguru shows a mean maximum temperature of 30.8°C in August and 39.8°C in April and mean minimum temperature of 12.1°C in January and 29.1°C in June. The effect of continentality is clearly brought out from the above means. Rainfall in Yobe State decreases both in dura tion and amount from place to place. Generally, it lasts for about 120 days in the northern part of the state and more than 140 days in the south.
There is a marked dry season of between eight to nine months and a wet season of only three to tour months. Rainfall in the state is highly irregular in space and time, which makes farming difficult since small differences in the amount and timing of rain received at a site may determine the success or failure of critical stages in vegetation development and hence crop production. The development of agriculture would, therefore, effectively depend on irrigation farming especially in the drier parts of the state.
Soil: Soils play an important role in the devel opment of Yobe State. The soil in most of Yobe State is derived from drift
Cattle Market, Potiskum
materials which vary in textural characteristics, but are mainly silt clay or clayey. The profile of the soils is poorly developed, and it has a low water retention capacity (Price, Justice and Los, 1990).
The productivity of the soil is greatly impaired due to lack of adequate vegetation cover to supply organic matter. Wind erosion poses a serious threat to the quality of soil in the active areas of the north. It has been observed that the windblown fine soil particles have nutrients essential for plant growth. Alluvial soils are also found in the major river valleys, such as the Yobe, and are suitable for the cultivation of crops like rice and wheat, around Gashua.
Vegetation: There are two vegetation zones in the state. These are the Sahel in the north and the Sudan Savannah in the south.
Yobe Flour Mills Complex, Potiskum
Vegetal cover is sparse as the grass grows in individual tufts leaving bare surfaces inbetween. The grasses in the Sahel are short and tussocky, 0.5m to 1.0m high. They are interspersed with sand dunes are the most common types here.
The acacia is a thorny, narrowleafed tree, fairly short and some times umbrellashaped. In the Sudan Savannah, the actual vegetation is made up of short grasses, 1.5m to 2.0m high, and some stunted tress. Typical trees include the aca cia, dum palm, silk cotton and baobab. The baobab stores water in the trunk like a sponge and it draws water from this source during the dry season. It has short and undersized branches shooting out from the head of a fat juicy trunk.
The dum palm has tall straight branches and fan shaped foliage. The silk cotton tree is the tallest of the group, and grows to a height of 9m to 15m. It is from this tree that silk cotton, which is used for making local mattresses and pillows, is obtained. The vegetation is also exploited for a number of medicinal and other purposes. Most of it is now exploited as firewood, and for thatched roofing and mat making. Deforestation has now made the environment vulnerable to desertification. Tree planting campaigns are launched yearly by the state government to reforest the environment.
Ecological Problems: The increasing inci dence of desertification is the most disturbing eco logical problem faced in Yobe State. Wind Erosion is found to aggravate the problem by creating sand dunes in the northern parts of the state, especially in Yunusari, Yusufari, Geidam, Nguru and Machina areas. Today, the lives of the people living in these areas are seriously threatened such that the trend in migration is southwards.
The poor management of the fragile land resources through deforestation, overgrazing, overcultivation, bush burning, and adverse climatic conditions are identified as some of the factors responsible for the growing menace of desert encroachment. In the most affected parts of Yusufari and Yunusari areas, for example, it is difficult to maintain any definite track of vehicular movement, due to the increasing impact of the dunes.
Thus, the construction of modern roads is least considered in such an environment. The marginal fertile lands of TuloTulowa are often overcul tivated. Loss of soil nutrients, resulting from the action of wind erosion, has been commonly reported in the desert prone areas of the state.
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