brown and gray mountain with white smoke

EFFECTS OF CONTINENTAL DRIFT

Most of the relief features are related with continental drift due to the fact that forces such as tensional and compression forces affected many parts of the world. Features which have been formed as a result of continental drift include; rift valleys, basins, plateau, highland ranges, coastal plains and associated features, block mountains etc.

A rift valley is one of the spectacular features associated with continental drift. This is an elongated depression bordered by two in facing escarpments. It is formed due to either compressional forces or tensional forces or through differential uplift theory, basin and swell theory and the sea floor spreading theory.

Plate tectonics also caused the vertical movement of the crust which led to the formation of Block Mountains. A block mountain is also known as a Horst. It is formed when the middle block bounded by more or less parallel faults is made to rise or is uplifted by the compressional forces. The best example of a block mountain in East Africa is mount Rwenzori, also known as the mountain of the moon. Others include Mathews and Nyiru, Ndoto in Northern Kenya.

Plate tectonism also led to the formation of down warped depressions which are indirect effects of faulting for example warping of central Uganda thus the formation of lakes Victoria and kyoga.

Plate tectonism also led to the formation of volcanic landforms due to radio activity and geo chemical reactions which create a lot of heat that melt the mantle and asthenosphere rocks.  

Landforms due volcanic activity are;

Volcanoes: – These are hills or mountains formed when magma erupts and piles up around the vent until a cone is formed. There are basically four types of volcanic cones.  

Ash/cinder cone: – These are small but steep sided hills formed when explosive eruptions throw lava high into the air, breaking up lava into small fragments or pieces known as Pyroclasts (fire rocks). The erupted materials build up or accumulate around the opening known as vent; layer after layer forming steep sided cones of about 150 metres high. Examples in Kenya are Suswa and Menengai hills and Teleki hills south of Lake Turkana and Longnot. The hills are characterised by a large crater /caldera at the top because of violet eruptions.

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Crater: – This is a circular depression on top of at top of volcano.
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Caldera: – This is an enlargement of a crater as a result of violent eruption. Examples are found on menengai, suswa, longnot in Kenya, Napaka, and elgon in Uganda, Ngorongoro in Tanzania.
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Explosion craters: – These are found in lowland areas Explosion craters are flat floor depressions formed when explosions eruptions of gases blow off the rocks at the surface leaving a shallow circular depression, depressions are filled with water to form explosion crater lakes. Examples are; L. Katwe, L. Nyamunuka, L. Munyanyang, L. Saka, and Kyegere and others. Found in western Uganda, in Kasese, Kabalore and Bushenyi districts.  

Basic lava cone/shield volcano – This is a hill with gently sloping sides. It’s formed when hot fluid lava, with low silica content, flows from one or two faults in a quiet eruption. It spreads out in flat layers. The layers build up a broad volcano with gently sloping sides, shaped like a shield and hence the nameshield volcano. It’s common in Uganda- Rwanda boarder along the Nyamuragira ranges.

Acid lava dome: – These are doom shaped hills, thick lava rich in silica content, solidifies quickly on reaching the surface, forming a volcanic dome or cone of viscous lava, an example is sernal volcano domes in Tsavo national park in Kenya.  

Volcanic plug: – The thick lava (viscous) lava, at times solidifies in the vent, after prolonged erosion, the plug is exposed to the surface of the earth due to erosion. Examples are the Tororo rocks in Eastern Uganda.  

A composite cone: – A composite cones are large mountains formed when volcanic eruptions alternate between quite and violent eruptions. An exposure period releases gas and ash and cinder layers. Thenthe eruption changes to a quite period erupting lava over the top of ash layer, when the cycle of ash and lava is repeated over and over in alternating layers, a composite volcano is formed. At times lava is diverted sideways from the vent forming dykes, Corrects or parasite cone. Examples are Mt. Kenya, Kilimanjaro in Tanzania, Muhabura in South west Uganda.

Lava plateau: – This is formed as a result of quite eruptions, when lava moves out slowly along cracks/faults .the lava fluid lava flows for a very long times on the plateau before it solidifies, forming lava plateau. Examples are; Kisoro lava plain in Uganda, Yatta, Laikipia and Turkana plateau in Kenya.

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Hot springs /geyser:-These are features produced when heated water in volcanic areas flow out queitely in form of hot springs or erupt periodically shooting out water /steam in the air. Examples – Katagata in Bushenyi, Sempaya in fort portal, Majimoto in Tanzania, Majiyamoto in Kenya.

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Lava dammed lakes: – these are formed when lava blocks channels. Water pools behind leading to formation of lakes. Examples are L.Bunyonyi and L. Mutanda in southwest Uganda.  

INTRUSIVE FEATURES

These are formed when magma solidifies underground. Magma forms in many different shapes and sizes, the most common are: –

1. Batholiths: these are mostly massive rocks. They are dome shaped, formed at great depth and at times they are exposed at the surface by denudation forces as inselbergs. Examples are Mubende hills, parabong and labwor hills in Acholi, Mumias and Kisi batholiths in Kenya.  

2. Dykes: – These are formed when magma solidifies into vertical cracks, cutting across rock layers. When affected by erosion dykes may stand as a ridge. There are ridges in most of Turkana and Sukulu hills South of Tororo town.  

3. Sills: – These are formed when lava solidifies in between rock layers, after prolonged erosion, Sills may be exposed as escarpments and while they occur across a river valley they cause waterfalls and rapids. Examples are Thika and Thompson falls in Kenya, Karuma falls and Bujagali in Uganda.  

4. Laccoliths: – this is magma which solidifies in a shape similar to a mushroom. After prolonged erosion, it may form upland.  

5. Lapoliths: – This is saucer shaped magma, after erosion. It can be exposed as a shallow basin. Examples are Arenas in Ankole.

Continental drift has also been responsible for the formation of different types of lakes such as down warped lakes like Kyoga and Victoria, rift valley lakes like Lake Albert, Tanganyika, Malawi etc

It has also influenced the formation of swamps especially in areas associated with gentle gradients due to down warping. Fault guided valleys have also been formed like Aswa valley in Northern Uganda. Plateaus have also been formed and these include; Northern Uganda plateau, Central and south western Tanzania plateau, The west central Tanzania plateau, Lake Victoria plateau and central eastern Tanzania

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