Presentation on theme: "Geography seminar at UMSS Namugongo By : Kembabazi Gloria and Kisakye Irene Henrietta."— Presentation transcript:
Geography seminar at UMSS Namugongo By : Kembabazi Gloria and Kisakye Irene Henrietta
QUESTION EXPLAIN THE INFLUENCE OF WEATHERING ON LANDFORM DEVELOPMENT IN EAST AFRICA.
QUESTION APPROACH: INTRODUCTION: Define weathering, identify the types of weathering, effects…… MAIN BODY ( EXPLANATIONS and I LLUSTRATIONS ): Explain the features formed under each type giving clear examples in East Africa CONCLUSION : Write a conclusion
DEFINITION Weathering is the chemical decomposition of rocks or mechanical fracturing and break down of rocks to form small particles at or near the surface of the earth insitu.
There are two main types of weathering: Physical and Chemical Physical involves rock disintegration without changes in chemical composition. It is also known as mechanical Weathering
Chemical is one that involves changing the chemical composition of the rocks and some of the rocks may suffer decay. Biological weathering involves plants and animals and may aid the processes of physical and chemical weathering.
Physical weathering processes includes: granular disintegration, block disintegration, crystal growth, pressure release, freeze and thaw action and aridity shrinkage.
Chemical weathering processes includes: hydration, oxidation, hydrolysis, carbonation, chelaition, spheroidal and solution.
LATERITE FORMS : These are wide spread rock like fossilized crusts in tropical Africa. They are relic of ancient phase of soil formation composed of highly weathered rock minerals concentrated in thick layers(2m- 12m thick).
These include; ferricretes-iron and silica, silicrete( bauxite - aluminium ) for example in Buganda, they are about 9meters thick.
Cemented by wetting, drying and heat to form hard rock. Iron compounds are organically produced in swamps by capillary action on rotten or decayed rock for example Conditions: low relief, heavy rainfall, dry season, top soil removal, flat-topped hills.
INSELBERGS: These are isolated hills that stand prominently above a leveled surface. They are common in arid areas like Nakasongola, Mubende, Soroti in Uganda, Voi in Kenya and Sukuma land in Tanzania. These include the following;
a)Tors: These are ridges of spheroidically weathered boulders normally of granite and surrounded by weathered debris due to chemical rotting along joints below the surface.
At high points they are called skyline tors and on hills and depressions, sub-skyline tors they may be 20meters to 30 meters thick and 3m to 8m in diameter.
b)Castle kopjes: These are rock piles that have suffered little spheroidal weathering. They are steep sided massive crystalline boulders that are cube like and blocky. They have a castle like profile and kopjes means hill as illustrated below:
The are found in the dry corridor of Tanzania, North eastern Kenya, Teso, Lango and North eastern Uganda.
c) Bornhardt (domed inselberg) They are prominent dome shaped hills in platonic- igneous or metamorphic rock areas. They are common in humid or semi desert areas for example inselberg corridor in Tanzania.
The stripping exhumation theory explains that they are formed by the increased removal of the regolith by weathering leaving isolated hills.
The Lester king’s scarp retreatment theory explains that they were formed by lateral retreatment of valley side leaving a remnant inselberg.
ETCH PLAIN This is an extensive rock studded plain common in tropical and semi arid region. It is formed at two levels,the surface and some level below the surface. It is formed by the gradual lowering and stripping of the regolith.
The different types of etch plains include: laterised, dissected, partly stripped, stripped and incised.
KARST LANDSCAPE These are found in lime stone and dolomite areas for example Hima, Tororo, Fort Portal, Mombasa- Bamburi. These include:
a)Cave : is a chamber in the rock found underground. It is formed by solution when ground water dissolves and forms cavities by attacking joints and bedding planes together with mechanical erosion by underground streams and occasional rock collapse.
b ) Stalagmite : is a mass of crystalline calcium carbonate growing upwards from the floor of the cave. It forms as water sips through cracks in the rocks and drips from the cave ceiling to the floor.
d) Pillars : this is when a stalagmite and stalactite meet either accidentally or the stalagmite grows upwards until it reaches the ceiling for example in Kiomoni and kange on either side of Mukulumuzi valley in Tanzania.
e) sinkholes : these are deep holes with nearly vertical sides leading to an underground cave system, as a result of surface solution and subsurface collapse. It is a sink where a river disappears underground and is lost from the surface.