BEG+4218+REGIONAL+GEOLOGY+OF+EAST+AFRICA

- **Welcome to the class of Regional Geology of East Africa January April 2017** - **Our mode of study will be F2F and On-line** - **This is blended mode** - **WELCOME** - **Dr. Kennedy Obiero will be your facilitator**
 * BEG 4218 REGIONAL GEOLOGY OF EAST AFRICA **


 * INTRODUCTION TO LESSON ON 11/4/2017 **
 * Hallo my dear students, **
 * We agreed on 4/4/2017 that we were to meet during the **
 * revision week on 11/4/2017 at our usual room NC 2 from 7.00 – 10.00 a.m. **
 * I came late by 7.30 a.m. and found no student. **


 * Download this material by copying and pasting in word. **
 * Print and read off-line. **
 * This is what we were supposed to cover during the revision **
 * Class. **


 * During exam, ensure you come with your complete **
 * Assignments. **


 * Thanks **
 * DR. KENNEDY OBIERO – YOUR UNIT FACILITATOR **


 * (NB THE OTHER MATERIALS I HAVE PUT THEM IN CLASS e-mail**


 * __ LESSON CONTENT __**

- **Processes operating on the earth’s surface ** - **Driven by solar energy and force of gravity ** **Erosion ** - **One process of denudation involving wearing away the earth’s crust ** - **It is an exogenic process ** - **By wind, water, glacier and waves ** - **Agents of erosion ** (a) **Wind ** (b) **Water ** (c) **Glacier ** **- Water is the most destructive in East Africa ** - ** River Erosion ** – vertical and lateral erosion. - Water draining downhill does a lot of erosion leading to formation of - erosional features such as:
 * LESSON 7 BEG 4218 REGIONAL GEOLOGY OF EAST AFRICA**
 * EXOGENIC PROCESSES IN EAST AFRICA**
 * Exogenic Processes, Associated Landforms and Desertification **
 * 1) **Erosion e.g., in deserts – features **
 * 2) **<span style="color: #ff0000; font-family: "Calibri","sans-serif";">Weathering **
 * 3) **<span style="color: #ff0000; font-family: "Calibri","sans-serif";">Slope processes – mass movement **
 * 4) **<span style="color: #ff0000; font-family: "Calibri","sans-serif";">Transportation **
 * 5) **<span style="color: #ff0000; font-family: "Calibri","sans-serif";">Deposition – features **
 * 1) Interlocking spurs in upper course of a river
 * 2) V-shaped valley
 * 3) Rapids and Water falls

River Erosion – If erosion continued long enough, mountains will be flattened into plains – __peneplains – peneplanation__ <span style="font-family: "Times New Roman","serif";">- Several areas in East Africa eroded to near ly-level plains. <span style="font-family: "Times New Roman","serif";">- Some 100 million years old <span style="font-family: "Times New Roman","serif";">- Examples of such erosional surfaces are in central and northern Uganda <span style="font-family: "Times New Roman","serif";">- Around Voi in Kenya near Sultan Hamud <span style="font-family: "Calibri","sans-serif"; font-size: 14.66px;">- Central Tanzania

Deposition leads to: <span style="font-family: "Times New Roman","serif";">- Aggradation process <span style="font-family: "Times New Roman","serif";">- Takes place at the lower reaches of a river. <span style="font-family: "Times New Roman","serif";">- Stream energy has decreased <span style="font-family: "Times New Roman","serif";">- Low gradient of a river <span style="font-family: "Times New Roman","serif";">- Depositional features formed: (i) Braided channels (ii) Meanders (iii) Ox-bow lakes (iv) Alluvial Fans etc (v) Deltas eg River Rufiji delta in Tanzania Erosion in Desert areas
 * Deposition Process and features **

Wind erosion major agent of erosion in Arid /desert areas

Reasons:


 * 1) Flat topography wind moves at high velocity
 * 2) Limited or no vegetation – no wind breakers
 * 3) Limited or no soil moisture – loose soils


 * Features of Erosion in Desert areas **

Wind erosion major agent of erosion in Arid /desert areas

Features include:


 * 1) Depression hollows – oases
 * 2) Zeugens
 * 3) Yardangs
 * 4) Rock pedestals
 * 5) Mushroom blocks among other


 * Depositional Features in Desert areas **

<span style="font-family: "Times New Roman","serif";">- **Seif dunes**

<span style="font-family: "Times New Roman","serif";">- **Barchans** <span style="font-family: "Times New Roman","serif";">- Semi-arid areas gradually becoming desert-like Reasons:
 * Desertification **
 * 1) Natural factors such as erosion
 * 2) Climate change
 * 3) Over-cultivation
 * 4) Over-grazing
 * 5) Cultivation in marginal areas
 * 6) High population in ASALs

Weathering <span style="font-family: "Times New Roman","serif";">- Weathering : Breakdown/disintegration of rocks in-situ – with little or no movement <span style="font-family: "Times New Roman","serif";">- __Types of Weathering__ <span style="font-family: "Times New Roman","serif";">- Three types of weathering <span style="font-family: "Times New Roman","serif";">- Breakdown due to temperature changes <span style="font-family: "Times New Roman","serif";">- No change in chemical composition of rock <span style="font-family: "Times New Roman","serif";">- Ice also cause physical weathering (frost action) 2. Chemical Weathering <span style="font-family: "Times New Roman","serif";">- Breakdown due to chemical alteration of rocks <span style="font-family: "Times New Roman","serif";">- Changes the nature of the rock itself <span style="font-family: "Times New Roman","serif";">- Depends on the mineral composition of the rock <span style="font-family: "Times New Roman","serif";">- Types of chemical weathering – solution, <span style="font-family: "Times New Roman","serif";">- carbonation, oxidation, among others 3. Biological Weathering - Breakdown due to effects of plants and animals <span style="font-family: "Times New Roman","serif";">- Roots of plants widen cracks in rocks and disintegrate them. <span style="font-family: "Times New Roman","serif";">- Decaying vegetation release chemical substances that break down rocks Debate on this type of weathering as – physical and chemical weathering
 * 1) Physical/mechanical weathering

<span style="font-family: "Times New Roman","serif";">- Divided into two: 1. Endogenic factors – factors related to the nature of rock itself (a) __Structure of rocks__ – presence of lines of weakness in rocks such as bedding planes, cracks, joints weaken rocks. - Act as foci for weathering processes (b) Texture of the rocks – smoothness of rocks – size of particles. Large – low weathering. Small – high weathering (c __) ** Mineralogical composition **__ – rocks made of different minerals - Rocks made of iron – oxidation, Limestone rocks – carbonation, Rock salt - solution 2. ** Exogenic Factors ** – environmental factors influencing rocks (a) __Climatic factors –__ more rain and high temp – high rates of weathering (b) __Slope –__ steep slopes high rates of weathering
 * Factors Influencing Weathering **
 * (c __) Vegetation__ ** __–__ expose rocks to physical disintegration (roots) and chemical disintegration (decaying vegetation)
 * (d) Human activities ** – quarrying, construction of roads, buildings among other engineering works

Significance of weathering


 * 1) Formation of soils as rocks break down
 * 2) Weakens foundations of buildings
 * 3) Statures among other structures are weathered
 * 4) Formation of valuable minerals
 * 5) Formation of features that attract tourists

<span style="color: #00b0f0; font-family: "Times New Roman","serif";">Slope Processes <span style="font-family: "Times New Roman","serif";">: This is also known as mass movement <span style="font-family: "Times New Roman","serif";">- Materials move down hill in response to force of gravity <span style="font-family: "Times New Roman","serif";">- Make slopes unstable <span style="font-family: "Times New Roman","serif";">- Landscape is a mosaic/combination of slope <span style="color: #00b0f0; font-family: "Times New Roman","serif";">Factors affecting slope stability <span style="font-family: "Times New Roman","serif";">(a) Angle of slope – the higher the angle, the higher the degree of instability <span style="font-family: "Times New Roman","serif";">(b) Climate – during rains, slope are very unstable causing landslides <span style="font-family: "Times New Roman","serif";">(c) Nature of slope materials – wet and loose materials make slope very unstable <span style="font-family: "Times New Roman","serif";">(d ) Tectonic forces – earthquakes will make slopes unstable <span style="font-family: "Times New Roman","serif";">(e) Climate – slopes very unstable during rains and vice versa <span style="font-family: "Times New Roman","serif";">(f) Human activities – e.g., quarrying, construction among others weaken slopes <span style="color: #ff0000; font-family: "Times New Roman","serif";">Why Study Slope? <span style="font-family: "Times New Roman","serif";">1. Slopes are associated with hazards such as rock falls, land slides – kill people <span style="font-family: "Times New Roman","serif";">2. Steep slope accelerate erosion <span style="font-family: "Times New Roman","serif";">3. Construction of buildings and other structures influenced by slope <span style="font-family: "Times New Roman","serif";">4. Influence rock disintegration <span style="font-family: "Times New Roman","serif";">5. Soil and water conservation influenced by slope <span style="color: #ff0000; font-family: "Times New Roman","serif";">Conclusion <span style="font-family: "Times New Roman","serif";">Exogenic process change or even modify features of endogenic processes
 * <span style="font-family: "Times New Roman","serif";">Volcanic features
 * <span style="font-family: "Times New Roman","serif";">Fault features
 * <span style="font-family: "Times New Roman","serif";">Fold features all affected by weathering.
 * <span style="font-family: "Times New Roman","serif";">Rocks are highly affected by exogenic processes.
 * <span style="font-family: "Times New Roman","serif";">Exogenic processes lead to formation of various landforms