To what extent have human activities been responsible for the occurrence of landslides in East Africa. 

Candidates should define landslides as:

Landslide is a Fast/rapid/sudden movement of weathered materials of rocks from the upper to the lower slopes under the influence of gravity.

Candidates should identify highland areas in East Africa where landslides occur and they include; Kenya highlands, Kilimanjaro highland, Southern Tanzania highlands, Rwenzori highlands, Kigezi highlands, Mt Elgon etc.

Candidates should identify the various farms/types/processes of landslides.

• Talus creep: Movement of angular particle screes of all sizes down a moderate slope at a moderate/fast speed
• Mudflow: Movement of semi-liquid mud with gravels, boulders on moderate to steep slopes at a fast speed.
• Rock slumps: Movement of large masses of rock materials ar1d debris on over steepened slopes/cliffs/scarps/roads cuttings at a fast speed.
• Rockslide: Rapid movement of large masses of detached rock particles/debris rolling down at a fast speed along a slippery over steepened slope.
• Rock fall: Free fall of individual rocks and boulders down very steep slopes/vertical slopes at very fast speed.
• Avalanches: Sudden downfall of rock materials embedded in ice and snow on steep slopes.

Candidates should hen explain human activities responsible for occurrence of landslides which include:

• Construction of roads, settlements etc. in highland/hilly areas which leads to cliffs that encourage rock slump, rock fall and rock slide.
• Mining and quarrying that involves use of explosives that cause vibrations, steepening and exposing slopes triggering rock slide, rock fall, mud flows etc.
• Poor agricultural methods like up and down ploughing makes unconsolidated soils and weathered rock materials to move down slope in form of mudflow, rockslide, rock fall etc.
• Deforestation along slopes leaving the slopes bare exposing it to rain water which encourages mud flows, rock slump.
• Overstocking and overgrazing on the steep slopes loosens the rock structure leading to slumping and mud flow. This may be due to exposure of the soil/rock material and trumping of animals.
• Movement of heavy vehicles, trailers, buses and trains cause vibrations along road cuttings and steep slopes that encourage rock slump, rock fall e.g. Kabale – Kisoro road, Simu- Kapchorwa road etc.

Candidates should then bring out other factors:

Climate:

• Heavy rainfall avail water that saturates rocks and weathered material making it heavy and also lubricates the slopes resulting into mudflow, rock slump etc.
• Pounding effect of heavy rainfall destabilizes surface layers of rocks triggering movement of rocks and weathered materials under influence of gravity.
• Temperature changes that lead to alternate freezing and thawing makes the ground slippery and water made available increases weight leading to mud flows, talus creep, rock fall and avalanches.

Relief/Topography

• Very steep slopes encourage rock fall
• Over steepened scarps, cliffs and road cuttings encourage rockslide, rock slump, avalanches.
• Steep slopes encourage rock slide, mud flow and avalanches.
• Moderate to steep slopes encourage mud flow and talus creep.

Nature of the rock

• Permeable weathered rocks overlying impermeable rods absorb water, get saturated. overloaded and lubricated encouraging mudflow and rock side and vice-versa.
• Well jointed rocks may encourage landslides in form of rock fall, rock slides, avalanches etc.
• Alternate layers of hard and soft rocks also cause landslides in form of rock slump/ rock slides etc.

Nature of the soil:

• Heavy wet massive clay soils encourage landslides when they absorb water, the weight increases, become lubricated, are much slippery thus leading to mud flow.
• Earthquakes and earth tremors cause vibrations that trigger off landslides like rock slump, rock slide, rock tall etc.
• Tectonic movements like faulting, warping create steep slopes, cliffs and escarpments that encourage rock slide, rock fall etc. While vulcanicity involving basic lava flows down slope mixed with ashes promote rock slump, mudflow.
• Over steepening of slopes as a result of undercutting at the base of river cliff/sea cliff/ Lake cliff lead to landslides like rock slump.
• Over loading/accumulation of rock debris in large masses on over steepened slopes promote landslides.
• Additional weight from materials or rain water promotes overloading hence rock slump, rock fall, mud flow.
• Living organisms like burrowing animals loosen the soil/rocks allowing water hence overloading and lubrication encouraging rock slump, rock slides and mud flow while movement of animals cause vibration that encourage rockslides, rock slump etc.