Mass Movement

Mass movement can be defined as the movement of weathered materials (regoliths) on slope under the force of gravity. It can also be referred to as the movement of rock materials from one place to another under the influence of gravity.

Factors Affecting Mass Movement

These are factors that affect mass movement:

• Gradient of the slope
• Human activity
• Natural and weight of materials
• Pressure of lubricating moisture
• Presence of vegetation

1. GRADIENT OF THE SLOPE: The gradient of the slope is one of the most important factors that affects mass movement. For example, rock materials move faster in steep slopes or hilly areas than in gentle slope.

2. HUMAN ACTIVITIES: The activities of man like construction, farming/agriculture, grazing, mining on the slope of mountains or highlands to promote or reduce the movement of rock materials.

3. NATURE AND WEIGHT OF MATERIALS: it is noted that the loose rock materials tend to move faster than tightly held materials, i.e. the heavier the weight of the materials, the slower the movement.

4. PRESSURE OF LUBRICATING MOISTURE: The presence of lubricating moisture like rain water, ice etc, tends to produce, promote or increase the movement of rock materials down the slope.

5. PRESENCE OF VEGETATION: The presence of vegetation can either increase or reduce the movement of rock materials.

TYPES OF MASS MOVEMENT

There are two main types of mass movement

• Slow movement
• Fast movement

1. SLOW MOVEMENT: They are more effective in areas of chemical weathering. There are three most important which are (i) Soil creep (ii) Tallu creep (iii) Solification

SOIL CREEP: It is a slow, almost unnoticeable continues movement of weathered materials down a slope under the influence of gravity.

It operates on a very gentle slope and the speed of the movement would be as slow as 1cm per year. This movement is aided by water which acts as a lubricant which enebles rock materials to creep over each other. Alternative wetting and drying, heating and cooling of soil etc. are other factors that influence soil creep.

Soil creep can be noticed when fence or trees bend towards the direction of movement of the soil in a gentle slope, electric and telegraphy pole are titled, vertical rock layers are covered down slope, leaning on tree trunks and down slope, bulging of walls and fences soil accumulated behind walls which may collapse as a result of the soil erosion.

TALUS CREEP: This is less perrasive thin soil creep. Talus creep is the movement of angular rocks down moderately through steep slopes. Large talus creep move enmass especially in mountaneous region where freeze – thaw action is frequent.

SOIL SLOPE: This is a slightly faster movement usually are raging 5cm and 1m a year on moderate slopes. It occurs on temperature and polar regions. During the winter, the whole ground is frozen. In the summer, the surface layers thaws while the ground is still frozen. The saturated top soil may now begin to move on active layer over the frozen sub – soil.

2. FAST MOVEMENT – TYPES

i. Land slide                 (ii) Rock fall                 (iii) Earth flows and mud flows

LAND SLIDE: This takes place when large quantities of loosed surface rocks and soil suddenly slide down and the steep slope such as a cliff face, a valley’s side or embanment.

Land slides are caused by the lubricating acting action in water and pull off gravity. The actions that help to produce a land slide are the undercutting of the base of steeps slope by a river or sea or by human action. They are often treggared off by an earthquale or by prolong erosion.

ROCK FALLS: This refers to a mass of rock which falls from a steep cliff. This type of mass wasting is the most rapid of it.

When this continues for a long period of time, the broken rock coils at the base of the slope in mould.

EFFECTS OF MASS MOVEMENT

• It can lead to loss of farmland
• It can lead to displacement of settlement
• It can cause destruction of transportation network
• It can lead to tilting of electric and telegraphy poles
• It can cause the damage of rivers
• It leads to loss of soil fertility