The Geomorphic Importance of Mass Movement (Wasting)

The Geomorphic Importance of Mass Movement (Wasting)

This refers to the landforms developed upon the landscape as a result of mass movement. Since different types of materials are involved in varying rate of movements, mass movement creates a variety of landforrns.

As materials move from one area and are deposited in another, erosional and depositional landfonns are created. The material point of origin and the passage track develop shallow scars and scarps due to the removal of the materials, while the point of deposition or the terminus is built up temporary by the deposited materials.

The various types of movement have their modifying effects because each movement creates some land forms peculiar to the nature of the material and rate of the movement.

The valley-side of mudflow may change from being steep and rectilinear to gentle and concave. Examples of these landform types are found in Malawi and Zimbabwe range lands.

The rock fall/debris and debris/slumps may create a high steep relief, free face and this leads to slope retreat, thereby creating a gentle sloping surface in its wake.

Slumping and mud slush along actively eroding channels or incising valley floors may alter the channel geometry and initiate river channel pattern changes.

Accumulation of the debris especially rock fragments leads to formation of boulder fields and boulder slope which undergo rapid frost, shattering e.g. in temperate areas such as the case in the New Zealand Alps and in Natal.

Development of low step-like features on valley side slopes which are undergoing intense and widespread slides and slumping terracettes such as those developed in the Durwing Downs in Queensland (Australia) and in Nurit Island in New Zealand. The eroded areas develop scarps marking points of slope failure due to accumulation along the foot slope and the removal of surface material in between such slopes.

Generally, mass wasting (movement) is a process that is both destructive and constructive upon the landscape. Destructive in the sense that it is a member of the denudation processes and constructive since the moving materials are deposited to build up the landscape.

Distinction between weathering and mass movement (wasting)

Weathering and mass movement (wasting) are two different processes that affect the surface rocks of the landscape. A clear distinction between the processes that lead to each of the two terms is very necessary. This helps to wipe off any confusion that may arise when discussing them.

Weathering refers to the mechanical (physical) disintegration and the chemical decomposition of the rocks without removing the broken pieces from their positions. It is only after a certain amount of fragmentation has taken place that the removal of the particles commences by the agents of erosion. This marks the first step in shaping of the earth’s surface by external processes. It is the exposed rocks that are mostly affected by these processes.

The weathering agents which are completely different from those of erosion are few in number but complex in their interactions. These agents include those that are atmospheric in nature whose components are oxygen, carbon dioxide and water vapour which play a vital role in rock decomposition. Other atmospheric components are temperature changes and precipitation which greatly influence the physical disintegration of the rocks. The biotic agents play a dual role of causing the chemical decomposition and the physical disintegration of rocks.
The total effect of the weathering agents is influenced by a variety of other factors. These include the nature and the structure of the rock, the size of the rock openings and how abundance they are in the rock and the surface configuration of the rock.

Mass movement (wasting) on the other hand refers to processes that cause the movement of earth’s materials from a high elevation downslope under the influence of gravity. The materials which are involved in mass movement are variable. The size of such material cause a significant influenced because, the larger the materials, the more immediate and pronounced the effect of their movement downslope.
The facilitators of mass movement include water, clay, tectonic instability and undermining due to local erosion. Water serves as a lubricant. Clay provides a slippery surface while tectonic instability such as earthquake and earth tremor set up vibrations that destabilize cohesion of materials.
Undermining due to local erosion attacks the base of materials and forces the materials at the upper slope to trip down. Mass movement is categorized.

While some of the movements are termed as rapid and conspicuous others are slow and gradual. Listing these types of mass movements from the most rapids down to the slowest, the major types of mass movements are: