These are forces that are caused by human beings through their activities such as farming, mining, setting up settlements, road construction, transport, etc. Man can influence in destruction or removal of some parts of the earth’s surface.
This shows that man can modify natural landforms and, therefore, acts as the agent of weathering, mass wasting, erosion, transportation and deposition on the earth’s surface. Human modification of the land helps loosen large chunks of earth and cause them to slide downhill. Man produces forces that affect the earth through the following activities:
(a) Removing vegetation: A slope with lots of vegetation is less susceptible to mass movement than a bare slope. Bare, exposed soil is very easily eroded, and can contribute to mass movement activity. Vegetation: helps hold soil, loose rock, and regolith together by its roots; reduces the direct erosive impact of rainfall and other precipitation; actively reduces ground moisture by using it to contribute to plant growth; and produces litter and organic products (leaves, twigs, grasses, fruits) that help stabilize the soil.
(b) Mining: In the course of mining, man uses machines to dig the soil and blast rocks. These activities results to earth tremors which loosen the soil particles making then vulnerable to removal by agents of weathering and denudation. Blasting also causes fractures in rocks, a fact which makes them less stable and resistant to shear and stress. If this happens, especially on steep slopes, the probability of occurring landslide is very high.
(c) Farming activities: Farming involves digging the soil by using farm implements such as hoes, tractors, harrows, spades, etc. These activities involves breaking up the soil and rocks by the implements. In this way, crop cultivation directly leads to weathering and erosion. Overstocking (keeping many animals in just a small piece of land) also leads to soil erosion. This is because overstocking is usually accompanied with overgrazing, an act which removes the vegetation cover. This triggers soil erosion and other weathering processes.
(d) Building and construction: Breaking up the soil for construction of houses and other infrastructures can dramatically increase the potential of mass movement. These processes involve tearing rocks to get room for setting up infrastructures such as roads, railways, airports, seaports, etc. This leads to destruction of the soil, hence triggering mass movement, weathering and erosion.
(e) Fishing: Fishermen in less developed countries sometimes use weapons such as dynamites to kill and catch fish. Tremors produced by these illegal fishing tools can cause fracturing of the coastal rocks. This causes both weathering and erosion.
(f) Navigation: In some few cases, marine vessels accidentally crush onto stones in water, peeling or breaking then into pieces. This leads to rock disintegration, a typical form of weathering.
(g) Transport: Vibrations from machinery, traffic, weight loading, stockpiling of rock or ore from waste piles and from buildings and other structures loosen the soil and make it prone to soil erosion and weathering.
(h) Construction of dams and canals: Construction of dams, such as the Mtera dam in Tanzania and canals such as the Suez Canal in Egypt, involves removing a large junk of rock. This breaks up the soil, leading to weathering and soil erosion.
(i) Warfare: The use of atomic bombs and other heavy weapons in war leads to destruction of the soil. During times of war, heavy and destructive weapons such as atomic bombs, shells, rockets and grenades are dropped or fired towards the enemy. When these weapons fall on land, they detonate and blow up a large mass of the earth, causing weathering and erosion. Military equipment such as tanks, heavy trucks and caterpillars break up rocks over which they pass. At the same time, they loosen the soil and carry away some of it as they move along.