CHAPTER 11: MASS MOVEMENT PROCESSES, PATTERNS AND LANDFORMS 11.1 What is mass movement?
Mass movement is the movement of material downhill under the influence of gravity. The action of weathering (mechanical and chemical) and
erosional processes create soil and scree which lie on the surface of the earth. This loose material is called regolith. For mass movement to occur a slope must be present,
whether gentle or steep. Some mass movement is so very slow that it cannot be seen happening, while other types of mass movement are very fast and devastating. Mass movements are often triggered. These triggers may be natural or man-made.
Natural triggers 1. Torrential rains 2. Heavy snow 3. Earthquakes and volcanoes
Human triggers 1. Building road cuttings across hillsides 2. Placing waste material on unstable slopes 3. Quarry blasting 4. Deforestation 5. Skiing in soft snow
11.2 Factors affecting mass movement
Several factors encourage mass movement to happen. 1. Gravity 2. Slope 3. Water 4. Vegetation 5. Human activities 6. Type of material
1. Gravity
Gravity helps stick the regolith (soil) to a slope or move it downhill. The speed of movement is proportional to the weight of the regolith to be moved and the steepness of the slope. Heavy particles on a steep slope will move more quickly.
2. Slope
Steep slopes result in fast movements such as avalanches.
Slop Mass movement
Fig. 1 The LaConchita landslide of 1995 in Ventura County, California