High School Earth Science: Erosion and Deposition - Erosion and Deposition by Gravity — Flashcards

Types of Rapid Mass Movements    
Mass movement is any movement of Earth materials by the force of gravity. Several types of mass movement occur suddenly and rapidly. They include landslides, avalanches, mudflows, and lahars.    
Landslides and avalanches are the most dramatic, sudden, and dangerous types of mass movement. Landslides are sudden falls of rock, whereas avalanches are sudden falls of snow. When large amounts of rock suddenly break loose from a cliff or mountainside, they move quickly and with tremendous force. Landslides are exceptionally destructive. Homes may be destroyed as hillsides collapse. A landslide may bury entire villages. A landslide that dams a stream may create a lake. A landslide that flows into a lake or bay may trigger a tsunami. Landslides often occur on steep slopes in dry or semi-arid climates, especially following a heavy rain. The California coastline has steep cliffs and years of drought punctuated by seasons of abundant rainfall, so it is prone to landslides.    
On hillsides with soils rich in clay, a period of heavy rain that thoroughly saturates the soil may create a mudflow.    
This is especially likely if there is not much vegetation to hold the wet soil in place. Mudflows follow river channels, and they may wash out any bridges, trees, and homes that are along their path. A lahar is a mudflow that flows down the side of a composite volcano. Ash from an eruption mixes with snow and ice. The snow and ice melt and contribute to the formation of hot, fast-moving mud.