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Geology - Mass Wasting

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    Study Guide Geology – Mass Was Ɵ ng 1. Preven Ɵ on of Mass Was Ɵ ng Mass wasting can often be prevented — or at least reduced — through careful planning and smart engineering. Many slope failures happen because human activities accidentally make slopes less stable. 1.1 How Human Ac Ɵ vi Ɵ es Increase Risk Certain actions can greatly increase the chance of mass wasting: • Undercutting the base of a slope , such as cutting into a hillside for a road • Adding weight to the top of a slope by building large structures • Removing vegetation , which normally helps hold soil in place with roots • Saturating the ground with water , which adds weight and reduces friction between particles When these factors combine, slopes become much more likely to fail. 1.2 Engineering Solu Ɵ ons to Reduce Mass Was Ɵ ng Engineers use several methods to stabilize slopes and reduce danger: • Retaining walls and barriers help hold soil and rock in place • Drainage pipes remove excess water, preventing soil from becoming too heavy and slippery • Terracing breaks a steep slope into a series of smaller, flatter steps, reducing the force of gravity • Revegetation (replanting grasses, shrubs, or trees) helps anchor soil quickly after construction These methods are often used together for maximum effectiveness.

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    Study Guide 1.3 Preven Ɵ ng Rockfalls Rockfalls are especially common on steep, rocky slopes and road cuts. They can be reduced or prevented by: • Installing rock bolts and cables to secure loose rock • Using wire screens or nets to catch falling rocks • Cutting slopes at gentler angles , making them less likely to collapse 2. Introduc Ɵ on to Mass Was Ɵ ng Mass wasting is a natural result of weathering on slopes. As rocks and soil are loosened by weathering, gravity pulls them downhill . In simple terms, mass wasting is the downhill movement of rock, soil, and other Earth materials caused by gravity. Mass wasting is considered a type of erosion , but unlike erosion by water or wind, it does not require a moving agent. Gravity alone provides the force. The speed of mass wasting can vary greatly and mainly depends on: • How steep the slope is • How much water is present in the material Fast, destructive mass - wasting events are called landslides . When movement is extremely slow and cannot be seen as it happens, it is called creep . 2.1 Types of Mass - Was Ɵ ng Movement Geologists generally recognize three main types of movement : flow, slip, and fall. 2.1.1 Flow A mass - wasting event is called a flow when the material moves downslope like a thick liquid . This usually happens when the material contains a large amount of water, allowing soil and debris to move easily.

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    Study Guide 2.1.2 Slip A slip occurs when a mass of material moves downhill as a solid block along a distinct surface. • A slide is a type of slip where the movement happens along a surface that is parallel to the slope . • A slump is another type of slip, but the movement happens along a curved surface . o The upper part of the slump drops downward, leaving behind a steep scarp , or cliff. o The lower part of the mass moves outward along a more horizontal surface. Slumps are common on slopes made of weak or water - saturated material. 2.1.3 Fall A fall happens when rock or debris breaks free and drops straight down from a steep slope or cliff. This type of movement is sudden and often occurs where rock faces are very steep or fractured. 3. Mass - Was Ɵ ng Controls Mass wasting does not happen randomly. Certain conditions make slopes more unstable and increase the chance that rock or soil will move downhill. The more of these conditions that are present, the higher the risk of mass wasting. 3.1 Factors That Increase Mass Was Ɵ ng Mass wasting is more likely to occur when one or more of the following conditions exist: • Steep slopes , where gravity has a stronger pull • Large changes in elevation (high relief) • Thick layers of loose soil or sediment • Planes of weakness in rock that run parallel to the slope • Frequent freezing and thawing , which loosens material • High water content in soil or rock

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