Geology - Mass Wasting - Quick Guides | Geology

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Study GuideGeology–Mass WasƟng1. PrevenƟon of Mass WasƟngMass wastingcan often be prevented—or at least reduced—through careful planning and smartengineering. Many slope failures happen because human activities accidentally make slopes lessstable.1.1 How Human AcƟviƟes Increase RiskCertain 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 slopeby 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 particlesWhen these factors combine, slopes become much more likely to fail.1.2 Engineering SoluƟons to Reduce Mass WasƟngEngineers use several methods to stabilize slopes and reduce danger:•Retaining walls and barriershelp hold soil and rock in place•Drainage pipesremove excess water, preventing soil from becoming too heavy and slippery•Terracingbreaks a steep slope into a series of smaller, flatter steps, reducing the force ofgravity•Revegetation(replanting grasses, shrubs, or trees) helps anchor soil quickly afterconstructionThese methods are often used together for maximum effectiveness.

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Study Guide1.3 PrevenƟng RockfallsRockfallsare especially common on steep, rocky slopes and road cuts. They can be reduced orprevented by:•Installingrock bolts and cablesto secure loose rock•Usingwire screens or netsto catch falling rocks•Cutting slopes at gentler angles, making them less likely to collapse2. IntroducƟon to Mass WasƟngMass wastingis a natural result of weathering on slopes. As rocks and soil are loosened byweathering,gravity pulls them downhill. In simple terms, mass wasting is the downhill movement ofrock, soil, and other Earth materials caused by gravity.Mass wasting is considered a type oferosion, but unlike erosion by water or wind, it does not requirea moving agent. Gravity alone provides the force. Thespeed of mass wastingcan vary greatly andmainly depends on:•Howsteepthe slope is•How muchwateris present in the materialFast, destructive mass-wasting events are calledlandslides. When movement is extremely slow andcannot be seen as it happens, it is calledcreep.2.1 Types of Mass-WasƟng MovementGeologists generally recognizethree main types of movement: flow, slip, and fall.2.1.1 FlowA mass-wasting event is called aflowwhen the material moves downslope like athick liquid. Thisusually happens when the material contains a large amount of water, allowing soil and debris to moveeasily.

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Study Guide2.1.2 SlipAslipoccurs when a mass of material moves downhill as asolid blockalong a distinct surface.•Aslideis a type of slip where the movement happens along a surface that isparallel to theslope.•Aslumpis another type of slip, but the movement happens along acurved surface.oThe upper part of the slump drops downward, leaving behind asteep scarp, or cliff.oThe lower part of the mass moves outward along a more horizontal surface.Slumps are common on slopes made of weak or water-saturated material.2.1.3FallAfallhappens when rock or debrisbreaks free and drops straight downfrom a steep slope or cliff.This type of movement is sudden and often occurs where rock faces are very steep or fractured.3. Mass-WasƟng ControlsMass wasting does not happen randomly. Certainconditions make slopes more unstableandincrease the chance that rock or soil will move downhill. The more of these conditions that arepresent, the higher the risk of mass wasting.3.1 Factors That Increase Mass WasƟngMass 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 weaknessin rock that run parallel to the slope•Frequent freezing and thawing, which loosens material•High water contentin soil or rock

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