Mass WastingMass Wasting

Mass WastingMass WastingWhat do these pictures haveWhat do these pictures havecommon?common?

What is Mass Wasting ?What is Mass Wasting ?

• down-slope movement of rock,down-slope movement of rock, regolith, and soil under the direct regolith, and soil under the direct influence of influence of GRAVITYGRAVITY

What force acts What force acts alonealone – to create – to createmovements of the earth? movements of the earth?

The role of Mass wasting– What’s it good for?The role of Mass wasting– What’s it good for? Responsible for the evolution Responsible for the evolution

ofof landforms – features of the landforms – features of the earthearth

• Weathering weakens rock – Weathering weakens rock – doesdoes not create significant not create significant landformslandforms

• Need mass wasting to impact Need mass wasting to impact weathering and shape weathering and shape significant significant earth featuresearth features

I I I I mass wasting mass wasting mass wasting mass wasting

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:

1. What is mass wasting ?1. What is mass wasting ?

2. What single “force” acts alone to 2. What single “force” acts alone to produce mass wasting processes?produce mass wasting processes?

3. What is the sole purpose of mass3. What is the sole purpose of mass wasting?wasting?

So, what “triggers” a massSo, what “triggers” a masswasting episode allowing gravity towasting episode allowing gravity tomove the mass downward?move the mass downward?

• The role of waterThe role of water• Slopes to steepSlopes to steep• Removal of vegetationRemoval of vegetation• EarthquakesEarthquakes

So, what “triggers” a massSo, what “triggers” a masswasting episode allowing gravity towasting episode allowing gravity tomove the mass downward?move the mass downward?

• The role of waterThe role of water• Slopes to steepSlopes to steep• Removal of vegetationRemoval of vegetation• EarthquakesEarthquakes

The Role of WaterThe Role of Water

Saturated SandSaturated Sand

The Role of WaterThe Role of Water• Water saturates surface materials.Water saturates surface materials.

• Particles loose their cohesion (can’tParticles loose their cohesion (can’t stick together).stick together).

• Particles slide past one another andParticles slide past one another and slip downward under gravity forces.slip downward under gravity forces.

Slopes to SteepSlopes to Steep• steeper slopes exceed the steeper slopes exceed the “angle of“angle of repose”repose” and material moves downward to and material moves downward to stabilize or reach equilibrium.stabilize or reach equilibrium.

Angle of repose:Angle of repose: • the angle at which particles are overtaken bythe angle at which particles are overtaken by

gravity and move downwardgravity and move downward

• angle depends on size, shape, and moisture contentangle depends on size, shape, and moisture content of accumulated particlesof accumulated particles

Dry Sand Wet Sand

Over steepening exceeding the angle of repose, natureOver steepening exceeding the angle of repose, naturereacts by attempting equilibriumreacts by attempting equilibrium

Removal of VegetationRemoval of Vegetation• where plants are lacking – mass wastingwhere plants are lacking – mass wasting attackingattacking

• root systems bind soilroot systems bind soil

• where soil is removed frequentwhere soil is removed frequent down slope movements occurdown slope movements occur

The Role of EarthquakesThe Role of Earthquakes• Areas that have not moved in “years”,Areas that have not moved in “years”, are activated by seismic waves.are activated by seismic waves.

Mass slide produced by an earthquakeMass slide produced by an earthquakedammed a river forming a lake.dammed a river forming a lake.Mass slide produced by an earthquakeMass slide produced by an earthquakedammed a river forming a lake.dammed a river forming a lake.

I I I I Mass Wasting Mass Wasting Mass Wasting Mass Wasting

I will get an A on my exams and quizzesI will get an A on my exams and quizzes

Discuss with a friend:Discuss with a friend:

1.1.Describe the 4 triggers that enableDescribe the 4 triggers that enable mass wasting process.mass wasting process.

2. What the angle of repose?2. What the angle of repose?

3. What is the most dominant “trigger”3. What is the most dominant “trigger” causing the onset of mass wasting?causing the onset of mass wasting?

How do geologists How do geologists classifyclassify various mass wasting processes? various mass wasting processes?

• Classification is based on Classification is based on

MaterialMaterialUnconsolidated:Unconsolidated: debris, mud, earthdebris, mud, earth

BedrockBedrock: : rockrock

Motion Motion

FallFall: freefall of material: freefall of material

SlideSlide: material moves cohesively along: material moves cohesively along well defined surfacewell defined surface

FlowFlow: material moves down-slope as: material moves down-slope as a viscous fluida viscous fluid

ClassificationClassificationofof

Mass Wasting ProcessesMass Wasting Processes

SLUMP SLUMP • downward movement of a slidingdownward movement of a sliding mass, mass, rockrock or or unconsolidatedunconsolidated material material that moves as a single unit along a that moves as a single unit along a curved surfacecurved surface

• moves very slowmoves very slow• over-steepened slopes (T)over-steepened slopes (T)• water saturated (Twater saturated (T))

RockslideRockslide• blocks of bedrock break loose and slideblocks of bedrock break loose and slide down a slopedown a slope

Debris slideDebris slide• unconsolidated material break loose andunconsolidated material break loose and slide down a slopeslide down a slope

Debris slideDebris slide• unconsolidated material break loose andunconsolidated material break loose and slide down a slopeslide down a slope

Debris flowDebris flowDebris flowDebris flow

RockslideRockslideRockslideRockslide

Over steepness (T)Over steepness (T)

Debris FlowDebris Flow• rapid mass movement containing soil rapid mass movement containing soil and regolith with large amounts of and regolith with large amounts of waterwater

Water saturation (T)Water saturation (T)

LaharsLahars• debris flows composed largely of volcanicdebris flows composed largely of volcanic material from the flanksmaterial from the flanks

• flows down existing stream valleysflows down existing stream valleys• extremely destructive events’extremely destructive events’• water saturation (T)water saturation (T)

LaharsLahars• debris flows composed largely of volcanicdebris flows composed largely of volcanic material from the flanksmaterial from the flanks

• flows down existing stream valleysflows down existing stream valleys• extremely destructive events’extremely destructive events’• water saturation (T)water saturation (T)

Lahars buriedLahars burieda village a village Lahars buriedLahars burieda village a village

Earth FlowEarth Flow• form on hillsides in humid areas with form on hillsides in humid areas with abundant precipitationabundant precipitation

• water saturated – hill may break awaywater saturated – hill may break away under gravity and weight of soilunder gravity and weight of soil• water saturated (T)water saturated (T)• rich in clays and siltrich in clays and silt• slow moving flowsslow moving flows

Earth FlowEarth Flow• form on hillsides in humid areas with form on hillsides in humid areas with abundant precipitationabundant precipitation

• water saturated – hill may break awaywater saturated – hill may break away under gravity and weight of soilunder gravity and weight of soil• water saturated (T)water saturated (T)• rich in clays and siltrich in clays and silt• slow moving flowsslow moving flows

Soil CreepSoil Creep• the gradual downhill movement of soil andthe gradual downhill movement of soil and regolith. regolith.

• soil moves extremely slowsoil moves extremely slow• soil disturbed by rain, roots soil disturbed by rain, roots • water saturation (T)water saturation (T)

Soil CreepSoil Creep• the gradual downhill movement of soil andthe gradual downhill movement of soil and regolith. regolith.

• soil moves extremely slowsoil moves extremely slow• soil disturbed by rain, roots soil disturbed by rain, roots • water saturation (T)water saturation (T)