Mass Wasting

What do these pictures have common?

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 GRAVITY influence of GRAVITY What force acts alone – to create 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 of Responsible for the evolution of landforms – features of the earth landforms – features of the earth Weathering weakens rock – does Weathering weakens rock – does not create significant landforms not create significant landforms Need mass wasting to impact Need mass wasting to impact weathering and shape significant weathering and shape significant earth features earth features

II mass wasting I will get an A on my exams and quizzes. Discuss with a friend: 1. What is mass wasting ? 2. What single “force” acts alone to produce mass wasting processes? produce mass wasting processes? 3. What is the sole purpose of mass wasting? wasting?

So, what “triggers” a mass wasting episode allowing gravity to move the mass downward? The role of water The role of water Slopes to steep Slopes to steep Removal of vegetation Removal of vegetation Earthquakes Earthquakes So, what “triggers” a mass wasting episode allowing gravity to move the mass downward? The role of water The role of water Slopes to steep Slopes to steep Removal of vegetation Removal of vegetation Earthquakes Earthquakes

The Role of Water Saturated Sand

The Role of Water Water saturates surface materials. Water saturates surface materials. Particles loose their cohesion (can’t Particles loose their cohesion (can’t stick together). stick together). Particles slide past one another and Particles slide past one another and slip downward under gravity forces. slip downward under gravity forces.

Slopes to Steep steeper slopes exceed the “angle of steeper slopes exceed the “angle of repose” and material moves downward to repose” and material moves downward to stabilize or reach equilibrium. stabilize or reach equilibrium. Angle of repose: the angle at which particles are overtaken by the angle at which particles are overtaken by gravity and move downward gravity and move downward angle depends on size, shape, and moisture content angle depends on size, shape, and moisture content of accumulated particles of accumulated particles Dry Sand Wet Sand

Over steepening exceeding the angle of repose, nature reacts by attempting equilibrium

Removal of Vegetation where plants are lacking – mass wasting where plants are lacking – mass wasting attacking attacking root systems bind soil root systems bind soil where soil is removed frequent where soil is removed frequent down slope movements occur down slope movements occur

The 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 earthquake dammed a river forming a lake. Mass slide produced by an earthquake dammed a river forming a lake.

II Mass Wasting I will get an A on my exams and quizzes Discuss with a friend: 1.Describe the 4 triggers that enable mass wasting process. mass wasting process. 2. What the angle of repose? 3. What is the most dominant “trigger” causing the onset of mass wasting? causing the onset of mass wasting?

How do geologists classify various mass wasting processes? Classification is based on Classification is based on Material Unconsolidated: debris, mud, earth debris, mud, earth Bedrock: rock rock Motion Fall: freefall of material Slide: material moves cohesively along well defined surface well defined surface Flow: material moves down-slope as a viscous fluid a viscous fluid

Classificationof Mass Wasting Processes

SLUMP downward movement of a sliding downward movement of a sliding mass, rock or unconsolidated material mass, rock or unconsolidated material that moves as a single unit along a that moves as a single unit along a curved surface curved surface moves very slow moves very slow over-steepened slopes (T) over-steepened slopes (T) water saturated (T ) water saturated (T )

Rockslide blocks of bedrock break loose and slide blocks of bedrock break loose and slide down a slope down a slope Debris slide unconsolidated material break loose and unconsolidated material break loose and slide down a slope slide down a slope Debris slide unconsolidated material break loose and unconsolidated material break loose and slide down a slope slide down a slope Debris flow RockslideRockslide Over steepness (T)

Debris Flow rapid mass movement containing soil rapid mass movement containing soil and regolith with large amounts of and regolith with large amounts of water water Water saturation (T)

Lahars debris flows composed largely of volcanic debris flows composed largely of volcanic material from the flanks material from the flanks flows down existing stream valleys flows down existing stream valleys extremely destructive events’ extremely destructive events’ water saturation (T) water saturation (T)Lahars debris flows composed largely of volcanic debris flows composed largely of volcanic material from the flanks material from the flanks flows down existing stream valleys flows down existing stream valleys extremely destructive events’ extremely destructive events’ water saturation (T) water saturation (T) Lahars buried a village Lahars buried a village

Earth Flow form on hillsides in humid areas with form on hillsides in humid areas with abundant precipitation abundant precipitation water saturated – hill may break away water saturated – hill may break away under gravity and weight of soil under gravity and weight of soil water saturated (T) water saturated (T) rich in clays and silt rich in clays and silt slow moving flows slow moving flows Earth Flow form on hillsides in humid areas with form on hillsides in humid areas with abundant precipitation abundant precipitation water saturated – hill may break away water saturated – hill may break away under gravity and weight of soil under gravity and weight of soil water saturated (T) water saturated (T) rich in clays and silt rich in clays and silt slow moving flows slow moving flows

Soil Creep the gradual downhill movement of soil and the gradual downhill movement of soil and regolith. regolith. soil moves extremely slow soil moves extremely slow soil disturbed by rain, roots soil disturbed by rain, roots water saturation (T) water saturation (T) Soil Creep the gradual downhill movement of soil and the gradual downhill movement of soil and regolith. regolith. soil moves extremely slow soil moves extremely slow soil disturbed by rain, roots soil disturbed by rain, roots water saturation (T) water saturation (T)