Mass Wasting

Mass wasting

The downslope movement of rock, regolith, and soil under the direct influence of gravity.

Triggers of mass wasting

Gravity

Water

Oversteepened slopes

Removal of vegetation

Earthquakes

Human activity

The classification of mass wasting processes is based on?

Kind of motion

Velocity

Material carried

Types of motion

Fall

Flow

Slide

Flow

Material moves downslope as viscous fluid.

Moves as lobes or tongues.

Fall

Freefall of detached individual pieces. Common on very steep slopes. Caused by freeze/thaw and plant action.

Talus deposit

Produced by fall types of mass wasting.

Slide

Induced by a zone of weakness separating slide material from stable underlying material.

Has 2 types: rotational and translational.

Rotational slide

Downward and outward movement of a mass on top of a concave upward failure surface.

Translational slide

The descending mass moves along a plane (fault, joint, bedding plane) approximately parallel to the slope of the surface. Little rotation or backward tilting.

Types of movement based on rate

Avalanche

Creep

Avalanche

Moves at fast velocities (200kph). High velocity due to air trapped and compressed beneath falling mass and debris.

Creep

Incredibly slow (mm/cm per year). Due to alternating expansion and contraction. Aided by anything that disturbs the soil (raindrops, roots, burrowing animals).

Slump

Type of rotational slide.

A type of mass movement that occurs when a mass of material moves down a curved slope.

Debris does not travel fast and far. Common in areas of thick accumulation of cohesive materials (clay).

Due to oversteepened or overburdened slopes.

Rockslide

Type of slide.

Fast and destructive.

Material composed of rocks/consolidated matter.

Common in inclined strata.

Common during spring when ice from winter thaws.

Debris slide

Type of slide.

Fast and destructive.

Material composed of unconsolidated matter.

Common in inclined strata.

Common during spring when ice from winter thaws.

Debris flow

Type of flow.

Rapid mass wasting involving soil and regolith saturated with water.

Also called mudflow.

Common in semi-arid regions and areas near volcanoes.

Debris flow in semi-arid regions

Due to rapidly melting snow or cloudbursts.

forms well-mixed mud, soil, rock, and water.

Rate depends on slope and water content.

Spreads out at the end of narrow canyons to form alluvial fans.

Lahars

Saturated volcanic material.

Induced by heavy rainfall, melted ice/snow, and hot gases and near-molten materials.

Deadly volcanic hazard which can occur without an eruption.

Earthflow

Type of flow.

Forms in hillsides of humid areas during heavy precipitation or snowmelt.

Viscous and slow moving.

Associated with slumps.

Solifluction

Slow, downslope flow of water-saturated materials common to permafrost / hardpan areas.

Can occur in slopes with 2-3 degrees inclination.

Soil creep

Slow speed, minimal water content

Solifluction

Slow speed, abundant water content

Slump / Rotational slide

Moderate speed, moderate water content

Translational slide

Slower and has more water content than rotational slide

Earthflow

Faster and has more water content than rotational slide

Rockfall

Very fast movement, minimal water content

Debris avalanche

Very fast movement, moderate water content

Mudflow

Very fast movement, abundant water conten