EROSIONThe process by which sediments

are obtained and transported.

Erosion involves a transporting system with several components:

1. AGENT OF EROSION- (e.g. stream, glacier, wave, current, wind, or human activity).

2. SEDIMENTS BEING MOVED

3. DRIVING FORCE

The DRIVING FORCE behind most types of EROSION isGRAVITY

The downward movement of material under the influence of gravity is called mass wasting.

Water can play an important role, but gravity is the main element

MASS WASTING INVOLVES TWO MAJOR OPPOSING

FORCES

1. FORCE OF GRAVITY – constant downward pull

2. FORCE OF FRICTION – attempts to keep objects in place

Gravity > Friction – movement

Gravity < Friction – no movement

Gravity = Friction (equilibrium) – no movement

Oh no!

Factors that resist gravity includethe materials strength and cohesion

vegetation

internal friction between grains

Angle of underlying rock

increasing the slope angle

under cutting of the slope

amount of weathering

amount of water moving through material

overloading slopes with new material

Factors that help gravitational forces

Mass wasting is often caused by a force that temporarily disturbs the slope equilibrium

•Earthquakes

•Heavy rain

•Leakage from water pipes and swimming pools

•Volcanic eruptions

• explosions

• thunder

Excavation at the base of a slope can lead to slope instability

i.e. road cut along slopes

The angle at which the underlying rock is inclined has a major impact on mass wasting.

Slides:

These are slow to rapid movement of material along one or more surfaces.

Slumps are Usually slow to moderate in speed

Movement along a curved surface

Usually in unconsolidated materials like soil

Rockslides are rapid to very rapid

movement along a planar surface

A Slump

Slump caused by erosion in southern California

Mass wasting occurs when rocks weather at a higher elevation and fall

to a lower elevation.

This is called, (you guessed it), a

Rock Fall

Rock Falls: Free falling rock from steep mountain sides. Usually caused by ice

wedging.

Any sized material may

fall. The collected

debris at the bottom is

called TALUS

Talus Slope or Rock fall

Houses can be totally covered by sand and mud, like this:

In real life, landslides can be quite destructive:

Rate = 1 mm/day to 1 km/hr

This landslide tragically took the life of many unsuspecting woodland creatures.

Types of landslides

Flows:

These are mass movements where the material moves as a viscous fluid or plastic movement

Mudflows are very rapid and contain a lot of water and mud

Earthflows are slow to moderate movement of material down a slope which leaves an exposed scrape.

Solidification is the slow downward movement of water saturated soil. Common in areas of permafrost

Creep is extremely slow movement of soil & rock downhill

Mud Flows happen faster (1-5 km/hr)

THE PROBLEM WITH LANDSLIDES AND

MUDSLIDES IS THAT THEY ARE OFTEN

UNPREDICTABLE AND CAN BE VERY

DAMAGING TO LIFE AND PROPERTY

Mud Flow

Solidifluction: in Alaska

Soil creep

“Soil creep” happens very slowly (less than 1 cm per

year).

Soil gradually moves downhill

Bent trees are the most

obvious indicator of soil creep

Creep

Solutions to Mass wasting:

Surface and subsurface drainage of hillsides

Replanting of vegetation

Reduce the angle of slope

Putting in retaining walls and bolting rock faces