Mass Wasting

Mass wasting - is the name given to all downslope movements of material due to the influence of gravity. They are an important part of the denudation of the landscape.

Soil creep

• on just about any moderately steep soil covered slope there may be evidence of extremely slow downslope movement of soil.

• this is often evidenced by the tilting of trees, poles, gravestones and fences and broken retaining walls

• as particles are exposed to heating and cooling, frost action, rainfall and the action of plants and animals, gravity pulls the particles steadily downhill

Soil Creep

Earth Flow – LinearEarth Slump - Circular

- in humid climate regions where there are steep slopes, masses of water soaked soil, and overburden may slide downhill in a few hours

- sometimes in very saturated clay rich soils (usually left behind in areas that were formerly glacial lakes), the earthflow can become very fluidized very quickly

- the whole slope suddenly behaves like a liquid and flows rapidly downhill - Leda clays (“sensitive” or “quick clays”) are found in Ottawa and Quebec react this way

- potentially very dangerous - in St. Jean-Vianney, Quebec in 1971 a Leda clay slide killed 31 people

- the movement is associated with slumps. Slumps – are rotated blocks of earth – looks as if sitting on a couch.

failure surface

linear motioncurved motion

failure plane

Earth Flows

Leda Clays

Mudflow

- a stream of fluid mud that pours down canyons in mountainous regions like a river

- especially significant in desert areas where there is little vegetation to hold the soil and heavy rains sometimes occur

- they also happen on the sides of volcanoes from freshly fallen ash and dust (fatal eruption of Nevado del Ruiz, Columbia killed 20 000 in mudflow)

MudFlows

Leda Clays is a slump and a MudFlow involves movement like a river.

Landslides & Avalanches

• the rapid sliding downslope of large masses of rock with little or no flowage of the materials – in other words no water.

• rockslides are rare and occur where there are steep slopes

• Sometimes set off by kinetic energy – one rock hits another and two hit two more and so on…

• often set off by earthquakes or by excavations or construction - roads, railways, dams, etc.

• Skiers can also set off an avalanche

• Loud sounds do not set off Landslides and Avalanches

• eg., Frank, Alberta slide 1903, The Tragedies in BC in 2003

Rock slides is the movement of rocks down a slope.

Landslides are rock, earth and debris flows due to gravity

Avalanches are landslides involving snow.

Rock Slides

Avalanches

Landslides

The End!