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Lecture 6: Mass movement (the downslope…
Lecture 6: Mass movement
(the downslope movement of earth materials as a direct result of gravity
Slope stability
Gravity is the driving force, its effect increases with:
steeper slopes
This can be acheived by eroding the base of the slope with:
Glaciers
Waves
Rivers
Humans
height of slopes
weight on slope
This can be achieved with:
Water
Buildings
Water is usually a mojor factor in mass movement, it:
Adds weight
Seeps into cracks and loosens land
Forces land apart
Classifications of Mass movement
Falls: steep or vertical drops
Topples
: base of rocks stay on ground while the top 'toplles over
see slide for diagram
Usually formed by waves or rivers undercutting the base of cliffs
Landslides: A mass of land moving down a slope in one clump
Slide
: straight slip down
see slide 2 for diagram
Slump
: rotational slip down
Flows:
Land flows downwards at different speeds depending on depth
see slides for diagram
Creep
e.g. soil creep, frost creep, avalanches
see notes on slide 3
Mass rock creep: weight causes rock to buckle outwards, potentially causing a rock overhang, and a very large landslide
Earthflows
Slow
e.g Big Bar earthflow 3km long, fraser river, central British Columbia
Fast
e.g. St lawrence and Ottawa Valley Sensitive clays. Nicolet 1955
Saint jean vianney 1971
NE montreal 2010 4 died
Periglacial flows
Avalanches
Rock
e.g. Frank Slide 1930 in southern rockies, 70 killed
Mudflow (occur in cordillera)
Subsidence: collapse of a section of land, (not a mass movement)
eg.WIndsor july 2010