Lec 12/13

Homemade

Landslides

Canadas most destructive natural hazard

Factors of slope failures

1. slope angle/support

2. slope composition

3. Vegetation

4. Weight

5. Water

Internal causes of slope failures

1. Faults

2. Exposed bedding (layering)

3. Structures w/in rocks

4. Exfoliation joints

Exfoliation joints

rocks that are buried are compressed, when rise to surface they expand and weaken

Weak materials

Clay, expansive sediments

Mass movements downward

Fall/subsidence

Mass movements downward and outward

Slide/flow

Creep

slowest, most widespread form of slope failure

swelling and shrinking of soil in response to freezing of water, absorption of water, heating by sun

Solifluction

sun thaws top layer of permafrost, it slowly flows down slope overtop frozen soil

Slump/debris flow

La Conchita, California

Earthflow

Portugese Bend, California

Slides

movement of block above failure surface

Rotational slide (slump)

downward and outward movement, short distance

Translational slides

mass of debris flows downslope along slightly sloped surface (like a fault) with little/no rotation

Long-runout debris flows

massive rock falls that convert into highly fluid, rapid debris flows that travel far

Sturzstroms

movement of highly fluidized rock flows → fast and far movement (also on the moon, mars, ocean floor)

Falls

Elevated rock mass separates along joint/bedding/weakness, falls downward thru the air in freefall, hits the ground and bounces/rolls

Snow avalanche

Similar to earth mass movements

Loose powder avalanche

low cohesion, lotta volume is pore space

Slab avalanches

slabs of snow that break free, turning into flows on the way down

fast avalanche forming

Dry snow

Subsidence

ground surface gently sags or catastrophically drops as voids in rocks close

Subsidence caused by rock dissolution

catastrophic, sinkholes formed (groundwater levels drop)

Subsidence caused by mine collapse

caused by collapse of underground mine (coal, salt)

Subsidence caused by fluid withdrawal

When water is removed, loose sand packs very tight

Subsidence caused by sediment compaction

clay and sand, more initial void space means more slower settlement