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Slumping and Sliding - Started November 17th 2011 Envir Sc...

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Unformatted text preview: Started November 17th, 2011 Envir Sc 1G03: Earth & the Environment Slumping and sliding (Mass movement processes) Slumping and Sliding Introduction Types of mass movement slumps, falls and slides flows Slope stability Slope stabilization Read: Chapter 13 in Plummer et al. What is mass movement? - the downslope movement of rock or soil material under the influence of gravity Why is it important? - significant loss of life and property 1971 - Saguenay River, Quebec 27 hectare landslide 26 homes lost 31 killed 1903 Frank Slide, Alberta buried town of Frank killed 70 people lasted ~ 90 seconds St. Jude, Quebec (May 10, 2010) Landslide claimed lives of a family of 4 http://gsc.nrcan.gc.ca/landslides/stjude_e.php 1969 - Aberfan, Wales coal spoil heap failed killed 144, predominantly school children Landslides kill thousands each year often related to heavy rains Types of mass movement Two main types - Material moves downslope as a coherent unit slumps, falls, slides - Material deforms flows Flows Debris flows - downslope movement of unconsolidated material - move at rates of metres to kilometers per hour - often triggered by heavy rain, spring thaw Mudflows - debris flows with high water content - can travel up to 100 km/hr - common in volcanic areas Solifluction and creep Figure 13.4 - Movement of few mm to cm per year - common in periglacial areas Debris avalanche - very destructive flows - move at speeds of over 400 km/hr - often triggered by earthquakes - Yungay, Peru 1970, 17,000 killed Quickclays silts and clays deposited in glaciomarine setting salty porewater is leached out by groundwater clay becomes weak and easily fails common in coastal areas covered by sea during past glacial episodes Ottawa region Champlain Sea Rissa, Norway Quickclays in eastern Canada 1993 Lemieux quick clay slide - 3 million m3 sand, silt, clay - blocked river Triggered by heavy rainfall, high water table Slumps, falls and slides Slump - Downslope and outward rotational movement of rock or soil - often associated with earthquakes and heavy rains Fig. 13.1 ! Fall - Free fall of a single block or large mass from a cli or steep slope Fig. 13.1 Rockslide (debris slide) - sudden downslope movement of detached masses of bedrock - often occurs on dipping surfaces - builds talus Fig. 13.1 talus talus 1965: Hope slide, B.C. 1903: Frank slide, Alberta Slope Stability What factors affect the stability of a slope? Slope angle - steeper slope –– less stable - stability depends on nature of materials Angle of repose maximum angle at which material is stable - coarse grains -- steep angle - fine grains -- low angle sand grain is stable until 33º Fig. 13.2 Vegetation - helps stabilize slopes Water content - high pore water pressure reduces resistance to failure - adds weight to slope - lubricates bedding planes Fig. 13.3 Earthquakes - often trigger failures Slope modification Building, mining, deforestation increase likelihood of failure Fig. 13.22 How can we stabilize slopes? Drain water add drainage pipes Fig. 13.23 Reduce slopes Make road cuts in stable positions Fig. 13.24 Use rock bolts to secure surface layers Fig. 13.25 ...
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