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Mass Wasting. Mass wasting / slope failure / landslides refers to all downslope movement of rock, regolith, and soil under the direct influence of gravity. Speeds range from extremely fast to extremely slow. Landslide. General term for rapid downslope movements/failure. - PowerPoint PPT Presentation

Text of Mass Wasting

  • Mass Wasting

  • Mass wasting / slope failure / landslides refers to all downslope movement of rock, regolith, and soil under the direct influence of gravity. Speeds range from extremely fast to extremely slow.

  • Landslide General term for rapid downslope movements/failure

  • Classification of Landslides Based on the type of MATERIALS involved, the SPEED (velocity) of movement, and the TYPE or mechanism of downslope movement.

  • Downslope MovementsTypesFallToppleFlowSlideSubsidence

  • What types of material are involved?ROCK a hard or firm mass that was intact and in its natural place before the initiation of movement.SOIL an aggregate of minerals and rocks that either was transported or was formed by the weathering of rock in place.a) Earth 2 mm particles 80% b) Debris 2 mm particles < 20%

  • How fast does a landslide move? Very Slow e.g. Creep Moderate e.g.Slumps and earthflows Rapid to Very Rapid - e.g. Rockfalls and Avalanches

  • FallHalsema Highway H. Cabria, 2002 geology/rockfall.jpg Colorado River Valley, BC

  • Topple Canyon, NM geology%20gallery/ Charmouth, UK

  • Slide HighwayH. Cabria, 2002 River, BC Valtellina, Italy

  • Flow Nation River, Ontario Mt. Pinatubo Lahars Mt. Pinatubo Lahars El Salvador

  • Creep HighwayH. Cabria, 2002Black Hills, South struc_geo/primary/prim31.jpg

  • Complex typesFrank Slide, Alberta Huascaran Avalanche, Peru Thistle Slide, Utah Colalo Landslide Catane, 1999

  • Triggers: water inputMudslide after hurricane Mitch,Fall 1998Millbrae CA, March 2000 Water infiltrating into unstable slope increases pore pressure (loosens particles) and adds more weight to slope, favoring failure.

  • Triggers: earthquakeGround shaking due to earthquake activity can facilitate slope failure. Nevados Huascaran, Peru, 1970(18 000 dead)Northridge earthquake, CA,

  • How human activities increase the frequency of landslides? Logging operations Construction leads to oversteepening of slopes - road cuts, quarrying or open-pit mining operationsBuildings and structures on a naturally unstable slope Irrigation, watering the lawn, using septic tank for sewage disposal

  • Landslide ControlZoning is an effective way of reducing landslide-related risk, by keeping people from building and living in, or controlling the type of structure built in landslide-prone areas. This approach however is not always viable.

    Slope stabilization measures can greatly reduce the risk of catastrophic slope failure. In some cases, however, this only serve to delay the inevitable. Riprap wall to control undercutting by

  • Slope Stabilization

  • Slope stabilization: ground anchoringDrilling to install rock bolts and water pressure monitors (piezometers)Drilling and bolting across plane of weaknessGround anchoring (bolting)

  • Slope stabilization:retaining structuresWire meshGeogrid holds unconsolidated material in placeWire baskets filled with

  • Slope stabilization: keeping the water outDrains and trenches keep water from infiltrating the top of a slump Short-term precaution against further water input and erosionRevegetation and

  • SheltersIn some landslide- or avalanche-prone areas, slope stabilization is impractical due to the scale of the unstable slope. This is particularly true for roads in mountainous areas. In this case, sheds are used to divert slides from the road (and people on it). (Note use of old tires to absorb shock of falling rock.)

  • Slope StabilizationMarcos Highway Rock fence RockshedShotcreteFly-overH. Cabria, 2002Tuba Fault

  • Mankayan LandslideS. Catane, 1999

  • Mankayan LandslideAurora Street - 1999 2000 2002

  • Mankayan LandslidePVC pipes are used to prevent waste water from infiltrating the slope.The small PVC pipes were connected to a bigger pipe that directly drains into the creek located below the slope.H. Cabria, 2002H. Cabria, 2002

  • Miag-ao Landslide

  • Cherry Hills Landslide(Photo by R. S. Punongbayan)

  • Photo of landslide in Punta, San Francisco, Panaon Island, Southern Leyte, Central Philippines. December 17 20, 2003

  • The andesites are moderate to highly weathered while the matrix of the breccia is completely weathered. Soil thickness including highly weathered rocks is about 10 m.

  • Land Subsidence: Causes

    Man-made: Withdrawal of subsurface support (removing water, petroleum, rocks voids)Downwarping due to sedimentation, ice loading, dewatering and compaction of sedimentsFolding or faulting or earthquakeCollapse of underground cavern (sinkhole)

  • Sinkholes

    Winter Park, Florida sinkhole (100 m across x 34 m deep) formed 1981

    December giant sinkhole, Alabama (130 m long x 46m deep) formed 1972