Landslides, Part 2 Beverly Hills slide, Feb 2005
Outline • Slide examples • Flows • Avalanches
Block Slide The rapid movement of large blocks of detached bedrock sliding more or less as a unit.
Block Slide
Debris Slide Rock material and soil move largely as one or more units along planes of weakness.
Debris Slide
1925 Gros Ventre Slide, Wyoming
1925 Gros Ventre Slide, Wyoming
1925 Gros Ventre Slide, Wyoming
1925 Gros Ventre Slide, Wyoming
1925 Gros Ventre Slide, Wyoming
1925 Gros Ventre Slide, Wyoming
Gros Ventre Slide, Wyoming
Vaiont Reservoir Slide Debris slide caused reservoir wall to collapse, sent water downstream Fig. 12. 17
Lateral Spreading
Turnagain Heights, Alaska
Flows • • Mass movements behave like fluids Materials include boulders, sand, ice, mix Speed varies - barely moving to ~200 mph Various types of flow, depending on material, slip surface
Loess Flow • Dry flows of fine silt deposits • Example: 1920 China – 160 by 275 km hill of loess flowed after earthquake – Killed ~200, 000 people by burying villages very rapidly
Earth Flow • A fluid movement of relatively fine -grained material (soils, clays)
Earthflow
Debris Flow • A fluid mass movement of rock fragments supported by a muddy matrix. May move a speeds of up to 100 km/hr!
Mudflow • A flowing mass of material (mostly finer than sand, along with some rock debris) containing a large amount of water. • May travel large distances and high speeds • Can carry particles as large as a house!
Debris Avalanche • Fast (up to 280 km/hr) downhill movements of soil and rock, usually occurring in humid mountainous regions
Mt Huascaran, Peru (before 1970) Mountain region in Peru, before a Mw 7. 7 occurred in the subduction zone offshore
Mt Huascaran, Peru (after 1970)
Combination of Processes: Mt. Huascaran
Snow Avalanches • Snow has same pull from gravity – Can fail in creep, fall, slide, flow • Snowfall, wind-blown snow load slope towards failure – Also skiers
Snow Avalanche • Large events - slab of snow breaks away • Occurs because each layer of snow has different properties – Layers deposited at different times, vary in strength, hardness, density, thickness
Snow! Can travel at very high speeds, trapping skiers
Ways to Reduce Losses Due to Landslides Include: • Avoid construction in areas prone to mass movement • Build in a way that does not make naturally stable slope unstable • Engineer water drainage to prevent strata to become water saturated and prone to fail
Note dipping beds undercut by excavation for house
Failure occurs when watersaturated strata slide along slippery clay unit, breaching thin retaining wall Box 12. 1
Submarine Movements • Same types of failures occur underwater • Example: Hawaii has significant slumps, debris avalanches • Volcanic flank collapse - whole side of volcano falls off – Leads to tsunami
Hawaii
Big Island, Hawaii • Motion along blocks near Kilauea today!
Next Time • Subsidence and review for midterm
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