UPCOMING EXAM BRING PENCIL And A SCANTRON!

Transcription

1 UPCOMING EXAM BRING PENCIL And A SCANTRON! Let me know if you are interested in taking the optional comprehensive final. No programmable calculators or other electronic devices. No dictionaries. Covers Chapters Geologic Time, Glaciers, Shorelines, Mass Movement, Streams Bring blank paper in case you need to work out a problem (NO WRITING IN THE TEST BOOKLET).

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3 Mass Movement Landslides, Rockfalls, Debris Flows, avalanches and sinkholes Rockfall Newfoundland The 1995 La Conchita landslide, southern California, U.S.A.

4 Landslide destroyed road near Hwy 17 Scott s Valley, CA

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6 The Toll Landslide deaths in the U.S. have been estimated at people per year. Every year around the world hundreds of people are killed by mass wasting events (landslides, debris flows, and rockfalls). Infrastructure/property damage is a global occurrence, but a large portion of events are around the Pacific rim---that includes California. Every year California suffers property damage and/or loss of life due to landslides. Landslides are California s most common thus costliest natural disaster.

7 Before the Yungay Avalanche

8 After the Yungay Avalanche ~25,000 killed 1970 Peru

9 Process of Erosion Erosion: materials transported by wind, water, or gravity and deposited somewhere else. With mass wasting we will be focusing generally on gravity being the transportation force and water (liquid or ice) facilitating the process. Mass movement (also known as mass wasting) is the down slope movement of earth materials under the influence of gravity. The detachment and movement of earth materials occurs if the stress imposed is greater than the strength of the material to hold it in place. Landslides, rockfalls, debris flows and avalanches all have one thing in common, they occur on slopes. The angle of the slope can vary greatly and in some cases the slope angle can be very shallow.

10 Terms you need to know. Rockfall Rockslide Slump Debris Flow Creep

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12 External triggers Earthquake shaking, especially in steep topography, with saturated slopes, or in saturated sand (liquefaction) Volcanic eruptions create piles of loose material (e.g., ash), destroy vegetation, melt snow/ice, cause mountain collapse Heavy rainfall and melting snow, especially if continuous over days/weeks

13 Moisture and rate of motion characteristics. The slower events (creep) generally result only in property damage.

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15 Why are there so few landslides in the Sierras? A. There are few steep slopes there. B. The trees hold the land in place. C. Soil was removed by glaciers. D. There is no rain, only snow.

16 Soil Formation Rock chemically breaks down through the process called weathering.

17 California Coast Range--Factors that create slope instability. Slope Many steep slopes! Water A lot of wet weather and storms (especially in Northern California)! Geologic materials, Geologic structures, and Weathering Much of the rock is weak due to being highly fractured, folded and faulted, and weathered and some are just weak and slippery (e.g. serpentinite). Soils or unconsolidated sediments present on slopes. Vegetation?

18 Serpentinite mélange. Tectonically-rounded blocks of serpentinite, surrounded by a sheared-out, foliated paste of crushed serpentinite.

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20 Factors that determine slope stability Slope? Water? Geologic materials? Geologic structures? Weathering? Vegetation? The California Coast Range (and coast) regularly experiences mass wasting events. The majority are rotational slumps but debris flows are common as well. Most mass wasting events in California are triggered by wet storms.

21 Driving force (gravity) > resisting strength of rock/regolith Components of resisting strength? 1.Friction 2. Cohesion Figure 15.13

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23 View of the mudslide area in the town of La Conchita.

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26 The material that the slope is composed of is important for several reasons: -- plays a role in how steep of a slope can be maintained and also how high a cliff can be. -- the type of slope failures (mass wasting events) that may occur. -- the magnitude of these events. Shear strength is a measure if the resistance of earth materials to be moved. Angle of repose is the steepest angle from horizontal that an unconsolidated material can maintain. Grain shape strongly effects the angle as does size distribution. The angle of repose of dry sand is around 33 degrees. ~33 degrees for dry sand

27 The material that the slope is composed of dictates: -- how steep of a slope can be maintained. -- how high a cliff can be. -- the type of slope failures (mass wasting events) that occur.

28 Steep slopes vs. shallow slopes is controlled by the rock type. Grand Canyon formation through the Colorado River cutting down into the bedrock. Canyon widening through mass wasting events.

29 Consolidated materials: (tends to fall or slide) Cemented sediments = sedimentary rock. Crystalline materials: igneous, metamorphic, and some sedimentary rocks (evaporites).

30 Bedding Planes Safer

31 Rock Discontinuities

32 Masses of rock often are full of joints and fractures. columnar joints

33 Columnar joints Devil s Postpile, CA.

34 Napa area

35 Water and Water Ice Why does ice float on liquid water? Why is this important?

36 Water exerts pressure on particles and bedding surfaces which acts a lubricant on frictional surfaces.

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38 Water and Water Ice The density properties of water are very unique and have broad ranging implications in geologic and ecologic processes.

39 Mechanical Weathering: Frost Wedging

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41 Rockfalls

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43 SF Telegraph Hill

44 1996 Happy Isles rockslide. Photo by David Walter

45 Happy Isles Rockfall

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47 Granite Slide Just outside Yosemite, CA

48 Talus and talus slopes Talus is rock debris that is piled up (generally at the angel of repose) at the base of cliffs. Talus slopes are rockfall deposits.

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50 Talus cones on the north shore of Ifjorden, Svalbard, Norway.

51 TALUS SLOPES ROCKY MOUNTAINS

52 TALUS SLOPES ROCKY MOUNTAINS

53 TALUS SLOPES DEATH VALLEY

54 HWY 1 Landslide California Rockslide

55 Rockslide/Landslide Ferguson Slide on California State Highway 140

56 Massive landslide deposit.

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58 A massive landslide scar and deposit.

59 A massive landslide scar and deposit.

60 Weakly or unconsolidated material: (will slide, slump and often flow) Home destroyed by the April 1998 El Niño-triggered Anzar Road landslide, San Benito County, California, U.S.A. (Schuster et al., 1998).

61 Factors that determine slope stability Water: a small amount increases cohesion but a large amount reduces friction; weight of water increases driving force too. Water saturation of materials on a slope is the primary cause of landslides. Earthquakes can cause liquefaction of unconsolidated materials thus reducing the friction between grains.

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63 Roots can mechanically weather bodies of rock, but roots often hold rocks and soil in place on a slope.

64 Vegetation often stabilizes slope. Slopes are very susceptible to failure after fires remove vegetation. Failure generally occurs in the wet winter storms that follow the fire season.

65 Paseo Del Mar, San Pedro, CA (Southern California) November 2011

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68 Slump

69 Parts of a earth slump

70 Large landslide along the coast between Fort Funston and John Daly Blvd. (Daly City) what are the parts? Old coastal highway San Andreas fault Fort Funston scarp toe? body previous cliff top

71 LANDSLIDE TENESSEE VALLEY BEACH MARIN, CA

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73 Slumping and Scarps in Dorset, England

74 The head of a rotational slip in the Black Hills of North Dakota. (Source: Image provided by the National Geophysical Data Center, NOAA).

75 Earth flow

76 Seattle, Washington

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84 Clay bed prevented drainage due to being impermeable, thus overlying strata became saturated.

85 The Gross Ventre Slide Sheep Mountain

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88 Rock Slide of 1959

89 Quake Lake Landslide scar

90 Evidence for massive prehistoric landslide that would have triggered a great tsunami. Landslide debris Molokai Hawaiian Islands

91 Evidence for huge submarine landslides in Hawaii Debris from enormous landslides off Oahu and Molokai extends hundreds of kilometers (map generated from sonar data 2001 MBARI) Pali above Kane'ohe Bay on Oahu: the slide-scarp of the Nuuanu submarine landslide (photo 2004 J.B. Paduan)

92 As the big island grows, it s unstable flanks collapse forming major landslide deposits. Major landslide deposit around Hawaii. Landslides that enter water can cause a tsunami!

93 K ilueau Volcano Giant rift on Hawaii has people wondering if this is going to be a massive landslide.

94 Describe a hillside and its environment that is most susceptible to mass movement. Be thorough! Foliation, Bedding, Joints parallel to slope Slope is steep Slope consists of unconsolidated material Slope has lots of water (poor irrigation above) Slope gets a lot of traffic (animal or human) Lots of weight on top of slope Base of slope undercut

95 What are some things that can act as triggers for mass movement? Be thorough! Undercut highway slope (humans) Build atop hillside (or dump load) Stream or waves undercut hillside Earthquake Large Explosion Storms

96 La Conchita 1995 The town was built on a 10,000 year old landslide. Unconsolidated sediments formed steep hills around the town. Orchards at the top of the hills were irrigated. Wet weather oversaturated the slopes and fissures formed. On March 4 th 600 tons of mud destroyed 9 homes.

97 View of the mudslide area in the town of La Conchita.

98 Motorist are stranded between two mudslides on Highway 101 next to the community of La Conchita between Ventura and Santa Barbara.

99 La Conchita residents clear a path for water drainage on Fillmore Avenue after mudslides Monday morning.

100 A motor home is stuck in the mud on Pacific Coast Highway along the Rincon.

101 A helicopter surveys damage from a mudslide near La Conchita along Highway 101 Monday morning.

102 The Santa Clara River passes under the Harbor Blvd. bridge just south of the Ventura city limits. The ocean, top right, is filled with debris.

103 A work truck is stuck in the mud on Highway 101 at La Conchita Monday morning

104 Vehicles are stuck in the mud on Pacific Coast Highway along the Rincon.

105 Debris Flows

106 Schematic of typical hillslope setting for debris flows. Debris is earth material generally greater than coarse sand size. A debris flow occurs when the water content of the soil is sufficient for the material to flow like a viscous fluid. Debris flows usually travel down existing stream channels. Over geologic time debris can accumulate to form a fan-shaped deposit at the toe of the slope.

107 December 1999 debris-flow damage to the city of Caraballeda, north coast of Venezuela. (Photo by L.M. Smith, Waterways Experiment Station, U.S. Army Corps of Engineers).

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110 British Columbia debris flow during a one-night flood in a small stream.

111 Upstream view of concrete crib-type check dam with low-flow center section in southern California. (photograph by Los Angeles County Flood Control District).

112 Mudflow in Sarno, Italy, 1998

113 Rio Nido in Sonoma County. El Nino induced mudslide 1998

114 Creep

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119 Burrowing rodents and worms similarly play a part in moving materials downhill.

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