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).

The 1995 La Conchita landslide, southern California, U.S.A.

Mass MovementLandslides,

Rockfalls, Debris Flows, avalanches and sinkholes.

1999 Rockfall

Newfoundland

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

The Toll

Landslide deaths in the U.S. have been estimated at 25-50 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.

Before the Yungay Avalanche

After the Yungay Avalanche ~25,000 killed 1970 Peru

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.

Terms you need to know.

• Rockfall

• Rockslide

• Slump

• Debris Flow

• Creep

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

Moisture and rate of motion

characteristics.

The slower events (creep) generally result only in property damage.

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.

Soil Formation

Rock chemically breaks down through the process called weathering.

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?

Serpentinite mélange. Tectonically-rounded

blocks of serpentinite, surrounded by a

sheared-out, foliated paste of crushed

serpentinite.

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.

Driving force (gravity) > resisting strength of rock/regolith

Components of resisting strength? 1.Friction

2.Cohesion

Figure 15.13

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

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.

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.

~33 degrees for dry sand

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.

Steep slopesvs. shallow slopesis controlled by the rock type.

Grand Canyon formation through the

Colorado River cutting down into the

bedrock. Canyon widening through mass

wasting events.

Consolidated materials:(tends to fall or slide)

• Cemented sediments = sedimentary rock.

• Crystalline materials: igneous, metamorphic, and some sedimentary rocks (evaporites).

Bedding Planes

Safer

Rock Discontinuities

Masses of rock often are full of

joints and fractures. columnar joints

Columnar joints

Devil’s Postpile, CA.

Napa area

Water and Water Ice

Why does ice float on liquid water?

Why is this important?

Water exerts pressureon particles and bedding surfaces which acts a lubricant on frictionalsurfaces.

Water and Water Ice

The density properties of

water are very unique and

have broad ranging

implications in geologic

and ecologic processes.

Mechanical Weathering:

Frost Wedging

Rockfalls

SF Telegraph Hill

1996 Happy Isles rockslide. Photo by David Walter

Happy Isles Rockfall

Granite Slide – Just outside Yosemite, CA

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.

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

TALUS SLOPES – ROCKY MOUNTAINS

TALUS SLOPES – ROCKY MOUNTAINS

TALUS SLOPES – DEATH VALLEY

HWY 1 Landslide California Rockslide

Rockslide/Landslide

Ferguson Slide on California State Highway 140

Massive landslide deposit.

A massive landslide scar and deposit.

A massive landslide scar and deposit.

Home destroyed by the April 1998 El Niño-triggered Anzar Road landslide,

San Benito County, California, U.S.A. (Schuster et al., 1998).

Weakly or unconsolidated material:(will slide, slump and often flow)

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.

Roots can mechanically weather bodies of rock, but

roots often hold rocks and soil in place on a slope.

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.

Paseo Del Mar,

San Pedro, CA

(Southern California)

November 2011

Slump

Parts of a earth slump

Large landslide along

the coast between Fort

Funston and John Daly

Blvd. (Daly City)—what

are the parts?

Old coastal highway

scarp

previous cliff toptoe?

body

Fort FunstonSan Andreas fault

LANDSLIDE – TENESSEE VALLEY BEACH – MARIN, CA

Slumping and Scarps in Dorset, England

The head of a rotational slip in the Black Hills of North Dakota. (Source: Image

provided by the National Geophysical Data Center, NOAA).

Earth flow

Seattle, Washington

Clay bed

prevented

drainage

due to being

impermeable,

thus overlying

strata became

saturated.

The Gross Ventre Slide – Sheep Mountain

Rock Slide of 1959

Landslide scar

Quake Lake

Evidence for massive

prehistoric landslide

that would have

triggered a great

tsunami.

Molokai

Landslide debris

Hawaiian Islands

http://www.mbari.org/volcanism/Hawaii/HR-Landslides.htm

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)

Evidence for huge submarine landslides in Hawaii

Major landslide deposit around Hawaii.

Landslides that enter water can cause a tsunami!

As the big island grows, it’s unstable flanks collapse forming major landslide deposits.

K’ilueau Volcano Giant rift on Hawaii has people

wondering if this is going to be

a massive landslide.

Describe a hillside and its environment that is most susceptible to mass movement.

Be thorough!

Foliation, Bedding, Joints parallel to slopeSlope is steep

Slope consists of unconsolidated materialSlope has lots of water (poor irrigation above)Slope gets a lot of traffic (animal or human)

Lots of weight on top of slopeBase of slope undercut

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

EarthquakeLarge Explosion

Storms

La Conchita1995

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 4th 600 tons of mud

destroyed 9 homes.

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

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

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

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

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

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.

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

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

Debris Flows

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.

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).

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

Upstream view of concrete crib-type check dam with low-flow center section in

southern California. (photograph by Los Angeles County Flood Control District).

Mudflow in Sarno, Italy, 1998

Rio Nido in Sonoma County. El Nino induced mudslide 1998

Creep

Burrowing rodents and wormssimilarly play a part in movingmaterials downhill.