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 Movements

• Types– Fall

– Topple

– Flow

– Slide

– Subsidence

What types of material are involved?1. ROCK – a hard or firm mass that was

intact and in its natural place before the initiation of movement.

2. 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

www.goodearthgraphics.com/photo/ geology/rockfall.jpg

Colorado River

http://anaheim-landslide.com/types.htm

http://www.science.ubc.ca/~geol351/imgset.html

Similkameen Valley, BC

Topple

http://anaheim-landslide.com/types.htm

http://www.science.ubc.ca/~geol351/imgset.html

Chaco Canyon, NM

www.charmouth.org/html/geology/ geology%20gallery/gallery.ht

Charmouth, UK

Slide

http://anaheim-landslide.com/types.htm

Halsema Highway

H. Cabria, 2002

http://www.science.ubc.ca/~geol351/imgset.html

http://www.science.ubc.ca/~geol351/imgset.html

Liard River, BC

Valtellina, Italy

Flow

http://anaheim-landslide.com/types.htm

http://www.science.ubc.ca/~geol351/imgset.html

http://www.science.ubc.ca/~geol351/imgset.html

South Nation River, Ontario Mt. Pinatubo Lahars

Mt. Pinatubo Lahars

El Salvador www.brookes.ac.uk/geology/ 8361/images/mudflow.gif

Creep

http://anaheim-landslide.com/types.htm

Halsema Highway

H. Cabria, 2002

Black Hills, South Dakota

academic.emporia.edu/aberjame/ struc_geo/primary/prim31.jpg www.geol.umd.edu/~nathalie/GEOL120.htm

Complex typesFrank Slide, Alberta

Huascaran Avalanche, Peru

Thistle Slide, Utah

Colalo Landslide

http://www.science.ubc.ca/~geol351/imgset.html

http://www.science.ubc.ca/~geol351/imgset.html

S. Catane, 1999

Triggers: water input

Mudslide after hurricane Mitch,Fall 1998

Millbrae CA, March 2000

Water infiltrating into unstable slope increases pore pressure (“loosens” particles) and adds more weight to slope, favoring failure.

www.geol.umd.edu/~nathalie/GEOL120.htm

Triggers: earthquake

Ground shaking due to earthquake activity can facilitate slope failure.

Nevados Huascaran, Peru, 1970(18 000 dead)

Northridge earthquake, CA, 1994

www.geol.umd.edu/~nathalie/GEOL120.htm

How human activities increase the

frequency of landslides? • Logging operations • Construction leads to oversteepening of

slopes - road cuts, quarrying or open-pit mining operations

• Buildings 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 stream

www.geol.umd.edu/~nathalie/GEOL120.htm

Slope Stabilization

Slope stabilization: ground anchoring

Drilling to install rock bolts and water pressure monitors (piezometers)

Drilling and bolting across plane of weakness

Ground anchoring (bolting)

www.geol.umd.edu/~nathalie/GEOL120.htm

Slope stabilization:retaining structures

Wire mesh

Geogrid holds unconsolidated material in place

Wire baskets filled with rockwww.geol.umd.edu/~nathalie/GEOL120.htm

Slope stabilization: keeping the water out

Drains and trenches keep water from infiltrating the top of a slump

Short-term precaution against further water input and erosion

Revegetation and drainagewww.geol.umd.edu/~nathalie/GEOL120.htm

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.) www.geol.umd.edu/~nathalie/GEOL120.htm

Slope StabilizationMarcos Highway

Rock fence

Rockshed

Shotcrete

Fly-over

H. Cabria, 2002

Tuba Fault

Mankayan Landslide

S. Catane, 1999

H. Cabria, 2002

Mankayan Landslide

S. Catane, 1999

S. Catane, 2000

Aurora Street - 1999

2000

2002

Mankayan Landslide

PVC 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, 2002

H. 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 sediments

Folding or faulting or earthquakeCollapse of underground cavern (sinkhole)

Sinkholes

Winter Park, Florida sinkhole (100m across x 34 m deep) formed1981

“December giant” sinkhole,Alabama (130 m long x 46m

deep) formed 1972