mass wasting
DESCRIPTION
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 PresentationTRANSCRIPT
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