Case Studies: Italy and California
Vaiont, Italy
- When: 1963
Type: Rotational slide
Cause: The dam and reservoir was built on old landslides and weak & fractured limestone. Water filling reservoir saturated rocks in toes of slopes and elevated pore-water pressures, causing instability. The build up of water due to the reservoir and heavy rains in fractured limestone & along an old slide plane further unstabilized the area. The resulting landslide was 1.8 km by 1.6 km mass (240 million m3) slid at up to 30 m/sec into reservoir. This caused the water in the reservoir to over top the dam and rush downstream, flooding nearby towns.
Canadian Quick-Clay Slope Failures
Quick clays are common in eastern Canada. Like many natural disasters, if you can recognize problem areas, then you can take preventative actions (move towns, etc.)
Ontario, Canada: 3.5 million m3 mass liquefied, then flowed into river
Point Fermin, California
- When: 1929
Type: Translational slide
Cause: Adverse geology + residential development
Source: Sunken City landslide, Pt. Fermin by Dr. Melanie Patton Renfrew at L.A. Harbor College(http://www.lahc.edu/earthscience/geography/fieldtrips.htm)
Portuguese Bend, California
- When: 1950s
Type: Combination of an earthflow, rotational and translational slide
Cause:
Rock layers dip seaward
+ bentonitic clay layer
+ erosion of toe by ocean waves
+ Residential development of area in 1950s
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ancient earthflow reactivated, moving seaward
Source: Inspiration Point with Portuguese Bend Landslide complex on each side, Palos Verdes Peninsula Copyright © 2002 Kenneth & Gabrielle Adelman (http://www.californiacoastline.org/cgi-bin/image.cgi?image=8395&mode=sequential&flags=0&year=2002)
La Conchita, California
- When: June 10, 2005, 12:30 p.m. PST
Type: Debris Flow
Causes: Poorly indurated marine sediments, residential development of the area in 1924 and heavy rainfall caused the reactivation of 1994 (& older) slides. The 2005 slide moved at a rate estimated at 5 to 10 m/s. A total of 13 houses destroyed, 23 houses severely damaged, and 10 confirmed deaths.
View of the La Conchita landslide taken January 14, 2005. The light–colored, exposed rock in the upper part of the photograph is the main scarp of the 1995 slide. The southeast part of the 1995 deposit (right side of photograph) remobilized in 2005. At the bottom center of photograph, a wall built after the 1995 slide is visible; the 2005 slide overtopped and tilted parts of the wall forward. (http://pubs.usgs.gov/of/2005/1067/508of05-1067.html)
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