Case Studies 1963 Vaiont Disaster

Case Studies Ancient slide and recent small slide gave reason to worry

Case Studies Geology of the area led to problems

Rainfall and water level led to earth movement

Slumgullion

Translational Slide: goes along existing weakness This one cost taxpayers $400 million

Thistle, Utah: 1983 Snowmelt Town was flooded Lake was drained slowly Railroad/Highway moved Slide is still moving

Landslides Create Dams and Lakes Failure is inevitable: Time before failure and size of flood depends on –Size, height and geometry of dam –Material making up dam –Rate of stream flow, how fast lake rises –Use of engineering controls (artificial breaches, spillways or tunnels) Dams from mudflows, debris flows and earth flows are noncohesive and erode quickly

2008 Earthquake in China

Failure of Landslide Dams Most landslide dams fail when water overflows and erodes spillway that drains lake If dam-failure flood incorporates significant sediment, can turn into debris flow – much more dangerous Useful dams can be constructed on top of rock dams China solution: Use explosives to remove the dams

Landslides are a major problem Not covered by insurance In U.S., $2 billion and deaths/year Globally, $20 billion, 7500 deaths/year Disasters increase with population

Mitigation of Damages from Landslides Colorado Springs

Cities Can Map Ancient Slides Colorado Springs 1995: Rainfall and Landslides abundant Clay-rich rock and steep slopes of the Rockies 1999 major slides and flooding City purchased landslide-affected properties ($4.5M) GIS maps of old slides and potential slides Will this be used wisely?

Oakland, CA

USGS Landslide Hazard Program Research the causes of landslides Suggest mitigation strategies

Wildfires increase susceptibility

San Diego: 2003 and Fires led to 16 deaths from landslides $10sM in damage Moderate rainfall on burned areas Runoff increases, infiltration decreases San Diego: 2” rain in 3 hrs is 10 year storm

Fire and Rain Lead to Slides 30% slopes or steeper are vulnerable % of area burned Average storm intensity Clay volume in soil How much water can be absorbed by soil Variables include:

Videos

Chemical Weathering-dissolving rocks

Carbonic acid forms when CO 2 and H 2 O molecules combine. Carbonic acid ionizes to form hydrogen and bicarbonate ions. Feldspar KAlSi 3 O 8 Al 2 Si 2 O 5 (OH) 4 Kaolinite clay + Bicarbonate ions react with feldspar.

EROSION BY GROUNDWATER

Artesia: 7/19/08