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What You Need to Know About Mudslides

Brazil Slide

Jan. 12: Cars sit in debris in a flooded street in Teresopolis, Rio de Janeiro state, Brazil.AP

More than 350 people are dead, and at least 50 are missing, after mudslides swept homes and people away in mountain towns north of Rio. And landslides in the U.S. kill up to 50 people every year -- and cost $1-$2 billion in damage.  

Here's what you need to know about the deadly acts of nature.

Basic Landslide Facts

• Landslides in the U.S. kill up to 50 people every year

• Landslides cause $1 - $2 billion in damage a year in the U.S.

• Mudslides can reach speeds in excess of 100 mph

• Rain approaching one inch per hour can cause mudslides

Triggering mechanisms

Debris flows are commonly caused by intense surface-water flow, due to heavy precipitation or rapid snowmelt, that erodes and mobilizes loose soil or rock on steep slopes. Debris flows also commonly mobilize from other types of landslides that occur on steep slopes, are nearly saturated, and consist of a large proportion of silt- and sand-sized material.

Mitigation measures

Flows usually cannot be prevented; thus, homes should not be built in steep-walled gullies that have a history of debris flows or are otherwise susceptible due to wildfires, soil type, or other related factors. New flows can be directed away from structures by means of deflection, debris-flow basins can be built to contain flow, and warning systems can be put in place in areas where it is known at what rainfall thresholds debris flows are triggered. Evacuation, avoidance, and (or) relocation are the best methods to prevent injury and life loss.

Brazil's worst mudslides

• Heavy rain led to 473 deaths in Brazil in 2010, and destroyed the homes of 101,298, according to Brazil's Civil Defense Ministry.

•Jan 2010: Mudslides near Rio de Janeiro kill at least 506 people over 7 days, making it the country's worst flood disaster ever

• Nov 2008: Heavy rain causes mudslides that kill at least 109 and force 79,000 from their homes in southern Brazil

• Jan 2004: Mudslides in Northeast Brazil kill 91 and leave more than 4,000 homeless

• Jan 1997: Flooding and mudslides kill 68 around Rio De Janeiro and leave 40,000 homeless

• Feb 1988: Mudslides kill at least 131 in Brazil

• 1967: Mudslides kill 437 in Brazil