This month’s tragic mudslides in Montecito, California are a reminder that natural hazards lurk on the doorsteps of many U.S. homes, even in affluent communities. Similar events occur every year around the world, often inflicting much higher casualties yet rarely making front-page headlines.
Dave Petley, an earth scientist at the University of Sheffield, has calculated that landslides caused 32,322 fatalities between 2004 and 2010 – equivalent to over 4,500 deaths each year. For comparison, floods are estimated to have killed an average of roughly 7,000 people each year.
In the most destructive recorded cases of the 20th century, thousands of people died in single events. The highest numbers of fatalities from landslides occur in the mountains of Asia and Central and South America, as well as on steep islands in the Caribbean and Southeast Asia. For example:
– Catastrophic debris flows from Nevado Huascarán, the highest mountain peak in Peru killed as many as 4,000 people in 1962 and another estimated 18,000-20,000 in 1970.
– During the 2008 Wenchuan earthquake in China’s Sichuan province, 20,000 deaths were attributed to landslides – roughly one-fourth of the total deaths from the quake.
Wherever slopes are steep, there is a chance that they will fail. Heavy rainfall or a large earthquake can destabilize precarious balances and unleash the raw power of tumbling rocks and debris. The risks increase after wildfires. They also can be exacerbated by deforestation and land use change. Earthquake-triggered landslides, while less frequent than those induced by rainfall, have been responsible for some of the greatest losses of life.
Among the reasons the effects of landslides are disproportionately severe in developing countries reflect a number of factors, including the resilience of basic infrastructure and emergency services; the availability of health care to treat people who are injured or left homeless; and patterns of development that determine where people live, and the lack of early warning systems that can alert people to imminent risks.
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