Geologic map information helps us prepare for El Niño storms

The 1997-1998 El Niño climatic event br ought heavy rain and snow to the coast and mountains of California and the deserts to the east. During the past 40 years, nine El Niños have affected this area to varying degrees, but the El Niño of 1982-83, which was most similar to the 1997-1998 El Niño, caused considerable damage. Much of the damage was caused by moving water, rock, and mud, which are geologic processes that U.S. Geological Survey studies.

Geologists study deposits at the surface of the Earth that result from many seasons of storms with El Niño intensity. By mapping out these old deposits and deciphering how often the storm deposits are created, geologists learn where and how often El Niño events take place. They also can decipher from the old depsoits what processes were acting, from landslides to floods.This geographical and historical record of El Niño events is then used to make predictions for consequences of future El Niño events, consequences such as floods, landslides, and mud flows. These geologic processes of moving water and earth are described in more detail in the link below.

Understanding effects of the 1982-1983 El Niño

The 1982-83 El Niño directly affected United States fishing and agriculture industries (estimated crop losses of $10-12 billion), and caused severe storms with attendant flooding and landslides along the west coast. Abnormal weather conditions during the winter and spring of 1982-83 resulted in flooding of farms, mudslides, rockslides, and damage to roads and highways. Much of the fruit and vegetable crop was lost, and the prices of produce increased substantially. When the damage was complete, mudslides had affected 10,000 homes, 1000 businesses were damaged, and agricultural costs were estimated to be $200 million.

Predicting effects of the 1997-1998 El Niño

Geologists use the record of past storm-caused changes in the land surface to predict possible outcomes of strong storms that may be caused by the 1997-98 El Niño. By combining an understanding of how events such as landslides and floods take place with a knowledge of the landforms and projections of rainfall and snowmelt intensity, geologists can delineate areas where the land is vulnerable to destructive events such as landslides and floods. U.S. Geological Survey is producing maps that show susceptibility to destructive forces in the urban areas of coastal California.

What are landslides, debris flows, mudflows, and flash floods?

Studies in Southern California
Studies in San Francisco Bay area
Studies in Mojave Desert

For further information, contact David Miller

http://geology.wr.usgs.gov/wgmt/elnino/maps.html, 30 November 1999