El Ninåo, the occasional perturbation in global climate whose occurrence in 1982 and 1983 was the worst in 50 years, may have been happening for at least 10,000 years and in intensities 10 to 100 times worse, a Stanford University geologist has found.

The 1982-83 event brought flooding to California and Peru; drought to Australia, Mexico and China, and unseasonal hurricanes to Hawaii. Peruvian fisheries, the world's richest, failed for a season. Sea birds died on many Pacific islands.

Bad as it was, Stanford's Lisa Wells, a doctoral candidate in geology, said she believes there is evidence that El Ninåos of far worse proportions have happened roughly every 500 years over at least the last 10,000 years.

"El Ninåo," the Spanish term for the Christ child, is what Peruvian fishermen call the unusually warm currents that, when they come, arrive around Christmastime to signal a bad fishing season.

Wells' evidence comes from her studies of river valleys in Peru, especially some in desert regions where the annual rainfall is usually less than half an inch. She found recently formed river beds into which water had flowed only during El Ninåos, leaving characteristic profiles of sediments -- ranging from gravels at the bottom to fine silts at the top. From the relative amounts of these deposits, geologists can estimate the volume, speed and duration of the flow.

Wells also found evidence of ancient riverbeds whose sediment patterns matched those of El Ninåo riverbeds. Through geological means, she determined how long ago the major periods of flooding happened. The last big El Ninåo riverbed corresponded to one that historical records indicate occurred around 1720.