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Link between earthquakes and El Ninos?

Link between earthquakes and El Ninos?

The periodic, massive climatic upheavals known as El Nino-Southern Oscillations (ENSOs) may be triggered by intense tectonic activity in the seafloor near Easter Island in the East Pacific, a seismologist reported this week at the fall meeting of the American Geophsical Union in San Francisco.

Daniel A. Walker, from the Hawaii Institute of Geophysics in Honolulu, found that all five ENSOs occurring between 1964 and 1987 were preceded by spells of numerous earthquakes along the East Pacific Rise--one of a worldwide set of seafloor spreading centers that produce new oceanic crust.

"Since 1964 the track record on that correlation is, as far as I'm concerned, five for five,' Walker told SCIENCE NEWS. "If you pick out the five most intense periods of tectonic activity that have occurred since 1964, you'll see that they coincide-- within about six months--with all these five El Ninos.'

The ENSOs--a reorganization in Pacific climate patterns--bring torrential rains to normally arid parts of South America, while Australia and Indonesia suffer from abnormal droughts for up to a year and a half. On average, ENSOs recur every four to five years, but the timing and severity of the cycle are highly irregular.

Since the turn of the century, scientists have attempted to develop theories that explain the El Nino (an East Pacific warming trend) and the southern oscillations (abnormal shifts in air pressures over the Pacific), which were originally thought to be separate phenomena. In the last two decades they have learned that ENSOs result from an interaction between the ocean and the atmosphere. Without completely understanding how ENSOs begin, meteorologists have discovered that the ocean and atmosphere combine forces as an amplifier, generating a full-blown event out of some subtle initiating factor.

According to Walker, this factor may be tectonic activity. When he analyzed the seismic history of a long stretch of the East Pacific Rise around Easter Island, he found that the ridge tends to stay relatively quiet for a period of five to seven years, averaging only 1.8 earthquakes a month. Punctuating these quiescent times are periods of intense activity, which last only one or two months. During one active period, 21 earthquakes shook the ridge.

While the correlation between earth-quakes and the onset of ENSO events may be coincidental, Walker suggests that the periods of seismic activity result from episodes of seafloor spreading along the East Pacific Rise. This kind of tectonic activity is known to generate hydrothermal fluids that contain many dissolved gases and minerals.

Walker proposes that the heat of these fluids could raise the temperature of the surface water near Easter Island, thereby lowering the air pressure over this part of the Pacific. Both these characteristics are hallmarks of an ENSO event. Another possibility is that the dissolved nutrients in the fluids indirectly affect the temperature and pressure of the air by stimulating biological activity.

Meteorologists, however, have not warmed to such unorthodox ideas about the climate. "It doesn't impress me,' says Stephen E. Zebiak at the Lamont-Doherty Geological Observatory in Palisades, N.Y. "Over the past few years, various people have correlated everything in the world with ENSOs. You can take a really short period like this and find correlations with almost anything imaginable.'

Moreover, says Zebiak, the latest theories about ENSOs downplay the role of a triggering factor. Instead, he says, it seems that wave and wind patterns might "precondition' the Pacific, making it sensitive to any number of secondary effects that could trigger the start of an ENSO. If this is true, says Zebiak, then the preconditioning factors are more critical than any specific trigger.

But seismologist Don L. Anderson of the California Institute of Technology in Pasadena says that Walker's findings--if they can be confirmed--may help in understanding ENSOs. "It is a phenomenon that involves oceanography, meteorology and probably the influence of the sun. But nobody has ever really thought about there being some coupling with the inside of the earth . . .. We might not have discovered the explanation of the ENSO because we haven't looked broadly enough.'
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Author:Monastersky, Richard
Publication:Science News
Date:Dec 12, 1987
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