Volcanoes on earth may follow the sun.

Volcanoes on Earth may follow the sun

Does the timing of volcanic eruptions around the globe fit any sort of pattern? According to a statistical study of hundreds of eruptions over the last four centuries, the solar cycle may have an influence on when volcanoes blow their cool.

Before he began the study, Richard B. Stothers of NASA's Goddard Institute for Space Studies in New York City held little hope of finding any correlation between eruption frequency and the 11-year solar cycle -- a faint waxing and waning in the sun's energy output. Several researchers over the past 150 years had proposed such a connection but did not conduct largescale statistical studies to test the theory, says Stothers.

Stothers analyzed two immense catalogs, published in the early 1980s, that list more than 55,000 known eruptions since the year 1500. Concentrating on several hundred of the moderate-to-large-eruptions, he found statistically significant patterns in eruption frequency that match the solar cycle. Eruptions seemed most numerous during the weakest portion of the solar cycle, he reports in the Dec. 10 JOURNAL OF GEOPHYSICAL RESEARCH. He cautions, however, that these tests are not perfect. The observed correlation may result from a statistical coincidence rather than reflecting a relationship between the solar cycle and volcanoes.

For instance, one analysis detected a 10.8-year period in the frequency of 114 large eruptions. To check whether the apparent periodicity arose from a statistical accident, Stothers performed a Monte Carlo test, in which a computer generates 1,000 lists, each containing 114 random dates between the years 1500 and 1980. The computer then determines how many random lists had strong periods close to the length of the solar cycle. Stothers found that only three out of every 100 random lists produced a solar cycle period. This gives a 97 percent confidence level to the conclusion that the 10.8-year period in the real eruption record is not a statistical accident, he says.

How on Earth could the sun influence eruptions? One possibility, Stothers says, is that during the peak of the solar cycle, emissions from the sun cause small but abrupt changes in the Earth's atmosphere, jarring the planet slightly. This might trigger tiny earthquakes that relieve stress under volcanoes, thereby staving off a large eruption.