Are Volcanic Eruptions Tied to Lunar Cycle?

Brian Handwerk
For National Geographic News
February 15, 2002

The horrors unleashed by the recent eruption of Congo's Mount Nyiragongo have demonstrated once again our uneasy relationship with the fires that rage below Earth's surface.

In January, tons of molten rock from Nyiragongo streamed into the city of Goma, demolishing many of its neighborhoods and killing dozens of people. It was a harsh reminder that, although volcanoes have been ravaging populated areas throughout history, we still lack the ability to accurately predict deadly eruptions and save lives.

If predicting eruptions is a confusing puzzle, volcano hunters Steve and Donna O'Meara believe that they may have identified a key piece. The husband-and-wife team are investigating a connection that some volcano watchers have noted since early times, but none has adequately studied—the role of the moon in affecting volcanic activity.

The O'Mearas' interest in this lunar theory began by chance back in 1996, while the duo was studying an erupting volcano in the field. Steve is an astronomer by training, and it was his experience in this seemingly unrelated field that led him to a fateful discovery.

While compiling detailed journals of his scientific observations, he began to notice a correlation between increasing volcanic activity and lunar cycles. Pouring through stacks of data he had collected over twenty years in the field, Steve examined past eruptions and saw some of the same patterns. Further research suggested that a lunar pattern was also apparent in some famous historic eruptions, such as Krakatoa in 1883.

Other observers throughout history had noted the possibility of such a connection, but always as a footnote, and always when looking back at eruptions that had already occurred. No one had given the matter comprehensive study, and no one had attempted to employ these lunar patterns as one of the tools to predict future volcanic eruptions.

Stromboli, a Volcanic Hotspot

Supported by the National Geographic Society, the husband-and-wife team set out to test just that possibility at one of Earth's volcanic hotspots, the summit of Stromboli on Italy's Aeolian Islands.

Stromboli is one of the most active volcanoes on the planet. The restless mountain has been in a state of nearly continuous eruption for at least 2,000 years. Although large eruptions and lava flows are uncommon, smaller eruptions occur very frequently and often hurl blobs of lava above the crater rim.

Stromboli's slopes can be inhospitable. Visitors have to contend with toxic gases, noxious fumes, and showers of hot ash. While on site the team (composed of Steve, Donna, and several research assistants) also endured unusually brutal weather conditions at their mountaintop camp. Yet, fueled by their enthusiasm, they carried on making observations 24 hours a day, working in six-hour shifts. Despite the skepticism of some volcanologists, the group was determined to put the lunar theory to the test.

Although living conditions on Stromboli left much to be desired, the climate was ideal for research because of the continually active eruptions and the occurrence of several important lunar events. The moon entered some important phases during the team's time on Stromboli. In the 14-day span of observations the moon reached perigee (the point when its orbit is nearest the Earth) and also experienced a full moon phase. The full moon is a point at which the moon exerts particularly great influence on the Earth, as evidenced by high tides.

The team's task was to determine when the greatest peaks in eruption activity occurred, and what connection the increased activity might have with the moon's gravitational pull. Following the patterns they had seen in the past, the O'Mearas predicted that during the volcano's ongoing eruptions, there would be peaks in volcanic activity at perigee and at full moon. In this case, events bore out that hypothesis and in fact the greatest spike in volcanic activity occurred at a point in time just between full moon and perigee.

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