Problematic ash crisis headache for travelers.

• Position: Volcanoes

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Air travel may have resumed in Europe--although there still have been sporadic shutdowns across the continent--but the future behavior of the volcanic ash cloud and the eruptive system that spurred it is difficult to predict, remarks volcanologist Michael E Sheridan, founder of the Center for Geohazards Studies, Buffalo, N.Y.

"It's hard to forecast the behavior of this volcanic system," he admits. "It is shortsighted to assume that even if air travel returns to normal that the environmental problems related to the eruption will end immediately." In addition to air travel woes that the massive ash cloud already has caused, it may trigger longer-term changes in climate and health hazards, Sheridan indicates.

His concern stems from his understanding of similar kinds of eruptions that have occurred in this part of Iceland. "The oceanic crust in this region is slowly pulling apart along giant fissures that extend deep enough to reach magma sources," he reveals. "The volcanic magma rises along these fissures and erupts in episodes when and where the fractures break at the surface."

Eruptions at adjacent volcanoes could be linked to the same spreading episode, he adds, producing a compound effect. The Eldgja eruption of 934 A.D. was the largest outpouring of flood basalt lava in...