So, how do you predict the eruption of a volcano?

The year of the earthquake has suddenly become the year of the volcano.

The eruption in Iceland is not large as volcanoes go, but the cloud over Europe has shed light on the awkward overlay of human commerce and a hot, churning, unpredictable Earth. It raises the question of what governments can do to prepare for -- and adapt to -- wild-card geological events that not only affect airliners but can also alter the planet's climate for years at a stretch.

The volcano with the difficult name of Eyjafjallajokull is not powerful enough to change the climate -- it has ejected material only as high as about 20,000 feet and would need to launch the ash to at least 33,000 feet to have global climatic effects, according to the National Oceanic and Atmospheric Administration (NOAA).

Now airports are beginning to open again in Britain and the Netherlands, but no one can be entirely sure what will happen next in Iceland. Eyjafjallajokull could incite an eruption of its larger neighbor, Katla, which hasn't erupted since 1918 and might be ready to rumble. In all three historically recorded eruptions of Eyjafjallajokull -- in 920, 1612 and 1821 -- Katla erupted soon thereafter.

"The eruption that's going on right now is small in comparison to what we expect Katla would be like," said Jay Miller, a volcanologist at Texas A&M University.

Events in recent days have demonstrated the inherent uncertainties of volcano science. Although volcanoes are far more predictable than earthquakes, they remain quirky, with each one having its own personality. Scientists rely primarily on past performance to predict future activity for any given location. The Iceland volcano initially produced little ash, but a new vent opened beneath a glacier and the situation turned explosive. What precisely happened is still being researched, but it appears that meltwater and magma produced steam quite suddenly and the volcano popped its top like a shaken soda bottle.

No one knows how much material will be ejected, or how high into the atmosphere it will travel. Scientists using computer models are frantically trying to track plumes of ash that become widely and chaotically dispersed even as new ones shoot up. No one knows whether the ash will reach the airspace over the United States and affect domestic travel, though that doesn't seem to be an imminent threat. The ash has reached eastern Canada, however.

"I think there might be some nicer sunsets by the end of this week over North America," said Stan Benjamin, director of the Forecast Research Branch of NOAA's Global Systems Division.