Photograph by Rakel Osk Sigurda, NordicPhotos, Getty Images

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Horses are herded away from the Eyjafjallajökull volcano's ash plume on April 17, 2010.

Photograph by Rakel Osk Sigurda, NordicPhotos, Getty Images

Iceland Volcano Has "Quieted Down"—Ash Crisis to End?

Lower plume and visible lava raise hopes European travel will soon resume.

Iceland's Eyjafjallajökull volcano is changing the pace of its eruption, volcanologists reported Monday, raising hopes that the volcanic ash plume that has paralyzed air travel in Europe will soon scatter.

"The activity has quieted down, and the plumes are lower at the moment, rising only 500 to 1,000 meters [1,650 to 3,300 feet] above the vent," said Icelandic volcanologist Thorvaldur Thordarson.

The volcanic ash plume once soared as high as 36,000 feet (11,000 meters). (Related: "Iceland Volcano Ash Plume Prompts Health Worries.")

"I think at the moment, because the plume is lower, it might help with the ash problem. It won't get into the jet stream and won't travel as far, and at lower altitudes it could be washed out by precipitation," added Thordarson, of the University of Edinburgh in Scotland.

"But it's difficult to say whether it will clear completely or not. It could pick up again."

Iceland's weather office also reports that lava is flowing in Eyjafjallajökull's basin, suggesting that much of the glacial ice overlying the vent that's the source of the ash has melted. (Pictures: Iceland Volcano Erupts Under Ice.)

The ice cap has been putting pressure on molten magma below, helping to propel the plume of vapor and volcanic ash skyward. An increase in flowing lava may mean a new, gentler phase of the Iceland eruption—at least in the short term.

"A lot of what's enhancing the explosiveness of this eruption and the ash generation is the interaction between the lava and the glacier and the meltwater that's being created," said Mike Poland, a geophysicist at the Hawaiian Volcano Observatory.

"If you remove that element, I'd imagine that the explosiveness and the ash generation would decrease—but that's kind of an unpredictable element to this."

Iceland Volcano Quieting—Or Reloading?

Even if the volcanic ash plume dissipates, experts say it's possible further disruptions are imminent.

Eyjafjallajökull has a history of lengthy eruptions: An 1821 event lasted, intermittently, until 1823. (See pictures of Mount St. Helens immediately after its major 1980 eruption and 30 years after the blast.)

With the current eruption, "the [seismic] tremor has increased in the last 18 hours. That's not manifesting itself in more powerful output, and we don't have a very good explanation for that yet," Thordarson said.

A spike in seismic tremors doesn't necessarily mean the Eyjafjallajökull volcano is reloading for another eruption, noted Tina Neal, a volcanologist at the Alaska Volcano Observatory in Anchorage.

"Lots of things can increase tremors," she said, "including surface hydrology, like boiling waters, or gas release."

But volcanologists will be watching for several signs that could indicate a new round of activity at the Eyjafjallajökull volcano.

Iceland Volcano Trackers Watching for Magma Swells

One tool volcano trackers have been using is a satellite technique known as Interferometric Synthetic Aperture Radar, or InSAR, said the Hawaiian Volcano Observatory's Poland.

This method uses ultrasensitive radar images taken from space to tell whether a volcano is swelling ever so slightly as magma rises to the surface for an eruption.

For the Eyjafjallajökull volcano, InSAR has already yielded "some fantastic results [and seen] that, during the years leading up this eruption, it has been inflating in little fits and starts. That's one of the major signs of a volcano moving toward an eruption," Poland said.

Though the peak of Eyjafjallajökull is hidden by an ice cap, scientists have been able to see deformations that preceded the current eruptions far down the volcano's flanks, tens of kilometers outside the glacier's boundaries.

Other observation techniques using GPS and seismic equipment can also help scientists anticipate the Iceland volcano's next moves.

But when volcanoes are involved, an element of the unknown remains.

"There is always uncertainty," the Alaska Volcano Observatory's Neal said, "because there is still a lot to learn about interpreting all of these signals."