Iceland's spectacular volcanic eruption is catastrophic near the blast. Rapidly-melting glaciers are flooding farmland, while pulverized particles of ash, now 30,000 feet up, are blowing across Europe.
Made up of microscopic particles as hard as a knife's blade, the dust cloud crept across the industrial powerhouses of Europe, into the steppes of Russia and as far south as Hungary on Friday.
How long it lasts and how far it spreads depends entirely on two unpredictable events: whether the volcano beneath Iceland's Eyjafjallajokull glacier keeps pumping tons of dust into the air, and what wind patterns do.
The invisible cloud could split, reaching down into northern Italy, and perhaps break apart over the Alps. Scientists say the volcano could continue erupting for months, with more chaos ensuing with each big belch of basalt powder and gas.
Eventually gravity will take over.
"Because the particles are heavier than the air, they fall out or they hit a rainstorm and get washed out," said Alan Robock, professor of environmental sciences at Rutgers University. "They'll basically just disappear from the atmosphere over a period of days."
The climatologist said the volcanic cloud would have to climb much higher - 40,000 to 50,000 feet - to affect Europe's climate.
"Only if the eruption becomes much stronger and puts a lot more particles, a lot more sulfur gas in the atmosphere, could it have a large effect on climate," said Robock.
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The volcano is coughing up about 3,000 tons of sulfur dioxide each day. When that combines with water vapor in the upper atmosphere, it can reflect sunlight away from the Earth, cooling temperatures on the ground.
That's what happened when Mount Pinatubo erupted in the Philippines in 1991.
The ash flow from that eruption spread around the world in a few days, said Professor Jonathan Lees of the University of North Carolina-Chapel Hill. "There was enough material in the atmosphere to cause the average temperature of the Earth to go down one degree."
Since the last time the Icelandic volcano erupted was nearly 200 years ago, scientists are having a hard time predicting how long this eruption will last.
And it is feared the cloud of grit, once it settles on Earth, will endanger the lungs of children, asthmatics and others with respiratory ailments.
"We're very concerned about it," said World Health Organization spokesman Daniel Epstein. "These particles when inhaled can reach the peripheral regions of…the lungs and can cause problems."