Iceland's Eyjafjallajokull volcano has been actively erupting since March. The most recent event on April 14 produced an ash cloud sufficiently massive to disrupt air travel throughout the British Isles and nearly all of Europe, with ripple effects for travelers around the world. Continuous eruptions are so rare that vulcanologists have insufficient data to determine how much longer the current event will continue.
Iceland is a geolological paradox -- a land of active volcanoes and glaciers. It is the interaction of the two which has made the current eruptions so ... well, seismic. Before it erupted, the Eyjafjallajokull volcano was overlain by an ice sheet which prevented the possibility of earlier, smaller eruptions to release in smaller doses the titanic magma pressures beneath. Only after the pressures reached epic proportions were they intense enough to break the ice barrier. In addition to the spreading ash cloud, meltwater from the superheated ice sheet poses a threat of significant flooding.
As Simon Winchester points out in a NYTimes article, the last time the planet experienced such force was in 1883, when the island of Krakatoa (located between Java and Sumatra) erupted. The explosion was heard as far as 3000 miles away, and destroyed the entire island, ejecting five cubic miles of ash, rock and pumice into the atmosphere. For years after, airborne ash created light displays around the world -- vibrant sunsets, horizon rainbows and a blue moon. An entire art movement was born. Many thousands of paintings of landscapes with red, yellow, salmon, amber and purple skies were produced, the most famous of which was Edvard Munch's "The Scream."
The current ash cloud is being carried to altitudes as high as 30,000 feet, which may allow it to spread across Asia, perhaps reaching North America. In addition to the potential for destroying any air-breathing engine, ash presents serious health risks, particularly for those with asthma or other breathing disorders. The individual ash particles are so fine that once breathed in, they adhere to the moist linings of the lungs -- in effect creating cement.