No idea how you really pronounce it, but the "listen" link on Wiki sounded kinda like: ai'yavuhlo'vik (they say it's pronounced AY-ya-fyat-la-yo-kult)
E-etc (sorry, I am way too lazy to type Eyjafjallajökull) is the name of a glacier; by Icelandic standards a small one. This smallish glacier, known as an ice cap, is over a volcano which has been erupting from time to time since the last Ice Age.
An ice cap is a type of a glacier that isn't a gigantic sheet, or stream, of ice. It's just a huge blob that covers everything around it, including mountains. The ice will flow from the highest point of the ice cap, called the ice dome, down in all directions.
Earthquakes in the area of E-etc became frequent in December 2009. In February geologists noticed that the Earth's crust in that area had shifted south about 3 centimeters--it shifted 1 centimeter in the space of four days. That's fast for crust. This told geophysicists that magma was moving from the crust to the magma chamber of the volcano.
A magma chamber is a large pool of molten rock under the Earth's surface.
Between March 3 and March 5 nearly 3,000 earthquakes were measured at the epicenter of the volcano. First volcanic eruption was 20 March 2010.
The area is not heavily populated. About 500 farms were evacuated. Flights to two airports in Iceland were postponed, but only for about 24 hours. On 22 March, the farmers were allowed to return.
This eruption was a fissure, 500 meters long, with 10 to 12 erupting lava craters spewing lava up to 150 meters into the air. So far it has formed a 200 meter long flow of lava.
"On 25 March 2010, while studying the eruption, scientists witnessed, for the first time in history, the formation of a pseudocrater during a steam explosion."
A pseudocrater looks like a volcanic crater but it is formed when lava passes over a lake, swamp, stream or other wet surface--in this case, a glacier. Pseudocraters do not have any connection to the magma below the surface as real craters do.
Another smaller fissure opened on 31 March. It shares the magma chamber with the first fissure.
This eruption is considered small by Icelandic standards. It did not happen under the ice, but instead in a mountain pass to the side of the glacier. This was good for the community because there is less flooding from melting glacial ice.
At first there was not a lot of volcanic ash from this eruption. But after two days an explosion sent eruption columns 4 to 7 kilometers into the air.
Eruption columns are the ash rising into the air out of the volcano. Everyone loves lava, but eruption columns are pretty danged amazing on their own. In a major explosion they can go 40 kilometers into the air, reaching the stratosphere. This can cause short-term climate changes globally as well as locally.
The volcano paused for a couple of weeks, then on April 14 the center of the glacier erupted about 20 times stronger. This eruption sent glacial meltwater flooding down the sides of the ice cap in two flows. 800 people were evacuated from the surrounding area, which is mostly farmland.
The cold water from the melted ice chills the lava and fractures it into tiny particles of glass that are carried up into the eruption column. This formed a plume of volcanic ash and glass that drifted eastward to Europe.
This sort of plume is a major hazard to aircraft. It can "sandblast" the windshield, preventing the crew from seeing. But more severely, the ash and glass are sucked into jet engines. The glass melts onto the blades and other parts which can cause jams and destroy parts.
The volcanic ash plume from E-etc has caused flights to be canceled all over Europe. An air traffic halt on this scale has never happened before. Although there hasn't been a crash from planes flying into volcanic ash, planes have flown through volcanic ash plumes in the past and it is very dangerous. It can cause the engines shut down and that's never good. Flights were canceled and airports closed starting in Norway on April 14; by April 16 flights have been delayed or canceled in at least 19 countries, including the United Kingdom. Several students at our school were on a trip with to the UK with their history teacher during break. They returned over the weekend. If their return were scheduled just a couple of days later, they would be able to give us a first-hand account of what it's like to need to fly in a land with no air travel. Many European leaders were just in Washington for the major nuclear summit with President Obama. Some of them are now stranded as they are not able to fly back to their countries. I read that the prime ministers of Germany and Norway both had to fly to Spain and then take a train the rest of the way (that's a long way by train -- Spain to Norway!)
As of April 17, weather and air travel authorities are not certain when flights will begin to return to normal. Other issues that arise when all air travel is halted like this are shipments and deliveries. The UK, for instance, imports 90% of its fruit.
The ash is dangerous for planes because it rises so high into the atmosphere. This ash plume, though it is causing so much trouble for aircraft, is not expected to cause health problems for the people who live under its path. It is too high to have a serious effect on the air we breathe.
However, it could have an effect on the weather. People in Europe will be able to see fantastic red sunsets as the sunlight slants through and reflects off of the glassy ash.
In the past, volcanic eruptions in Iceland have been severe enough to lower the average temperature of the Earth's surface by up to half a degree for one to three years. In 1821, a relatively small eruption began and continued with varying degrees of intensity through 1823. In 1783 a volcano near E-etc, called Laki, erupted for 8 months, affecting both summer and winter in Northern Europe to the extent that many crops failed and people starved. It is believed that Laki contributed to the French Revolution because of its effect on food crops.
East of the vent that is erupting now is a much bigger volcano called Katla. It is also under a glacier. It has been known to erupt when E-etc erupts. But... it is a volcano and cannot be relied upon to behave consistently.
P.S. I love Wikipedia.
Oh, and Flickr: http://www.flickr.com/photos/yahooeditorspicks/galleries/72157623855495574/