5. Grímsvötn, Iceland (60)
Since last year's Eyjafjallajökull eruption (the 2010 Pliny winner) that brought air traffic over Europe to its knees, nothing gets the media's attention like an eruption in Iceland. Eyjafjallajökull and Katla both stayed quiet, but Grímsvötn, another active volcano on the island nation, did see its first major eruption since 2004. The eruption started as a subglacial event that was highly explosive - producing a plume that reached 15-20 km / 55,000-60,000 feet, one of the tallest Icelandic plumes of the last century. An eruption of this magnitude did cause a few minor flight disruptions due to ash from the eruption, but overall, Grímsvotn did not produce major issues. Within a week of the start of the eruption on May 21, it was deemed as over.
Image: The eruptive plume from Grímsvötn seen on May 21, 2011. Image by Ólafur Sigurjónsson courtesy of the Icelandic Meteorological Office.