Iceland has about 130 volcanic mountains, 18 of which have erupted since settlement.  Some erupt every couple hundred years, some every 50-80 years.  Typically there's some kind of volcanic activity every few years.  Eyjafjallajökull (pronounced: "Eyjafjallajökull" just like it's written) erupted rather famously in 2010 interupting air travel in Europe for several weeks.  However, in Iceland this was considered a relatively minor event, dwarfed by a larger eruption in 2011 at Grímsvötn.

While in Iceland we explored the Eyjafjallajökull visitor's center and also hiked several craters and lava fields in other areas including Mt Laki and Hverfjall.  Some portions seemed eerily like hiking into Mount Doom on bad day.  Watch for the Yule Lads, descendents of mountain trolls.  Here are some more photos: