"Teams monitoring Bardarbunga volcano have found evidence of a possible underground eruption as powerful earthquakes continue to shake the area, authorities said on Thursday.
Scientists flying over the area on Wednesday discovered a 2.5-4 mile line of giant craters or cauldrons – 10 to 15 metres deep and 1km wide – on Vatnajokull glacier which covers the giant volcano."
http://www.theguardian.com/world/2014/aug/28/underground-eruption-earthquake-iceland-bardarbunga-volcano