A metal sign reads, Warning! The glacier can be dangerous. A rumbling growl from under the mountains speaks far louder.Solheimajokull glacier is part of the ice cap sealing Katla, a volcano 10 times more powerful than neighbouring Eyjafjoell, whose eruption last week clogged Europe's skies with ash and grounded the continent's airlines.If Katla blows up, the current eruption will resemble 'a small rehearsal,' Iceland's president, Olafur Grimsson, warned. A metal sign on the Myrdalsjokull glacier, which is part of the ice cap sealing the Katla volcano, reads, Warning! The glacier can be dangerous.The frightening reputation of Katla is mirrored in a savage landscape of black volcanic ridges, blue ice, and snow swept and hardened by powerful winds.Reaching the glacier requires a four-wheel-drive vehicle, or mountaineering equipment and snowmobiles to go further. During a visit on Thursday, a huge raven on a boulder was the sole living creature visible.The worry for Icelanders is that each time Eyjafjoell has erupted over the last millennium, Katla, named after an Icelandic witch, quickly followed.Some believe the volcanoes are directly linked underground so that magma from one can flow into the other.Katla has erupted approximately every 80 years since Vikings first settled on this island nestled under the Arctic Circle more than a thousand years ago.The last eruption was in 1918.