Blue pools form atop Katla volcano

Beautiful blue pools have formed at an elevation of 1,300 metres on Mýrdalsjökull, the glacier above Katla volcano, mbl.is reports. The pools are estimated to be 150 to 200 metres wide and several metres deep.

Katla is described as one of Iceland’s most active and dangerous volcanoes. The pools are two adjoining ice cauldrons at Austmannsbunga on the northern rim of Katla’s caldera.

Benedikt Bragason, a farmer at Ytri-Sólheimar directly south of the glacier, told Morgunblaðið that Austmannsbunga was named after Jón Austmann, a priest who ran up the mountain during a Katla eruption. Benedikt took tourists to the mountain by snowmobile for 30 years but has now stopped.

He said visitors were fascinated by Katla and that there was plenty to explain and discuss on the mountain. The pools are strikingly blue but disappear when a glacial flood emerges. Cracks then form in the glacier surface, allowing the water to drain away.

Longstanding expectation of an eruption

Benedikt said he had long expected Katla to erupt, although the likelihood might now be decreasing. He said people living beneath the mountain had to live with stories about what previous Katla eruptions had been like.

He said he was not afraid but had great respect for the volcano. He hoped he would not have to experience a Katla eruption under conditions like those during the 2010 eruption of Eyjafjallajökull, which he described as extremely difficult.

Benedikt said he had seen water in the ice cauldrons before but did not remember ever seeing as much as there is now. He also noted that the glacier looked particularly white and fresh, indicating that it had snowed recently.

Snow can fall on the glacier throughout the year, he said. When warmer weather follows fresh snowfall, more snow can melt and collect in pools such as these.

Geothermal heat creates the depressions

Glaciologist Helgi Björnsson told Morgunblaðið that the ice cauldrons form because of geothermal heat beneath the glacier. The heat melts the ice and creates depressions in the surface, where meltwater can collect.

Helgi said the water in the depressions was not geothermal fluid. Instead, it came from snow and ice melting at the surface in the middle of the depressions.

Water can also accumulate beneath the cauldrons. Pressure at the glacier bed around the depressions becomes greater than beneath them, trapping meltwater at the bottom. The water eventually escapes from beneath the glacier when its pressure becomes high enough for channels to form under the ice blockage.

Helgi said that was what happened recently when a flood entered Múlakvísl. Such floods empty the lakes beneath the glacier. Cracks then form in the surface, allowing the water in the pools to drain away, after which the pools gradually form again.

The accompanying image shows the western Skaftárketill, an ice cauldron, and is not connected to the flood in Múlakvísl.