Rare sub-glacial eruption at Casey

Australian scientists are hoping a rare sub-glacial water eruption near Australia’s Casey station, will reveal why meltwater is present, and the extent of a river and dam system flowing deep under the Law Dome ice cap.

In only the second reported incident of its type in Antarctica, a Jökulhlaup, or sudden outburst of basal melt water from beneath the ice cap, erupted near Robinsons Ridge, 15 kilometres south of Casey.

Associate Professor Ian Goodwin from Macquarie University observed the first recorded Antarctic Jökulhlaup, also near Casey station, in 1985–86, and located a large sub-glacial lake near the ice margin. The new eruption was first noticed by Casey expeditioners over the 2014 winter.

‘The expeditioners saw the melt water rising to the surface and dispersing over the surrounding ice sheet, before refreezing,’ Professor Goodwin said.

‘The refrozen Jökulhlaup water is very prominent because of its striking olive-green colour, which contrasts sharply with the surrounding blue glacial ice and white snow.’

Samples of the frozen Jökalhlaup water were collected by Dr David Etheridge from the CSIRO and Dr Andrew Smith from the Australian Nuclear Science and Technology Organisation in February this year.

The ice is now being analysed at Macquarie University, Curtin University and the Antarctic Climate and Ecosystems Cooperative Research Centre, to find out more about the conditions under Law Dome.

‘There have been advances in technology and techniques since the last known eruption 30 years ago, which will allow us to measure the hydro-chemistry of these samples in much more detail,’ Professor Goodwin said.

‘We will measure the major ionic chemistry and isotopes to find out how the bottom of the ice sheet is melted, how far the water has travelled, and to get an insight into the stability of the ice sheet. We will also attempt to estimate the age of the water, which is potentially tens of thousands of years old.’

Previously, scientists thought the Law Dome ice cap was frozen to the bedrock. However, the 1985 Jökalhlaup showed water is produced underneath some parts of the ice cap, at least episodically.

‘Our observations of the Jökulhlaup confirmed Law Dome had high geo-thermal heat emanating from the Earth’s crust, which was melting the bottom of the ice cap,’ Professor Goodwin said.

‘This water then flowed in river systems under the ice sheet out into the ocean, or in this case, where the rivers are dammed by frozen ice, the water flows up to the surface through weaknesses in the ice sheet.’

Program leader with the Australian Antarctic Division, Dr Tas van Ommen, said recent aerial radar work through the ICECAP project (Australian Antarctic Magazine 19: 7, 2010) will help the researchers pinpoint the origin of the water.

‘The ICECAP project used ice-penetrating radar to map the conditions at the base of the ice sheet in East Antarctica, and this can help identify which areas are more likely to produce basal melting and water,’ Dr van Ommen said.

‘Putting the whole picture together, with data from ICECAP, deep ice core temperature measurements from Law Dome, and samples from the Jökalhlaup, will help us understand the past and present behaviour of the ice cap, and how it might evolve in the future,’ he said.

Analysis of the Jökalhlaup samples is expected to take several months.

Nisha Harris
Australian Antarctic Division