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Antarctic lake released massive under ice flood

Southern flood Five years ago one of Antarctica's subglacial lakes burst its banks creating one of the largest flooding events ever recorded on the continent, according to a new survey.

The researchers, from the United Kingdom and the Netherlands, estimate up to 6.4 trillion litres of water was released into the ocean -- enough water to meet the needs of Australia for almost half a year.

Their study appears in the latest edition of the journal Geophysical Research Letters.

Beneath the ice sheet of Antarctica there is a network of 379 subglacial lakes filled with water from melting glaciers -- the most famous of them is Lake Vostok.

Scientists discovered these lakes when they noticed that parts of the ice sheet moved vertically, as though bobbing on water. Using modelling and satellite radar data, scientists deduced that the movement was caused by subglacial lakes. These are fed by the melting of glaciers, and sometimes the lakes overflow and drain into the surrounding ocean.

Between November 2006 and March 2008, scientists noticed that the ice sheet on top of Cook Lake -- which sits beneath 2700 metres of slow-moving ice -- was subsiding. During that time, the ice sank by 21 metres to form a deep crater, which suggested that the lake was losing water.

Data collected by two Earth observing satellites was analysed to determine the geometry of the crater and calculate the volume of the space caused by the subsidence. They assumed the volume would be equal to the amount of water lost by the lake.

Their calculations showed that the lake had lost between 4.9 and 6.4 teralitres of water. That would have caused a massive under ice flood, causing a rapid flow of water to the ocean.

If the higher estimate of the flood size were true, the flow rate of the resulting 'river' would have been 160 cubic metres per second.

"To provide context, this is equivalent to about 10 percent of the annual subglacial melting beneath the Antarctica Ice Shelf," the researchers write.

They say further surveys are needed to calculate the frequency of large drainage events, and improve our understanding of glacial melting and water movement under the Antarctic.