17 November 2011, by Tamera Jones
The mystery of why there's a mountain range the size of the European Alps buried deep beneath the East Antarctic Ice Sheet has finally been solved.
The results of one of the most ambitious and challenging expeditions during International Polar Year reveal that the enigmatic Gamburtsev subglacial mountains didn't form in the same way that almost all other mountain ranges do.
Instead, it seems they started forming a billion years ago, when the Earth's continents looked nothing like they do today and Antarctica was still part of a massive supercontinent called Gondwana. Survey data suggests they only attained their present height and shape through a series of rare and complex geological processes.
'This range is in one of the least explored frontiers on Earth and it's hidden beneath the ice. We know more about Mars than the interior of East Antarctica.'
Dr Fausto Ferraccioli, British Antarctic Survey
The Gamburtsev mountain range was discovered in 1958 during International Geophysical Year by a Soviet Antarctic expedition, and was named after Russian geophysicist Grigoriy Gamburtsev. Sited deep in East Antarctica, it lies below the highest, and perhaps the coldest, place on the East Antarctic Ice Sheet – Dome A. The range is around 1200 kilometres long and some peaks are nearly 3000 metres high.
Researchers think the mountains could be the birthplace of the vast East Antarctic Ice Sheet, which covers 10 million square kilometres – an area the size of the United States.
But finding out more about them is particularly challenging because of where they are. Indeed, this is the first time scientists have comprehensively explored the range since the first Russian survey.
'We understand the mechanisms of how most mountain ranges form well, because there's a degree of exposure and so we can investigate their geophysical structure,' says Dr Fausto Ferraccioli from the British Antarctic Survey, lead author of the study, published in Nature.
'But this range is in one of the least explored frontiers on Earth and it's hidden beneath the ice. We know more about Mars than the interior of East Antarctica,' he adds.
The mountains are unusual because they are in the heart of Antarctica. Ranges like the Himalayas and the European Alps form when continents collide and crunching tectonic plates force peaks upwards. This explanation does not fit what polar researchers know about the Gamburtsev range. Mountains can also form above volcanic hotspots like Hawaii, but so far, no volcanic activity has been found in the region. So how on Earth did they form?
To find out, a seven-nation team of scientists set up a remote field camps either side of Dome A and spent two and half months surveying Antarctica's Gamburtsev Province (AGAP). In some of the harshest conditions imaginable, with temperatures averaging -30ºC, the researchers flew two survey aircraft over the ice sheet. The aircraft covered 120,000 kilometres, the equivalent of three trips around the globe. They surveyed over 20 per cent of the East Antarctic Ice Sheet with radar, aeromagnetic and gravity sensors.
'This survey was only possible because of International Polar Year: seven nations were able to pool their resources,' says Ferraccioli.
The survey data revealed a very thick crustal root that extends deep beneath the mountain range. Ferraccioli and his colleagues think that when multiple continents collided a billion years ago, the oldest rocks of the mountain range got crushed together, creating this very stable root.
'This root appears to be incredibly stable, which is unusual. Most geological processes would've led to it eroding, but it is still preserved today' Ferraccioli explains.
They also found a section of rock either side of the Gamburtsevs scored with a series of rifts that stretch for around 2500 kilometres from East Antarctica towards India.
It looks like this region of rifts – around the same size as the Great Rift Valley in East Africa – was formed around 250 to 100 million years ago, when dinosaurs walked the Earth. This rifting may have let the supercontinent Gondwana break apart, causing the old crustal root to warm up.
These processes would likely have forced the land upwards, creating the Gamburtsev range.
'We think the flanks of the rifts lifted up to create the mountains,' Ferraccioli says. 'So the rifting was the tectonic trigger.'
But since then, he explained that rivers and alpine glaciers would have carved deep valleys, giving the Gamburtsevs their jagged alpine appearance.
'There's a distinct possibility that Antarctica was in a polar position by then, so perhaps the mountains were the nucleation point for ephemeral ice sheets that came and went,' Ferraccioli adds.
He is keen to explore this region even further. 'We still don't quite know where the rift system goes. We know it extends to India, but we're not sure what its route is. And of course, we'd ideally like to drill down to the rock so that we can test our geophysical models.'