Smack bang in the middle of Antarctica sits a mysterious mountain range. Its jagged peaks cover an area similar to that of the Alps, and its highest point is around 3500 metres above sea level. Yet by rights these mountains shouldn't exist at all.

The peaks are tucked under thousands of metres of ice, so no one has ever seen them. No one knows how old they are nor even what they are made of. Yet the biggest mystery of all is how they got there in the first place.

There are three competing theories to explain how the mountains formed. What's missing is the evidence to prove which, if any, is correct. So earlier this year an international team of scientists made plans to head back to Antarctica to probe deep beneath the ice and finally figure out what made the mountains.

A team of Russian scientists discovered the range as long ago as 1958 and named it in honour of geophysicist Grigoriy Gamburtsev. They had been trundling along at around 8 kilometres per hour in a tractor-train, taking seismic readings every 50 kilometres on a journey from what is now the Vostok station in East Antarctica to the Pole of Inaccessibility, the furthest point from sea. By chance their line of seismic readings crossed the backbone of the Gamburtsevs, revealing for the first time the spiky peaks buried under the ice.

The Gamburtsevs' existence was confirmed in the Antarctic summer of 1977-1978 by a consortium of international scientists who overflew the region and bounced radio waves through the ice to measure its depth. Their scan revealed mountains beneath the ice that stood 2000 metres tall .

The most recent visit was in 2005 when a Chinese research team spent 29 days battling their way across the 1228 kilometres of ice from the Zhongshan research station to Dome A, the highest point on the Antarctic ice sheet. They installed an automatic weather station there, drilled a shallow ice core and carried out a radar survey over the mountains. Sun Bo from the Polar Research Institute of China in Shanghai confirmed that at some points the ice was less than 1000 metres thick, making it feasible to drill down and take a rock sample. Analysing such a sample will help to determine which of three theories is most likely to explain how the mountains formed.

Most mountain ranges are born when the Earth's tectonic plates converge. Sometimes an oceanic plate sinking under a continent will push up a bulge, like the Andes or the Rockies; other times mountains rear up when two continental plates collide, creating ranges like the Himalayas and the Alps.

Antarctica has its share of conventional ranges, including the Transantarctic mountains, which formed through a combination of volcanic eruptions and the interaction of the East and West Antarctic continental plates. The Gamburtsevs defy these mundane mountain-building mechanisms. They sit proudly in the middle of Antarctica, with not a plate boundary or a volcanic fissure in sight.

So how might they have formed? First up is the volcanic theory. It is possible the mountains were pushed up by a "hotspot" or column of hot rock bubbling up from deep in the mantle, like the one that created the Tibesti and Hoggar massifs of North Africa. The problem with this theory is finding the hotspot. "When we do plate reconstructions we find that there have been no obvious hotspots under this part of Antarctica during the last 100 million years," says Ian Dalziel, a geologist at the University of Texas in Austin. And the Gamburtsevs are unlikely to be much more than 100 million years old, otherwise weather and ice would have worn them down.

Ancient hotspot?

Michael Studinger, from the Lamont-Doherty Earth Observatory of Columbia University, New York, thinks he has a way around this problem. "Possibly the Gamburtsevs have a hard cap rock that is resistant to erosion, like the Lesotho highlands in South Africa do," he says. A tough protective top could push back the mountains' age by tens of millions of years. In this case the Kerguelen hotspot, which is sitting 5500 kilometres away in the Indian Ocean, could have been the trigger that made the Gamburtsevs punch through the Earth's crust. This hotspot could have passed under the Antarctic plate around 150 million years ago.

Is there a way to prove the hotspot theory? "The hotspot is probably no longer there, but we expect that the rocks may still [be warm]," says Studinger, a principal investigator on one of the Gamburtsev exploration teams. One part of their project will be to set up earthquake recording stations in many positions above the Gamburtsevs and record earthquake waves for one year. The speed at which seismic waves move through the earth is affected by the temperature of the rock. The lower the temperature the faster the waves go, so slower waves would indicate warmer layers of rock.

The team will also be looking at magnetic data from the region because volcanic lavas are easily magnetised. "A strong positive or negative magnetic signal would indicate a volcanic feature," says Studinger. And that would add credence to the hotspot theory.

If this theory draws a blank then there is another possibility. In 1994, John Veevers, a geologist at Maquarie University, Australia, suggested the Gamburtsevs may have formed around 250 million years ago, when Antarctica was part of a huge supercontinent called Pangaea. When Pangaea was forming, the collision of continents created mountain ranges such as the Appalachians and the Urals. What is now Antarctica may have felt the echoes of these mountain ranges forming, causing the Gamburtsevs to pop up in one particularly soft spot. This mountain building mechanism is known as "far-field compression" and can be seen today in mountains such as the Pico da Neblina in northern Brazil, a mountain that popped up in response to the stress transmitted as the Andes formed.

But if far-field compression was responsible for the Gamburtsevs they would have to be around 250 million years old, which again means they would have fallen prey to erosion. It is an implausibly long time for such tall mountains to have survived, says Dalziel.

If they aren't volcanic or ancient, what are they? For the last 15 million years Antarctica has been covered in ice. Martin Siegert, a geologist at the University of Edinburgh, UK, who heads a rival team to Studinger's, thinks that this huge body of ice may have been responsible for moulding the mountains.

It probably started out with a small ice sheet growing in the middle of Antarctica. This ice would have scoured away the crust, making it thinner at this point than around the edges of the continent. So Antarctica would have looked like a cake that had failed to rise, with a pool of icing filling the hollow.

Underneath the hollow the flexible lithosphere would adjust to these changes and flow inwards to prop up the thin bit of crust, so the theory goes. "In some models, depending on the lithospheric structure, this can lead to extra uplift in the middle of Antarctica," says Siegert. This would have pushed up the crust in that area, creating the mountains.

To try to prove this theory, Siegert and his team plan to do a detailed airborne radar survey, chopping the area up into a grid of 20-kilometre squares and bouncing radio waves down every grid line to create a detailed contour map of the Gamburtsevs. "Radio waves travel straight through the ice like light through glass," explains Siegert. "We can fly along at 300 kilometres per hour and get brilliant data really quickly."

Siegert and his colleagues will then look for the presence of glacial features. These could only have formed as the Antarctic continent was being covered in ice, meaning the mountains were already there and hence ruling out the ice-erosion formation theory. On the other hand, "if the mountains formed after the glaciation began then we wouldn't expect to see upland glaciological features such as hanging valleys, cirques and ar�tes," he says.

If the ice erosion theory turned out to be right then it would represent a completely new way of forming mountains, not seen anywhere else on Earth. Dalziel is sceptical about the ice erosion theory. "I would expect lithospheric flexing to result in continental scale features, rather than point features like the Gamburtsevs," he says.

One way or another it is crucial that scientists work out how and when the Gamburtsevs formed. If they were there before the ice then they were probably a nucleation point for glacier growth. "The presence of a mountain range like the Gamburtsevs will have been critical in establishing patterns of ice flow," says Stewart Jamieson, a glaciologist at the University of Edinburgh, UK.

For now Jamieson's ice sheet models are limited by the quality of the bedrock data. "We need more detailed topographic data to generate better models of ice flow and erosion," says Jamieson. Such information will be vital for predicting how Antarctica will respond to future climate change.

By the end of this year, East Antarctica will be buzzing with scientists, and hopefully Jamieson will get some answers. The new data should provide enough clues to crack the Gamburtsev mystery. Unless, of course, none of the existing theories are right, in which case it will be back to the drawing board and time to dream up a completely new way to make mountains grow.

Kate Ravilious is a science writer based in York, UK