The cold, hard facts behind Antarctica's frozen peaks
Fifty years ago, no one knew they existed. Now scientists are finally starting to unlock the mysteries of the huge mountains frozen deep beneath the flat Antarctic ice
Wednesday 23 May 2007
In 1958, a team of Russian seismologists was taking readings every 50 kilometres as it headed for the continent's most remote point. The line of reading hit something buried deep below. This turned out to be the peak of a mountain range spanning about 1,000 kilometres, with an elevation of up to 3,400 metres. It was like finding a range as long as the Alps buried underneath the ice.
The members of the Third Soviet Antarctic Expedition carried on to their destination, deposited a statue of Lenin with his arm outstretched, and turned it so that it was pointing to Moscow. When they returned, they named their discovery in honour of Grigoriy Gamburtsev, a highly respected Soviet seismologist who had died three years previously.
But how did the range get there? According to many scientists, the usual methods by which mountains form do not seem to apply in this case. So many are asking the question: can erosion from ice-sheets create mountains?
Mountains are most commonly formed when continental plates collide, pushing up high ridges of rock. However, while there are mountain ranges on the edge of Antarctica, such as the Transantarctic Mountains, that were caused by this kind of plate-convergence, there is no evidence of plate collision in the centre of the continent.
"There are no plate boundaries in the middle of Antarctica, and the shape of the Antarctic plate has barely changed over hundreds of millions of years," says Stewart Jamieson, a glaciologist based at the University of Edinburgh, who uses ice-sheet models to simulate the evolution of the Antarctic continent.
One idea is that the mountains were created more than 250 million years ago by far-field compression. This occurs when tectonic plates collide and the stress is transmitted over long distances until it finds a weakness. There it forms a bulge. However, if the Gamburtsevs did form this way, they must have been there for long a period of time, many believe, for them to have survived. Surely, it is argued, the mountains would have been worn down by weather water, or ice.
Another theory is that the erosion caused by ice itself helped formed them. The Antarctic ice sheet has been in existence for the last 15 million years. At the early stages of ice-sheet growth, there would have been snow and ice forming on the central portion of the continent, which would have started to erode the area, thinning the crust, and potentially leading to a weak spot that could be pushed upwards by molten rock.
"Depending on the structure of the underlying lithosphere [the Earth's solid, rocky, outer layer], material may have flowed into the area underneath the Gamburtsevs," says Jamieson. "So from the ice, you have erosion on the high area in the centre of Antarctica, while under the lithosphere, hot rock may be surging into the area and pushing up the region. We know that glaciers can alter the shape of mountains, but if they have helped form the mountains in this way, that would be a new way for ranges to form.
"In order to prove this theory, that erosion from the ice sheet helped form the mountains, we first need to look for any evidence of local glaciation - of relatively small-scale features in the rock formed by smaller, earlier glaciers. These small features could include cirques, for example, which are small bowl-shaped valleys in mountainous areas. If we find these, it proves that the larger ice-sheet, that has covered the mountains for the past 15 million years, has not been eroding the Earth's crust. This would indicate that the mountains were not formed by the ice sheet thinning the earth's crust - and would mean that the Gamburtsevs are much more than 15 million years old."
A third suggestion is that the mountains were pushed up by a "hotspot" - a volcanic feature that punched its way through the earth's crust. Hotspots created the Hawaiian islands in the Pacific. But there have been no obvious hotspots under this part of Antarctica during the last 100 million years.
Jamieson is working on computer simulations of the landscape's evolution underneath the ice. "I'm making predictions of where erosion is occurring underneath the ice, and that will tell me whether ice is modifying the Gamburtsev region or whether more of the erosion is occurring near the edges of Antarctica. What we want to know is: could the Gamburtsevs have survived after 15 million years of glaciation. If my models show that there is no erosion occurring in the area, and it's all occurring elsewhere, then we can say that the ice sheet may have protected the mountains and therefore they must have formed before the ice was present."
So how does he believe they were formed? "The timescales over which these things occur would mean that the glacial-erosion theory is slightly less likely. I think this mountain range may well have been formed by a hotspot pushing them up - though that would mean the mountains have survived for 100 million years. If the mountains were formed by far-field compression, then that could put them at 250 million years old. That would mean they have survived for much, much, longer than we thought they could. The big question is: for how long can a landscape be preserved under ice?"
The Gamburtsevs were mapped in the 1970s, when scientists flew over the region and fired radio waves through the ice to measure their size. Martin Siegert, also a glaciologist at the University of Edinburgh, hopes to repeat the exercise now to obtain more information about the mountains. His project has funding from the National Environment Research Council, but is dependent on matching finance coming from America. "If it happens it will take place in two years' time at the earliest," says Siegert. "The exciting thing for me is that it's pure exploration. We think we know a little bit about the underside of the ice sheet in Antarctica, but actually we know very little. It's one of those areas where you can guarantee to find new things.
"The biggest store of water in the planet is in Antarctica and it would have a huge impact globally if it ever changed. We know far more about the surface of Mars than we do about the underside of the Antarctic ice sheet, which is more critical right now."
Paul Cooper, the geographic information systems manager for the British Antarctic Survey, who has been involved in mapping the continent since 1979, says that discovering how the Gamburtsev mountains were formed is crucial to our greater understanding of the southern hemisphere. "Millions of years ago all the continents in the southern hemisphere were joined together. Antarctica is right in the centre of a block of continents that broke apart about 100 million years ago. Understanding the evolution of the Antarctic will enable us to understand better the development of the geology of South America, Africa, India and Australia. Without that we can't make sense of things like minerals exploitation, and we can't readily understand how the earth's climate has developed. Because of Antarctica's isolation it has made a vast difference to the climate of the southern hemisphere."
Chinese researchers hope to obtain rock and ice samples from a drill hole, which would help to determine which of the three theories is most likely to explain how the mountains were formed. Whether they will be the first with the answer remains to be seen. Meanwhile, the statue of Lenin remains where it was left in 1958, pointing towards Moscow, in case anyone should lose their bearings.
A continent of extremes
* Antarctica is the highest continent, at an average 2,300 metres above sea level.
* The deepest piece of the Earth's crust not to be under sea is in Antarctica, at about 2,500 metres below the sea level.
* The continent is 1.4 times the size of the USA, and 58 times the size of the UK.
* It is the coldest place on Earth, with a record low of -79C.
* Mawson Station is the windiest place on Earth; average wind speed 23mph.
* Antarctica has 70 per cent of the world's fresh water, frozen as ice, and 90 per cent of the world's ice.
* The world's thickest ice is in Antarctica, at 4,776 metres.
* More than 150 lakes have been found under the ice.
* Antarctica was imagined by the ancient Greeks, but not seen until 1820. The first time anyone there set foot there is claimed to be the following year.
* In winter, Antarctica doubles in size due to the sea ice that forms around its coasts. Its true boundary is the Antarctic Convergence, a line around the southernmost reaches of the Atlantic, Indian and Pacific oceans, varying between about 45 degrees and 60 degrees south.
* Between 1996 and 1997 a river ran between two subglacial lakes for 16 months, with a flow similar to that of the Thames. It was only spotted in 2006 from archive satellite measurements .
* Antarctica's population consists of about 4,000 people on scientific bases in the short summer, and 1,000 in winter. There are around 25,000 summer tourists. There is no native population.
* Many regions of Antarctica have yet to be explored.
* Despite appearances, the interior of Antarctica is the largest desert on Earth. It has a mean annual precipitation which can be as low as 2cm per year, drier than much of the Sahara. This is because most of its snow falls near the oceans (which are the sources of moisture) and so the air is almost dry by the time it travels to the centre of the landmass.
* This is International Polar Year. Its scientific programme is focused on the Arctic and Antarctic regions and, in order to have full and equal coverage of both, the "year" actually covers two full annual cycles from March 2007 to March 2009, and will involve more than 200 projects, with thousands of scientists from more than 60 nations examining a wide range of physical, biological and social research topics.
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