Is climate change making Earth 'EXPAND'? Melting ice sheets could be altering the shape of our planet
comments
At the surface, Antarctica is a motionless and frozen landscape.
Yet hundreds of miles down the Earth is moving at a rapid rate, new research has shown.
The study, led by Newcastle University and published this week in Earth and Planetary Science Letters, explains for the first time why the upward motion of the Earth's crust in the Northern Antarctic Peninsula is currently taking place so quickly.
An international team of researchers led by Newcastle University have revealed what they say is rapid growth of Earth's crust in Antarctica. The reason for the growth, they say, is the lightening load above as ice on the surface melts, which in turn allows the mantle to move upwards more quickly
Previous studies have shown Earth is 'rebounding' due to the overlying ice sheet shrinking in response to climate change.
This movement of the land was understood to be due to an instantaneous, elastic response followed by a very slow uplift over thousands of years.
THE 'EXPANDING EARTH' THEORY
The theory that Earth is growing, a separate theory to this study led by Newcastle University, suggests that the movement of the continents could be caused by our planet getting bigger.
There are three different forms of the theory; the first is that the mass of the planet has stayed the same as the planet grows, so gravity has decreased.
The others suggest Earth has grown in accordance with mass to keep gravity constant.
The final theory suggests gravity has increased as the mass has grown ever more.
In 1888 Russian engineer Ivan Yarkovsky said this added mass could come from space itself.
However, despite other supporters, the theory has been deemed implausible.
The scientific consensus is that there is significant evidence contradicting the 'expanding Earth' theory.
But GPS data collected by the international research team, including experts from Newcastle University, Durham University, and the University of Colorado has revealed that the land in this region is actually rising at a phenomenal rate of 0.6 inches (15 mm) a year – much greater than can be accounted for by the present-day elastic response alone.
And they have shown for the first time how the mantle below the Earth's crust in the Antarctic Peninsula is flowing much faster than expected, probably due to subtle changes in temperature or chemical composition.
This means it can flow more easily and so responds much more quickly to the lightening load hundreds of miles above it, changing the shape of the land.
Lead researcher, PhD student Grace Nield, based in the School of Civil Engineering and Geosciences at Newcastle University, explains: 'You would expect this rebound to happen over thousands of years and instead we have been able to measure it in just over a decade.
'You can almost see it happening which is just incredible.
'Because the mantle is "runnier" below the Northern Antarctic Peninsula it responds much more quickly to what's happening on the surface.
'So as the glaciers thin and the load in that localised area reduces, the mantle pushes up the crust.
'At the moment we have only studied the vertical deformation so the next step is to look at horizontal motion caused by the ice unloading to get more of a 3D picture of how the Earth is deforming, and to use other geophysical data to understand the mechanism of the flow.'
The land in Antarctica, pictured in elevation from blue to red, is rising at a 'phenomenal rate of 0.6 inches (15 millimetres) a year' say the researchers - much greater than can be accounted for by an 'elastic response' as had been suggested by previous studies
Nield explains to MailOnline however, that while this particular region may be expanding, the retraction of other areas means as a whole the land stays the same.
'This effect causes the land to uplift (or expand) in the region of the ice-mass loss and this has been measured by GPS stations to be up to 15 millimetres (0.6 inches) a year,' she says.
'The land will uplift at a greater rate closer to the location of the greatest ice-mass loss, so although we do not have GPS stations right next to the thinning glaciers, we would expect the land there to be rising at much more than 15 millimetres a year.
'Likewise the uplift will diminish with distance away from the source of the ice-mass loss, so our GPS site around 200 kilometres (125 miles) away from the source records around one to two millimetres (0.04 to 0.08 inches) a year in uplift.
'Further away still we expect small amounts of subsidence (downwards motion), so Earth as a whole is not expanding or contracting.'
Since 1995 several ice shelves in the Northern Antarctic Peninsula have collapsed and triggered ice-mass unloading, causing the solid Earth to 'bounce back'.
'Think of it a bit like a stretched piece of elastic,' says Nield, whose project is funded by the Natural Environment Research Council (NERC).
'The ice is pressing down on the Earth and as this weight reduces the crust bounces back. But what we found when we compared the ice loss to the uplift was that they didn't tally – something else had to be happening to be pushing the solid Earth up at such a phenomenal rate.'
Collating data from seven GPS stations situated across the Northern Peninsula, the team found the rebound was so fast that the upper mantle viscosity - or resistance to flow - had to be at least ten times lower than previously thought for the region and much lower than the rest of Antarctica.
Professor Peter Clarke, Professor of Geophysical Geodesy at Newcastle University and one of the authors of the paper, adds: 'Seeing this sort of deformation of the earth at such a rate is unprecedented in Antarctica.
'What is particularly interesting here is that we can actually see the impact that glacier thinning is having on the rocks 250 miles (400 km) down.'
Put the internet to work for you.
0 comments:
Post a Comment