What lies beneath: Scientists discover a giant granite slab half the size of WALES hidden under the West Antarctic Ice Sheet

Scientists have discovered a giant granite body hidden beneath the West Antarctic Ice Sheet.

At 62 miles (100 km) wide and over four miles (seven km) thick, the massive rocky structure is roughly half the size of Wales.

Scientists from the British Antarctic Survey (BAS) say the enormous slab of granite is buried underneath the Pine Island Glacier and likely formed during the Jurassic period.  

However, finding the massive structure was only possible thanks to a handful of mysterious pink boulders scattered over the continent's frozen volcanic peaks.

The unusual boulders, perched on the high mountaintops, had baffled scientists for decades. 

Now, researchers have realised the rocks are actually tiny parts of the granite giant, dropped on top of mountains by glaciers in the distant past. 

Dr Tom Jordan, lead author and geophysicist at BAS, says: 'It's remarkable that pink granite boulders spotted on the surface have led us to a hidden giant beneath the ice.

'We've not only solved a mystery about where these rocks came from, but also uncovered new information about how the ice sheet flowed in the past and how it might change in the future.'

When scientists first started finding pink granite boulders on the tops of the Hudson Mountains, it raised an obvious question: where were these rocks coming from?

'The pink granites we found in the Hudson Mountains were a total contrast with the underlying black basalts, meaning it was instantly clear that they had been transported from elsewhere,' says Dr Jordan.

By looking at the radioactive decay of minerals trapped within microscopic crystals, scientists discovered that they were formed around 175 million years ago.

That made them about 75 million years older than most of the rock in the western part of Antarctica.  

However, it was only when researchers started making aerial surveys of the region that the full picture started to emerge.

Flying aircraft over the Hudson Mountains, researchers from the BAS measured subtle changes in the Earth's gravitational field.

Dr Jordan explains: 'Gravity is the attraction between you and everything underneath your feet, so for example, if you stand on a slab of lead, there is more mass pulling you down than if you stand on a slab of wood.

'These variations are so tiny you can never feel them directly, but the very precise sensors we have on the survey aircraft can.'

By flying over the area in a grid pattern, the researchers were able to build a map of where dense and less dense rocks could be found.  

These gravitational surveys revealed an unusual geological signal coming from beneath the Pine Island Glacier, one that was consistent with buried granite.

Linking these findings to the mysterious granite boulders, the scientists had finally discovered where the rocks had come from.

In the distant past, when the ice sheet was much thicker, the Pine Island Glacier had plucked the boulders out from the rocky bed and deposited them on the tops of nearby mountains. 

Since the pink boulders were only found on half the mountains, this also shows that there were two distinct rivers of ice that transported material up into the mountains.  

Co-author Dr Joanne Johnson, a geologist for the BAS, says: 'Rocks provide an amazing record of how our planet has changed over time, especially how ice has eroded and altered the landscape of Antarctica. 

'Boulders like these are a treasure-trove of information about what lies deep beneath the ice sheet, far out of reach.'

However, beyond solving an interesting geological puzzle, this discovery could also have big consequences for understanding the continent's future.

Understanding how ice flows have changed since the last ice age, around 20,000 years ago, helps scientists predict how the ice sheet will respond to climate change in the future.  

Likewise, underlying geology is one of the biggest factors affecting how ice slides over the bed and how meltwater drains beneath it.

In the Pine Island Glacier, which has seen some of the fastest ice melt in Antarctica over the last few decades, the presence of a massive granite body will have a big impact on the region's future. 

The scientists hope that their discovery can be used to improve computer models of the ice flow that are used to project sea level increases. 

Dr Johnson says this finding gives scientists 'clues about how the West Antarctic Ice Sheet may change in future – information that is vital for determining the impact of sea level rise on coastal populations around the world.'