A enormous cavity two-thirds the area of Manhattan and nearly 300 metres tall has been found at the bottom of Thwaites Glacier in Antarctica. The size and explosive growth rate of the newfound hole, however, surprised them.

According to NASA, the cavity once contained some 14 billion tons of ice, most of which has supposedly melted in last three years.

"We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it", study author Rignot said in a NASA statement.

"Thanks to a new generation of satellites, we can finally see the detail".

Instead, the team used airborne and satellite ice-penetrating radars to reveal the cavity.

"There's more heat and water under the glacier, melting it faster", says Pietro Milillo from the Jet Propulsion Laboratory of Nasa in Pasadena.

Thwaites Glacier alone holds enough ice above sea level to raise sea levels by more than 65cm if it was to melt. Sinking areas are in red and rising areas are in blue.

The cavity is 300m tall and is growing fast. The mottled area (bottom left) shows extensive iceberg calving.

The findings illustrate the need for detailed observations of Antarctic glaciers' undersides in calculating how fast global sea levels will rise in response to climate change. Moreover, the glacier acts as a backstop for neighboring glaciers, meaning that it slows the rate at which they lose ice. The Thwaites Glacier melting could also lead to nearby glaciers melting, which could lift sea levels around the world an additional eight feet. It is thought that the water that comes from Thwaites represents up to 5% of the seal level rise that is now taking place around the earth. The collaboration includes the U.S. National Science Foundation and British National Environmental Research Council. This information is extremely useful to scientists because how quickly a glacier melts depends a great deal on what's going on near that bedrock.

The discovery of cavity beneath Thwaites Glacier along with a number of other disconcerting features offer a new wrinkle to the harrowing tale of West Antarctica.

From 1992 to 2011, the centre of the Thwaites grounding line retreated by almost 14 kilometres.

However, there's been more retreat than advancement as of late.

It's feared the melting of "the world's most risky glacier" could cause catastrophic flooding across the planet.

Despite this high rate of retreat, melt rates are still higher on the western side, where the void is located.

The complex pattern the new readings reveal - which don't fit with current ice sheet or ocean models - suggest scientists have more to learn about how water and ice interact with one another in the frigid but warming Antarctic environment.

The glacier is developed on different sides in different ways.