Hole almost the size of Manhattan found under glacier

The discovery of a cavity with an area equivalent to two-thirds of Manhattan beneath an Antarctic glacier has raised urgent concerns about the speed of ice-melt in the polar regions.

The cavity, which is almost 300 metres tall, was revealed in data gathered by NASA’s Operation IceBridge, which since 2010 has used airborne ice-penetrating radar to map connections between changes in polar mass and global climate.

The hole sits beneath the Thwaites Glacier in West Antarctica, and represents, researchers say, a dramatic increase in melt rates not predicted by current models.

Writing in the journal Science Advances, scientists led by Pietro Milillo from NASA’s Jet Propulsion Laboratory in Pasadena, California, US, reveal the cavity to be 10 kilometres long and four kilometres wide. It indicates the loss of 14 billion tonnes of ice – most of it during the past three years.

The cavity sits directly below the glacier, above the bedrock. The researchers had expected to find gaps between the ice and the rock – having long suspected that Thwaites was not tightly anchored – but the sheer size of what the satellite data revealed indicates that the relationship between the two is more volatile than predicted.{%recommended 681%}

“The size of a cavity under a glacier plays an important role in melting,” says Milillo. “As more heat and water get under the glacier, it melts faster.”

This is no small consideration. The Thwaites Glacier occupies roughly the area of Florida. Previous research found that in recent years it has been losing about 50 billion tonnes of ice every year, and is responsible for 4% of global sea-level rise. It has been described as “the world’s most dangerous glacier”.

If it were to melt completely, it would boost ocean levels by 65 centimetres – a catastrophic outcome then compounded because its loss would trigger melts in neighbouring glaciers, pushing levels by another 2.4 metres.

“Understanding the details of how the ocean melts away this glacier is essential to project its impact on sea level rise in the coming decades,” says co-author Eric Rignot.

To this end, the researchers, together with colleagues at the US National Science Foundation and British National Environmental Research Council have formed the International Thwaites Glacier Collaboration.

The project aims to gather more, and more precise, information on the way the glacier is behaving, starting with a series of field experiments kicking off late in 2019.