http://www.digitaljournal.com/tech-and-science/science/huge-cavity-in-bottom-of-antarctic-glacier-signals-rapid-decay/article/542222

Huge cavity in bottom of Antarctic glacier signals rapid decay

Posted Jan 31, 2019 by Karen Graham
A massive cavity that is two-thirds the size of Manhattan and nearly the height of the Chrysler Building is growing at the bottom of Thwaites Glacier in West Antarctica - a discovery that NASA scientists called “disturbing.”
A massive cavity that is two-thirds the size of Manhattan and nearly the height of the Chrysler Buil...
A massive cavity that is two-thirds the size of Manhattan and nearly the height of the Chrysler Building is growing at the bottom of the Thwaites Glacier, one of the world’s most dangerous glaciers.
NASA/OIB/Jeremy Harbeck
The cavernous hole is almost 1,000 feet (300 meters) tall and is but one of several disturbing discoveries reported in a new NASA-led study of the disintegrating glacier on Wednesday. The hole is big enough to contain 14 billion tons of ice, most of which has melted over the last three years.
Basically, the findings in the study highlight the need for detailed observations of the undersides of Antarctic glaciers'in calculating how far ocean levels will rise due to global warming.
The Thwaites Glacier is not the easiest place on Earth to reach. It has also been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, due to its apparent vulnerability to significant retreat. This description has resulted in the glacier being dubbed the "most dangerous glacier in the world."
"We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it," says glaciologist Eric Rignot from the University of California, Irvine, and NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "Thanks to a new generation of satellites, we can finally see the detail."
The cavity was found using ice-penetrating radar in NASA's Operation IceBridge, an airborne campaign that began in 2010. Additional data was supplied by German and French scientists.
"The size of a cavity under a glacier plays an important role in melting," said the study's lead author, Pietro Milillo of JPL. "As more heat and water get under the glacier, it melts faster." About the size of Florida, the Thwaites Glacier is responsible for about 4.0 percent of global sea level rise.
MODIS Mosaic of Antarctica (MOA) image map is a composite of 260 swaths comprised of both Terra and ...
MODIS Mosaic of Antarctica (MOA) image map is a composite of 260 swaths comprised of both Terra and Aqua MODIS images acquired between November 20, 2003 and February 29, 2004 of the Thwaites glacier in West Antarctica.
NASA Visualization Studio - Lori Perkins (NASA/GSFC): Lead Animator Bob Bindschadler (NASA/GSFC): Sc
Moreover, the glacier holds enough ice to raise the world's oceans just over 2 feet or 65 centimeters. There is another troubling issue, though. The Thwaites Glacier is the only thing holding back neighboring glaciers that would raise sea levels an additional 8.0 feet (2.4 meters) if all the ice were lost.
Additionally, there is another casualty besides the hidden cavity among the "complex pattern of retreat and ice melt." According to current readings, sections of the ice shelf are retreating by as much as 800 meters (2,625 ft) every year. "We are discovering different mechanisms of retreat," Milillo explains.
Just how long the Thwaites Glacier will hold is why scientists are right now embarking on a major expedition to learn more about Thwaites. If the world seems to have forgotten about the Antarctic lately, the Thwaites Glacier will be the entire story for 2019.