Huge cavity in Antarctic glacier signals rapid decay

Huge cavity in Antarctic glacier signals rapid decay
Thwaites Glacier. Credit: NASA/OIB/Jeremy Harbeck

A gigantic cavity—two-thirds the area of Manhattan and almost 1,000 feet (300 meters) tall—growing at the bottom of Thwaites Glacier in West Antarctica is one of several disturbing discoveries reported in a new NASA-led study of the disintegrating glacier. The findings highlight the need for detailed observations of Antarctic glaciers' undersides in calculating how fast global sea levels will rise in response to climate change.

Researchers expected to find some gaps between ice and bedrock at Thwaites' bottom where could flow in and melt the glacier from below. The size and explosive growth rate of the newfound hole, however, surprised them. It's big enough to have contained 14 billion tons of ice, and most of that ice melted over the last three years.

"We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it," said Eric Rignot of the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, California. Rignot is a co-author of the new study, which was published today in Science Advances. "Thanks to a new generation of satellites, we can finally see the detail," he said.

The cavity was revealed by ice-penetrating radar in NASA's Operation IceBridge, an airborne campaign beginning in 2010 that studies connections between the polar regions and the global climate. The researchers also used data from a constellation of Italian and German spaceborne synthetic aperture radars. These very high-resolution data can be processed by a technique called radar interferometry to reveal how the ground surface below has moved between images.

"[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."

Numerical models of ice sheets use a fixed shape to represent a cavity under the ice, rather than allowing the cavity to change and grow. The new discovery implies that this limitation most likely causes those models to underestimate how fast Thwaites is losing ice.

About the size of Florida, Thwaites Glacier is currently responsible for approximately 4 percent of global sea level rise. It holds enough ice to raise the world ocean a little over 2 feet (65 centimeters) and backstops neighboring that would raise sea levels an additional 8 feet (2.4 meters) if all the ice were lost.

Thwaites is one of the hardest places to reach on Earth, but it is about to become better known than ever before. The U.S. National Science Foundation and British National Environmental Research Council are mounting a five-year field project to answer the most critical questions about its processes and features. The International Thwaites Glacier Collaboration will begin its field experiments in the Southern Hemisphere summer of 2019-20.

Huge cavity in Antarctic glacier signals rapid decay
Changes in surface height at Thwaites Glacier's grounding line, 2011 to 2017, with sinking areas in red and rising areas in blue. The growing cavity (red mass, center) caused the greatest sinking. The mottled area (bottom left) is the site of extensive calving. Contours show bedrock topography. Credit: NASA/JPL-Caltech
How Scientists Measure Ice Loss

There's no way to monitor Antarctic glaciers from ground level over the long term. Instead, scientists use satellite or airborne instrument data to observe features that change as a glacier melts, such as its flow speed and surface height.

Another changing feature is a glacier's grounding line - the place near the edge of the continent where it lifts off its bed and starts to float on seawater. Many Antarctic glaciers extend for miles beyond their grounding lines, floating out over the open ocean.

Just as a grounded boat can float again when the weight of its cargo is removed, a glacier that loses ice weight can float over land where it used to stick. When this happens, the grounding line retreats inland. That exposes more of a glacier's underside to sea water, increasing the likelihood its melt rate will accelerate.

An Irregular Retreat

For Thwaites, "We are discovering different mechanisms of retreat," Millilo said. Different processes at various parts of the 100-mile-long (160-kilometer-long) front of the glacier are putting the rates of grounding-line retreat and of ice loss out of sync.

The huge cavity is under the main trunk of the glacier on its western side - the side farther from the West Antarctic Peninsula. In this region, as the tide rises and falls, the grounding line retreats and advances across a zone of about 2 to 3 miles (3 to 5 kilometers). The glacier has been coming unstuck from a ridge in the bedrock at a steady rate of about 0.4 to 0.5 miles (0.6 to 0.8 kilometers) a year since 1992. Despite this stable rate of grounding-line retreat, the melt rate on this side of the glacier is extremely high.

"On the eastern side of the glacier, the grounding-line retreat proceeds through small channels, maybe a kilometer wide, like fingers reaching beneath the glacier to melt it from below," Milillo said. In that region, the rate of grounding-line retreat doubled from about 0.4 miles (0.6 kilometers) a year from 1992 to 2011 to 0.8 miles (1.2 kilometers) a year from 2011 to 2017. Even with this accelerating retreat, however, melt rates on this side of the glacier are lower than on the western side.

These results highlight that ice-ocean interactions are more complex than previously understood.

Milillo hopes the new results will be useful for the International Thwaites Glacier Collaboration researchers as they prepare for their fieldwork. "Such data is essential for field parties to focus on areas where the action is, because the grounding line is retreating rapidly with complex spatial patterns," he said.

"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," Rignot said.


Explore further

Seal behaviour to inform on rising sea levels

More information: P. Milillo et al. Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica, Science Advances (2019). DOI: 10.1126/sciadv.aau3433
Journal information: Science Advances

Provided by NASA
Citation: Huge cavity in Antarctic glacier signals rapid decay (2019, January 31) retrieved 19 June 2019 from https://phys.org/news/2019-01-huge-cavity-antarctic-glacier-rapid.html
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Jan 31, 2019
We're all doomed now. Quick give somebody some cash.

Jan 31, 2019
That's two feet. Like the two feet of yours they're going to tie up before they hang you over the cess pool to wait for the tide.

Jan 31, 2019
That's two feet. Like the two feet of yours they're going to tie up before they hang you over the cess pool to wait for the tide.

Da Schitt, the "meat" loving, knob gobbler, soils the forum again, with the shite from between his ears, as his boyfriend pummels the stupid out of his ass. Hey Da Schitt, is your boyfriend aware of your bondage fetish?
It is quite impressive how Da Schitt, can still bray at the heretics, while his boyfriend feeds him "meat".

Jan 31, 2019
You can try that when they come for you. I bet it doesn't work. Watch out for spotters from the coast. Maybe you can spout "tehalgore" at them and they'll only shoot you.

Jan 31, 2019
And so, the AGW Cult must continue with their PATHOLOGICAL LIES, to feed their hungry, ignorant Chicken Littles.

Using radar techniques to map how water flows under ice sheets, UTIG researchers were able to estimate ice melting rates and thus identify significant sources of geothermal heat under Thwaites Glacier. They found these sources are distributed over a wider area and are much hotter than previously assumed.

The geothermal heat contributed significantly to melting of the underside of the glacier, and it might be a key factor in allowing the ice sheet to slide, affecting the ice sheet's stability and its contribution to future sea level rise.

https://oceanlead...sources/

Jan 31, 2019
The ocean is rising. People in Florida's cess pools have flooded their lawns. How long before they go get ropes and rifles and come looking for you?

You should maybe shut up and go start finding someplace to hide.

Jan 31, 2019
Antiporacle, the puss infected scab, oozes once again. Ooze, Ooze, Ooze. Your entire existence is dedicated to making the problem of Global Warming even worse. You have done absolutely nothing to help and instead attack the science and positive efforts of others at every turn with lies and obfuscation. How do you live with yourself knowing that you are the lowest puss infected scab on the body of humanity? Do you fear karma catching up with you some day? Perhaps it would be fitting if your cells turned cancerous and consumed you as you turned traitorous against humanity.

Jan 31, 2019
About the size of Florida, Thwaites Glacier . . . holds enough ice to raise the world ocean a little over 2 feet (65 centimeters) and backstops neighboring glaciers that would raise sea levels an additional 8 feet (2.4 meters) if all the ice were lost.


Wired called Thwaites Glacier, "Antarctica's Most Terrifying Glacier."

https://www.wired...g-point/

The magazine, Scientific American, has referred to Thwaites Glacier many times. For Old Code, Scientific American is a magazine that has been covering science for 173 years. We need to pay close attention to Thwaites Glacier because its collapse could result in 10-11 feet of sea level rise on its own and much sooner than Deniers would ever acknowledge.

https://www.scien...glacier/

Jan 31, 2019
So Mark didn't read the cause of the glaciers activity, doesn't know how CO2 works and hates antigoracle and believes one person can make global warming worse....LMAO, just when I was getting bored with the usual stupidity...new stupid shows up to brighten the day...thanks mark.

Scientific American is a pop-sci rag that publishes whatever "science" is in fashion. Just as the supporters of mainstream science can only get behind what's in fashion.

Jan 31, 2019
Blah, bah, blah, you are boring me. I think I will go for out for lunch and take a ride in my lightning fast Electric Vehicle (EV) while you wallow in your grade school taunting. LMFAO.

Jan 31, 2019
vulcanism , its sits on a subduction zone

Jan 31, 2019
As silly as some of the name-calling banter is here, I must say -- at least this site gets comments on a topic as important as this!

Looks like other news channels with the same story go quite commentless. Perhaps people are saving themselves for ~2040 when it will finally fully affect them.

Jan 31, 2019
@ lorint , its the 'arguement clinic' from monty python

Jan 31, 2019
lorint, my apologies for my role in the "name-calling banter." By analogy, it is like the 1930s and the Scumbag Deniers are telling us how kind the Nazis are, even though we can see the shitstorm approaching.

Every time I think I have grip on how bad things are going to get due to global warming, the outlook just gets worse. It seems like this has been happening to me since the 1980s. I just read about the serious risks posed by the Thwaites Glacier in West Antarctica collapsing later this century, then a gigantic crack nearly the size of Manhattan appears in 2019 showing the process is already well underway. I have to wonder if that 10-11 feet of sea level rise will happen much sooner than anyone expects. We are already in very serious trouble.

Jan 31, 2019
lol !

Jan 31, 2019
Yet more real world evidence of serious ongoing ice loss from Antarctica - unwelcome news all round, whether people have their deep concerns confirmed or are presented with yet more evidence that belief it isn't serious is wrong, but hardly surprising. That's the thing with mainstream science; it doesn't care that those deeply committed to their belief that the science must be wrong will refuse to accept it.

Good on Phys.org for keeping us up to date with real science on climate - and leaving the climate science deniers to the comments section. Reminds me of those people at the back of court rooms making a big fuss - after the judgement has been handed down.

Feb 02, 2019
The 'arguement clinic' from monty python:
https://youtu.be/A1gf957Qw7A


Feb 02, 2019
@snoosebaum.
https://www.theguardian.com/world/2017/aug/12/scientists-discover-91-volcanos-antarctica
From your own above link:
However, he pointed to one alarming trend: "The most volcanism that is going in the world at present is in regions that have only recently lost their glacier covering – after the end of the last ice age. These places include Iceland and Alaska. "Theory suggests that this is occurring because, without ice sheets on top of them, there is a release of pressure on the regions' volcanoes and they become more active."
I have been pointing out that danger to you for years, mate. That you still don't get it, is indicative that you are either too stupid or just a troll who doesn't care because you are employed by (long proven) Russian/GOP/Fossil lobbies/troll factories paying 'thirty pieces of silver' blood money to trolls not realising the real dangers (which even you, your family/friends will increasingly be facing). You poor greedy/stupid slob.

Feb 02, 2019
The ocean is rising. People in Florida's cess pools have flooded their lawns. How long before they go get ropes and rifles and come looking for you?


That's been happening down there for 60 years.
Da'shnibble you are such a chicken chit.

Feb 03, 2019
The most volcanism that is going in the world at present is in regions that have only recently lost their glacier covering – after world at present

LOL ! ,,, somehow ''world at present '' doesn't match with '' end of the last ice age.'' or with the many tropical eruptions over that time ,,,,

Feb 03, 2019
'' a cavity about two-thirds the area of Manhattan and roughly 1,000 feet tall ''

wow! thats quite the 'cavity' how does the ice support that ?

fake news

Feb 03, 2019
The first-hand, deadly proof is coming QUICK!
-15 degrees here in Chicago...the Arctic convection currents stopped in 2017. The alarmism of the movie "The Day After Tomorrow" is proving itself.
So, what if every year from now on, the Polar Vortex comes down 5 degrees colder and lasts one week longer? Death, that's what.

Deniers can put a gun in their mouths or maybe we can all take up prayer, as that will be the only thing that will help (for consolation).

Feb 03, 2019
@snoosebaum.
Article:
The most volcanism that is going in the world at present is in regions that have only recently lost their glacier covering –
LOL ! ,,, somehow ''world at present '' doesn't match with '' end of the last ice age.'' or with the many tropical eruptions over that time ,,,,
It's the same process/feedback effect regardless when it occurs. The latest loss of covering ice/weight, that previously both cooled and pressurised underlying volcanic 'caps' in Antarctica and elsewhere is what matters NOW. Hence the dangers are from such feedbacks; not only in this aspect, but also the AGW-warming-caused massive releases of CO2/Methane previously sequestered from atmosphere in permafrost/clathrate etc reservoirs under oceans/on land.
Article:
a cavity about two-thirds the area of Manhattan and roughly 1,000 feet tall
wow! thats quite the 'cavity' how does the ice support that?
FYI, ice at Antarctic temps is as hard/strong as concrete. :)

Feb 03, 2019
wow ,'' ice at Antarctic temps is as hard/strong as concrete. :)''

gee, i thought it was getting warmer ! ie ''The latest loss of covering ice/weight, that previously both cooled and pressurised underlying volcanic 'caps' in Antarctica ''

u seem to be having trouble keeping it straight ! :}

and Eric in chicago is going to freeze from global warming ! lol !

Feb 03, 2019
@snoosebaum.
ice at Antarctic temps is as hard/strong as concrete.
gee, i thought it was getting warmer! ie ''The latest loss of covering ice/weight, that previously both cooled and pressurised underlying volcanic 'caps' in Antarctica''
Only that ice contacting warming ocean water/hot volcanic tips/warming air are susceptible to warming/melting faster than overall mass. That mass stays at very cold temps until the whole mass is gone (a bit like boiling water in a cooking pot stays at boiling temp until all the water is turned to steam/gone). The interplay between warming and ice loss/melting is complex, and 'see-saws' during the process.
u seem to be having trouble keeping it straight! :}
No; it's just that you have simplistic/uninformed assumptions/expectations which make you incapable of understanding what's really going on around you. :)
and Eric in chicago is going to freeze from global warming!lol
You really are an unfeeling/uncomprehending clot.

Feb 03, 2019
You really are an unfeeling/uncomprehending clot.

I bet you blame your non-existent, haven't gotten it done yet TOE on AGWism too.

Feb 04, 2019
@cantdrive85.
@snoosebaum,
and Eric in chicago is going to freeze from global warming!lol
You really are an unfeeling/uncomprehending clot.

I bet you blame your non-existent, haven't gotten it done yet TOE on AGWism too.
You just shot yourself in the foot with that uncalled-for jibe, @cd. Not only is AGW not a joking matter, but my ToE does exist; and some of the trolls with whom you also have trouble have seen snippets of it before I publish complete; they've been deriding same, and attacking me for it....despite my being increasingly proved correct all along by recent mainstream astro/cosmo/quantum physics discovery/reviews! So take my advice, @cd, stop adding your own faux pas against me to the long list of faux pas by those other trolls...as it never ends well (egg on face) for those who have derided me without any basis in fact. Good luck in your future choices, @cd, especially regarding whom to be a smart aleck with next time! :)

Feb 04, 2019
nd Eric in chicago is going to freeze from global warming! lol
You really are an unfeeling/uncomprehending clot.

so we are going to freeze from global warming ?

and
''contacting warming ocean water''

haven't u heard, water is very hard to heat with a light bulb

Feb 04, 2019
nd Eric in chicago is going to freeze from global warming! lol
You really are an unfeeling/uncomprehending clot.

so we are going to freeze from global warming ?

and
''contacting warming ocean water''

haven't u heard, water is very hard to heat with a light bulb

That's why the proper term is climate change. The greatest effect will be in weather extremes, which we are seeing now, if you get out of your basement and away from your computer screen.

Feb 04, 2019
oh the 'proper term '

yes! you can't go wrong with ' climate changey ' its always changing ! like getting colder

'' greatest effect will be in weather extremes,''

u mean like during ;

The Maunder Minimum, also known as the "prolonged sunspot minimum", is the name used for the period around 1645 to 1715 during which sunspots became exceedingly rare, as was then noted by solar observers.

Feb 04, 2019
@snoosebaum.
nd Eric in chicago is going to freeze from global warming! lol
You really are an unfeeling/uncomprehending clot.

so we are going to freeze from global warming ?

and
''contacting warming ocean water''

haven't u heard, water is very hard to heat with a light bulb
It's clear that you are just another time-water troll employed by Russian/GOP/Fossil lobby/troll-factory to post drivel on all sites on the internet that have host/present discussions/news that are a threat to your/their business/political/criminal interests/profits. Shame, @snoose, betraying your intellect, family, fiends and future generations for thirty pieces of silver blood money from said troll-factory funders. Good luck to you and yours when the global reality gets to the point you/they are directly adversely impacted health/life/costswise, mate. Shame on you.

Feb 04, 2019
удачи мой друг lol

Feb 04, 2019
These liar deniers are whistling past the graveyard. The cess gangs are coming for them and have more guns.

Feb 14, 2019
As RealityCheck suspected, snoosebaum probably is a Russian troll.

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