Mountains and ice floes, Antarctic Peninsula, Antarctica 123rf.com

Study: Ice flow is more sensitive to stress than previously thought

More settled science

The rate of glacier ice flow is more sensitive to stress than previously calculated, according to a new study by MIT researchers that upends a decades-old equation used to describe ice flow.

https://www.eurekalert.org/news-releases/946074

Here’s a new paper in communications earth & environment

Ice viscosity is more sensitive to stress than commonly assumed

CC4.0

Communications Earth & Environment volume 3, Article number: 57 (2022) 

Abstract

Accurate representation of the viscous flow of ice is fundamental to understanding glacier dynamics and projecting sea-level rise. Ice viscosity is often described by a simple but largely untested and uncalibrated constitutive relation, Glen’s Flow Law, wherein the rate of deformation is proportional to stress raised to the power n. The value n = 3 is commonly prescribed in ice-flow models, though observations and experiments support a range of values across stresses and temperatures found on Earth. Here, we leverage recent remotely-sensed observations of Antarctic ice shelves to show that Glen’s Flow Law approximates the viscous flow of ice with n = 4.1 ± 0.4 in fast-flowing areas. The viscosity and flow rate of ice are therefore more sensitive to changes in stress than most ice-flow models allow. By calibrating the governing equation of ice deformation, our result is a pathway towards improving projections of future glacier change.

https://www.nature.com/articles/s43247-022-00385-x

And the conclusion: It’s worse than we thought.

Conclusion

The result that n ≈ 4 challenges the long-held practice of assuming the flow-law exponent is n = 3 everywhere, and at all times, in large-scale ice-sheet flow models. While our observations focus on specific regions in extensional flow regimes on ice shelves that experience stresses of order 100 kPa (Supplement Fig. S6), complementary laboratory work showing that n = 4 is suitable at higher stresses15 supports extending our conclusion that n ≈ 4 to other dynamic regions in Antarctica. Additionally, our conclusion complements a growing body of work advocating for the use of n > 3 in other areas of the cryosphere19,26. Taken together, this work calls for a broader community effort to quantify the uncertainties in the flow-law parameters and the consequences of these uncertainties on models of glacier dynamics. A higher value of n increases the sensitivity of viscosity to changes in stress but the impact of n = 4 on large-scale ice-flow models used for projections of sea-level rise and ice-sheet evolution remains unclear as few sensitivity analyses have been conducted10 and n is not a parameter explored in current ensemble-model analyses1,2. The value n = 4 has the potential to increase the sensitivity of ice-sheet mass loss to ongoing climate change considerably relative to n = 3 due to the stronger dependence of flow rates to changes in resistive stresses.

By applying continental-scale satellite observations to standard models in glacier dynamics, we have validated Glen’s Flow Law, a constitutive relationship that helps form the foundation of modern glaciology, and calibrated the stress exponent in Antarctic ice shelves. This work serves as a pathway towards a standard calibration framework for the community using publicly available remote sensing data. Our conclusion that n ≈ 4 across much of Antarctica’s ice shelves is a step towards reassessing the governing equations of ice flow in the satellite age, and reveals an increased sensitivity of flow rates to applied stresses relative to the commonly used n = 3. As a consequence, future sea-level rise is likely more sensitive to climate forcings than predicted by present models using common assumptions of the flow law.

https://www.nature.com/articles/s43247-022-00385-x

Here’s the press release from EurekAlert!

Study: Ice flow is more sensitive to stress than previously thought

Changes to a key ice flow equation could refine estimates of sea level rise.Peer-Reviewed Publication

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

Ice Flow
IMAGE: THE RATE OF GLACIER ICE FLOW IS MORE SENSITIVE TO STRESS THAN PREVIOUSLY CALCULATED, ACCORDING TO A NEW STUDY BY MIT RESEARCHERS THAT UPENDS A DECADES’ OLD EQUATION USED TO DESCRIBE ICE FLOW. PICTURED IS THE JUNEAU ICE FIELD IN ALASKA. view more  CREDIT: PHOTO: JOANNA MILLSTEIN

The rate of glacier ice flow is more sensitive to stress than previously calculated, according to a new study by MIT researchers that upends a decades-old equation used to describe ice flow.

Stress in this case refers to the forces acting on Antarctic glaciers, which are primarily influenced by gravity that drags the ice down toward lower elevations. Viscous glacier ice flows “really similarly to honey,” explains Joanna Millstein, a PhD student in the Glacier Dynamics and Remote Sensing Group and lead author of the study. “If you squeeze honey in the center of a piece of toast, and it piles up there before oozing outward, that’s the exact same motion that’s happening for ice.”

The revision to the equation proposed by Millstein and her colleagues should improve models for making predictions about the ice flow of glaciers. This could help glaciologists predict how Antarctic ice flow might contribute to future sea level rise, although Millstein said the equation change is unlikely to raise estimates of sea level rise beyond the maximum levels already predicted under climate change models.

“Almost all our uncertainties about sea level rise coming from Antarctica have to do with the physics of ice flow, though, so this will hopefully be a constraint on that uncertainty,” she says.

Other authors on the paper, published in Nature Communications Earth and Environment, include Brent Minchew, the Cecil and Ida Green Career Development Professor in MIT’s Department of Earth, Atmospheric, and Planetary Sciences, and Samuel Pegler, a university academic fellow at the University of Leeds.

Benefits of big data

The equation in question, called Glen’s Flow Law, is the most widely used equation to describe viscous ice flow. It was developed in 1958 by British scientist J.W. Glen, one of the few glaciologists working on the physics of ice flow in the 1950s, according to Millstein.

With relatively few scientists working in the field until recently, along with the remoteness and inaccessibility of most large glacier ice sheets, there were few attempts to calibrate Glen’s Flow Law outside the lab until recently. In the recent study, Millstein and her colleagues took advantage of a new wealth of satellite imagery over Antarctic ice shelves, the floating extensions of the continent’s ice sheet, to revise the stress exponent of the flow law.

“In 2002, this major ice shelf [Larsen B] collapsed in Antarctica, and all we have from that collapse is two satellite images that are a month apart,” she says. “Now, over that same area we can get [imagery] every six days.”

The new analysis shows that “the ice flow in the most dynamic, fastest-changing regions of Antarctica — the ice shelves, which basically hold back and hug the interior of the continental ice — is more sensitive to stress than commonly assumed,” Millstein says. She’s optimistic that the growing record of satellite data will help capture rapid changes on Antarctica in the future, providing insights into the underlying physical processes of glaciers.   

But stress isn’t the only thing that affects ice flow, the researchers note. Other parts of the flow law equation represent differences in temperature, ice grain size and orientation, and impurities and water contained in the ice — all of which can alter flow velocity. Factors like temperature could be especially important in understanding how ice flow impacts sea level rise in the future, Millstein says.

Cracking under strain

Millstein and colleagues are also studying the mechanics of ice sheet collapse, which involves different physical models than those used to understand the ice flow problem. “The cracking and breaking of ice is what we’re working on now, using strain rate observations,” Millstein says.

The researchers use InSAR, radar images of the Earth’s surface collected by satellites, to observe deformations of the ice sheets that can be used to make precise measurements of strain. By observing areas of ice with high strain rates, they hope to better understand the rate at which crevasses and rifts propagate to trigger collapse.

The research was supported by the National Science Foundation.

###

Written by Becky Ham, MIT News correspondent

Paper: “Ice viscosity is more sensitive to stress than commonly assumed”

https://www.nature.com/articles/s43247-022-00385-x

DOI

10.1038/s43247-022-00385-x 

ARTICLE TITLE

“Ice viscosity is more sensitive to stress than commonly assumed”


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fretslider
March 13, 2022 6:25 am

“By calibrating the governing equation…”

I [remote] sense a tweak coming on….

Latitude
March 13, 2022 6:56 am

to better understand…..we exaggerated something else….it’s worse than we thought

Joao Martins
March 13, 2022 7:07 am

Cracking under strain

Are they applying torture also to ice sheets or just sticking toothpicks beneath the nails of the equations?

Last edited 2 months ago by Joao Martins
Rob_Dawg
March 13, 2022 7:08 am

A decades old formula in the settled science turns out to be wrong.

Clyde Spencer
Reply to  Rob_Dawg
March 13, 2022 1:46 pm

… turns out to be wrong.

Maybe!

HeaterGuy
March 13, 2022 7:59 am

“My n goes to 11”, Spinal Tap scientist says.

Shoki Kaneda
March 13, 2022 8:05 am

Who knew ice was so sensitive? Maybe if we said kind, nurturing things?

Clyde Spencer
Reply to  Shoki Kaneda
March 13, 2022 1:47 pm

Even a lot of ‘snowflakes’ packed closely together are sensitive. It is their nature.

TonyL
March 13, 2022 8:18 am

Let’s have fun!!!

Let’s do some curve fitting and see how well we can determine coefficients.
We shall do two choices to start.
y=x^3
y=x^4
Lets graph them up for the range y=0.8 to y=1.2. Remember, you get the range you get, not the range you want.
Now we draw in some error bars, considering we are simulating glaciers in Antarctica as seen by satellite. In other words, be generous, no fake precision, thank you. Perhaps +/- 100%, (been there, done that).

Now tell the difference, n=3 to n=4.
{please spare me the “Studies Suggest” and “Research Indicates” nonsense.}
Have A Nice Day!

Curious George(@moudryj)
Reply to  TonyL
March 13, 2022 8:58 am

Are you an expert in drawing error bars?

TonyL
Reply to  Curious George
March 13, 2022 9:31 am

Ever work down at your detection limit?
A situation I used to call “fraught with statistical mischief”.
Those were the days!


Bruce Cobb
March 13, 2022 8:41 am

The ice just needs to chillax.

Walter Sobchak
March 13, 2022 8:43 am

I’m sensitive too. But, do you people care?

TonyL
Reply to  Walter Sobchak
March 13, 2022 8:47 am

Do not complain.
We just might put you under stress and measure your deformation.

Gary Pearse
March 13, 2022 8:58 am

It’s not n=3…it’s n=4! That will blow them out of the water.

https://m.youtube.com/watch?v=rnso4nfdM9w

Ed Zuiderwijk
March 13, 2022 9:24 am

Must be the wrong type of ice.

Brad-DXT
Reply to  Ed Zuiderwijk
March 13, 2022 9:46 am

Must be white ice. Ice of color would be better. 😉

Last edited 2 months ago by Brad-DXT
LdB
Reply to  Brad-DXT
March 13, 2022 5:46 pm

White ice has privilege

TonyL
Reply to  Ed Zuiderwijk
March 13, 2022 11:07 am

It is Ice-9, and it is Waaaayy worse than we thought.

Gordon A. Dressler
March 13, 2022 9:33 am

From the above article’s quoted abstract:
” . . . a pathway towards improving projections of future glacier change.”
followed by this from the above article’s quoted conclusion section
“As a consequence, future sea-level rise is likely more sensitive to climate forcings than predicted by present models using common assumptions of the flow law.”

You’re kidding me, right? Previously, I was assured multiple times, by multiple organizations, that the science on climate change™ was “settled”.

Oh dear, what has happened to that meme?

william Johnston
Reply to  Gordon A. Dressler
March 13, 2022 10:46 am

That was last year. Please try to keep up.

Clyde Spencer
Reply to  Gordon A. Dressler
March 13, 2022 1:58 pm

A problem here is that the authors are talking about the plastic deformation of ice, which may not translate to the forward motion of the glacier itself. The ice can and does shear over obstacles. However, the most important factors are the slope of the bedrock, and if smooth, whether it is lubricated with meltwater.

I suspect that “n” is not constant and may be a function of things like temperature, thickness of the ice, and slope of the bedrock.

Gordon A. Dressler
Reply to  Clyde Spencer
March 14, 2022 7:06 am

Yes, as stated in the abstract of the Communications Earth & Environment article as quoted above:

“The value n = 3 is commonly prescribed in ice-flow models, though observations and experiments support a range of values across stresses and temperatures found on Earth. Here, we . . . show that Glen’s Flow Law approximates the viscous flow of ice with n = 4.1 ± 0.4 in fast-flowing areas.”

(my underlining emphasis added)

MFKBoulder
Reply to  Clyde Spencer
March 15, 2022 5:06 am

“However, the most important factors are the slope of the bedrock […]”

Nope, more important then bedrock slope is glacier surface slope (Glaciology 201).

Clyde Spencer
Reply to  MFKBoulder
March 15, 2022 11:48 am

Glacier surface slope is a function of both bedrock slope, rate of snow accumulation in the Zone of Accumulation, and the distance from the Zone of Accumulation. The glacier surface slope will not only steepen if the bedrock slope increases, but crevasses will develop also. Lastly, the character of the bedrock (resistance to abrasion/plucking, macro-texture, and topography) will control friction, which will control basal and average speed, and surface slope. They are all inter-related.

Last edited 2 months ago by Clyde Spencer
rah
March 13, 2022 9:40 am

Nothing like a stressed out glacier.

Dave Fair
March 13, 2022 9:47 am

Since the Antarctic is cooling, is that the climate change they are so afraid of?

DMacKenzie
March 13, 2022 10:59 am

Our human understanding of energy conservation with respect to collapsing high cliffs of solids is terribly poor, whether ice or rock. At least we recognize that ice is slippery. Landslides are another matter. They can end at the bottom of the mountain, but there are many examples of long runout landslides ending many km from their starting point….reasons not understood….

TallDave
March 13, 2022 11:48 am

Here, we leverage recent remotely-sensed observations of Antarctic ice shelves to show that Glen’s Flow Law approximates the viscous flow of ice with n = 4.1 ± 0.4 in fast-flowing areas. The viscosity and flow rate of ice are therefore more sensitive to changes in stress than most ice-flow models allow. By calibrating the governing equation of ice deformation, our result is a pathway towards improving projections of future glacier change.

that actually sounds pretty helpful in mapping what future glaciers might look like

As a consequence, future sea-level rise is likely more sensitive to climate forcings than predicted by present models using common assumptions of the flow law.

oh no and you were doing so well

lee
Reply to  TallDave
March 13, 2022 9:44 pm

Now all they have to do is release their new paper on slow-flowing glaciers. 😎

stinkerp
March 13, 2022 12:20 pm

And the conclusion: It’s worse than we thought.

Yet, strangely, the supposed increase in glacier flow and ice loss doesn’t appear in sea level rise data; an inconvenient truth. Like stage magicians, they constantly wave their hands to direct attention away from certain fundamental and insurmountable facts that destroy their story: the slow rate of sea level and temperature rise.

Last edited 2 months ago by stinkerp
J. R.
March 13, 2022 1:20 pm

Perhaps Big Pharma can come up with a pill for this.

mal
Reply to  J. R.
March 14, 2022 8:19 am

Yes and charge 10,000 time there total cost.

Peta of Newark
March 13, 2022 1:39 pm

So Climate Change changes the stress that glaciers are under….
But we’re told that Gravity is the stressor – so how does that work.

Anyway, why not follow the human example and give them a big plate of pasta and a glass of wine.
That works to relieve stress.
Yeah OK, politics, science and relationships all go down the pan but, who cares when you’re asleep on the sofa with the telly still on?

Ain’t that right Boris?

Clyde Spencer
March 13, 2022 1:45 pm

Textbooks generally state that the change from brittle behavior to plastic flow, thus closing up crevasses, occurs at around 60 meters of depth. It seems to me that this revised formula implies that the transition should occur at a shallower depth. Does their formula support or contradict the field observations of the transition from brittle to plastic behavior?

Duane
March 13, 2022 5:22 pm

This sounds very scary, until one thinks about it a second or two.

As the one researcher was quoted in this article, “ice flow is like pouring honey in the center on a piece of toast.” Well, it is in fact gravity that controls ice flow, just as it controls the flow of liquid water or any other liquid in an open channel (not pressurized as in a full pipe). The only difference is the viscosity.

Which of course means that when glacial ice is moving faster towards a discharge point to the sea, that is only driven by a greater height or thickness of the glacier, since the land slope underneath remains relatively static.

Therefore when the warmunists claim that observations of accelerated glacial velocity means that the glaciers are melting, it actually means exactly the opposite … ie that glaciers are gaining thickness and therefore gaining mass upslope. So faster moving glaciers are getting bigger, not smaller.

Think of a river – when more rain or snowmelt in the upstream watershed causes the river to get deeper upstream, what does it do? It flows faster. Everybody knows that. Well, a glacier follows the same laws of gravity and physics as does a river. A glacier is just a frozen river … a river consisting of a liquid with a higher viscosity than that of liquid water.

Last edited 2 months ago by Duane
Clyde Spencer
Reply to  Duane
March 15, 2022 11:58 am

since the land slope underneath remains relatively static.

Not so. In Greenland, while working in the ice tunnel at Camp Tuto, what were called “shear moraines” were quite evident in the tunnel walls. (I’ve never seen it mentioned in a text book.) It was clearly the result of an irregular topography causing the ice to shear upwards over a hill or ridge.

In New England, randomly oriented glacial striations are evidence of turbulent basal flow in the over-topped pre-glacial valleys. Accumulations of weathered grus in some locations are evidence that the ice was stagnant in pressure shadows and did not remove the weathered rock in those locations.

Doonman
March 13, 2022 6:22 pm

Since it is now apparent that everything is worse than we thought, we need to make some serious adjustments to how we live.

This means:

Everything you know is wrong.
Past predictions can never be right.
There can never be any future solutions based on past knowledge.
Going to school is a waste of time because what you learn is wrong.
There is no such thing as common sense.

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