Nav: Home

Experiments lead to slip law for better forecasts of glacier speed, sea-level rise

April 02, 2020

AMES, Iowa - Backed by experimental data from a laboratory machine that simulates the huge forces involved in glacier flow, glaciologists have written an equation that accounts for the motion of ice that rests on the soft, deformable ground underneath unusually fast-moving parts of ice sheets.

That equation - or "slip law" - is a tool that scientists can include in computer models of glacier movement over the deformable beds of mud, sand, pebbles, rocks and boulders under glaciers such as the West Antarctic Ice Sheet, said Neal Iverson, the project leader and a professor of geological and atmospheric sciences at Iowa State University. Models using the new slip law could better predict how quickly glaciers are sliding, how much ice they're sending to oceans and how that would affect sea-level rise.

A paper published online today by the journal Science describes the new slip law and the experiments and data that motivate it. Authors are Lucas Zoet, a postdoctoral research associate at Iowa State from 2012 to 2015 and now an assistant professor of geoscience at the University of Wisconsin-Madison, and Iverson.

Why do glaciologists need a slip law?

"The potential collapse of the West Antarctic Ice Sheet is the single largest source of uncertainty in estimations of future sea-level rise, and this uncertainty results, in part, from imperfectly modeled ice-sheet processes," Zoet and Iverson wrote in their paper.

Glacier-in-a-freezer

Iverson started experiments with the 9-foot-tall ring-shear device inside his laboratory's walk-in freezer in 2009. At the center of the device is a ring of ice about three feet across and eight inches thick. Below the ring is a hydraulic press that can put as much as 100 tons of force on the ice and simulate the weight of a glacier 800 feet thick. Above the ring are motors that can rotate the ice at speeds of 1 to 10,000 feet per year.

The ice is surrounded by a tub of temperature-controlled, circulating fluid that keeps the ice ring right at its melting temperature so it slides on a thin film of water - just like all fast-flowing glaciers.

A $530,000 grant from the National Science Foundation supported development of the device. Iverson worked with three engineers from the U.S. Department of Energy's Ames Laboratory - Terry Herrman, Dan Jones and Jerry Musselman - to turn his ideas into a working machine.

And it has worked for about a decade, providing data on how glaciers move over rigid rock and deformable sediment.

A drag on the ice

For the experiments that led to the new slip law, Zoet drove from Ames to Madison to fill six, 5-gallon buckets with real, glacially deposited sediment called till that had the right mix of mud, sand and larger rock particles.

He'd scoop that into the ring-shear device to make the till bed. He'd then construct an ice ring above it by freezing layers of water seeded with ice crystals. He'd apply force on the ice, heat it until it was melting and turn on the machine.

"We were after the mathematical relationship between the drag holding the ice back at the bottom of the glacier and how fast the glacier would slide," Iverson said. "That included studying the effect of the difference between ice pressure on the bed and water pressure in the pores of the till - a variable called the effective pressure that controls friction."

The data indicated the relationship between "drag, slip velocity and effective pressure that is needed to model glacier flow," Iverson said.

"Glacier ice is a highly viscous fluid that slips over a substrate - in this case a deformable till bed - and friction at the bed provides the drag that holds the ice back," Iverson said. "In the absence of friction, the weight of the ice would cause it to accelerate catastrophically like some landslides."

But it's nearly impossible to get drag data in the field. Zoet said the act of drilling through the ice would change the interface between the glacier and bed, making measurements and data less accurate.

So Iverson built his laboratory device to collect that data, and Zoet has built a slightly smaller version for his Wisconsin laboratory. Zoet's machine features a transparent sample chamber so researchers can see more of what's happening during an experiment.

The resulting experimentally based slip law for glaciers moving over soft beds should make a difference in predictions of glacier movement and sea-level rise:

"Ice sheet models using our new slip relationship," Iverson said, "would tend to predict higher ice discharges to the ocean - and higher rates of sea-level rise - than slip laws currently being used in most ice sheet models."
-end-


Iowa State University

Related Glaciers Articles:

Rock debris protects glaciers from climate change more than previously known
A new study which provides a global estimate of rock cover on the Earth's glaciers has revealed that the expanse of rock debris on glaciers, a factor that has been ignored in models of glacier melt and sea level rise, could be significant.
New 'law' to explain how glaciers flow over soft ground
Addressing a major source of uncertainty in glacier-flow models, researchers present a new slip law to describe glaciers sliding on soft, deformable material.
Melting glaciers will challenge some salmon populations and benefit others
A new Simon Fraser University-led study looking at the effects that glacier retreat will have on western North American Pacific salmon predicts that while some salmon populations may struggle, others may benefit.
How the ocean is gnawing away at glaciers
The Greenland Ice Sheet is melting faster today than it did only a few years ago.
Last remaining glaciers in the Pacific will soon melt away
The last remaining tropical glaciers between the Himalayas and the Andes will disappear in the next decade -- and possibly sooner -- due to climate change, a new study has found.
Drones help map Iceland's disappearing glaciers
Dr. Kieran Baxter from the University of Dundee has created composite images that compare views from 1980s aerial surveys to modern-day photos captured with the help of state-of-the-art technology.
Disappearing Peruvian glaciers
It is common knowledge that glaciers are melting in most areas across the globe.
New insight into glaciers regulating global silicon cycling
A new review of silicon cycling in glacial environments, led by scientists from the University of Bristol, highlights the potential importance of glaciers in exporting silicon to downstream ecosystems.
Tidewater glaciers: Melting underwater far faster than previously estimated?
A tidewater glacier in Alaska is melting underwater at rates upwards of two orders of magnitude greater than what is currently estimated, sonar surveys reveal.
Asia's glaciers provide buffer against drought
A new study to assess the contribution that Asia's high mountain glaciers make to relieving water stress in the region is published this week (May 29, 2019) in the journal Nature.
More Glaciers News and Glaciers Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.