Ice streams and their smaller cousins, glaciers, don't just sit around looking frosty; they mosey along, albeit at different rates of speed. They also lose mass when snowfall cannot replace what is lost to melting. Global warming has hastened this loss, and may potentially raise sea levels to devastating heights. The big questions are: How important a player is climate change in the process—and what will its impact be in the future? In an effort find answers, scientists have created models based on what they know about global warming to help them predict its potential consequences.

Current models, however, are missing a major ingredient that a new study of Whillans Ice Stream in West Antarctica may provide: just how ice streams move. Finding out is key, because it may show what happens to slow glaciers down.

Until now, scientists had only observed glaciers creeping along. But the study of Whillans, which drains into the Ross Ice Shelf (the world's largest such ice mass spanning land and sea), shows that it moves quite differently, inching forward in fits and starts.

Douglas Wiens, professor of earth and planetary sciences at Washington University in St. Louis and lead author of the study published today in Nature, says his team has uncovered evidence that the mammoth 60-by-120-mile (95-by-193-kilometer) expanse of ice is powered by seismic energy in the watery, rocky terrain beneath it. He says researchers detected  two seismic waves—each equivalent to powerful magnitude 7 earthquakes—daily, which apparently come from a single, "sticky spot"—glaciologist lingo for epicenter—on the southern end of Whillans.

Previously, scientists had no clue that energy from a single spot could budge an ice stream, much less that such bodies could move with such regularity.

Wiens initially discovered the daily tremors while monitoring seismic waves from 2001 to 2003 with seismographs (instruments that measure and record vibrations in the ground such as earthquakes) at the South Pole and in Antarctica's McMurdo Dry Valleys. In an effort to pinpoint their source and function, glaciologist Sridhar Anandakrishnan of the Department of Geosciences and the Earth and Environmental Systems Institute at Pennsylvania State University mounted global positioning system (GPS) monitors on poles placed in various locations on the Whillans Ice Stream.

Using a GPS system similar to that used for car navigation Anandakrishnan was able to track the poles' motion on Whillans, which he measured every 10 seconds for two weeks. The GPS  indicated that the stream moved in what glaciologists call a stick-slip motion: Pressure builds on a single spot—that's the stick part. When this pressure becomes too strong, the ground moves below the stressed spot—the slip part. Translation: when the underlying surface moves, so does Whillans above it.

Co-author Matt King of the School of Civil Engineering and Geosciences at Newcastle University in England processed the data and confirmed that the seismographic signals were, indeed, coming from Whillans. Wiens then scoured a global network of seismographs for activity and detected waves generated by the ice sheet thousands of miles away in Australia and New Zealand.

So why have scientists never noticed such seemingly powerful seismic events before? Because they are virtually undetectable. Anandakrishnan says he has actually stood on Whillans during the quakes and not felt them. The reason: the ice sheet moves at a snail's pace of just 24 inches (61 centimeters) per half hour. He would have been able to feel the shift, Wiens says, if the ice sheet picked up the pace to, say, 24 inches per 10 seconds.

The team is not certain why the seismic waves occur like clockwork. But Wiens notes that the ice speed appears to take its cues from ocean tides in the Ross Sea and also beneath the Ross Ice Shelf—the part of the Ross Sea with a floating mass of ice. Stress builds as the tides fall; once a certain amount of stress builds, the ice slips.

Robert Bindschadler, head of the Hydrospheric and Biospheric Sciences Laboratory at NASA's Goddard Space Flight Center in Greenbelt, Md., agrees that the tides build pressure on the sticky-spot, prompting the ice to move. The reason why, however, remains a mystery.

He wonders: "How does a tide that only goes up and down 39.37 inches (one meter) influence a chunk of ice the size of a small New England state?"

Wien's team may have a better idea once the results are in from an array of GPS stations they plan to set up around Whillans's sticky-spot.

5 Comments

1. 1. jnffarrell 01:03 AM 6/5/08

   Consider two elastic springs connected to a friction pad. One spring (the ice) has a much less stiffness (lower modulus of elasticity) than the rock. Hence the ice snaps foward much more than the rock snaps backward. Since seismometers measure earth movementthe report says the earth moved, but more elastic movement and energy was in the ice.

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2. 2. Robert L Fraga Jr 05:52 PM 6/5/08

   Consider with our modern GPS and satellite imaging, that we can collect updated information daily, we monitored the world, but can anyone put this information together?

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3. 3. Rainstorm 08:15 PM 6/9/08

   I am no scientist, but the question about how the tides and pressure buildup are related has sparked my interest. My two best guesses are that water flows under the ice, and since ice is bouyant, during high tide, the ice would have more support, more cushion. During low tide, perhaps some of that cushioning goes away, causing the glacier to settle down more. Another idea is that the same factor that causes the tides, the moon, has the same effect on ice as it does the ocean. That would mean during high tide, the glacier would have a force pulling slightly upward, and during low tide it would settle back down.

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4. 4. czbrucie 07:07 PM 6/21/08

   Question, how many tons of co2 in the atmosphere is the proper amount?
   Do we know? I think not. When will have gone too far and produce such an insugnificant amout that we create global cooling?
   When we cannot even accurately predict the current huricane season, Daily weather forecasting is a joke. Check your 5 day forecast and day by day the forecast changes throughout the week.
   You expect me to believe that global warming, and the effects can be proved conclusively. whatever happened to the next ice age from the 70's? I guess we did such a good job preventing that, that we now have the reverse problem, until we overdo this.

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5. 5. PrescottSmall 04:19 PM 7/6/10

   czbrucie - Home School Much?
   
   Tell me, did Adam & Even ride the saddled triceratops too?
   
   What you are pointing out is the nature of science and how the finding can alter and completely reverse a predicition or hypotesis and alter a theory.
   
   Weather predition is based on models and they use the most likely scenario, but it isn't 100% accurate because they only know parts of the drivers. They still haven't figured out tornadoes much less hurricanes.
   
   According to geologic records Earth should be on a cooling trend. Human caused global warming has not only prevented it but has sent it into a never before observered nor recorded level of increase in the past several million years.
   
   Be a sceptic, that is healthy. But to deny science that is based on factual evidence and is repeatable in hundreds of well documented experiements is to intentionally remain ignorant, in other words - stupid.
   
   Ignorance is curable, stupidity is a choice.
   
   Gravity, Evolution and Global warming are all theories with equal merit.
   
   If you don't believe in one how can you believe in others.
   
   Better hold on in case you start to float away ;-)
   

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