Yale prof. makes ice dynamics discovery

One Yale professor’s research on the interaction between sheets of ice explains a phenomenon that has been mystifying scientists for years and could have implications for later research.

When sheets of ice meet in specific circumstances, they interlace to form a zigzag pattern similar to that of the teeth in a closed zipper. In a recently published report in Physical Review Letters, physics professor John Wettlaufer uncovered the mechanism behind the phenomenon. His research, which he conducted with Dominic Vella, a graduate student at Cambridge University, may have useful applications to geology and engineering.

Wettlaufer’s and Vella’s conclusions explain why ice sheets behave in ways that have surprised scientists until now. Intuition would suggest that the interacting ice sheets would either lay one on top of the other, similar to the earth’s crust, or would pulverize each other into a plane of crushed ice, similar to the event that occurs in thick ice floes.

The research describes the actual result, in which the ice sheets form a series of interlocking blocks that ride alternately over and under each other. This process is called “finger rafting.”

While scientists have known about this phenomenon for over 50 years — it occurs most often when the ice sheets are of the same thickness — they had never before been able to artificially reproduce these results.

Wettlaufer said the findings are also important because they allow scientists to recreate a physical phenomenon that had previously only occurred naturally. The problem of finger rafting was originally suggested to him during a trip to the Arctic in 1987, he said.

“Someone who had been around the stuff for a long time said, ‘This is so intriguing and ubiquitous that it is surprising that no one has figured it out,’” Wettlaufer said in an e-mail. “I had always casually mused over it.”

But he did not explore the process in depth until last summer, when he ran a fellowship program studying geophysical fluid dynamics.

Others in the geology field said they were impressed by the research.

“[It is] quite a significant piece of work,” said Michael Patterson, a postdoctoral associate in the Department of Geology and Geophysics. “This [finger rafting] is a particularly special event. It is not that this happens all of the time, but some of the time. It depends on the thickness of the ice.”

Because the research proves that it is possible for finger rafting to be recreated artificially, some scientists believe this same event may occur in materials other than ice that have similar characteristics in terms of thickness and flexibility. Stephen Peppin, a postdoctoral associate in the Department of Geology and Geophysics, said the research could be applied to producing tiny structures using a thin solid that floats on a liquid.

“It could be useful for creating structures on the nanoscale,” Peppin said. “They think that it’s generic — as long as you have the size ranges and the material has certain properties, it will happen with any material.”

The research was published in Physical Review Letters on Feb. 23.

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