Here's something that might seem counterintuitive: the faster a glacier moves, the less friction it experiences on the ground below it. This surprising finding from researchers at Iowa State University is helping scientists better understand why some glaciers are speeding up — and what that means for rising sea levels.
Neal Iverson next to the Iowa State University Sliding Simulator, which replicates how glaciers slide over their rocky beds. (Credit: Bob Elbert/Iowa State University)
The Mystery of Glacier Friction
When we think about friction, we usually assume that more speed means more resistance. A car skidding on ice experiences friction; the faster you go, the more the brakes struggle. But glaciers work differently. Scientists have long suspected that as a glacier picks up speed, pockets of empty space (called cavities) form behind the bumps and rocks on the ground beneath it. These cavities reduce the contact area between ice and rock, which in turn reduces drag.
This idea was first proposed theoretically by glaciologist Louis Lliboutry, but it had never been convincingly demonstrated in a lab — until now.
Building a Glacier in a Lab
Lucas Zoet and Neal Iverson built what is essentially a miniature glacier: a 90 cm wide ring of ice rotating over a wavy, bumpy surface in a cold room kept at just 0.01°C above freezing. They embedded marker beads in the ice to track deformation, and ran the experiment at different speeds.
The results confirmed Lliboutry's theory. As the ice moved faster, cavities grew larger behind the bed's bumps, reducing friction. Beyond a certain threshold speed, faster motion actually decreased drag rather than increased it.
Why Sea-Level Rise Depends on This
This isn't just an academic curiosity. Glaciers around the world are accelerating, and scientists need accurate models to predict how much ice will melt and how fast seas will rise. Getting the friction law right is a fundamental part of those models. This new experimental data gives climate scientists a much more reliable foundation to work from.
Source: Physics World
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