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Homemade ice cream parlor. To reproduce the formation of the glacial table, cylindrical stones made of polystyrene, PVC and granite were placed on a plate of ice. As the ice melted, the plastics (polystyrene and PVC) formed tables because they are relatively poor conductors of heat, while granite, a more powerful heat conductor, sank into the ice. Credit: M. Hénot et al.
A trio of researchers from the University of Lyon learned through laboratory experiments how ice tables form. Marceau Hénot, Nicolas Plihon and Nicolas Taberlet published their findings in Physical examination letters.
Glacier tables are large boulders sitting atop columns of ice on glaciers. They are commonly seen around the base of glaciers and do not occur at higher elevations. How they form has been a matter of opinion for many years. In this new effort, the researchers sought to answer the question.
Glacier tables appear unnatural at first glance as they appear to balance on top of a much thinner column of ice. They also raise the question of why they don’t just sink into the glacier while the ice below is melting. To find out why they don’t, the researchers set up several experiments in their lab.
The experiments began by creating patches of ice 3 cm thick tilted at angles similar to those of glaciers in nature. Each of the slabs was left on a counter to melt, allowing researchers to understand the factors contributing to their melting. They found it to be both heat radiating from the lab walls and heat from the air around them. They noted that the water runoff didn’t seem to have much of an impact on the time it took for their small glaciers to melt.
Next, the researchers placed small cylinders made of several materials with varying thermal conductivity on top of the ice sheets and allowed them to melt again. They discovered that some of the cylinders had formed ice tables and some had not.
By studying the differences between cylinders that formed tables and those that did not, the researchers found that thermal conductance was the main factor – those that were poor conductors of heat formed tables. Polystyrene cylinders, for example, formed a kind of blanket, protecting the ice under the cylinder from the cast iron, but only under the cylinder. The ice surrounding it melted, leaving the cylinder sitting atop a column of ice. The researchers also found that shape played a role. Thinner cylinders were more likely to cause ice tables than thicker cylinders. Thicker cylinders (or boulders), they noted, absorb more heat, which can make its way to the ice below.
Scientists see much higher rate of submarine glacial melt than expected
Marceau Hénot et al, Onset of Glacier Tables, Physical examination letters (2021). DOI: 10.1103 / PhysRevLett.127.108501. At Arxiv: arXiv: 2103.09760v3 [physics.flu-dyn], arxiv.org/abs/2103.09760
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Quote: How the glacier tables are formed (2021, September 16) retrieved September 18, 2021 from https://phys.org/news/2021-09-glacier-tables.html
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