Tiny drops of dirty water, often erratic air bubbles, tell the story of the growth of icicles.
The waters of Styria are pure and smooth. But salt or other impurities cause tight circles to develop while hanging from branches, bridges and power lines.SN: 11/24/13). Impurities are also responsible for the cloudy appearance of the air bubbles that are typically attributed to air bubbles. Those bubbles are actually tiny gallons of contaminated water, researchers report in November Physical Review E.
While examining 3-millimetre-thick cross-sections grown in the labrum, University of Toronto physicists Stephen Morris and John Ladan discovered pockets of impure, liquid water surrounded by relatively pure ice (SN: 8/13/10). “There are very few air bubbles in an icicle,” says Morris. He calls the pockets of water inclusions to distinguish them from air bubbles.
What’s more, “inclusions mark the growth history of the circles. Like the rings on a tree,” says Morris. Inclusions form in layers around the surface of the ice, with older layers covered by younger ones as the ice grows. “You can infer something about the growth history by looking at the pattern of inclusions.”
To trace the sturgeon, researchers used fluorescent dye mixed with water instead of other types of impurities and water to grow the sturgeon’s lip. The dye ended up in higher levels in the liquid inclusions in the contracted icicles, like any other contaminant. It also glowed brightly under ultraviolet light, which made the inclusion layers easier to see.
By varying the concentration of the dye in the water, the researchers showed one way that impurities affect the shapes of icicles (SN: 10/10/02). The whole pollution became comparable to the sound of water, says Morris, “before they change their form from light to ripply.”
The underlying causes that lead to contaminant clusters are not yet clear. As an experimentalist, Morris says, this is a puzzle to leave the claimants.
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