Photographer: Rob Sheridan

Summary Author: Rob Sheridan

This photograph of an icy, shallow cove off the Massachusetts coast nicely illustrates, in miniature, the phases of sea ice formation. The light grey surface slush in the middle part of the photograph is frazil ice. Frazil ice consists of free-floating ice crystals that form an icy mix often called grease ice. It can extend down several meters from the surface. Frazil ice will coalesce into thin sheets that are initially transparent but soon thicken and whiten. When this occurs, the ice is referred to as nilas ice, which can be detected in the upper right part of the photograph. Pancake ice is seen in the foreground. This ice forms when surface turbulence breaks up nilas ice. Collisions cause the fragments to round off. Alternatively, pancake ice can form when turbulence and wind compress frazil ice causing it to coalesce. Drift ice, observed in the center of the photograph, is isolated segments of thick nilas, floating free. Fast ice is seen in the background, against the shore. This is sea ice that's become fixed to land, not moving with tide or current. Photo taken during the winter of 2009.

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