Author(s): Edward F. Chacho; Daniel E. Lawson; Bruce E. Brockett

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Abstract: A unique form of frazil ice aggregate, the frazil ice pebble, occurs in large quantities in the Tanana River near Fairbanks, Alaska. Frazil pebbles consist of a mixture of individual particles, including other aggregates, which are bound together to form a consolidated, compact mass that is similar in appearance to water-worn stream pebbles. Frazil pebbles have been found incorporated into the ice cover, in transport beneath the ice cover and in frazil deposits. They range in length from less than 5 mm to greater than 150 mm. Internally, grains composing the frazil pebbles do not possess a preferred C-axis orientation, but appear to show an alignment related to grain size and shape. An underwater television camera revealed that frazil pebbles are generally transported within a thin layer along the underside of the ice cover. Analyses suggest that the mechanism of pebble formation and growth Involves initial incorporation of particles by freezing at grain contacts and then continued freezing of interstitial water to form a solid ice mass. Mechanical or thermal abrasion during transport may contribute to their rounded shape.

DOI:

Year: 1986