Author(s): Vincent Mcfarlane; Mark Loewen; Faye Hicks
Linked Author(s): Mark R. Loewen
Keywords: No Keywords
Abstract: The formation and growth of anchor ice has been attributed to two different processes: deposition of frazil ice crystals and in-situ crystal growth. It is commonly assumed that frazil deposition is responsible for initial anchor ice formation, and that continued frazil accretion in combination with in-situ ice growth causes the anchor ice accumulations to rapidly increase in size (Kempema and Ettema, 2011; Qu and Doering, 2007). These accumulations can then become massive enough to partially dam stream flow, block water intakes, and raft large cobbles or gravel (Kempema and Ettema, 2011). However, each of these growth processes has proven difficult to measure in field environments. During a deployment of the University of Alberta’s FrazilCam to measure suspended frazil ice particles in the North Saskatchewan River at Edmonton, Alberta in November 2014, a large frazil floc became trapped in the field of view between two polarising filters. Subsequently, high-resolution photographs were captured of this floc in nine second bursts at a frequency of 1Hz every 90 seconds for a period of one hour. During this time, the floc was observed to grow by frazil accretion and in-situ crystal growth. Individual crystals were seen to grow as perfect discs for a period of time, followed by the formation of scalloped edges and growth in a dendritic fashion, referred to as stellar growth. The mean growth rate was calculated to be 0.13and 0.18 mm/min for disc and dendritic shaped crystals, respectively. The observed growth rates are compared to the laboratory data of Arakawa (1954) and Williamson and Chalmers (1966), the theory provided by Daly (1994,1984), and field observations made by Kempema and Ettema (2013).