Continuous in situ measurements of anchor ice formation, growth, and release

Abstract. In northern rivers, turbulent water becomes supercooled (i.e. cooled to slightly below the freezing point) when exposed air temperatures. water, frazil (small ice disks) crystals are generated in column, and anchor starts form on bed. Two formation mechanisms have been reported literature: either by accumulation of suspended particles, which adhesive (sticky) nature, riverbed or situ growth bed material. Once has formed bed, typically continues grow (due further and/or crystal growth) until release occurs due mechanical (shear force flow buoyancy accumulation) thermal (warming column weakens ice-substrate bond) forcing a combination two. There number detailed laboratory studies literature, but very few field measurements processes reported. These relied sampling accumulations from qualitatively describing observed release. this study, custom-built imaging system (camera lighting) was developed capture high-resolution digital images riverbed. A total six events were successfully captured time-lapse images, for first time, different initiation, growth, measured field. Four stages cycle identified: Stage 1: initiation growth; 2: transitional phase; 3: linear 4: phase. Anchor three events, remainder, appeared be initiated deposition. The 1 rates ranged 1.3 2.0 cm/h, 2 3 varied 0.3 0.9 cm/h. releasing modes: lifting entire accumulation, shearing layers rapid accumulation.