What shapes can frazil ice take on the surface of a river?

In rivers, frazil ice typically begins as small, thin, disk-shaped particles. Depending on the flow conditions and environmental factors, these particles can take on several distinct forms on the water surface:1

• Thin, sheetlike formations: These occur when current velocities are very low.1
• Slushlike masses: Frazil particles may flocculate, or clump together, creating a slushy appearance on the surface.1
• Irregularly shaped pans: These are masses of frazil that appear shallow but can actually possess significant depth.1
• Dispersed mixture or slurry: At high current velocities, the ice particles may form a dispersed slurry within the flowing water.1

Over time, these pans may enlarge and freeze together to form larger floes, or they may accumulate at the leading edge of an ice cover to form a layer that progresses upstream.2