How does fixed ice cover form along river shorelines?

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ice in lakes and rivers Heat flow through an ice cover (see text).

In some rivers, the initial formation of fixed ice occurs along the shorelines while the central regions remain open to the air. This shore ice gradually widens from the banks toward the center of the river. The final fixed ice cover is then completed either when the two sides of the shore ice meet or when the central region forms through the accumulation of frazil ice.1

Once this initial cover is established and stabilized, it can thicken through the growth of columnar crystals into the water below, a process similar to the development of lake ice.1