How does snow ice form on the surface of a frozen lake?

Snow ice forms on a frozen lake when the weight of accumulated snow becomes heavy enough to overcome the buoyancy of the underlying ice sheet.1

This process occurs as follows:

• Submergence: The weight of the snow cover causes the supporting ice to be pushed downward, submerging it partially below the water level.1
• Infiltration: Water from the lake flows upward through cracks in the ice sheet.1
• Saturation and Freezing: The infiltrating water saturates the snow layer, which subsequently freezes into a new layer of ice known as snow ice.1

This mode of growth differs from the standard thickening of ice that occurs at the bottom surface of the ice cover through thermal conduction. While standard ice growth is driven by heat loss to the air above, snow ice formation is a result of the mechanical interaction between the snow load and the ice's buoyancy.12