Lake Ice and 
Snow Science 

LAKE ICE: Phenology

The phenology of an ice cover is the freeze-up date, break-up date and ice cover duration.

Freeze-up (FU) defines the period between initial ice formation and the establishment of a complete ice cover. The FU data is the day that the pond is completely ice covered.

After the lake cools to 4°C (maximum density of water), the water surface cools to the freezing point and ice begins to form.

The first ice to form (initial ice skim) often appears first as border ice in shallow, protected areas. However, the entire lake surface can reach the freezing point simultaneously and a continuous ice cover will appear in a matter of a hours.

Break-up (BU) defines the period between the onset of snow melt and the complete disappearance of the ice. The BU date is the day when the lake is completely ice free.

When average daily air temperatures rise above the freezing point, ice begins to decay by:

• dimensional thinning and
• deterioration of the ice crystal grains at their boundaries.

Thinning of the ice layer is caused by heat transfer and by melting at the top or bottom surface (or both) or by contact with inflowing warm water.

Taken together freeze-up and break-up denote the endpoints of the ice cover duration.

Click here to see the variability in the ice phenology at Poker Flat Research Range (PFRR).

New ice cover.