How do ice ridges form on a lake?

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How do ice ridges form on a lake?

ENLARGE

Photo: Jeff Miller
Pressure ridge near shore on Lake Mendota in Madison, WI

Lake ice formation is dynamic. Even when a lake is completely frozen, the ice is not stagnant. It expands and contracts as it warms and cools. Differences in day and night temperatures can be large enough to cause the ice to crack. As the air temperature drops at night, lake ice cools and contracts. Since the ice is stuck to the shoreline, the entire sheet cannot contract as a whole, so cracks develop in the ice.

When the ice warms during the day, it expands. This expansion can cause a collision between both sides of the crack, which can cause the ice to buckle up at that pressure point. Cracking, collisions and buckling can cause loud noises.

This expansion can even push the ice up on shore. This can happen because, at night, the ice contracts and cracks develop which can fill with water. This water freezes. In the day, as the ice warms, it expands and pushes some ice up on shore.

A layer of snow on the ice acts like a blanket, insulating the ice. This keeps the ice from warming or cooling too much. Snow-free conditions can lead to the greatest temperature changes in the ice, particularly in early spring when the temperature can change so much during one day. When a spell of cold weather is followed by weather with temperatures in the 60s F, lake ice will warm, expand, and buckle anew.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.