Ice fissure

A fissure meanders across the ice of Lake Mendota near Picnic Point in Madison on January 6, 2010. Massive plates of ice shift and grind against each other, pushing up ridges in some places.

CRAIG SCHREINER - State Journal archives

Q. How do ice ridges form on the lake?

A. 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. This cracking and the collisions and buckling can cause loud sounds.

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, pushing 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 weather can change so much in one day. For instance, Madison just came out of a cold snap, followed by warm weather with temperatures in the 60s. This caused ice on the city's lakes to warm and expand. We saw new buckling of ice as a result.

Steven A. Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA Radio (970 AM) the last Monday of each month at 11:45 a.m.

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