I had no idea what ice quakes were until moving to the shore of Lake Monona. We were quite surprised. There are varying sounds. A small one sounds like the front door slamming hard. A bigger one sounds like a heavy dresser upstairs fell over. The really big ones sound like a boom and the condo shakes. My desk is about 25' from the lake. So I have a ring side seat.

Interesting recent Cap Times article.

This is what it initially looks like. A crack in the ice.

Ice quakes happen when the ice expands and contracts. The ice cracks and one layer comes up and over the other layer. This year there has been a crack very close to our condo. I took all these photos from inside.

Here you see two pieces of ice. Ice is probably 15" thick now.

Madison.com article from Feb. 2008.

Apparently the big one was on January 15, 1948.

The American Journal of Science published this short note:

American Journal of Science, vol. 246, no. 6, page 390. Charles C. Bradley.
MENDOTA QUAKE
On Jan. 15, 1948, at 11:40 A.M. an earth tremor jolted the University of Wisconsin campus. It was of sufficient intensity to shake some plaster off the ceiling of an office and to crack the sewer drain of one fraternity house. Otherwise little damage was done.
The quake was felt by many students. One saw his books shaken off a stool and drop to the floor. Others heard windows vibrate and dishes rattle. Still others felt only a barely perceptible motion as they sat quietly studying.
The quake occurred opportunely for the beginning class in geology. They were studying earthquakes that week. When the class met the next day the instructor placed a map of the city on the board and called for a show of hands of those who had felt the tremor. Each student in turn related where he was at the time, what he was doing and what he felt. Using the modified Mercalli Scale of Intensity the isoseismal lines of the quake were plotted on the board, the results being approximately as indicated in the accompanying map.
As a classroom exercise it was very successful, increasing many-fold the students' interest in this aspect of geology.
They had not been aware that the tremor was occasioned by an ice fracture on Lake Mendota resulting from a warm day of expansion following a protracted period of cold. The position of the isoseismal lines, however, indicated the approximate focus of the quake. Following the lecture several students visited the "fault zone" where they found a four-foot overthrust in ice 1 1/2 feet thick.

The Wisconsin GNHS Report, 1984, also reported that this event was an icequake.