Photo, seismograph from Mendota 'Ice Quake' posted

Feb. 2, 2008

by Jill Sakai

The shaking felt Thursday afternoon in areas near Lake Mendota was most likely an ice quake, according to University of Wisconsin-Madison geologists. A tremor was recorded by a geology department seismometer at 12:50 p.m. Thursday, Jan. 31, 2008, and lasted approximately two or three seconds.

Seismograph from ice quake

A geology department seismometer in Weeks Hall recorded a tremor at 12:50 p.m. on Jan. 31, 2008. Seismologist Cliff Thurber linked the tremor to an ice quake caused by shifting ice on Lake Mendota.

Image: courtesty courtesy Clifford Thurber

The event was very localized and did not have the hallmarks of an earthquake, but it did grab the attention of employees in lakeshore buildings. Dozens of staff had called either UW Police or facilities staff to inquire about the rumbling disturbance.

Ice quakes, usually accompanied by loud cracking noises, are caused by large shifts in ice and are most commonly triggered by drastic temperature changes, similar to those of the past few days, says UW-Madison seismologist Cliff Thurber. The size of Thursday's event was enough to leave a visible fresh break in the ice on Lake Mendota.

Photo of ice quake

A fresh snowfall highlights the contrast of a large fracture and fresh pressure ridge, still wet, in the ice covering Lake Mendota near the Memorial Union Terrace shoreline.

Photo: Jeff Miller