Rare ice quake on Gull Lake?

Shortly after 7 p.m. Jan. 13, Jodi Schwen was watching television at her Gull Lake home when she and husband Kent heard a loud boom and felt the earth move.

"It was the deepest rumbling under the house," Jodi Schwen said. "I've never been in an earthquake but that's how I imagine it would feel."

The sound was so pronounced, they immediately went outside thinking a home may have been destroyed in a gas explosion.

Kent Schwen's parents, Maurice and Marvel Schwen, live on a nearby lakeshore lot and experienced the same noise and vibration along with several other neighbors, some more than one-half mile down the shore.

It was not until this past weekend that they took a closer look along the shore and discovered damage to structures and the landscape. A sidewalk on the elder Schwens' property is pushed up and broken in several places and sand on a nearby beach is mounded up where it's normally flat. A boathouse next door appears to have shifted from its foundation and previously straight trees are protruding at odd angles.

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"It just looked like a bomb went off underground," Jodi Schwen said.

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"It just looked like a bomb went off underground," Jodi Schwen said.

The Gull Lake property has been in the Schwen family since 1942. Maurice Schwen said in more than 70 years, he's never experienced anything like this before.

Kevin Huyck, meteorologist with the National Weather Service (NWS) in Duluth, checked the seismic records with U.S. Geological Survey for Jan. 13. No earth tremor or earthquake was recorded in the area. Although rare, earthquakes can occur in Minnesota. Huyck said it's exceedingly unusual for a Minnesota earthquake, which tends to be weak, to damage structures.

Damage reports from the Brainerd area, Huyck said, sounded like a frost or ice heave. As water in the ground freezes and expands, Huyck said the result may include loud banging sounds and upheaval. A frost heave is able to damage sidewalks and can contribute to building damage. If it's big enough, it can shift the ground.

Temperature records were mild on Jan. 11-12 with highs nearing 20 degrees. In the 24 hours leading up to the boom, however, temperatures plummeted to 20 degrees below zero.

Amanda Graning, NWS meteorologist, said the dramatic swing in temperature likely caused the lake to rapidly develop ice, which in turn can lead to stress cracks in the ice accompanied by loud sounds. A massive ice ridge, which is created by two sheets of ice colliding with one another, has formed a few hundred feet from the Schwens' shore.

In Graning's assessment, the damage to the shore probably happened in another event, when wind pushed lake ice up onto the shore. The above average temperatures at the end of January could have been enough to melt the lake ice, leaving no evidence of it having been there.

Another possibility for what the Schwen family experienced is cryoseism, or an ice quake. In 2008, one of these quakes was reported on Lake Mendota in Madison, Wis., according to a news release from the University of Wisconsin-Madison. University employees in buildings along the shore felt shaking and the event registered on a seismometer in the geology department.

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"Ice quakes, usually accompanied by loud cracking noises, are caused by large shifts in ice and are most commonly triggered by drastic temperature changes," a news release from the University of Wisconsin-Madison stated.

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"Ice quakes, usually accompanied by loud cracking noises, are caused by large shifts in ice and are most commonly triggered by drastic temperature changes," the release states.

These events are rare and have the potential to cause damage, although whether this can explain the damage to the shoreline on Gull Lake is unclear.

The Minnesota Department of Natural Resources (DNR) notes a pushing action of an ice sheet is a common cause of shoreline property damage, particularly in a year with little snow cover. As ice cracks develop, water rises in the opening and freezes, causing the ice sheet to expand.

"When rising air temperature warms the ice, the additional expansion exerts a tremendous thrust against the shore," the DNR reports. "Alternate warming and cooling of an ice sheet causes additional pushing action that possesses enough power to nudge masonry bridge piers out of plum and push houses off their foundations."

Ice pushing onto shore appears to be widespread this winter with numerous reports on area lakes. Stacey Waidelich said lake ice has been inching closer to their North Long Lake home since Christmas break.

"We actually watched one day where it came up a good foot-and-a-half between the time we got up in the morning and went to work and came home," Waidelich said. "People have lost multiple trees. Some of these ice heaves are just feet off the front door and porch (of neighboring homes)."

Waidelich said rocks that were once in the lake close to shore are now 10 feet into their yard. In the 13 years her family has lived on the lake, she has not seen heaving this drastic or early in the season.

"Typically, it heaves out in the middle of the lake and there are ice ridges. This just moved the entire lake," she said, noting her husband Randy estimated some of the ridges to be about 8 feet high.

CHELSEY PERKINS may be reached at 855-5874 or chelsey.perkins@brainerddispatch.com . Follow on Twitter at www.twitter.com/DispatchChelsey .