Alberta Beach ice quake mystery solved
Researchers at the University of Alberta worked for almost a year to solve a riddle.
What caused lake ice to shatter so violently on New Year's Day that it damaged homes in three central Alberta beach communities?
On Jan. 1, 2018, residents of Alberta Beach on Lac Ste. Anne, northwest of Edmonton, awoke to a loud bang, the ground shaking and cracks forming in their homes and in the ground.
Similar quakes, with a magnitude of 2.0 on the Richter scale, occurred at Pigeon Lake and Gull Lake.
"Central Alberta is a pretty seismically quiet place, and so the fact that these tremors were felt in several communities across the region, and with this much power, is quite noteworthy," said Jeff Kavanaugh, associate professor of earth and atmospheric sciences at the University of Alberta
At the time, researchers knew the tremors were caused by fracturing of the lake ice, but didn't know what caused the ice to shatter so violently.
Ice quakes — or cryoseisms — are normally caused by a sudden drop in temperatures as a cold snap causes water in the ground to freeze and expand. The ice has nowhere to go, so as pressure mounts it eventually cracks the soil, causing the earth to shake.
Temperatures on New Year's Day were warming rapidly, rising by 30 degrees over 24 hours.
"The mystery there is, why would it warm, expand and then crack?" Kavanaugh asked at the time.
Solving the mystery would involve expertise in several fields, bringing together Kavanaugh, physicist Mirko van der Baan, Ryan Schultz, a geophysical research scientist and seismologist at the Alberta Geological Survey, and other geoscientists.
The work paid off. On Tuesday, Schultz said they have found the answer.
As New Year's Day dawned, a series of unlikely weather conditions came together, he said.
A lack of insulating snow cover, high water levels and a dramatic rise in temperature over 24 hours — from -35 C to -5 C — caused lake ice to rapidly warm.
The suddenly brittle ice began failing.
The factors also contributed to ice-jacking — a repeating process in which thermal contraction produces tensile cracks in lake ice. Those cracks are then filled with water that freezes during the cooling cycle, according to the research abstract.
Any subsequent expansion creates more pressure that causes the ice to shatter, it said.
"This caused a rapid thermal expansion of the ice, up to four metres toward the shoreline," Schultz said. "With nowhere for the expanding ice front to go, it eventually buckled and broke suddenly — resulting in the ice quake shaking and the spectacular ice ridges forming near the lakefront."
Ice quakes of such magnitude are especially rare, van der Baan said.
"Lake ice ruptured nearly instantaneously over hundreds of metres, which is very unusual," he said. "The last time this happened on the Albertan lakes was probably several decades ago."
The research paper, "A New Year's Day Icebreaker: Icequakes on Lakes in Alberta, Canada," was published in the Canadian Journal of Earth Sciences
