The sound of giant explosions tied to the weather are once again rattling Arkansans.
Two winters ago, Arkansans saw the rare winter phenomenon of "thundersnow," when lightning and thunder accompany snowfall.
Now, the abnormality is cryoseismic activity, or "ice quakes."
It sounds like a campy Syfy Channel disaster movie, but it's actually a weather-related occurrence caused by rapidly freezing water underground that expands. The expansion creates a sonic-boomlike explosion.
Residents in Jonesboro, Blytheville and Pocahontas reported hearing them last week as the temperatures plummeted well below freezing. Police in eastern and central Tennessee also received dozens of calls about the ice quakes.
"It sounded like a shotgun exploding," Joseph Richmond, the director of the Mississippi County Office of Emergency Services, said after hearing an ice quake in the southern end of his county Thursday.
"I didn't know what it was," he said. "We hear booms like that near the steel mills sometimes when they drop slag."
Deputies at the Randolph County sheriff's office in Pocahontas also heard a boom Thursday afternoon.
"We thought it was ice falling onto the metal roof here," a dispatcher said Friday. "I've never heard of 'ice quakes.'"
The cryoseismic activity is more common in northern states -- primarily around the Great Lakes region -- and in Canada, where temperatures shift rapidly.
The activity has been mistaken for earthquakes, gas line explosions, tires blowing up, gun blasts, building collapses and other mayhem.
It's the first time the ice quakes have been reported in the mid-South, said National Weather Service meteorologist John Moore of Memphis.
"It's been so cold, and the temperatures have changed quickly," he said. "We've been getting reports from all over lately."
The events aren't dangerous, said Gary Patterson, director of education at the Center for Earthquake Research and Information in Memphis.
"They aren't natural seismic activity," he said. "They are weaker than earthquakes and are closer to the surface and aren't felt as widespread as earthquakes are."
Still, they are startling, he said.
Some in Tennessee called police after the sound of ice quakes made them think people were breaking into their homes.
"These happen at areas where there is already stress building up," Patterson said of the ground. "The freezing water is the straw that breaks the camel's back. If they are deep enough, they may feel like little earthquakes."
Because the ice quakes are so localized, seismic monitors don't often record their movements, he said.
Two years ago, a Christmas night winter storm created the rare "thundersnow" in Arkansas. That happens when the air temperature on the ground is warmer than air above but still cold enough to produce snow. The warm air rises, creating "convection," or instability, and creates the thunderstorm activity.
This time, it's "ice quakes."
"It's been a strange winter," Moore said. "It's always something new with the weather."
State Desk on 02/23/2015