Extreme heat across the U.S. has caused roads in Minnesota and elsewhere to buckle. The Minnesota Department of Transportation tweeted to alert drivers of the issue. “Driver alert: extreme heat could cause pavement buckles across the state,” it wrote.

“If you see buckling on your route, try to avoid driving over it and call 911 to report it. Pavement buckles are emergencies and we fix them ASAP.” On its website, the department explained that pavement buckles occur when the air temperature changes from moderate to extreme heat.

“When a road is constructed it is cut into segments creating a space for expansion and contraction. Sometimes that space is not enough and when that happens the pavement buckles or blows up, particularly when the pavement is older and weaker. The warmer the temperature the more the pavement material expands.

The sun heats the pavement, and the pavement expands and then buckles,” it said. Buckles occur most commonly on older concrete pavements. Conversely, blacktop pavement is a more flexible material. While it does not usually blow up, it could create a bump that is similar to a frost heave. Drivers, the department warned, should not try to drive over buckles on roads, if possible.