Normally, one doesn’t expect water to flow backward up a creek, fronted by a tsunami-like wave. But that’s exactly what happened in Avoca, Pa., on Tuesday thanks to an ice jam. The video is a sight to behold.

Here’s how it happened.

In the first half of January, the polar vortex was unleashed and Pennsylvania witnessed some of its coldest weather in memory. Rivers and creeks froze solid. But then came a great thaw, and the ice began to break apart into jagged blocks.

When these blocks of ice clump together, they can form a blockage, stopping the flow of water and creating an ice jam. Such ice jams can cause flooding along the waters’ shores. They are pretty common events in cold climates through which water flows.

At Avoca’s Mill Creek, midway between Wilkes-Barre and Scranton, an ice jam Tuesday caused the flooding of a road and the inundation of a business, six homes and two cars.

Like a clogged toilet, the ice jam also apparently made the creek flow backward. The aforementioned video from the local fire department shows the creek’s flow headed in reverse, led by a wave packed with icy shards and debris. Officials watch in disbelief and warn bystanders to stay off the bridge crossing the creek.

Excavators were brought in to remove some of the ice to help clear the blockage.

Here is what the creek looks like under normal circumstances:

(Google Maps)

The ice jam is now cleared and the flooding has subsided, but it left behind a mess.