After a monster “bomb cyclone” and frigid Arctic blasts that set some new records on the US East Coast, temperatures have been a bit more merciful this week. And that’s setting the stage for some pretty cool phenomena — like this ice jam on the Ausable River in Au Sable Forks, located in upstate New York.
In a time lapse video posted on Twitter by the National Weather Service office in Burlington, Vermont, you can see the frozen river very quickly rise up, and then break up into chunks almost out of the blue. The chaotic mess of ice and tree branches then flows downstream, bringing the river level back down. The whole video condenses three hours of footage, taken today by a NWS webcam that runs 24/7.
Ice jams happen when ice-covered rivers get extra water from rain or snowmelt, rising up quickly and breaking up the ice in big chunks. They usually occur where the river narrows or goes under a bridge, or where the river slope flattens out, allowing the ice pieces to accumulate and clog. This happens usually in the spring, in March or early April, when temperatures are starting to rise, says John Goff, lead meteorologist at the NWS Burlington office. But ice jams are not unheard of at this time of the year either.
It’s been raining in New York today, and temperatures hovered between 50 and 60 degrees Fahrenheit. That allowed for the snowpack to melt and raise the Ausable River by 10 feet, Goff tells The Verge. In fact, there were several ice jams along the river, not just at Au Sable Forks, he says. Usually ice jams result in a little bit of flooding: if the ice functions as a dam, the river will start flowing around it, flooding the surrounding fields and lowlands.
But at times, the jams can cause serious damage. In 1992, one of these ice piles changed the course of the Winooski River in Vermont, burying parts of Montpellier in six feet of water and interrupting power in the process. In that case, big ice lumps had wedged under a bridge and had to be dislodged by a crane, according to a New York Times article about the event. The ice on the Ausable River shown in the video was probably only about 8 to 10 inches thick, Goff estimates, and it flowed downstream fairly quickly. In fact, the NWS office received just a few reports of minor flooding, not connected to the ice jam at Au Sable Forks.
Still, the time lapse looked so cool that the NWS decided to post it to social media. “That one was the most dramatic,” Goff says.