On Monday morning, the residents of Westbrook, USA, woke up with an impressive face. In the middle of the Presumpscot River, which flows through the place, a huge, circular ice floe revolved. A vortex of melt water explains the phenomenon.
The Presumpscot River, which flows through the state of Maine in northeastern US, is currently the scene of a special natural science phenomenon that was only explained a few years ago.
In the middle of the town of Westbrook, where the river makes a turn, a huge, round ice floe rotates. The inhabitants discovered the phenomenon Monday morning.
The hospitality industry at Westbrook was like the chickens to take a look at the spectacular sight. "Come along, take a selfie and grab a breakfast at one of our fantastic restaurants," the city council wrote on Facebook on Tuesday under the heading "Mysterious ice circle is still there."
Rotation grinds edges off
The media and citizens had two questions: what makes the ice floe as round as a circle, and why does it spin? The first question is fairly easy to answer.
The enormous ice floe originated from smaller pieces of ice in the river, which were frozen together. That is only possible if the water is calm, and that is where the river broadens. The broad part is clearly visible on the drone images.
The edges of the slow-growing giant ice floe are constantly being sharpened because it scrapes the river bottom on low tide. That is why he keeps his round shape. But how does it turn around at all?
Scientists previously thought that the rotation was caused by turbulence - irregular movements of the water - in the river. But six researchers from the physics faculty in Liège, Belgium referred that theory to the trash because all ice circles seem to rotate at about the same speed, regardless of size.
That would not be the case if they were caused by turbulence in the water.
Melt water creates low pressure under water
In the laboratory, the scientists quietly melted smaller ice circles in a water bath. After a few minutes, they started rotating on their own.
Further investigation revealed that this was due to a vortex of melt water that formed under the ice and sank to the bottom of the basin.
The force in such a vortex depends on the amount of melt water, which in turn is influenced by the size of the ice circle. In this way it can be explained that all ice circles spin at approximately the same speed.
Rotating ice circles are rare, and with a diameter of 90 meters it is one of the best known in Westbrook. The phenomenon not only occurs in North America, but has also been observed in Scandinavia, including the Swedish river Piteälven and the Norwegian Nidelva.