Scientists have finally unraveled the mystery of the strange crop circles that appeared off the coast of the Island of Møn, Denmark, in 2010. Unlike the crop circles on land, however, these are not made by humans.
They are not made by alien spaceships either. Or rest of craters from bombs dropped during World War II, like some theorized. According to Dr Marianne Holmer and Dr Jens Borum, the secret is on the mud that accumulates in the eelgrass, which is very rich in sulfide.
This mud, they say, can destroy young eelgrass plants, but it can't kill the adult specimens. Since these underwater grass colonies grow in circles, the youngest plants get obliterated on the outer layer of the circumference when there's an influx of toxic mud, ending in those mysterious rings.