Mysterious 'Ice Rings'

From Live Science:

In Siberia's colder months, Lake Baikal — the largest freshwater lake in the world, by volume — freezes over. The ice is so thick, people routinely drive over it, said study lead researcher Alexei Kouraev, an assistant professor at the Laboratory for Studies in Spatial Geophysics and Oceanography (LEGOS) at the Federal University in Toulouse, France.

"It's a no-brainer," Kouraev told Live Science. "It's a very long lake, and if you want to go from one side to another, either you do 400 kilometers [248 miles] one way and then 400 kilometers on the other coast." But the trip across the ice is just about 25 miles (40 km), "so the choice is evident," he said. However, while the ice is thick outside of and inside these rings of thin ice, the rings themselves can put vehicles and their occupants at risk, Kouraev said. (Read more.)