For several decades, scientists and astronauts observing Lake Baikal have noticed giant rings in the spring ice on one of the world’s oldest and deepest lakes.
While the rings have attracted speculation and a few conspiracy theories, decades of satellite data and field-based studies collected by NASA have shed light on why they form.
Warm eddies of water circulate in a clockwise direction under the ice cover. The ice melts near the eddy boundary, but not at the eddy center where the currents are weak.
The research team is still investigating what causes the eddies, but data suggests that they typically get going in autumn, before ice has covered the lake.