Overflow...

One of the main trail hazards up here, besides over enthusiastic snow machiners, is overflow. Technically it's known as aufeis, a German word that means "ice on top."
What happens is that most winters, the smaller creeks freeze to the bottom, but if their source water is an underground spring, it will continue to flow and force water to the surface through cracks in the ice, creating continuous layers of water and ice. Sometimes it can build up to 8 to ten ft thick (that's about 3 meters to the French). Where a trail crosses a creek, it can create an ice dam that will back up the overflow water, so that it spreads laterally up and down the trail, freezing into a sloping, slippery mess.

Here we are entering the overflow. It had snowed the night before, so for the next 100 yds, the trail is a patchwork of snow, ice, and water. Tried to get a better shot further in, but hit some sloping ice and with the plastic bottoms on the runners loosing traction, slid sideways off the trail.  Hanging on to the sled became more important than taking photos!