One of the most interesting of the many millions of Twitter accounts out there is that of Chris Hadfield (@Cmdr_Hadfield), a Canadian astronaut serving as flight engineer on the International Space Station. Recently Commander Hadfield was over Chicago, and posted a picture of the city; the snow puts the change in urban density into relief:

Closer to the ground, the Backyard Geographer, the blog of the Geographic Society of Chicago, has been looking at the lake's ice formations, which have been interesting even during this warm winter. Ice volcanoes, for instance:

This active ice volcano is connected to the open water of the lake by an under-ice plumbing system.  Each wave reaching the ice front causes the plumbing system to pressurize, spouting slush into the air.  The slush cools further in the cold air and freezes in place upon contact with the ice front.  If temperatures stay low, the volcano will continue to grow in height and breadth until the ice front advances far enough out into the lake that the plumbing system becomes cut off from its supply of partially-frozen slush.  Each ice volcano sews the seeds of its own extinction as it grows.

They also found instances of pancake ice (update: here's pancake ice on the lakefront, beautifully shot by Carlos Javier Ortiz) but the really neat formations are over near Traverse City.