Over the next few days we’ll be posting installments of an ongoing series here at the Backyard Geographer documenting winter ice formation on Lake Michigan. For previous coverage, see parts 1 and 2 from 2009-2011, and parts 3 and 4 from winter 2012-2013.
The following series of pictures was taken on January 22, 2013. The air temperature on this morning was 8⁰F following several days of below freezing temperatures. Lake Michigan water temperature is about 37⁰F.
This picture was taken from the bluff overlooking Lake Michigan in Langdon Park. Immediately below the bluff is a stretch of frozen sand, then a strip of shore ice varying in width from about 50 to 150 feet, followed by a stretch of open water and breaking waves, and floating ice perhaps ½ mile offshore below the deck of clouds at the horizon. With the water temperature only a few degrees above freezing and the air temperature well below freezing, any water thrown up on the shore solidifies in the air or upon contact with the surface causing the ice to grow out into and over the lake.
This range of extinct ice volcanoes stretches southward about 50 feet off the sandy shore. They were formed when the developing ice shelf edge was near this position. The edge of the ice shelf is about 50 feet further out into the lake now. As the ice front grows out over the lake, ice volcanoes that were once active become cut off from the supply of water at the liquid/frozen interface.
Here is the view looking down into the vent of one of the extinct ice volcanos in the previous view. The vent pipe extends down about four feet to a frozen plug.
Here is an ice volcano spouting near the edge of the ice shelf. 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.
The origin of this this large and level platform of nearly circular plates of ice separated by raised rings of crunchy ice was a mystery to me until I returned the next day to spot a clue. I found similarly sized and shaped ice sheets riding the surf and crashing into the ice front. These also had raised edges, probably from jostling against each other in the swells. Five days later I found similar chunks filling the outer parts of Wilmette harbor. Perhaps this deposit formed under calm and cold conditions when the floating ice plates froze into a solid mass.
*update* The formations in the picture above are known as pancake ice. Dimensions of the pancake ice platform estimated to be 250′ x 75′.
text and images by Steve Jansen