Monday, February 18, 2013

Snake mountain and lake closings (freeze overs)

What: I hiked up Snake Mountain with Jon and his family yesterday. Looking out at the southern end of Lake Champlain, I was surprised by how the sharp line at the edge of the ice was. The ice seemed to be corralled into the southern bay, perhaps by the harsh northerly wind. The freezing point I think was between Potash Bay in Addison, VT and Mullen Bay near Westport, NY.

The image to the right shows data collected on the lake between 1816. Rectangles on the left side, colored in red, indicate years in which the lake did not freeze over completely at the widest point (from Burlington Bay across the lake about 9 miles to Corlaer Bay; 6 miles if you don't include the 2 bays).

In total, since data collection began, the lake has not frozen over 38 times in the past 197 years. 32 of these are in the last 54 years! While it might be convenient to readily assume that climate change is the culprit, there might be some confounding factors that have also changed over the past 197 years. Things that lower the freezing point of water could include increased:
  • Turbidity (suspended solids absorb more heat from sunlight)
  • Wind
  • Turbulence (like flow in a river)
  • Concentrations of salt, alcohol or any other substance that has a lower freezing point than water
I don't know for sure if these have any bearing on the fact that the lake is consistently less likely to freeze over, but they are likely a part of the story. I found an article from Feb 15, 1993 in the Daily Gazette about Lake Champlain closing dates (when it freezes over completely). The article states:
"Whether the lake freezes over or not has no effect on the fish and other creatues that live there, said George LaBar, a UVM fisheries biologist. 'The bays are always going to be frozen, those shallow areas are going to freeze over,' and the fish who live in those bays are used to that, he said. A frozen lake doesn't affect teh overall temperature of the lake water, he said. Winters with less ice cover might encourage fish to spawn earlier, he said, which allows the young fish to grow larger."
I really doubt that the lake not freezing over has no effect. I think it probably means something pretty significant for some things and not so much for others. Complex system with complex feedback loops.

No comments:

Post a Comment