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pressure ridgeThe winter had its fair share of dramatic weather swings and minimal snow creating a good recipe for pressure ridges to erupt in the ice around the lake. A few different ridges crossed Raquette Lake this February and March altering our  activities and traffic patterns a bit.
If you have had the pleasure of walking across the ice road, you have likely heard the ice groaning. Ice is constantly in flux
either growing or melting, depending on temperatures. As the ice warms, thermal expansion creates compression stress in the ice as it pushes toward the shore. The ice can only withstand so much compression before it ruptures in an undulating line. Pressure ridges typically occur between two points of higher land since they create pressure points as opposed to a beachlike area.
Pressure ridges are described in two types – folded and overlapped. Overlapped ridges are sudden and erupt with a loud bang, breaking the ice into smaller pieces that push and pile up on each side of the fault line. The ice can pile up to over 10 feet depending on the pressure it was under, making the ridges an easy hazard to see. 

pressure ridgesFolded ridges buckle down into the water rather than overlap above the surface; however, folded ridges can fold upward too. Over several hours, the ice folds down into the water getting deeper and longer; water pools in the buckled area. Upfolded ridges may look like a mountain peak with a moat around the base. Downfolded ridges are hard to see, especially if they have started to ice over again. Ridges can be a mix of both overlapped and folded.

Snow-free situations, like this year, can lead to rapid changes in the ice, especially with high daytime temperatures. A cold spell followed by warm days can cause expansion and buckling. Pressure ridges of any kind can be dangerous and should be avoided whenever possible. Folded ridges are hard to see especially if they have skimmed over with ice and
snow. Areas that were safe to cross in the morning may not be later in the day.

Photos courtesy of Richard Fey