Frazil Forms on the Rivers

Saturday, January 15:  Still very cold today, but not so windy as on Friday,  and we even had some bright sunshine this afternoon, so I had no excuse to not get outdoors today.  I drove up to Hadley, where the Hudson River joins the Sacandaga, hoping to catch sight of eagles fishing in the waters kept open by turbulence on both rivers.  No eagles in sight today, but I still saw a fascinating phenomenon:  the formation of "frazil" ice in the turbulent waters.

Both rivers were running full and fast today.  Here's the Hudson as it roars through a gorge at Rockwell Falls.

Here's the Sacandaga in full rowdy flow as it charges toward the restored Bow Bridge that joins both sections of Hadley. The two rivers come together just beyond the Bow Bridge.

At the confluence of the two rivers, I noticed accumulations of slushy ice that had congealed into the distinctive cakes or pans so typical of the special ice called "frazil."  This is a kind of fluid ice that forms when turbulent water throws droplets into the frigid air, where the droplets form crystals and fall back into the water.  The frozen droplets stick together to form thick mats that build on themselves, often creating "hanging dams" that obstruct the river's flow, causing the mats to rise and be deposited along the river banks.  Certain stretches of the Hudson to the north of here are renowned for amassing huge accumulations of this ice, sometimes as thick as 15 or 20 feet.

I climbed down the snow-covered bank to the water's edge and followed the Hudson upstream from where it joined the Sacandaga.  As I approached the bridge that joins the villages of Hadley and Lake Luzerne, I noticed a thick raft of what looked like heaps of snow just downstream of the bridge.

Here's a closer look at that raft, which is not snow at all (we certainly haven't had anything like this amount yet this winter), but rather an accumulation of frazil ice.

I then climbed up the bank and out onto the bridge to observe the river from above, looking downstream.  The river was flowing freely both above and below this frazil raft, so the frazil had obviously not "grounded" here -- an unlikely occurrence, since the river is exceptionally deep at this point.

Walking over to the upstream side of the bridge, I looked directly down to where the torrent, constrained by steep rocky cliffs on both sides, suddenly explodes in a froth of swirling whitewater.  I wondered if frazil ice was forming just as I watched, since I saw milky trails of slushy ice collecting into a mass along the right bank.   This mass would grow in size until its edge reached the swirling current, which then swept much of the slushy ice downstream as more began to accumulate in the shelter of the bank.

This process was rather mesmerizing to watch, and I could have stayed there a long time, but my face grew numb and my nose started dripping from the cold wind.  So I took a little video to watch in the cozy warmth of my home.