Projections, or “dendrites,” try to grow from the frazil disks but break off in rough water (in the ocean and big lakes, too), creating billions more nuclei for frazil crystals to grow on. (There has to be a nucleus for an ice crystal to start growing, and in water that pretty much has to be ice, which can come from bubbles bursting and the droplets freezing and falling into the water.) The whole river, top to bottom, will then have frazil crystals tumbling in the water, hitting the bottom.

Oldtimer Adirondackers around here call frazil “anchor ice,” which is the term ice engineers use for ice that collects underwater, clinging to rocks in masses on the river bottom in shallow areas and on objects such as water intakes for turbines, and in our case in North Creek, for making snow. Engineers here designed a heated intake to prevent frazil from sticking to the grid and stopping the water. One-hundred years ago, seamstresses in the shirt factory in Warrensburg would have a day off when anchor ice shut down the water turbines necessary to power their sewing machines.

So, what makes the Hudson fill up with frazil (and are not just covered by solid ice) when most other rivers and streams in the Adirondacks do not? Hanging dams. Ice jams are made mostly of big chunks of solid ice during warm weather rain storms when the river and tributaries are still full of ice and when the flooded river meets a constriction like a bridge.

Hanging dams, an engineering term, form in very cold weather after a complete cover of frazil bridges the river. The ice cover usually starts in a relatively calm area of the river and often where there is a big curve, from what I have observed. When the surface water carrying the frazil is moving over 2 miles an hour, the water ducks under the cover carrying the frazil with it. Underneath the cover, the frazil floats up wherever the water slows down, plating out on the underside of the cover, then thickening downwards in huge masses of frazil.

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