Why There is No Ice

Yesterday's post prompted a very good question. In effect: "Why isn't the river frozen at -30℃?

The Quick Answer: Because the water is flowing very fast.

The longer answer is that the river does freeze where the river flows slowly. In point of fact, about two miles upstream, they can drive their trucks onto the river and set up their huts for ice fishing. You can see ice huts in the distance in this ↓ picture that I took way back in 2013.

To further explain, I grabbed and annotated a map view from GMaps.

I took yesterday's photo (first one today too) from Bridge Flows Fast, pointing toward the top of the map, looking downstream (the direction that the water flows).

The second photo with the ice huts was taken from the bottom red rectangle at Hay's Shore. The width of the river results in a slow flow, so the water freezes. It is wide enough here that we call in Mississippi Lake.

As the river narrows, the rate of flow increases. The middle red rectangle is approximately where the conditions change from ice to water, somewhere in Riverside Park from where I post a lot of photos over the course of the year. This ↓ photo from December shows mostly ice, but there are a few spots of water. Shortly after this, if we were to get nearer the bridge (off the photo to the right), there would be no ice but open water. The line where it changes from ice to water is variable, depending on how cold it is. I imagine the ice extends quite a long way right about now.