Saturday, April 30, 2016

Why Do Ponds Freeze Differently?

I'm afraid this post raises questions rather than answering them.   Limited time and physics savvy make this necessary.  But there are some links to offer a little bit.

These are pictures of frozen puddles I saw at Denali.  And naturally I wanted to know why they were so different.

First this one in our campsite the first morning.  Why did the ice freeze in the long roundish spikes?

Second, why did this puddle freeze round, but then have more angular geometric patterns in the middle?

I'd note, the next morning, there was no more ice.  In fact these two puddles were gone altogether.  Just depressions in the soil.

Why is this puddle in the tundra frozen yet clear?

While this one is frozen by clouded?

The internet offers some insight into the freezing of puddles.

Here's  Story of Snow's explanation of why puddles get these curvy lines as they freeze.   Here's an excerpt (it has good illustrations too.)
"The thick, continuous curves show places where the ice is thicker underneath. Other lines may mark the boundary where the ice thickness changes. The ice thickness varies because of the way the meltwater drained below the ice. The sketch below shows a puddle just starting to freeze. We are viewing a cross-section, and the ice is coming in from the edge."

There's some conjecturing on the geometric patterns on the ice in this discussion board.

I could only find posts on why ice cubes are sometimes clear and sometimes cloudy.  Here's part of an explanation at Today I Found Out:
"The answer to this mystery lies in the temperature of the water. You see, at room temperature there are a lot of impurities that are dissolved in regular old tap water. And as you may recall from high-school chemistry, the warmer water is, the more of a given substance it is possible to dissolve in it. For example, sugar has very weak molecular bonds that require only a small amount of energy to break. Thus, as you supply water with more energy by heating it, the amount of sugar you can dissolve within it increases and vice versa. You perhaps have noticed this phenomenon when sweetening hot tea vs. cold, or after letting a sugared cup of coffee get cold, with the sugar dissolving fine when it’s hot, but showing up at the bottom of your cup when the coffee gets cold. This is essentially what happens with ice. As you cool the water, all of the impurities that were happily dissolved in it at room temperature separate themselves from the liquid and become visible."
It goes on to explain why the cloudy part is usually in the middle of the ice cube.  I suspect this could explain the differences between the puddles that were clear and that were cloudy.  But I'm not sure.

Actforlibraries  explains why puddles freeze at different temperatures.  This one is short and easy to follow.

UCSB Science Line explains why water freezes on the surface of a lake, but not below.  That seemed pretty obvious (the air temperature is colder than the ground temperature.)

Another article on the Thermodynamics of Freezing Puddles in Autumn-Winter Period looks at sea water.  I could only see the abstract and decided not to pursue the whole article since it was about fresh water.  I also wasn't sure I'd understand much of it, but someone else might find it interesting.

There's even something called an ice spike which sticks up out of the water.  I've never seen one and they're rare it says

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