Ice: Freezing Lakes

Ice – Freezing Lakes (Memorial Program)

Music; Ambience: Ice Skating

We’re listening to the sounds of ice skates on a frozen pond. Ice skating, ice fishing, and other winter activities depend on water freezing in a very particular way. I’m Jim Metzner and this is the Pulse of the Planet. This program is in memory of Mariana Gosnell, author of “Ice: the Nature, History and the Uses of an Astonishing Substance.

Gosnell: A lake usually freezes in degrees. By steps. And the first is that the water has to turn over. It gets cool on top and that water sinks and then warm water on the surface sinks, until it reaches the temperature of 39 degree Fahrenheit. That’s when it is at its most dense. From that point on, the water on the top is ready to freeze as soon as it reaches a little below 32 degrees. At 32 degrees, it cools a little bit more. Maybe just a fraction of a degree. And then you get a skim. And a skim may be a twentieth of an inch thick. And then it thickens, by growing downward, on the underside of it. An individual crystal may be three feet tall. If this didn’t happen, it didn’t freeze from the top and instead froze from the bottom, which is what would happen if water were an ordinary material, it would be heavier in the solid phase and it would just sink to the bottom. And if that happened, it would keep freezing from the bottom up. And, you’d have a lake that wouldn’t ever thaw, maybe except for the very top part. And there’d be no fish or other aquatic life and it would be, in the long run, barren.

Pulse of the Planet is made possible by the National Science Foundation. I’m Jim Metzner.

Ice: Freezing Lakes

The unusual way that water freezes allows fish and other aquatic life to survive the winter months.
Air Date:12/05/2006
Scientist:
Transcript:

Ice - Freezing Lakes (Memorial Program)

Music; Ambience: Ice Skating

We're listening to the sounds of ice skates on a frozen pond. Ice skating, ice fishing, and other winter activities depend on water freezing in a very particular way. I'm Jim Metzner and this is the Pulse of the Planet. This program is in memory of Mariana Gosnell, author of "Ice: the Nature, History and the Uses of an Astonishing Substance.

Gosnell: A lake usually freezes in degrees. By steps. And the first is that the water has to turn over. It gets cool on top and that water sinks and then warm water on the surface sinks, until it reaches the temperature of 39 degree Fahrenheit. That's when it is at its most dense. From that point on, the water on the top is ready to freeze as soon as it reaches a little below 32 degrees. At 32 degrees, it cools a little bit more. Maybe just a fraction of a degree. And then you get a skim. And a skim may be a twentieth of an inch thick. And then it thickens, by growing downward, on the underside of it. An individual crystal may be three feet tall. If this didn't happen, it didn't freeze from the top and instead froze from the bottom, which is what would happen if water were an ordinary material, it would be heavier in the solid phase and it would just sink to the bottom. And if that happened, it would keep freezing from the bottom up. And, you'd have a lake that wouldn't ever thaw, maybe except for the very top part. And there'd be no fish or other aquatic life and it would be, in the long run, barren.

Pulse of the Planet is made possible by the National Science Foundation. I'm Jim Metzner.