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Anchor Ice
Name: William M.
Status: Other
Grade: N/A
Location: MT
Country: United States
Date: December 2006
Question:
Although I am from Georgia, I have recently
bought a house on the Madison River in Montana. The lore out
here and retold by many is that the Madison River is one of
three rivers in the world that freezes from the bottom up. This
river does gorge when the ice piles up downstream and then backs
up but I have a hard time believing or even understanding that
this river --or any river--- can freeze from the bottom up.
Knowing the density of water as a liquid and as ice, it seems
impossible. Can you explain or demyth this?
Replies:
I agree with you for several reasons: 1. The density difference,
as you pointed out. 2. If any body of water froze from the bottom
up, after a Montana cold spell in your case, all the fish would end
up flapping around on the surface -- a phenomenon that would
certainly not escape international recognition. I do not usually
like to mention specific books that are in "popular circulation"
lest someone think I might profit from doing so, but I will make an
exception here (I am not making any money off this!!). There is a
captivating book entitled, simply enough, "ICE" by Mariana Gosnell
that discusses ice in most of its technical and non-technical
aspects. She addresses the ramifications of what would happen if
the density of ice exceeded water in equilibrium with it. The "fish
thing" is just one of the more graphic.
Vince Calder
William,
The river does not really freeze from the bottom up.
Like many rivers, frazil ice (small shards of ice
or "crystallized" snow) can actually sink from the river
surface into the river water, even down to the river bed
forming piles of anchor ice on the river bed.
When the Spring breakup occurs (or sometimes even before)
this frazil ice breaks off in small chunks and floats down river
immersed in the water. It gets caught on obstacles under the
water surface and piles up under the surface ice sheet. In
this way it, and the anchor ice on the river bed, may appear
to have formed on the riverbed, but that is not actually
the case.
This build up of frazil ice as well as the surface ice causes
the horrific ice jams in the Spring. I hope that your home
on the Madison is well above the river level, as the ice jams
on the Madison have often caused floods several feet above
normal river level.
There is an informative presentation at
www.crrel.usace.army.mil/icejams/presentations/Montana_Part_1.pdf
that talks about frazil ice and ice jams.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012
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