Posts Tagged ‘local ice physics’

Ice Needles (not to be confused with Space Needles)

December 2, 2014

Yesterday on my way to┬áthe office I noticed that the ground looked weird. Inspecting it more closely I discovered that the apparent “surface” was actually composed of lots of dirt clods and small rocks on top of two-inch-tall pillars of ice.

All of these rocks and bits of dirt are on 2-inch-tall ice columns

All of these rocks and bits of dirt are on 2-inch-tall ice columns

I had never seen anything quite like it before, at least not in person. The physics involved is actually quite complicated and I don’t fully understand it myself, but it boils down to something like this: if ice is freezing at some particular spot, it “pulls” water toward itself. You mostly see this effect in porous materials that water can flow through by capillary action, like soil.

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So the water gets pulled toward the ice and freezes on to it, pulling yet more water along behind it, and gradually more and more ice forms. In this case you end up with columns that lift pebbles off the ground, a.k.a. needle ice. In other cases, where the freezing is happening underground, you can get frost heaves or weird permafrost landforms (this is called ice segregation.

You can see the ground through the hole.

You can see the ground through the hole.

An ice column I plucked out to examine.

An ice column I plucked out to examine.

Under the bushes the columns got surreally twisted.

Under the bushes the columns got surreally twisted.

Side view of the ice columns lifting some pebbles and a small ice sheet

Side view of the ice columns lifting some pebbles and a small ice sheet

You can see there was a change in the freezing process; the short, whiter columns seem to have been lifted by the taller, darker columns underneath.

You can see there was a change in the freezing process; the short, whiter columns seem to have been lifted by the taller, darker columns underneath. The bottoms of the small columns have frost on them.

Side view.

Side view.

More images here.

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