Category: "Ablation"

Drainage Lines on Snow

October 18th, 2019

Last night I dreamed of a passage along a narrow river in a thick forest followed by a perilous descent down steep snow on a mountain.

And then this morning a friend sent me this picture.

Drainage Lines on Snow

Actually, I had asked him about the photo yesterday, so that explains my receiving it. I had asked because the lines in the picture had originally puzzled me. They appeared to be flow-lines, but this is a snowfield, not a glacier, and even if it was a glacier, the cause of the darkening wasn't obvious. But after talking about them with Steve Warren at the UW on Monday, I came to a simple conclusion. They are indeed flowlines of a sort, but it is not the ice that flowed. Rather, it is liquid water. That is, they are channels created by rainwater drainage.

Still, it doesn't detract from their beauty, does it?
And, in a weird way, it connects to my dream... as if my mind had assumed the form of a raindrop and fallen onto the snow.


Dark lines in melting snowpiles

March 30th, 2019

Snow cleared from a city street slowly vanishes, leaving lines of "dirt".

Dark lines in melting snowpiles

(Click on images to view more closely.) Where the snow has a distinct edge, you can see the dark lines are ridges, some of which can be quite sharp:

Dark lines in melting snowpiles

Why is this?

Cryoconite ridging

This all happens because the snow is vanishing but the dirt is not. The vanishing is actually called "ablation", meaning some combination of melting, sublimating, and evaporating. It is mostly melting in the above case, but it is possible that evaporation helps to form the lines. About the dirt, it is not clear exactly what it is. The term "cryoconite" is used when similar dark dirt falls and clusters on glaciers and ice sheets, so to be specific, we might call it "cryoconite ridging".

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