Trees and snow

October 27, 2013 9:41 AM

Trees in deep snow often have a gap around them where the snow is lower (see here and here). Why is this? Do trees give off enough warmth to melt snow, or do they absorb the snow as water, or is it because falling/blowing snow is blocked by the tree trunk, leaving a kind of shadow?
posted by oulipian to Science & Nature (11 answers total)

Tree wells!

A tree well is a void or depression that forms around the base of a tree can and contain a mix of low hanging branches, loose snow and air. Evergreen trees in particular (fir, hemlock, etc) can have large, deep tree wells that form when low hanging branches block snow from filling in and consolidating around the base of the tree. These voids can be hidden from view by the tree’s low hanging branches.

There is no easy way to identify if a particular tree has a dangerous tree well by sight therefore, treat all tree wells as dangerous.

In simple terms, a tree well is a hole or void in the deep snow, which is clearly marked by a tree. You can easily identify and avoid these areas.

posted by jessamyn at 9:50 AM on October 27, 2013 [6 favorites]

Those are called tree wells, and form because the branches shelter the base of the tree from snowfall.
posted by Specklet at 9:50 AM on October 27, 2013

trees absorb some amount of solar radiation, so area around trunk is sometimes warm enough to melt snow.
posted by The_Auditor at 9:50 AM on October 27, 2013 [2 favorites]

or...maybe not. (tree wells!)
posted by The_Auditor at 9:52 AM on October 27, 2013

Best answer: A tree well is different than what is being described here.

Basically, the tree warms up during the day - being darker than snow, and more dense - they then radiate that for quite a long time. Rain and/or melting snow from above can run down the trunk and accelerate this process.

You can observe similar effects near walls, sign posts, and other such things.
posted by Pogo_Fuzzybutt at 9:57 AM on October 27, 2013 [5 favorites]

More than you ever wanted to know about tree wells!
posted by emilyw at 10:02 AM on October 27, 2013

I may be wrong, but I don't think the asker is asking about "tree wells" (the lack of snow under a tree due to the umbrella-like passive action of the tree's branches blocking the snow from reaching the ground beneath), but rather those curious little donuts of snow-free space that occurs around some trees trunks.

I found this image online, with the following description:

A sight I associate with maple sugaring season with its warm days and frosty nights is the circle of sunken snow surrounding tree trunks, their warmth pushing back the snow. Soon the ground will begin to show and form a brown skirt around each tree.
http://altoonsultan.blogspot.com/2010_02_01_archive.html

posted by blueberry at 11:06 AM on October 27, 2013 [1 favorite]

You can also see this phenomenon around big dark boulders in the snow, especially in spring time where the dark rock absorbs more solar heat.
posted by monotreme at 11:08 AM on October 27, 2013 [2 favorites]

Yeah, your pictures are more to do with warming and radiation of the trunk. A tree well is most common in deep, unconsolidated snow around a tree that has low hanging branches. The branches prevent the snow from building up as much near the trunk, creating a pit. Very dangerous - see "NARSID" - Non Avalanche Related Snow Immersion Death:

http://www.backcountryaccess.com/2012/10/22/issw-2012-snow-immersion-suffocation-the-silent-killer/
posted by Pantengliopoli at 11:10 AM on October 27, 2013

Clearly, to me at least, what the photographs show in the questioner's links are snowless spaces around tree-trunks (with no low branches) which are caused mainly by solar heat absorbed by the trunks and radiated out. When snow is accompanied by high winds, you can often see similar, but not as deep or complete, spaces around any stationary object.
posted by Hobgoblin at 12:21 PM on October 27, 2013 [5 favorites]

Response by poster: Tree wells are interesting in themselves but they aren't really what I was referring to, which happens around even very thin trunks without low branches. Radiated heat makes sense! And I suppose when snow melts it would pull away from most surfaces in the same way. Funny I've always mostly associated it with trees. Thanks for the answers!
posted by oulipian at 2:51 PM on October 27, 2013 [2 favorites]