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Tunnel Vents


Frequently you find a hole about an inch wide in the snow in the middle of a field, with no tracks going in or coming out of it. Logic tells you it leads to the subnivean layer – where the snow, warmed by the ground, sublimates into water vapor, creating a small space between the surface of the ground and the snow where the temperatures is relatively stable at 32 F. It is here that small rodents such as mice and voles create a maze of tunnels through which they travel from their sleeping quarters to feeding stations, undetected by many predators.

However, the lack of tracks into and out of this hole indicates that it is not an exit or entrance to the subnivean layer, but rather, it is a vent leading from the subnivean tunnels to the surface of the snow. Carbon dioxide from animal respiration as well as carbon dioxide released from the ground builds up to an unhealthy level in these tunnels. The holes we see in the snow are ventilation shafts, allowing the carbon dioxide to escape from the tunnels. The formation of crystals around the edge of the pictured vent indicates that warm, moist air from rodent lungs is rising up out of it.

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20 responses

  1. Alice Pratt

    An ice crystal chimney.

    December 21, 2016 at 7:01 am

  2. Looks like you have a duplication of a paragraph in this post. As always, a great posting. Many thanks and enjoy this lovely, cold weather! John

    December 21, 2016 at 7:03 am

    • Thanks so much, John. Happy Solstice!

      December 21, 2016 at 8:06 am

  3. Cheron barton

    So there!! 🤔 Hope u have a good day!! Almost here!! Kids must be CRAZY!! Lol

    Sent from my iPhone


    December 21, 2016 at 7:14 am

  4. Is this created by the temperature beneath the snow or by the animals?

    December 21, 2016 at 7:57 am

    • The subnivean layer is primarily related to the temperature of the ground and its affect on the snow above it.

      December 21, 2016 at 8:07 am

    • The vent is created by the animal, the temperature of the ground produces the subnivean layer.

      December 21, 2016 at 1:10 pm

  5. Thank you for mentioning the “thawed cavity” beneath the snowpack. I’ve measured frost depth in fields and woodlands for about 20 years (part of an ongoing study started over 50 years ago). I see that hard frozen ground forms before snowfall. After the snowpack reaches about 12 to 14-inches deep, frost begins to leave the soil.

    Frozen ground with deep frost penetration exists mainly where snow is removed on roads or other snow-cleared areas. With a nice snowpack there is little frost in fields and woodlands. Later in winter (during studies of the snowpack) I’ve measured the height (thickness) of these thawed cavities at the base of the snowpack. Planet Earth is warm. Heat flow is affects us locally, in our cellars and at the snow – soil interface.

    December 21, 2016 at 8:35 am

    • Pat

      Thanks for this info, sweetpotato7. That’s fascinating! I didn’t realize that frost actually leaves the soil if there is enough snowpack.

      December 21, 2016 at 11:38 am

    • Thank you so much for your additional information!

      December 21, 2016 at 1:21 pm

  6. Does the critter create this CO2 vent or is it a natural result of build up?

    December 21, 2016 at 9:27 am

    • Pat

      I’m still not clear about this either, Jaime. And if we get a couple of feet of snow in a single storm, do these vents still occur? It seems that they’d need animal help. Or will the CO2 build up enough to be lethal to animals before any vents open?

      December 21, 2016 at 11:42 am

      • Hi Pat,
        I should have made it clearer – it’s the inhabitants of the subnivean layer that create these vents! And you find them no matter how deep the snow is.

        December 21, 2016 at 1:12 pm

      • Pat

        Thanks for clarifying how these are made, Mary. And that’s really interesting that it doesn’t matter how deep the snow is. There sure is a lot of activity happening below that we (or most of us!) are unaware of.

        December 21, 2016 at 1:39 pm

    • The critter (most often a meadow vole) creates the vent.

      December 21, 2016 at 1:10 pm

  7. Awesome offering for the day!

    December 21, 2016 at 9:40 am

  8. Elisabeth Russell

    Kind of neat!

    December 21, 2016 at 11:07 am

  9. Viola

    Wow! Who knew? Amazing! You enhance my day, Mary!

    December 21, 2016 at 11:50 am

  10. Paula Haubrich

    are the vents created by the animals?

    December 21, 2016 at 1:43 pm

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