When snow piles up across snowy woods and fields, the landscape can look calm. 

But underneath the snow, in an area called the subnivean zone, a hidden world of mice is wide awake, using the elements for protection. 

What is the subnivean zone?

Once snow is about 6 inches deep, it forms a roof over the ground. The space below is the subnivean zone. 

It has the ability to hold temperatures near 32°F no matter how cold or stormy the weather is above, according to Northern Woodlands.

Snow lands on rocks, shrubs and grasses, leaving gaps underneath. 

Heat, which is a relative term here, from the ground turns the lowest layer of snow into tightly packed ice crystals. It essentially creates a ceiling of ice. 

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In a way, it reminds me of a naturally forming igloo. 

While not being super warm, it is stable. For a tiny animal, this can save their lives. 

Who lives there

Mice, voles and shrews rely on these zones.

They build tunnel networks with air shafts to the surface, nibble grass, seeds and insects that stay unfrozen, and stash leftover food in caches.

The fanciest burrows even include a sleeping area, which is a nice setup and an extra layer of protection from the predators above.

The predators that know

A couple of predators are well aware of these zones and work hard to catch their prey.

Red foxes listen for movement beneath the snow, even when it's several feet deep. They spring, then plunge headfirst, steering with their tails, according to the Deschutes Land Trust in Central Oregon.

Great gray owls can hear prey from about 30 yards away, and they have their own trick. According to a November 2022 study in Proceedings of the Royal Society B, snow actually can bend sound waves, potentially distorting where prey is located.

The owls counter this by silently hovering over snow. When a prey is directly beneath them, they punch through crusted snow to grab voles as deep as 18 inches.

A fragile world

This snow can vary based on many factors.  Warmer winters can bring denser, wetter snowpack that insulates less. 

Snowmobiles and other recreation can crush the tunnels below. 

So the next time you cross a snowy field, remember that the quiet is only on the surface.