Naturalist's Corner - What's Cool? What's Hot?

You may be expecting a post on the trendiest hiking gear or maybe climate change...

...but instead I want to reflect on two recent curiosities of nature and our seasons that I encountered. It's also about the delight we can find in learning - and learning more - on our hikes and interactions with nature.

The Cool

Northern-facing algific talus limestone cliffs

I spent time recently in Decorah, exploring a loop trail in Phelp's Park, especially at the start of its Trollkor's Trail. As we began our hike, we immediately went past a series of high limestone cliffs with a profusion of broken rock at the bottom and many small crevices and holes. Hmmm, what was this? We soon came upon a kiosk, detailing the algific talus slopes that are quite common in northeast Iowa. 

Checking out the cold-air flow

Then, past the kiosk, we noted large swaths of bright delicate fern moss covering the hillside. While moss isn't unusual at this time of year, the absolute masses we were seeing were. On that first hike on a 39F day, we were puzzled by this proliferation. 

It took a second visit, later in the week in much warmer 70F weather, to put two and two together. We were within touching distance of the north-facing algific (cold producing) talus (loose rock) slopes venting cold air from the beginning of our hike! Cool!

A chilly 55F in 71F weather

On that second warmer weather hike, as we passed the first short broken cliffs and the subsequent mossy slopes, we were blasted with cold air coming out of those vents.  The verdant moss on the hillside surrounded and covered those blast holes which were emitting 55F air. I had to hop into the sun after lingering there while confirming the temp! Our first hike was in air so cold we never felt the cold-air outflow. On a warm day, it was noticeably colder as we passed.

Ferns covering a vent

Living in the Driftless area, I have often heard about these slopes but never experienced them myself. According to the WI DNR biodiversity page, these steep north and east facing slopes occur when water enters through cracks in the limestone, freezes and slowly melts during the summer. It produces an outflow of cold air - a microclimate that supports rare plant and animal life. In general, these slopes are protected and not widely publicized to preserve their fragile ice age ecology.

So it was with great delight that I experienced their frosty air on a warm November day. I can hardly wait to return in spring and summer to observe what rare plants, within touching distance from the trail, prosper on these IA slopes  

THE HOT
Like many of you, with our early December snows, I often take snow cover for granted. It's there for snow fun, right?  But there's something special underneath the snow - the subnivean zone. It's a layer under the snow that retains heat throughout the winter and allows life to continue. Hmm, heat in the outdoors!

What's under that snow?

Subnivean is a such a lovely word that rolls off the tongue - and such an important piece of our winter landscape. The Latin roots of this word (sub and nivis) simply mean "below snow." After reading a recent post on naturalist Emily's Stone's amazing blog Natural Connections from the Cable (WI) Natural History Museum about the subnivean zone, my curiosity was piqued.

Over the years, I have seen spiders and snowfleas atop the snow and small tunnels and faint trails as the snow melts - all evidence that something was happening under the snow I hiked. We've all also probably seen, in nature photos and documentaries, foxes and owls honing in on small rodents beneath the snow cover. This subnivean zone provides an important part of winter survival for living things, from, as Emily Stone writes, "mice to martens, bacteria, fungi, spiders, hibernating insects, frozen wood frogs, and more."

So how does it happen? As the first substantial snow falls, it piles up on rocks, fallen trees, and vegetation that act like umbrellas creating space below. The snow cover creates a kind of thermal blanket and insulates the space. Those open spaces make up the subnivean zone. The temperatures remain constant at about 32F even if the air above the snow is much colder. Water vapor that forms from the earth's residual heat freezes at the bottom of the snowpack to create a type of ceiling.

Image - Emily Stone
Used with permission

In the photo at left from her blog post, Emily Stone writes: "All winter long I will monitor the air temperature and the temperature of a thermometer I recently buried in the Subnivean Zone under the snow. In it’s first day of existence this winter, the Subnivean Zone did not drop below 33 degrees!"

No wonder there is abundant life in that warmer zone.

It was delightful to spend time over the past few weeks learning more about both natural phenomena. If you want to dive a little more deeply, please check out some of the resources below:

Resources

The Cool - Algific Talus Slopes

A Global Treasure

 - Erica Place. Iowa Heritage Foundation. 2025

Karst Topography

 - Winneshiek County Conservation Board

Algific Talus Slopes

 - Wisconsin DNR

The Hot - Subnivean

Below the Snow

 - Ellen Horowitz. Montana Outdoors. March-April 2024

The Subnivean Zone: Shelter in the Snow

 - Barbara Mackay. Northern Woodlands Magazine. December 29, 2014.

 Anaamaagon: Under the Snow: Exhibit Guide 

 - Cable Museum of Natural History, 2024

Images, unless noted - Marge Loch-Wouters

Standing in the 71F sunshine to warm up
after exploring the algific talus vents

You can read my quarterly column on seasonal hiking suggestions in Inspire(d) Driftless magazine available online or pick up a free copy at businesses and organizations around the Driftless areas of Minnesota, Wisconsin and IA.

[Note: For those who accessed an unfinished version of this post on Thursday, my apologies. The holiday prep clearly helped me lose track of time and I forget to complete it.]