Most topics we explore in this project have a significant background of research. Some subjects have such an extensive knowledge base that distilling them into a readable chunk is a laborious exercise in curation. Periodically, an issue pops up with scant information on the internet. This occurrence is a modern rarity; at this point, nearly everything is somewhere on the digital compendium.

Still, these unicorns do exist. It’s always interesting to see which topics live in a data vortex. I would have assumed today’s topic would have at least a modicum of research attention. Instead, the pickings were as thin as a sheet of cat-ice.

Cat-ice at Walnut Woods Metro Park - photo by Chelsea, courtesy of Frankiln County Metro Parks

Columbus & Franklin County Metro Parks recently posted a photograph that had been shared by a local resident. At Walnut Woods Metro Park, someone snapped the above photo of cat-ice.

Despite the bizarre inclusion of squiggles that resemble contour lines on topographic maps that might indicate this formation is relatively rare, cat-ice is probably something you have experienced before (as long as you live in an area that gets cold).

Sometimes called shell ice, this phenomenon transpires when water underneath a sheet of ice disappears, leaving only the slight, top layer of ice.

Why call this happening “cat-ice?” 

Contour lines on topographic maps - graphic by REI

Fellow nature writer Robert Macfarlane featured “cat-ice” as his word of the day in January 2018, providing a denotation to explain the origin of the word:

When shell ice appears, it’s often so thin that only a feline that can deftly distribute its weight could walk on it.

Many people will instantly recognize this type of ice, even if it occurs without the contour lines. Any time you have walked over ice in puddles, fields, or shallow waterways that easily crunches beneath your feet, you’ve experienced cat-ice. Sometimes it happens when rain inundates a grassy area and the temperature drops quickly. When the ground absorbs most of the rain, just the thin layer on the acme remains.

Despite the frequency with which humans experience cat-ice, shockingly little exists in the scientific realm regarding the spectacle. The American Meteorological Society includes shell ice/cat ice in its Glossary of Meteorology, defining it as ” Ice, on a body of water, that remains as an unbroken surface when the water level drops so that a cavity is formed between the water surface and the ice.” But that’s the extent of their entry. A similar, terse characterization appeared in the US Navy Hydrographic Office’s 1956 Navigation Dictionary.

Cat-ice - photo by elzbeth26

Perhaps the best snippet regarding the etymology and usage of this term comes from a short blurb in a book from 1901, called Old Time Gardens: Newly Set Forth by Alice Morse Earle. This tome, which collects information and tales about gardening and the outdoors, related to the lives of European colonists in 17th-century New England, is a wonderful compendium of regional dialect and terminology. 

It includes the following quote:

“‘Cat-ice,’ too, is a good old New England word and thing; it is the thin layer of brittle ice formed over puddles, from under which the water has afterward receded. If there lives a New Englander too old or too hurried to rejoice in stepping upon and crackling the first “cat-ice” on a late autumn morning, then he is a man; for no New England girl, a century old, could be thus indifferent. It is akin to rustling through the deep-lying autumn leaves, which affords a pleasure so absurdly disproportioned and inexplicable that it is almost mysterious.”

I had never connected the joy of trouncing through fall’s leaves to crunchy ice, but the comparison is apt. Some of us also appreciate partaking in puddles, mud, and squishy ground.

So, cat-ice is an old New England term that has survived the past few centuries. Old Time Gardens goes on to mention “cat-slides,” a term which must have evolved simultaneously, meaning to run a few steps on thin ice and then to glide until the loose friction finally takes hold.

Cat-ice in Dartmoor, England - photo by Mark Bullock

These small details of the universe – autumn leaves and cat-ice – add a thin layer of tactile pleasure in one’s physical existence. One user in Macfarlane’s thread noted the term for cat-ice in Sweden translates to “witch circles.” These regional differences point to a rich diversity across the globe, akin to interpreting literature or painting differently; still, we all seem to notice the same sorts of things. Big things, such as mountains, oceans, and stars, get most of the plaudits, but the cat-ices and the witch circles of our planet leave a deep impression.

Of course, our minds interpret names in all sorts of ways. Some of the best ways are the literal ones!

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