When Dew Flowers into Frost…

Frost ‘leaves’ formed on ice over Thompson Creek, ON (photo by Nina Munteanu)

Someone once said that frost, ice and snow are just winter versions of summer’s dew, mist and rain.

During my walks along the Otonabee and Thompson Creek, I get to witness many versions of frost, ice, and snow. In the often clear sheet ice of the calm bay leading to the larger river, some of the most beautiful formations aren’t actually ice but frost on ice; they arise when water vapour condenses directly into hoarfrost (radiation frost) or rime when it’s cold enough during a freezing fog. Frost, particularly hoarfrost, often forms at night, when the air temperature is cold. This frost often melts quickly as the sun rises and warms the air around the frosted object. That’s why I prefer to do my first walk of the day in the early morning. Hoarfrost will form on many objects like twigs, branches, leaves, grass blades, ice and even snow.

A miniature ‘forest’ of hoarfrost crystals covers a snow field in the morning after a cold night, ON (photo by Nina Munteanu)
Early morning hoarfrost covers a snow field with a forest of crystal ‘leaves’, ON (photo by Nina Munteanu)
Early morning hoarfrost formed on a snowbank on a clear cold night, ON (photo by Nina Munteanu)
Close up of hoarfrost on snow, ON (photo by Nina Munteanu)

Unlike ice that forms from liquid, frost forms from vapour. Frost forms when an outside surface cools past the dew point; the vapour attaches to a nearby twig, grass blade or other surface and turns into a solid. Frost crystals then grow into various forms and patterns. If there is enough water vapour to create large flakes of frost this becomes hoarfrost.

Hoarfrost ‘leaves’ develop on ice sheet covering Thompson Creek, ON (photo by Nina Munteanu)
Hoarfrost on reed stem on Thompson Creek ice, ON (photo by Nina Munteanu)

Frost crystals that form directly on cold surfaces such as a snow surface or an ice sheet from freezing water vapour grow larger and flower into beautiful leaf-like shapes or hexagonal snowflakes. The different frost shapes and patterns arise from the topography of the ice sheet, often specks of dust, salt, or residue, twigs and other organic material that lies on the surface. The ice crystals nucleate on the particles and branch out, forming unique fractal patterns that resemble leaves, ferns, feathers and more. This ground frost closely resembles snowflakes, given that their formation and structure are similar—only the nucleation particles for snow are dust and for frost they’re surface objects.

Ice fragments covered in ‘legs’ of frost form on previous ice sheet on the Otonabee River, ON (photo by Nina Munteanu)
Hoarfrost flakes on branches of a Black Locust tree, ON (photo by Nina Munteanu)
Hoarfrost ‘feathers’ form on the windshield of my car, ON (photo by Nina Munteanu)

Glossary of Terms

ADVECTION FROST: A collection of small ice crystals in the shape of spikes that form when a cold wind blows over branches of trees, poles, and other surfaces.

FERN FROST: Frost that appears on windows and ice as moist air comes into contact with the freezing surface. The tiny water droplets freeze into patterns that resemble leaves or ferns.

FROST: Deposit of small white ice crystals formed on the ground or other surface when the temperature falls below freezing. A more extensive and larger crystalline structure of frost formed with more moisture, such as a freezing fog, is called hoarfrost. When frost forms rapidly, often during windy weather, it is called rime.

GRAUPEL: Heavily rimed snow particles or pellets, typically white, soft and crumbly.

HOARFROST: a grayish-white crystalline deposit of frozen water vapor in clear still weather on vegetation, fences, ice and snow, and other surfaces. It often resembles spiky hairs. The word ‘hoar’ comes from ‘ancient’ given it resembles an old man’s bushy, white beard. Also called radiation frost.

RIME FROST: Rime frost resembles sugar sprinkled on the edges of leaves and flower petals. It occurs whenever damp winds conspire with extremely low temperatures. Rime frost forms rapidly; the word ‘rime’ means ‘crust.’

Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit www.ninamunteanu.ca for the latest on her books. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press(Vancouver) was selected by Margaret Atwood in the New York Times ‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” was released by Inanna Publications (Toronto) in June 2020.

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