Ice crystals cover southeastern Idaho’s Christmas landscape
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Last week while photographing owls along the Henrys Fork of the Snake River with a friend, we discussed the beautiful flocked trees, rose hips, powerlines, fence wires and even weeds in the freezing fog. The beautiful pure white ice crystals seemed to cover everything.
In our conversation, both of us referred to the ice crystals as “hoar frost” because that is what we were taught while growing up. All the beautiful ice crystals formed during the winter had come from the old English word, “hoar” meaning “showing signs of Old Age.” We were both wrong.
Hoar ice crystals are formed on cloudless, windless nights when snow which is warmer than the air forms water vapor, a gas, into a feather-like solid. The real name of the crystals that we were admiring were “rime” ice crystals. These were created as the freezing fog, water in a liquid state, freezes the fog into a solid state usually during a wind.
The crystals covered trees and most plants with “hard” rime crystals that appeared dense enough to cover everything. These hard crystals were created during the night when a strong breeze or a light wind occurred when the temperature was between 17 to 28 degrees freezing the liquid droplets.
As I observed and photographed American robins and Cedar waxwings flying into Hawthorn bushes to feed, they would create small clouds of ice crystals as they landed for a meal. A Great gray owl created a large crystal-flurry as it left its perch to harvest a vole, later seen wearing some of the crystals as it landed near me to listen for another victim.
The thickets along the Henrys Fork were blanketed in the white crystals until a breath of wind came along to shower the river with fairy dust. While watching all the beautiful showers of crystals from different vantage spots, I noticed some rose hips that was protected from breezes from every direction. The ice crystals near the rose hips were miniature six-sided designs, not a mass of ice crystals. These ice crystals are called “soft rime crystals.”
These crystals are very fragile and sugary and are formed when the fog particles turn into a solid state when the air is calm and the area is protected from air movement. I also found some of them in thickets where the branches were thick or dead leaves remained on the branches.
For three days and nights last week, thick fog blanketed southeastern Idaho with a few moments when the fog burnt off, allowing the frost crystals to fall. As the fog rolled back in, it didn’t take long for the crystals to rebuild or to build another layer on top of the old one. Some twigs and branches ended up with up to three inches of ice crystals on them.
One highlight of the week occurred when a Sharp-shinned hawk decided that it wanted a robin for brunch. It was unsuccessful in capturing one out of a large flock, but it knocked off a lot of frost crystals as it tried to maneuver through the thick branches.
With the bitter cold temperatures the last few days with fogless winds and the sun returning, the rime crystals have disappeared. They may reappear as a predicted heat wave comes during the week between Christmas and New Year’s Day, but the cold was a welcome event for me. Ririe Reservoir is now capped with ice and by the time you read this, I hope to be on it chasing kokanee and with the sun shining, it makes taking pictures a lot easier.
I would like to wish all of you a very healthy, happy and safe Merry Christmas. I hope you get a chance to enjoy your family and friends during this festive time.
