Tuesday, January 19, 2021

The Rime Is Sublime - Nature's Artwork Revealed



A look across the Roan Massif from Round Bald, looking out to Little and Big Hump mountains reveals the beauty of the snow and rime ice adorning the landscape. 

Wintertime is a magical season in the mountains.  In addition to a lot of snowfall, there are all sorts of other atmospheric processes that maximize their effects when you deal with elevation. One of my favorites is rime ice.

Rime ice forms when super-cooled water droplets freeze upon contact with surfaces below 32 degrees. It may sound like science fiction, but tiny water droplets, like you see in fog near the ground or up in the clouds, will actually remain in their liquid state when the temperature is several degrees below the freezing mark.  Also known as freezing fog, these droplets float along on their merry way in that sub-freezing air until they contact an object, whereupon they immediately freeze to it. 

If it’s a roadway that has not been treated with salt, especially a bridge or elevated highway, freezing fog can create very dangerous, icy conditions.  On an aircraft  that flies through a cloud of super-cooled water droplets, rime ice can quickly build up on the wings and potentially weigh down and change its aerodynamics.  In fact, rime icing on aircraft has been responsible for some catastrophic accidents. However, if you are on a walk where rime ice has occurred, whether it’s on a twig or tree or building, you may get to see some amazing sculptures. On a recent hike, I was treated to just that.

In calm or weak wind conditions, the process of riming will produce icy spikes as drops accumulate on objects.  In stronger wind conditions, the droplets impact the windward (direction from which the wind is coming) side of the objects and continue to build into awesome billowy, aerodynamic shapes and designs as shown below.  The "whitish" appearance to the formation is due to tiny air pockets in between the frozen droplets that help to scatter light waves so it appears white. I encourage you to click on the images below to get a look at the details, it's amazing! 


These two images above are in different locations/perspectives on Round Bald atop The Roan Massif. They are proxies for wind direction, the photo on the left has winds coming from the left side of the image and the one on the right has winds coming from the right. 

The photos above were from a trip I made up to Roan Mountain, on the North Carolina-Tennessee border, a perfect place to see these formations. The Roan Massif is one of the most beautiful and spectacular sections of the Appalachian Trail. The Trail itself climbs through the clouds to over 6,000 feet and passes through the largest stand of Catawba rhododendrons in the world. 

When I trekked up to the “The Balds” at Carvers Gap, a region of treeless meadows that extend along the ridges at 5,500-6,000 ft., that morning, I was treated to beautiful works of Nature!  Because of the lack of dense forests across The Balds, widely spaced trees, dormant fields and even rocks and boulders are open to the prevailing wind. When super-cooled clouds race across the ridges, they paint the vegetation and topography in a beautiful icing of white. 

This lone pine tree atop Round Bald looked like a nice photo opportunity on this beautiful, sunny day.  As we got up close and looked at the tremendous build-up of rime ice on a pine branch, we were in awe!

The park road up to the rhododendron gardens at Carvers Gap is closed in the winter to traffic, but its a perfect place to hike and see some of the more heavily vegetated area adorned with rime ice. In contrast to the open areas, where the evidence of "wind riming" is readily apparent, in sheltered areas the riming is more uniform.

Even after a few days, a walk up the park road unveiled some beautiful formations of rime ice, still stuck to the sheltered trees. 

Every season brings a new palette for Mother Nature to work her miracles. Winter can be especially fascinating, in some cases "other-worldly". From beautifully crafted snow crystals, to the rime ice we have gotten to know in this blog, winter is a great time to see what is out there. With a little effort, you too can uncover these beautiful aspects of the world we live in!


1 comment:

  1. Thanks for your amazing photos and clear explanation of hoar frost. My wife, Cathy, and I met you and your wife near Round Bald in a foggy day several months ago. Jack Ollis