Exploring Kootenay Lake

In which, something normally hidden is disclosed: a thin layer of snow reveals internal structure. The same is true of frost and dew.

I first became aware of these things as a student when I discovered a book (Geiger, 1957, The Climate Near the Ground) that discussed how an otherwise-hidden structure had been revealed by frost. Geiger showed an aerial view of a frost-covered farmer’s field in the U.K. in which a previously unknown sub-surface Roman foundation was suddenly outlined. The greater thermal conductivity of the stone foundation prevented the formation of frost over it and so offered a map of underground structures. 

Wow! That prompted a long-term fascination with patterns revealed by the distribution of snow, frost and dew on all manner of surfaces (a recent discussion of it being beach frost). The patterns do not all arise from differences in thermal conductivity, but today’s do—and they depend upon house construction. 

Internal structure: the patterns shown here result from sub-surface (hidden) structures, not surface structures such as the ribs on a metal roof.

My knowledge of house construction is scanty. I think that all of today’s pictures illustrate snow on what is referred to as a hot roof. This often happens when the attic is occupied. One way of protecting attic space is to place insulation between the rafters. Although, rafters and insulation are normally hidden below roofing, the construction becomes visible after a light snow. The wood of rafters is more thermally conductive than typical insulating material and so the snow is ablated preferentially above rafters with the result that a pattern emerges. 

The term, ablation applied to snow or ice, says that the loss might be a result of either melting or evaporation. In the present case, the temperature might stay below 0C, so the snow does not melt, but evaporation does increase as the temperature rises, with the resulting loss of snow.

See the windows: this house clearly has an occupied attic. The insulation between the rafters results in a greater snow ablation above the wood.

This house shows much the same structure as did the last, but, in addition, there is the striking band of snow above the roof’s overhang. Here the roof is not being heated from below and so the snow is thicker.

This house shows the variable ablation between the location of rafters and insulation. It also shows the greater depth above the roof’s overhang. In addition, it shows almost no snow ablation above the unheated deck.

This house shows many of the same features, but also the effect of the warmer air rising to the top of the attic. 

Anchor ice (also called bottom-fast ice) is ice attached (anchored) to the bottom of a stream.

At first blush, it seems rather odd that any ice should form on the bottom of a water body. After all, for ice to form, the water temperature must be 0C (or slightly less). But, water with such a freezing temperature is not as dense as the somewhat warmer water with a temperature of 4C. Consequently, the warmer water sinks to the bottom and the freezing water rises to the top. So, it is at the surface of ponds, lakes, and oceans where ice forms. (If the water is shallow enough, freezing that starts at the top might progress right to the bottom, but that is a different matter than ice that builds up on the bottom).  

The game changes slightly in a rapidly flowing river or creek. Turbulence mixes the water so thoroughly that density stratification does not take place. During particularly cold weather (such as at present) the stream cools, but being well stirred, it does so fairly uniformly. The temperature of the whole stream drops to 0C and now ice begins to form as tiny crystals or platelets throughout the depth of water. As these ice fragments are carried along in the turbulent waters, some brush against the stream bottom and stick, adhering first to rocks and subsequently to other ice. This ice that collects on the stream bottom is the anchor ice; it is quite porous as it is a composite of shards. 

The ice at the upper and lower left of this picture is on the surface of the creek. It has formed on the creek edges where the water is shallower and the flow gentler. In the main channel, between these edges, a creek bottom of sand and rocks is visible. Locally, adhering to some rocks is the distinctly greenish anchor ice.

Anchor ice is occupying most, but not all, of the channel between the surface ice.

Very little of the creek bottom is seen in this picture. Surface ice occupies the shallow edges of the creek and anchor ice covers most of the stream bottom in the channel.

This morning, Kootenay Lake was a devils’ playground. It was spellbinding to watch, but also tooth chattering and bone chilling. Within easy sight, dozens upon dozens of devils frolicked.

The experience was bone chilling as the temperature was about -12C and the wind was brisk. What with open water on the Lake, it was an ideal time to watch for steam devils; when they came, they did not disappoint. Alas, after a time, the raw conditions drove me indoors.

Steam devils are fairly easy to distinguish from normal steam fog. Convective wisps of steam fog are chaotic and will usually evaporate by the time they have risen a metre or so. Sometimes though, a wisp will concentrate the wind shear in the atmosphere’s surface layer and begin to spin. This protects the droplets inside from evaporating in the surrounding air. The spinning column can retain its shape to heights of tens of meters. This is the steam devil.

While steam devils appeared all over the Lake, they only stood out dramatically in a narrow region on the edge of a mountain’s shadow. Here, steam devils were in the sunlight, but nicely contrasted with the dark backdrop.

As with dust devils and tornadoes, the hollow structure that results from spinning was sometimes evident.

Now and then one devil would wrap around another. Now that is playful.

All in all, a grand—if chilling—experience.