Plastic snow

Sastrugi - the sharp features of a windswept snow surface bordering fractured plates of ice in middle of photo.

When I was younger, I had one word to refer to all that white stuff in winter: snow. As I got older and had more experiences with it, particularly through snowboarding, I realized that not all snow is created equal. Snow taxonomy has a history much older than winter ecologists, and much of the rich language found in cold climates to describe snow has been adapted by winter ecologists (like the Russian sastrugi - above, or Innuit qali - below).

Snow can be grouped into three categories:

1. Falling snow
2. Snow on the ground
3. Surface-generated ice features (like ice needles being pushed up from the ground on wet trails, hoar frost, icicles seeping out of cracks in bedrock)

Qali describes snow hanging from trees (like in the image above). Because our snow the other night fell in a frenzy of blustery winds, there wasn't a whole lot of qali left on the trees. Sintering is a natural process where snowflake crystals fuse together. Sintering can happen due to pressure (like stepping on the snow pack) or temperature (melt-freeze together). Because the snow crystals actually bond together, qali will act as a liquid moving in slow motion. Snakes, like in the image above, are common features in northern woods after a good snow storm. We observed a spot today where the sintered snow had bent down around the rock, creating a perfect overhang for a weasel to pop in and out of while hunting.

Getting closer...

What: Sam and went out to the lake yesterday to check in on the progress of the lake freezing over. Boy oh boy did it look frozen all the way across! With the continued cold weather the lake just might be crossable this winter! This would be the first time since 2007. Lake Champlain won't be the only large lake to freeze across. Looks like Superior is on the same trajectory (news story here)!!!

In the afternoon there were people playing hockey out on the ice (specks in bottom left of above photo). Later that evening Jon and I ran out to the light house and followed snowmobile trails. So at least as fall as the break wall, the ice is solidly frozen.

A photo essay in ice

What: Not to inundate the ecstatic beauty with overanalysis, I wanted to cap the week with a photo essay of the things that caught my eye.

Where do all them ducks go

What: A few winters ago I spotted large numbers of mallards (200-400) flying westward towards the lake around 4:30pm or so, just around dusk. Despite Burlington Bay being frozen at the time, as it is now, the ducks were still flying that direction. My interest was piqued and I wondered where o where those ducks were all spending the night. I spent the next few nights out around the same time trying to spot them. Sure enough, around the same time, a large flock of ducks would fly westward over Centennial Woods.


Audio of the ducks. You can hear them flapping their wings as scores of them would leave and others arrive. Our presence seemed to make them jumpy.  

As with the crows (I have yet to follow the ring-billed gulls) I decided to track them down and see where they were roosting each night. A few days after seeing them for the first time, I fortuitously wound up spotting - or rather hearing - them while out on a run. As I was coming north on the bike path, I passed the water treatment center's clarifiers (those big circular tanks with exposed water) and heard some noises. I peeked over the fence and there they were!

Mallards landing in circulator

I hadn't been back in a while, and the recent postings on the Vermont Birds list host about ice closings on the lake inspired me to back last Thursday night with Jon. We were greeted with a raucous reception. Our estimate put the number of mallards in just one of the clarifiers well over 1000. In the photo above, there were probably about 20% of the original number of ducks.

The other question is where do they go during the day? I would assume that there are a number of small openings in rivers, industrial parks, and other spots where they have access to open water (eBird gives a good sense of this with birders' postings from around Vermont: Map)

Illusion of open water

What: When we first arrived at the Thrust Fault, looking north to Apple Tree Bay it appeared as though the bay hadn't frozen entirely on the other side of the bay. In the picture above you can notice the thin strip of darker area that's reflecting the houses and trees in it. I've often noticed this effect when looking across the lake at NY, where the thin strip of land closest to the lake often appears twice as thick, as though in reflection. I'd always kind of unthinkingly attributed this to simply being a reflection of the horizon in the water.

But when we climbed up to the top of the point and changed our perspective, it became quite clear that the bay was indeed completely frozen over and the "reflection" wasn't simply a reflection (the surface of the ice is super rough and not reflective. What was it then?

I had also noticed a thin rippling effect in the air while looking out across the lake. It reminded me of my childhood in Southern California. I loved watching those heat waves dance up off the pavement - the phenomenon of a distorted horizon when looking down a long road in the middle of the desert. As a child I remember seeing the ripples on the road, but I don't remember the reflective quality. I was more than surprised to see those with mid-day temperatures hovering around 0.

I remembered looking into this in regards to the lake a couple of summers ago, but had forgotten the details so wanted a good refresher. The cause of the effect is the same in the winter as in the summer, as the ripples are indeed caused by heat, but it's actually relative heat. The effect, known as an inferior mirage occur when the surface is much warmer than air directly above it. The gradient needs to be about 5degrees per meter (normal atmospheric change is about 1degree of cooling for each 100m you travel up in elevation). While the lake is frozen, it's not super thick ice in parts so the warm water temperature (about 35) heats up the air right above the ice while the ambient temperature was frigid (about 8 on that day). So sufficient temperature gradient to cause the optical illusion!

The refraction occurs only at shallow angles, so as soon as we changed our vantage by going up to the point (as in the photo above), the mirage disappeared and we were left wondering when the rest of the lake would freeze over already!!