I enjoy breakup. Oh, not the puddles, or the mud, or having to wear waterproof boots to get anywhere. And some of those puddles are deep, especially in areas which should be drained by culverts. The highway department does a lot of steam thawing this time of year, as the culverts don’t thaw without help. But it’s fun to watch how the breakup takes place.

Breakup happens early if there is a building nearby. The sun heats the structure, and the structure radiates that heat onto the snow. The thermal radiation is in wavelengths the snow can absorb — unlike the sunshine, which the snow just reflects away. All of these photos were taken today, when I still have 15″ of unmelted (and pristine-looking) snow in my back yard, which is on the south side of the house and fully exposed to the sun. The building is the University of Alaska Fairbanks Museum, and the ground immediately around it is clear of snow.

The same can hardly be said of the snow across the street. The sun is striking this area from the right of the picture, and you can see some melting from the gravel that has been plowed from the road. But the gravel also actually protects the snow from melting if it is thick enough.

The end of my gravel road next to the pavement is thawing rapidly. It’s been plowed often enough that gravel is poking through the packed snow, and this end is more exposed to the sun. With the gravel darkening the snow, it’s starting to melt, so breakup is starting at this end. Getting my mail will be a real problem without boots.

The thawing doesn’t extend to the whole length of the road, though. Here, at the end of my driveway, the snow is still clean enough to reflect most of the incoming sunlight back to space, and very little melting has taken place.  From past experience, I know that the thawing at the end of the road will progress this way, though.

What about trees? Birch trees drop their seeds in spring, darkening the snow around them. As a result, the ground under birches, with little shade from the bare branches, thaws early. Open birch forest is one of the first natural areas to thaw. The rose bushes on the left of the picture are almost as early — they poke through the snow enough that the snow can warm the branches, which then radiate heat to the snow around them. Spruce trees shade the snow around them, and snow lasts longest in spruce forest. It seems like such a little thing, but it may make a week’s difference in how long before the ground is bare — and bare ground is far more efficient than snow at absorbing the heat from the sun.

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