Over the years that I have been watching the snow melt on the south-facing slope of Pleasant Valley Conservancy, I have noticed the patchiness of the melt. As the photo today show, there are bare strips and then there are strips with snow. Walking across this slope, I was impressed with how much snow there was in some of these strips, and then nearby there was no snow at all.
Although it was not sunny when the photo was taken, there have been many sunny days. Even if the air is quite cold, the sun will bring about significant snow melt. Also, remember, because of the angle of the sun, it warms up the surface lots more on the slope than it does on the level. (You can convince yourself of that if you work out the geometry of the system.)
In the area shown in the photo, there are at least two factors (in addition to the sun angle) which influence the snow melt. One is the big bur oaks themselves. You can see snow-free zones on the south sides of the trunks of all the trees. This is due to the fact that the large trunks absorb lots of the sun's rays and then transmit the heat to the snow surface.
The second reason is that the "slope" of the south slope is not uniform. As you climb up the hill, you go from a fairly steep climb, to an area where the ground is almost level, and then it starts to get steep again. This is because of the presence of a bedrock layer of Black Earth Dolomite, which is more resistant to erosion so that it remains level when the sandstone layers on each side erode extensively. Because the snow is level here, it gets less of the sun's rays, and hence melts less fast (or not at all).
The complex topography here influences the development of plants during the growing season. In fact, certain species are found along the Black Earth Dolomite and nowhere else. Also, some species are found on the north-facing sides of the big bur oaks but not on the south-facing sides, which correlates with the snow patterns you see in the photo.
Hopefully, the snow will soon melt completely (and stay away), so that we can start doing serious brush work by basal bark.
Very interesting post. My dad and I were just talking about this simple phenomenon while noticing that the snow was melted around the south side of a big elm in my yard. The ground around the tree is relatively flat, but due to the large diameter of the trunk, the snow was melted on the south side. We thought that wind may have had an influence on how much snow accumulated around the trunk too. Great post!
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ReplyDeleteTom Brock