The snow is FINALLY melting here, and as it does, I’m learning something new about the yard–where the soil is especially shallow. Like so much of this region, our yard has lots of ledge. But since I am no longer in the habit of digging holes just to see how deep I can go (a practice my brothers and I found inexplicably fun as kids), I only knew the whereabouts of the ledgy bits that had to be blasted to lay water pipes and electrical lines when the house was being built.
Looking around now, though, I see areas where the snow melted quickly, and other spots still covered by the dirty, crusty last vestiges. Some of the variation is due to location–there’s snow in the shadow of the house, for instance, and in the woods. But in other spots, no above-ground explanations suffice. So I went looking for insight as to why snow melts unevenly.
Here’s the best short answer I found on the web:
Snow ablation and melt
The rate of snow melt is dependent on energy availability, which is mostly in the form of radiation. Cold snowpacks have a negative energy balance, but warming causes the snowpack to become isothermal (0 degrees C) and additional energy results in positive energy balance and melt. Daily snow melt in forested areas is considerably less than melt in open areas, as forests protect the snow cover from solar radiation and wind. Canopy warming can increase longwave radiation, but the net effect of forest is reduction in melt. Rain falling on snowpack may accelerate its melt rate, but intense sunshine of late spring and summer is the principal melting energy source.
Most operational procedures for snow melt prediction rely on ambient air temperature as the index of the energy available for melt. The temperature index is usually used to characterize the level of the energy balance because it is superior to other simple methods for the full energy balance at the snow surface. The most common expression relating snow melt to the temperature index is:
M = Cm(Tair – Tmelt)
where M is the daily snow melt (mm/day), Cm is the melt rate factor (mm/oC per day), Tair is the daily ambient temperature (oC) and Tmelt is the threshold melt temperature (oC). The critical melt temperature is often set to 0 degrees C but can be optimized for a particular location.
Is that not awesome?!?
Unfortunately for me, it doesn’t really get at the reasons why snow on rock melts faster than snow on soil. So, I’ve decided to settle on conjecture for now….and that conjecture is: density. Here’s my thinking: soil heats up and cools down much more slowly than does air because it is so much denser than air. So, one can say that soil holds heat “better” than air. And rock is denser than soil, so by analogy it should hold heat even “better” than dirt. I’m sure a geothermal engineer could give me a more precise explanation, but I don’t know any geothermal engineers.
So now, I’m imagining an earth art project based on these new-found speculations/insights. We bury a message by writing in with rocks on a huge field, and then covering the whole field with another layer of soil and then grow some wildflowers on top. Every spring, when the snow melts, the message would be visible for a day or two, as the snow above the rock-line writing melts more quickly than that in the rest of the field. Ah, what to write, what to write?
Part of the reason I’ve been thinking about rocks and temperature is because of the joyful snow melt. But part of it is because of the far less joyful glacier melt.
As glaciers recede, hosts of folks are trying to figure out what can be done to slow the process. And one guy who came up with a possibly crazy/possibly genius proposal to slow glacial retreat in the Andes is Eduardo Gold. He doesn’t call himself an artist or a scientist, but what he’s doing is of a piece with other artful remediation projects. He’s painting the landscape. Literally. With the help of some men from a nearby village–and funds from the World Bank through their “100 Ideas to Save the Planet” competition, in which he was one of the winners in 2009–he is whitewashing the rocks near the peak of Chalon Sombrero, in hopes of shifting the micro-climate and encouraging the glacier to expand.
Gold and his assistants are using an environmentally-kind “paint” made of lime, egg whites, and water, which they slosh over the rocks. The premise is that by changing the reflectivity of the surface, the area will become a bit cooler, perhaps enough cooler to re-create the conditions that had been in place when the glaciers were larger. And if that works, the glaciers will slowly begin to regrow. Once there’s more glacier, its surface color will be the dominant one, and it will have the right reflectivity to self-maintain.
I hope it works. It would be amazing if grassroots efforts to stave off climate disruption could generate positive effects.
From an entirely different perspective, Gold’s work also calls to mind some of the issues that Jena Duncan’s project on eating local food brought to the fore. If I did what Eduardo Gold is doing, it would be an artwork. If my brother who is an environmental engineer did it, it would be a slightly quirky project, but still all in a day’s work–and decidedly not art. What is it when Gold does it?
And what does it mean that what an act “is” depends on who performs that act?