Slope angle/aspect and sun-cups??

What slope angle and aspect is most prone to sun-cup formation? Anyone thought about this or know the answer? Any glaciologists out there? As I understand it, sun-cups are formed by differential heating, say by a rock falling onto snow, absorbing more solar radiation locally, melting more snow, forming a sun-cup.<br><br>One can construct a thought experiment: take a large area of snow, randomly cover it with dirt/rocks/ect then vary the slope angle from flat through very steep and the aspect through all points on the compass. Fix the elevation and all meteorological variables on clear, warm, and sunny late June. Which combination of slope angle/aspect will form the largest sun-cups? Is it simply the one with the most solar radiation, or is there something more subtle here? Excepting the distribution and type of dirt/rock, are slope aspect and angle the most important factors? What effect does wind have? Elevation? Something to ponder perhaps during those otherwise idle moments.

just an amateur guess here, i'm no glaciologist. observations and logic suggest to me that slope angle is the critical factor. almost all aspects (not considering shade) receive enough sun to eventually suncup the snow.<br><br>however, not all slopes develop the cups, because the3 slope must be gentle enough to pool the melt water from the snow. on steeper slopes, the same action will lead to rill formation.<br><br>i bet that your experiment would determine that suncups tend to form on lower angle slopes (say, approaching 15deg and less) starting on south/east facing slopes and moving to the north/west facing slopes later in the spring/summer.

I don't have a good theory, but I have a recent observation. When we skied around Forbidden Peak in late June, we found lots of suncupping on the Forbidden Glacier, which faces NW, but much less on the Boston Glacier, which faces E-NE. It was almost like there was more than just suncupping going on--the surface was furrowed as well as suncupped. Besides the afternoon sun exposure, I suspect that wind had something to do with it. It was continuously windy on the Forbidden Glacier while we were there.<br>

No answers from me either, but more observations. I've always though of suncups as due to the differential melting in direct sunlight that ski_photomatt mentioned, and mostly due to dust/dirt rather than rocks (although those obviously will lead to a deep depression), but the wind factor is a good idea. Maybe wind can accentuate the uneven distribution of the dust, which would enhance the differential melting. I've seen a number of dirty slopes where the dust is evenly distributed and the surface is very smooth, so something must have to happen to make the dust become unevenly distributed (water, wind)? An unnatural example is when a skier makes turns on a smooth, dirty slope; within a few sunny days the dirty snow will have melted far more than the white turns, and the turns can become "raised" a foot or more above the surface.<br><br>Are "furrows" and "rills" the same feature described by "runnels"? The latter is what I've been calling the features which follow the fall line and look like water channels, but I've never seen any water in them. In my experience, runnels are usually a worse feature for skiing than suncups (although the combination of suncups on a runneled surface is the worst), but I guess I've ever been in truly large suncups, like Muir or south Adams in August. It is hard to imagine that runnels initially form from rain, because I've seen slopes with deep runnels right next to slopes with no runnels. My experience is that in a given area, the steeper and more north-facing the slope, the less likely it is to have a runnel problem. However, I've been on very smooth late summer/early fall snow which is south-facing and not steep. It also seems like runnels are more likely to be pronounced by July when we've had a June with lots of warm, sunny periods (like this year and last). Maybe with really fast melting, the snow surface collapses into subsurface channels which have been carrying the meltwater?<br><br>Can a suncupped and/or runneled surface ever get better as the summer progresses (not counting new snow filling it in), or is it always destined to get worse?<br><br>

Well, I've been thinking about the issue of suncups for several weeks now, and so I decided to research the subject in the proper way: hit the scientific journals. Several hours of work today, online and in the UW library, yielded nearly every journal article published on the subject of suncups (technically called "ablation hollows") from 1948 to 2003. <br><br>Unfortunately, the published literature on the subject is quite sparse, with less than a dozen useful papers and about a dozen more which are fairly useless. Worse yet, most glaciology textbooks and monographs seem to avoid the subject of suncups / ablation hollows, even though all of them discuss general ablation processes in detail. So these few scanty journal articles seem to represent the entirety of the world's body of knowledge on this very interesting subject. More research is definitely in order here, I'm shocked at how few papers have been written about this.<br><br>Nevertheless, I think I've now found answers to some of the questions asked above, but not all. I'll post a summary of these findings eventually, after I digest all the papers.

Hmmm.... Maybe that's what I should go back to school to study. Although I would have to spend the majority of my time in my smooth snow "control plot", where I would collect the bulk of my valuable research.