Slope angle/aspect and sun-cups??

I had a chance to look at some sun cups over the weekend.  The most interesting thing I noticed is that the dirt was concentrated on the edges of the suncups, not in the hollows. I suspect that the concentration of dirt shields the edges from erosion.  My theory is that suncups are largely an evaporation effect. Once they get started, free water on the surface enables dust to migrate to the edges where it accumulates and shields the edge from evaporation. Meanwhile the relatively clean hollow evaporates rapidly.<br><br>It's a positive feedback system--the more dirt accumulates at the lower edge of the cup, the more that edge is shielded from evaporation and the more pronounced the cup becomes, as the hollow continues to evaporate. Positive feedback explains how suncups can take over a slope so quickly. My guess is that suncups rarely (maybe never) actually form cups. The lower surface of the cup always slants downhill, which enables free water to continue transferring dust and dirt to the lower edge.<br><br>The thing I can't explain is how the process gets started. <br><br>---<br><br>p.s. Actually, I think there's positive feedback for only a little while, while the cup is forming. If the cup gets too pronounced, then dirt can't migrate anymore. Once the cups reach a certain size and shape, the process reaches a steady state condition. That fits what I've seen in the mountains.

Hummm...<br>I've been cogitating your theory, Lowell. It really started to take on an air of feasibility, especially when I substituted the words "self propagating" for your "positive feedback system" which didn't seem to fit in my simplistic, uneducated and semi-senile mind.<br><br>But then I happened to look at the photos that Thinker posted on cascade climbers of the ice caves on the summit of Rainier.<br>Here's an example:<br> <br>The "suncups" on the ceiling look pretty much to me like the cups on the regular (sun exposed) surfaces, with a couple of major exceptions...<br>one, they're on the ceiling and two, no dirt!!<br>Now I'm more puzzled than before.<br>More of thinker's cave pics are at:<br> www.cascadeclimbers.com/plab/showgallery...0&sort=1&ppuser=2185

Bump. I check this board everyday hoping for Amar's summary of suncup literature.

Hint hint...

Bump. I check this board everyday hoping for Amar's summary of suncup literature.

<br><br>Well, I guess I never did post the summary. I got distracted by other things, but a major reason is that I was quite disappointed with what I found in the scientific literature. The info in "Freedom of the Hills" referred to above is actually more useful than almost anything in the stack of 20+ papers I photocopied / printed from various journals (those few being the best of a bad lot). Curiously, one of the best of those papers was written in 2000 by a woman who had been my college classmate several years earlier, and she was just writing about suncups for fun, her real research being in theoretical physics. Surprisingly, several early papers (1940s-50s) came to the conclusion that suncups are caused by warm winds, just like the hollows in ice caves which Ron refers to. But these papers are simply wrong and were quickly refuted by other scientists, as proper field observations of suncups readily reveal a solar origin. <br><br>Now that the suncup season is fast approaching, I do plan to look into the subject further as time permits. I may even post that long-promised but as yet undelivered summary. <br><br>But I had also had an idea last summer, to do some more direct observational research. Discussion of optimal slope angle and aspect is very limited in the scientific literature, even though it seems to be the most obvious area of research and observation (at least for skiers it's quite obvious!). A good way to carry out this research would be by collecting photos from climbers and skiers taken over the course of a summer on all aspects of a single fairly-symmetrical mountain, such as a volcano. Shasta, Rainier, maybe even Baker would be ideal candidates for such a study, with climbing routes on every aspect and lots of climbers. It would then be easy to correlate the observations with archived weather data from nearby stations (sunlight/cloud, temps, wind direction and speed, etc). It would be an organizational challenge to convince climbers and skiers to collect photos of suncups with rulers across them (with date/location/elevation/aspect accurately recorded), but the web makes it possibly feasible. Is anyone interested in helping with such a project? There is even the chance that a publishable scientific paper could result.<br>

A user on TTips has posted a link to a paper which provides a model for the formation of snow "ablation morphologies", primarily neve penitentes. The paper can be seen here:<br><br> amath.colorado.edu/faculty/mdb/PRE56129.pdf