Ice rafts not sails: Floating the rocks at Racetrack Playa, Paper by Ralph Lorenz et. al. |
Ice rafts not sails: Floating the rocks at Racetrack Playa, Paper by Ralph Lorenz et. al. |
Dec 29 2010, 06:04 PM
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
Thanks once again to Jason B for making this intriguing paper accessible to all: http://barnesos.net/publications/papers/20...track.Rafts.pdf
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Dec 29 2010, 07:14 PM
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Senior Member Group: Admin Posts: 4763 Joined: 15-March 05 From: Glendale, AZ Member No.: 197 |
I suppose others have already thought of solar powered web cams and things like that. Though it seems that we are looking at movement during periods of partial immersion where the rocks may be barely visible from above.
-------------------- If Occam had heard my theory, things would be very different now.
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Dec 29 2010, 10:44 PM
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Member Group: Members Posts: 609 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
I suppose others have already thought of solar powered web cams and things like that. yes. Took a long time to get a permit but it can be done subject to certain Parks Service limitations. Since winter is the time of interest, and cameras cannot be left on the nice flat playa itself, solar power is less effective than it might be, but digital timelapse cameras can run on alkaline Ds for months. http://www.lpl.arizona.edu/~rlorenz/timelapse.pdf One would have to be very lucky to see the rocks move, but timelapse has been proving useful to understand the conditions on the playa (how often flooded, how often frozen etc.) That work is being written up right now. btw, I believe someone has been doing Gigapan surveys of the playa for a year or so. I tried a Gigapan myself but it drained the batteries in minutes and was overall rather frustrating. Having been going to the playa a couple of times a year since 2006, I've found walking around and doing manual pans from GPS-fixed locations to be a very time-efficient means of survey. Just wish the bastard rocks would actually move. |
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Dec 30 2010, 12:21 AM
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Senior Member Group: Admin Posts: 4763 Joined: 15-March 05 From: Glendale, AZ Member No.: 197 |
Reading your paper Ralph it looks like the occurrence and duration of ice is still being debated. Have you though of getting permission to bury a couple of temperature sensors just below and/or at the surface of the soil to record long term temperature profiles? Also, have you tested the water seasonally for saline content?
-------------------- If Occam had heard my theory, things would be very different now.
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Jan 12 2012, 05:10 AM
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Member Group: Members Posts: 609 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
Reading your paper Ralph it looks like the occurrence and duration of ice is still being debated. Indeed. I think much of the literature has been unfortunately cast in black-and-white terms 'Ice is essential'... 'Oh no it's not'...'oh yes it is' etc..... (qv Sharp and Carey, Reid et al., etc.) The reality is likely more nuanced - my take is that large rocks require ice, and that for most large-scale movements (i.e. when many rocks move) ice is involved. But small rocks can occasionally move without the help of ice sails (or more particularly, ice rafts). I suspect too that there is a spatial element to it - the south end of the playa where most of the rocks are delivered to the playa surface from the cliffs is also probably the area most often shadowed by same cliffs when the sun is low in the sky in winter. So the south end is more likely to see ice than the north. But all this is qualitative handwaving without quantitative data (as Kelvin sortof said). It may be in part that the problem has mostly been studied by geologists, who as a tribe (this is fightin' talk, I know) may be less inclined to apply probabilistic (or even quantitative) approaches to the problem. To remedy this deficiency, our efforts over the past few years at least now provide some basis for discussion on occurrence and duration of water and ice on the playa. Also, while it is all very well for someone to figure out that winds of X speed can move a rock of Y mass without ice, there has really been only handwaving 'this is reasonable/not impossible' etc. Can such winds occur often enough to explain the trails we see ? Some actual numbers on how often gusts of 50 m/s actually occur (at least at nearby locations) and how often is the playa flooded, are now published in Journal of Applied Meteorology http://www.lpl.arizona.edu/~rlorenz/racetrackweather.pdf |
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