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Full Version: Ice rafts not sails: Floating the rocks at Racetrack Playa
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ngunn
Thanks once again to Jason B for making this intriguing paper accessible to all: http://barnesos.net/publications/papers/20...track.Rafts.pdf
ElkGroveDan
Fascinating paper Ralph. This is one of my favorite geologic topics. I've often pondered methods to observe this or even "catch" one in the act.
djellison
I must get up there and Gigapan the place. It's a bit of a trek off the road but I think two Gigapans 12 months apart could be really interesting!
ElkGroveDan
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.
rlorenz
QUOTE (ElkGroveDan @ Dec 29 2010, 02:14 PM) *
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.
ElkGroveDan
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?
rlorenz
QUOTE (ElkGroveDan @ Dec 29 2010, 07:21 PM) *
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?


The subsurface temperatures are not of particular interest. We do have measures of air and surface temperatures nearby, though.

360 days of the year, there is no water. I imagine it would basically be fresh, as it runs off the hills. You don't see
much, if any, salt encrustation (unlike at Badwater or Devils Golfcourse) - it's all clay.
PDP8E
Ralph,
Thank you for that fascinating paper!
Cheers
nprev
Real blue-sky suggestion here, but would putting little RFID tags on the roving rocks be at all useful? What I'm thinking here is some way to obtain motion measurements (and, ideally, the rate of motion) without continuous human observation. If you had two RFID receivers plus recording and/or a remote telemetry hookup, presumably you could track 2D motion of the rocks 24/7/365.

Downsides:

1. This don't sound cheap (but there might be el cheapo ways to do it. I'm aware of the technology, just not conversant in it, but I do know that there's considerable commercial interest & concurrent development ongoing for logistics applications.)
2. Adding mass to the rocks might affect their behavior, even though this might be as little as a gram.
3. You might need more electrical power than I realize to keep an RFID interrogator running continuously, and it could be a royal (and expensive) pain to do fixes, maintenance, etc.

Julius
i've just seen a programme on weird or what>? must have been discovery channel
Juramike
QUOTE (nprev @ Dec 30 2010, 08:48 PM) *
remote telemetry hookup, presumably you could track 2D motion of the rocks 24/7/365.


LoJack for rocks? laugh.gif
rlorenz
QUOTE (nprev @ Dec 30 2010, 08:48 PM) *
Real blue-sky suggestion here, but would putting little RFID tags on the roving rocks be at all useful?


Things like that have been proposed, but I doubt it'd be that useful and I very much doubt that would
be permitted. Research activities that disturb the visual appearance of the playa are forbidden.
ZLD
QUOTE (nprev @ Dec 31 2010, 01:48 AM) *
Real blue-sky suggestion here, but would putting little RFID tags on the roving rocks be at all useful?


The issue I would see with RFID is that you would have to triangulate the position to track the motion. I'm not sure how far the stones have gone in a single move but if it is significant enough, it can make it difficult to get a good read on the tags. Usually the range is maxed out at around 9 meters, 20 if you use a parabolic dish on the reader. I would suggest using a micro three axis accelerometer (found commonly in smartphones) with a really small FM transmitter to transmit the output.
nprev
Hmm. Got it, Ralph.

Well, let's see: How about a small ground radar or sonar system? The analog here is the radar that major airports use to monitor surface movements of aircraft. This would be non-invasive for the playa.

A few of the admittedly many challenges are:

1. Available power (always).
2. Commercial availability of suitable equipment; might need some pretty high-freq stuff to get useable returns from small targets like those rocks.
3. Look geometry/suitable siting: You'd probably need to set it up on a small hill or rise to look down on the playa.
4. $$$

Hope you don't mind the goofy suggestions. It's an interesting problem to contemplate!

EDIT: Re RF hazard (if radar was selected), the good news here is that most modern equipment has very low peak power output compared to older systems. The innovation driving this has been improved receiver sensitivity & selectivity; radars don't have to blast out nearly as much energy as they once did.
djellison
QUOTE (ZLD @ Dec 31 2010, 08:59 AM) *
I would suggest using a micro three axis accelerometer (found commonly in smartphones) with a really small FM transmitter to transmit the output.


That's out.

QUOTE (rlorenz @ Dec 31 2010, 05:50 AM) *
Research activities that disturb the visual appearance of the playa are forbidden.



ZLD
If that is out, then so is just about every other way to track them in an accurate way. Any system used is going to need equipment in close vicinity to track the movements accurately. Units I was suggesting can be as small as a stack of a couple (3/4) small coins and have a range of several hundred feet to a mile or two depending on what your receiver is capable of. This would be a very minor footprint compared to some other possible systems that will require several pieces of equipment around each monitored stone. A UAV could also be used to circle the playa for several hours every couple of hours as another option. That would also provide a minimal footprint if flown high enough but it would also be costly and at risking a crash, seems less advisable.
Floyd
Ralph, very nice paper. My niece works for the Nature Conservancy and she suggested that it may be easier to get permits to do experiments on dry lakes under the management of BLM as their mission focuses on multiple land uses. She sent links to two very nice photos of Racetrack Playa

http://www.flickr.com/photos/jimpatterson/4281126185/
http://www.flickr.com/photos/gdanmitchell/512222313/
rlorenz
QUOTE (ElkGroveDan @ Dec 29 2010, 07:21 PM) *
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
Floyd
Well the rocks move slowly so it took a few years since the last post, but a nice paper is out in PLoS One. Ralph and other authors have have a great movie capturing rock movement. Link
Title: Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion
nprev
I remember first reading about this in 1973, and obviously the phenomenon was noticed far longer ago than that. Congratulations to Ralph for cracking this exceedingly cold (icy, even!) case!!!! smile.gif
rlorenz
QUOTE (Floyd @ Aug 27 2014, 06:28 PM) *
Well the rocks move slowly so it took a few years since the last post, but a nice paper is out in PLoS One.

There are more pics and info at www.racetrackplaya.org
A companion paper is out in Earth Surface Dynamics Discussions

http://www.earth-surf-dynam-discuss.net/pa...discussion.html

I was very lucky to have seen the rocks move myself. What is interesting to me (in an introspective way)
is how the problem has connections with so much of my 'day job' - wave generation, wind-blown drift of the
TiME capsule, evaporation rates, playa geomorphology, etc. etc.
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