Death Valley National Park: First Observation of Rocks in Motion(plosone.org)
plosone.org
Death Valley National Park: First Observation of Rocks in Motion
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0105948
10 comments
Assuming the roads have been graded / there hasn't been any big storms to cause washouts (or rain isn't on the horizon), one can get to the Racetrack in nearly any vehicle, certainly any non-4wd SUV/truck, cars as well. You have to drive carefully and be aware of the road ahead of you and not be dumb and try and drive through a sand drift, etc. Towing bills are spendy out there, even in the park proper (they get crazy stupid in the back country).
As another word of caution, just "renting a Jeep" doesn't mean you should go into all parts of the back country willy-nilly. Buddies and I have been going to Death Valley (and much of the back country) for over 14 years. We've never had a mechanical or other problem, but we are careful and we have had our share of road building (even just 2 years ago), helping out others, etc.
As another word of caution, just "renting a Jeep" doesn't mean you should go into all parts of the back country willy-nilly. Buddies and I have been going to Death Valley (and much of the back country) for over 14 years. We've never had a mechanical or other problem, but we are careful and we have had our share of road building (even just 2 years ago), helping out others, etc.
Sorry but this is terrible advice. The roads are deceivingly dangerous in the sense that there are so many sharp rocks everywhere that could puncture your tire. You have no idea what the condition of the roads are ahead of time, so taking any car without reinforced tires has the potential to get you in a lot of trouble, especially depending on the time of year. There is no cell phone signals and it's dozens of miles to the main highway.
Wouldn't this just mean we should bring one or more decent (not donut) spares, and possibly a plug kit and a 12V compressor? Isn't that just good advice in general for rural driving?
This isn't ordinary rural roads, the rocks you see are extremely sharp. Multiple flats are certainly a possibility, as it getting stuck, depending on the conditions, which as I mentioned you wouldn't know ahead of time because there are no weather reports or road reports for this area.
Most people aren't used to this environment, I certainly wasn't. But we rented a Jeep with reinforced wheels and a satellite communicator that we could use to get help at any time. And given how it's mainly tourists that would be going to places within Death Valley, you would get a lot of uneducated people attempting this trip in a normal vehicle, and without any proper way to contact help. Given that temperatures reach 120 F, it's not hard to imagine a scenario where people die because they are completely unprepared for how dangerous it is.
Most people aren't used to this environment, I certainly wasn't. But we rented a Jeep with reinforced wheels and a satellite communicator that we could use to get help at any time. And given how it's mainly tourists that would be going to places within Death Valley, you would get a lot of uneducated people attempting this trip in a normal vehicle, and without any proper way to contact help. Given that temperatures reach 120 F, it's not hard to imagine a scenario where people die because they are completely unprepared for how dangerous it is.
I'm glad you were happy with your rental. I'll be taking jmspring's more-plausible advice, if I ever find myself driving in Death Valley.
@jessaustin - the rule of any off road exploration is be prepared. Even renting a Jeep doesn't mean you won't have problems if you run into an issue and aren't prepared. Based on your prior messages, it sounds like you have a good grasp on that.
A drive out to the racetrack, assuming no recent storms/floods, in a 2wd drive vehicle is probably sane @25mph or so paying attention to where you are going. A jeep in the same situation, probably 35-40mph. I took my old tacoma 2wd pickup well back into the backcountry, but we were going through contortions to make up for lack of clearance (after 10 years of going, you know the challenges).
My last trip to DV two years back, a buddy and I rented a Jeep from Farrabee's near Furnace Creek (my buddy's 4wd vehicle was out of commission) and typically he rents to people taking the jeep to the racetrack or around the park, which makes total sense and if you are there for a day and want to do such is perfectly reasonable.
We were taking the jeep out for a week on a trip that included having to build up the road in places, a bit of trail blazing in one case, etc. For that adventure, since he hadn't rented the DV jeeps for such (Farrabbe has in his Moab location), we had to make him comfortable with our experience and knowledge.
All that said, it really comes down to being aware of what you are doing, where you are going, what the risks are, and being prepared. Lots of stories of people w/ 4wd vehicles going into the back country, getting lost/stuck (relying on GPS) and in some cases dying. It's not an area to take lightly, even in Fall/Winter.
A drive out to the racetrack, assuming no recent storms/floods, in a 2wd drive vehicle is probably sane @25mph or so paying attention to where you are going. A jeep in the same situation, probably 35-40mph. I took my old tacoma 2wd pickup well back into the backcountry, but we were going through contortions to make up for lack of clearance (after 10 years of going, you know the challenges).
My last trip to DV two years back, a buddy and I rented a Jeep from Farrabee's near Furnace Creek (my buddy's 4wd vehicle was out of commission) and typically he rents to people taking the jeep to the racetrack or around the park, which makes total sense and if you are there for a day and want to do such is perfectly reasonable.
We were taking the jeep out for a week on a trip that included having to build up the road in places, a bit of trail blazing in one case, etc. For that adventure, since he hadn't rented the DV jeeps for such (Farrabbe has in his Moab location), we had to make him comfortable with our experience and knowledge.
All that said, it really comes down to being aware of what you are doing, where you are going, what the risks are, and being prepared. Lots of stories of people w/ 4wd vehicles going into the back country, getting lost/stuck (relying on GPS) and in some cases dying. It's not an area to take lightly, even in Fall/Winter.
It's a beautiful area in Death Valley and driving out there is one of the best experiences I've ever had. If you do decide to go, I wish you a safe but exciting adventure.
Great to see off-the-shelf technology creatively applied to assist in good research in any field of science.
Lorenz (one of the co-authors of this piece) has disproven his previous theory--that the rocks were temporarily embedded in a slab of ice which then floated. [1] I mean, I know that's how science is supposed to work, but in these days of politicized everything it's cool to see someone say "new data disproves my previous hypothesis" and continue working to find the real truth.
[1] http://www.livescience.com/37492-sailing-stones-death-valley...
[1] http://www.livescience.com/37492-sailing-stones-death-valley...
To be fair, people saying "new data disproves my previous hypothesis" is how science does work, day in, day out.
If you can find a working experimental scientist who has never done that, then they are either absurdly lucky or a charlatan.
If you can find a working experimental scientist who has never done that, then they are either absurdly lucky or a charlatan.
I like to believe this happens fairly often.
It's just in the heavily politicized fields it becomes toxic to say "I was wrong."
Another reason I like to keep politics away from science.
It's just in the heavily politicized fields it becomes toxic to say "I was wrong."
Another reason I like to keep politics away from science.
I thought this did not disprove the previous theory. It just refined it, showing that it can be a 'sheet' of ice instead of a 'slab'.
I read about his theory about a year ago, and it described thin sheets of ice then, also.
I read about his theory about a year ago, and it described thin sheets of ice then, also.
It may not have "disproved" it, but he appears to have discarded his original hypothesis.
From linked article: > Floating ice may sometimes be ineffective at moving rocks since stones with low profile may be over-ridden by floating ice; rocks at the edges of ice panels may fail to sufficiently engage with floating ice to be moved, and rocks may be too massive for the available force (Fig. 8d). > A surprise is the thinness of ice involved in rock movement. Ice sheets 3–6 mm thick are insufficient to float rocks off the playa surface, as proposed in some models [8], [11], and, in any case, we observed that ice melts first around rocks. However, moving sheets of ice tens of meters in extent but only a few millimeters thick are clearly effective at moving rocks in their path. Forces on stones increase when multiple sheets of ice pile on the upstream side of a rock and increase the effective surface area of the rock exposed to stresses of wind and flowing water (Fig. 8a).
Author's 2011 publication (citation #11): > 11. Lorenz RD, Jackson BK, Barnes JW, Spitale J, Keller JM (2011) Ice rafts not sails: Floating the rocks at Racetrack Playa. American Journal of Physics 79: 37–42. doi: 10.1119/1.3490645 Abstract: >> We suggest that the existence of many of the rock-carved trails at Racetrack Playa in Death Valley National Park is predominantly due to the effect of arbitrarily weak winds on rocks that are floated off the soft bed by small rafts of ice, as also occurs in arctic tidal beaches to form boulder barricades. These ice cakes need not have a particularly large surface area if the ice is adequately thick—the ice cakes allow the rocks to move by buoyantly reducing the reaction and friction forces at the bed, not by increasing the wind drag. The parameter space of ice thickness and extent versus rock size for flotation is calculated and found to be reasonable. We demonstrate the effect with a simple experiment.
Perhaps if you were reading something 1yr ago, it was in correlation to this new hypothesis, but this 2014 publication sits contrary to the 2011 publication.
From linked article: > Floating ice may sometimes be ineffective at moving rocks since stones with low profile may be over-ridden by floating ice; rocks at the edges of ice panels may fail to sufficiently engage with floating ice to be moved, and rocks may be too massive for the available force (Fig. 8d). > A surprise is the thinness of ice involved in rock movement. Ice sheets 3–6 mm thick are insufficient to float rocks off the playa surface, as proposed in some models [8], [11], and, in any case, we observed that ice melts first around rocks. However, moving sheets of ice tens of meters in extent but only a few millimeters thick are clearly effective at moving rocks in their path. Forces on stones increase when multiple sheets of ice pile on the upstream side of a rock and increase the effective surface area of the rock exposed to stresses of wind and flowing water (Fig. 8a).
Author's 2011 publication (citation #11): > 11. Lorenz RD, Jackson BK, Barnes JW, Spitale J, Keller JM (2011) Ice rafts not sails: Floating the rocks at Racetrack Playa. American Journal of Physics 79: 37–42. doi: 10.1119/1.3490645 Abstract: >> We suggest that the existence of many of the rock-carved trails at Racetrack Playa in Death Valley National Park is predominantly due to the effect of arbitrarily weak winds on rocks that are floated off the soft bed by small rafts of ice, as also occurs in arctic tidal beaches to form boulder barricades. These ice cakes need not have a particularly large surface area if the ice is adequately thick—the ice cakes allow the rocks to move by buoyantly reducing the reaction and friction forces at the bed, not by increasing the wind drag. The parameter space of ice thickness and extent versus rock size for flotation is calculated and found to be reasonable. We demonstrate the effect with a simple experiment.
Perhaps if you were reading something 1yr ago, it was in correlation to this new hypothesis, but this 2014 publication sits contrary to the 2011 publication.
I think the previous theory was that ice formed under the rocks, then the rocks slid on that ice.
I heard him on NPR this morning, and he said that the sheets of ice are like tugboats, pushing the rocks instead of carrying them.
I heard him on NPR this morning, and he said that the sheets of ice are like tugboats, pushing the rocks instead of carrying them.
Still not quite sure how the trails themselves are formed if the rocks are riding on ice sheets 10's of meters in area, or am I reading this wrong / quickly?
Edit: n/m, it appears the ice sheets are massive and free-of-friction enough to actually push the rocks around. Cool!
Edit: n/m, it appears the ice sheets are massive and free-of-friction enough to actually push the rocks around. Cool!
The rocks are on the ground, not the ice. They are surrounded by floating ice sheets. But the ice sheets are gigantic and I assume the massive surface area combined with the right amount of wind friction generates enough force to push the rocks. (Of course now I'm wondering why the ice sheets don't buckle, especially in the spots where they abut the rock.)
> ice sheets don't buckle
Ice is quite strong, especially in compression.
To buckle the ice (i.e. flexure strength) you would need enough force to lift the ice both against gravity and against the air pressure holding it to the water below.
Ice is quite strong, especially in compression.
To buckle the ice (i.e. flexure strength) you would need enough force to lift the ice both against gravity and against the air pressure holding it to the water below.
Maybe the sheets do break, but that doesn't stop them:
https://www.youtube.com/watch?v=fqptbtwXUCs
https://www.youtube.com/watch?v=fqptbtwXUCs
Good question. Perhaps the pressure at any given point of contact is too low to cause the ice to buckle, but there's enough surface area of the rock in contact with the ice for the aggregate force to be large.
The rocks are embedded in the ice. Imagine the rocks are wearing really large ice "skirts" which mostly float over a layer of water, but the bottom point of the rock still contacts the ground.
Edit: Nope, not embedded, just pushed.
Edit: Nope, not embedded, just pushed.
Actually they don't embed themselves in the ice, the ice is free floating with very little friction on top of the water and pushes the rocks using inertia from the wind.
"Lorenz (one of the co-authors of this piece) has disproven his previous theory--that the rocks were temporarily embedded in a slab of ice which then floated."
"Lorenz (one of the co-authors of this piece) has disproven his previous theory--that the rocks were temporarily embedded in a slab of ice which then floated."
Whoops, missed that.
They are not "riding on" but rather being "pushed by" the sheets of ice.
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A little puzzled by all the effort put into this. Some wind moved some rocks - call out the physicists? Where is this research going?
We didn't know exactly what was going on, which bothered some people, because it's just some rocks sitting in the desert and we should be able to figure this out. So they did.
That's it. They solved a problem because not knowing the answer bothered them. This is how most science works, it's just rarely this naked.
That's it. They solved a problem because not knowing the answer bothered them. This is how most science works, it's just rarely this naked.
Iain M. Banks' book Feersum Endjinn contains a similar but more significant phenomenon (clearly inspired by Racetrack Playa). Reason enough to investigate fully.
So, gonna attack the wet-glass-sliding-on-the-table problem next? Measure the film thickness, glass curvature, weight of glass vs contents? Maybe a paper in that too.
We know what's going on there, there is no mystery. We did not know what was going on here.
Why does the fact that people spent time figuring this out bother you so much?
Why does the fact that people spent time figuring this out bother you so much?
Doesn't bother me 'so much'; just enough to spend 30 seconds typing the question. Other than scale the 'science' involved was small. My Aunt left an axe resting in the crotch of a tree 30 years ago; last year the wind broke the tree in half where the axe had grown into the trunk. Anybody going to run out there and calculate all the forces involved, the tensile strength of that tree, the minimum wind required to accomplish the break? Is this 'science' any different than rocks on a flat surface?
Yes, it is different. We can confidently explain the mechanisms that lead to the tree falling down. We could not confidently explain the mechanisms moving the rocks.
Um, horizontal force, low friction? What's left to explain was exactly how that force got applied, and under what conditions the friction got low. So the answer wasn't really physics at all - it was some empirical study I guess.
At least one of the scientists comes from a xenometeorology background. Figuring out strange phenomenon on our own planet will hopefully help us understand what's happening on other planets, too.
> In 2006, Ralph Lorenz, a NASA scientist investigating weather conditions on other planets, took an interest in Death Valley. Lorenz was particularly keen on comparing the meteorological conditions of Death Valley to those near Ontario Lacus, a vast hydrocarbon lake on Titan, a moon of Saturn. But while investigating Death Valley, he became intrigued by the enigmatic sailing stones of Racetrack Playa.
> In 2006, Ralph Lorenz, a NASA scientist investigating weather conditions on other planets, took an interest in Death Valley. Lorenz was particularly keen on comparing the meteorological conditions of Death Valley to those near Ontario Lacus, a vast hydrocarbon lake on Titan, a moon of Saturn. But while investigating Death Valley, he became intrigued by the enigmatic sailing stones of Racetrack Playa.
We did it because we were curious about it, do we need more reason than that? Funded the work ourselves too.
Thank you for doing this, it is really fucking cool.
You may as well ask why Feynman bothered spending time studying why dinner plates rotate faster than they wobble.
Feynman:
--begin quote-- Then I had another thought: Physics disgusts me a little bit now, but I used to enjoy doing physics. Why did I enjoy it? I used to play with it. I used to do whatever I felt like doing - it didn't have to do with whether it was important for the development of nuclear physics, but whether it was interesting and amusing for me to play with. When I was in high school, I'd see water running out of a faucet growing narrower, and wonder if I could figure out what determines that curve. I found it was rather easy to do. I didn't have to do it; it wasn't important for the future of science; somebody else had already done it. That didn't make any difference. I'd invent things and play with things for my own entertainment. So I got this new attitude. Now that I am burned out and I'll never accomplish anything, I've got this nice position at the university teaching classes which I rather enjoy, and just like I read the Arabian Nights for pleasure, I'm going to play with physics, whenever I want to, without worrying about any importance whatsoever.
Within a week I was in the cafeteria and some guy, fooling around, throws a plate in the air. As the plate went up in the air I saw it wobble, and I noticed the red medallion of Cornell on the plate going around. It was pretty obvious to me that the medallion went around faster than the wobbling.
I had nothing to do, so I start to figure out the motion of the rotating plate. I discover that when the angle is very slight, the medallion rotates twice as fast as the wobble rate - two to one [Note: Feynman mis-remembers here---the factor of 2 is the other way]. It came out of a complicated equation! Then I thought, ``Is there some way I can see in a more fundamental way, by looking at the forces or the dynamics, why it's two to one?''
I don't remember how I did it, but I ultimately worked out what the motion of the mass particles is, and how all the accelerations balance to make it come out two to one.
I still remember going to Hans Bethe and saying, ``Hey, Hans! I noticed something interesting. Here the plate goes around so, and the reason it's two to one is ...'' and I showed him the accelerations.
He says, ``Feynman, that's pretty interesting, but what's the importance of it? Why are you doing it?''
``Hah!'' I say. ``There's no importance whatsoever. I'm just doing it for the fun of it.'' His reaction didn't discourage me; I had made up my mind I was going to enjoy physics and do whatever I liked.
I went on to work out equations of wobbles. Then I thought about how electron orbits start to move in relativity. Then there's the Dirac Equation in electrodynamics. And then quantum electrodynamics. And before I knew it (it was a very short time) I was ``playing'' - working, really - with the same old problem that I loved so much, that I had stopped working on when I went to Los Alamos: my thesis-type problems; all those old-fashioned, wonderful things.
It was effortless. It was easy to play with these things. It was like uncorking a bottle: Everything flowed out effortlessly. I almost tried to resist it! There was no importance to what I was doing, but ultimately there was. The diagrams and the whole business that I got the Nobel Prize for came from that piddling around with the wobbling plate. --end quote--
--begin quote-- Then I had another thought: Physics disgusts me a little bit now, but I used to enjoy doing physics. Why did I enjoy it? I used to play with it. I used to do whatever I felt like doing - it didn't have to do with whether it was important for the development of nuclear physics, but whether it was interesting and amusing for me to play with. When I was in high school, I'd see water running out of a faucet growing narrower, and wonder if I could figure out what determines that curve. I found it was rather easy to do. I didn't have to do it; it wasn't important for the future of science; somebody else had already done it. That didn't make any difference. I'd invent things and play with things for my own entertainment. So I got this new attitude. Now that I am burned out and I'll never accomplish anything, I've got this nice position at the university teaching classes which I rather enjoy, and just like I read the Arabian Nights for pleasure, I'm going to play with physics, whenever I want to, without worrying about any importance whatsoever.
Within a week I was in the cafeteria and some guy, fooling around, throws a plate in the air. As the plate went up in the air I saw it wobble, and I noticed the red medallion of Cornell on the plate going around. It was pretty obvious to me that the medallion went around faster than the wobbling.
I had nothing to do, so I start to figure out the motion of the rotating plate. I discover that when the angle is very slight, the medallion rotates twice as fast as the wobble rate - two to one [Note: Feynman mis-remembers here---the factor of 2 is the other way]. It came out of a complicated equation! Then I thought, ``Is there some way I can see in a more fundamental way, by looking at the forces or the dynamics, why it's two to one?''
I don't remember how I did it, but I ultimately worked out what the motion of the mass particles is, and how all the accelerations balance to make it come out two to one.
I still remember going to Hans Bethe and saying, ``Hey, Hans! I noticed something interesting. Here the plate goes around so, and the reason it's two to one is ...'' and I showed him the accelerations.
He says, ``Feynman, that's pretty interesting, but what's the importance of it? Why are you doing it?''
``Hah!'' I say. ``There's no importance whatsoever. I'm just doing it for the fun of it.'' His reaction didn't discourage me; I had made up my mind I was going to enjoy physics and do whatever I liked.
I went on to work out equations of wobbles. Then I thought about how electron orbits start to move in relativity. Then there's the Dirac Equation in electrodynamics. And then quantum electrodynamics. And before I knew it (it was a very short time) I was ``playing'' - working, really - with the same old problem that I loved so much, that I had stopped working on when I went to Los Alamos: my thesis-type problems; all those old-fashioned, wonderful things.
It was effortless. It was easy to play with these things. It was like uncorking a bottle: Everything flowed out effortlessly. I almost tried to resist it! There was no importance to what I was doing, but ultimately there was. The diagrams and the whole business that I got the Nobel Prize for came from that piddling around with the wobbling plate. --end quote--
Yeah read his biography too. But this is rocks in the desert, cute but not especially noteworthy. I've put my wet glass on the table and had it slide several inches magically - I guessed right away that is was gliding on a film.
The OP research was just measuring exactly how much wind, how much water was required. Not really figuring out anything. And I get it - taking pictures of it is cool - Big rocks! Moving! But that's a youtube video, not something to spend govt research money on.
The OP research was just measuring exactly how much wind, how much water was required. Not really figuring out anything. And I get it - taking pictures of it is cool - Big rocks! Moving! But that's a youtube video, not something to spend govt research money on.
So, reading this comment it is clear that you still don't get it and haven't bothered to read the old paper or the new paper.
Yeah its easy to write mean comments, and still be 100% wrong. I'm done here.
What did you expect? You posted a comment complaining about scientists doing valid scientific research on something they found interesting. That is guaranteed to get downvotes.
Your comment was also inaccurate.
> Some wind moved some rocks
Well, no, not quite. The wind moved the ice, and the ice moved the rocks. The wind wasn't enough to move the rocks.
Your other comments mention films. The film of water isn't enough for the rocks to move, even if there are algal films reducing friction.
And it contains a bizarre bit of anti-science sentiment
> Where is this research going?
IvyMike has already given you a good example of where this research might be useful. But, actually, FUCK USEFUL. Science and math do not need to have useful purpose. It is still good that people pursue them.
Your comment was also inaccurate.
> Some wind moved some rocks
Well, no, not quite. The wind moved the ice, and the ice moved the rocks. The wind wasn't enough to move the rocks.
Your other comments mention films. The film of water isn't enough for the rocks to move, even if there are algal films reducing friction.
And it contains a bizarre bit of anti-science sentiment
> Where is this research going?
IvyMike has already given you a good example of where this research might be useful. But, actually, FUCK USEFUL. Science and math do not need to have useful purpose. It is still good that people pursue them.
It may be science, but its pretty soft. Clearly the only things at work here are wind and friction (discounting demons, crop circles etc). What's left could be an exercise left to the reader.
So ok, these guys are 'the reader' and do the legwork. Where can it go? Its not basic or fundamental research; its applicable only to 'rocks on a flat surface'; there aren't a whole lot of places where this will ever be reproduced.
That was what I was asking about: other than the novel circumstance what's to be gained? Got interpreted as anti-science.
So ok, these guys are 'the reader' and do the legwork. Where can it go? Its not basic or fundamental research; its applicable only to 'rocks on a flat surface'; there aren't a whole lot of places where this will ever be reproduced.
That was what I was asking about: other than the novel circumstance what's to be gained? Got interpreted as anti-science.
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Everything we know about land before recorded history is based off of theories including the idea that valleys are carved by things like wind, ice, water and falling debris. It's interesting to see these theories in action since it takes millions of years for large changes to be evident.
Any time there's a technological advancement, it comes from research that doesn't look like it's going anywhere. You might never know the destination until you arrive.
It starts with something completely boring, like learning how peptidoglycan cross-links form. Then it's another long series of research trying to determine what cycloalkanes bind to a DD-transpeptidase enzyme. These two boring pieces of research are combined to create Penicillin.
It starts with something completely boring, like learning how peptidoglycan cross-links form. Then it's another long series of research trying to determine what cycloalkanes bind to a DD-transpeptidase enzyme. These two boring pieces of research are combined to create Penicillin.
is the fact that people are curious about it really more interesting to you than the phenomenon itself?
Absolutely. Because people and their motivations are actionable.
"In addition, rock movement is slow and relatively brief—our GPS instrumented stones traveled at speeds of 2–5 m/minute for up to 16 minutes—so casual observation is likely to miss rocks in motion." Sounds like a passage that could be in Einstein's Dreams :)
They use the term velocity to mean speed a lot :(.
Don't know why this is being downvoted. It's important for scientists to use the correct, well-established terms when discussing their research. This is most true for formal publications.
Velocity is a vector quantity--it describes a directional rate of change. Speed is the magnitude of the velocity. When they use the term velocity, they mean speed. For example, even in the abstract:
"along trajectories determined by the direction and velocity of the wind"
Velocity has a direction! The use of direction in this sentence is redundant to anyone that has had a college level physics course. This trend of using "velocity" instead of "speed" continues through the entire paper. I find this very upsetting.
Of course, it may seem pedantic, but good science is pedantic.
I'm surprised that it made it through peer-review like this.
Velocity is a vector quantity--it describes a directional rate of change. Speed is the magnitude of the velocity. When they use the term velocity, they mean speed. For example, even in the abstract:
"along trajectories determined by the direction and velocity of the wind"
Velocity has a direction! The use of direction in this sentence is redundant to anyone that has had a college level physics course. This trend of using "velocity" instead of "speed" continues through the entire paper. I find this very upsetting.
Of course, it may seem pedantic, but good science is pedantic.
I'm surprised that it made it through peer-review like this.
Here's a human interest story on the study and its authors in a local paper: http://www.independent.com/news/2014/aug/27/death-valley-mys...
Ice sheets moving rocks, this has been seen before: http://skeptoid.com/episodes/4021
"The surrounding mountains were still covered with snow, and the playa itself was firm but had a large lake covering about a fifth of its surface, perhaps an inch or two deep at its edges, concentrated at the playa's south end where it's lowest. We ventured out, armed with cameras, shortly before sunrise. The temperature was just above freezing. The wind, from the south, was quite stiff and very cold. When we reached the lake, we found to our great surprise that the entire lake was moving with the wind, at a speed we estimated at about one half of a mile per hour. The sun was on the lake by now and we could see a few very thin ice sheets that were now dissolving back into water. This whole procession was washing past many of the famous rocks. It's easy to imagine that if it were only few degrees colder when we were there — as it probably had been a couple of hours earlier — the whole surface would be great sheets of thin ice. Solid ice, moving with the surface of the lake and with the inertia of a whole surrounding ice sheet, would have no trouble pushing a rock along the slick muddy floor. Certainly a lot more horsepower than wind alone, as has been proposed. The wind was gusty and moved around some, and since the surface is not perfectly flat and with rocks and various obstructions, the water didn't flow straight; rather it swapped around as it moved generally forward. Ice sheets driven by the water would move in the same way, accounting for the turns and curves found in many of the rock trails."
"The surrounding mountains were still covered with snow, and the playa itself was firm but had a large lake covering about a fifth of its surface, perhaps an inch or two deep at its edges, concentrated at the playa's south end where it's lowest. We ventured out, armed with cameras, shortly before sunrise. The temperature was just above freezing. The wind, from the south, was quite stiff and very cold. When we reached the lake, we found to our great surprise that the entire lake was moving with the wind, at a speed we estimated at about one half of a mile per hour. The sun was on the lake by now and we could see a few very thin ice sheets that were now dissolving back into water. This whole procession was washing past many of the famous rocks. It's easy to imagine that if it were only few degrees colder when we were there — as it probably had been a couple of hours earlier — the whole surface would be great sheets of thin ice. Solid ice, moving with the surface of the lake and with the inertia of a whole surrounding ice sheet, would have no trouble pushing a rock along the slick muddy floor. Certainly a lot more horsepower than wind alone, as has been proposed. The wind was gusty and moved around some, and since the surface is not perfectly flat and with rocks and various obstructions, the water didn't flow straight; rather it swapped around as it moved generally forward. Ice sheets driven by the water would move in the same way, accounting for the turns and curves found in many of the rock trails."
I would really enjoy seeing a time lapse video of this stuff. It is incredibly fascinating.
You need to rent a Jeep with reinforced tires, otherwise you could find yourself in the same predicament as some people we met, who got a flat tire on their rented SUV at Racetrack Playa.