The Bagnold Dunes on Mars

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Dick Gordon on a trip to revisit the Oregon coast in February 2013, with his back to the sea. The logs were gone. (Natalie Gordon)

When I was a graduate student in the Chemical Physics program at the University of Oregon (1963-67), I would occasionally take a break and drive with friends from Eugene to the Pacific coast. At that time huge logs that drifted in would be piled on the beach, and sometimes after we slept in an abandoned cabin up the steep cliffs, the next morning the logs would be seen totally rearranged. One does not turn one’s back on the sea.

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Tide pool with typical huge anemones on the Oregon Coast near Gold Beach. Dick put his glove down for perspective. (Natalie Gordon)

Besides the tidal pools in the rocks with their anemones, snails and small fish, I was fascinated by the sand itself. For with each retreating wave dendritic patterns of darker grains atop the lighter toned majority were made. As I was (initially secretly) doing my first paper on morphogenesis:

I became fascinated by all pattern mechanisms, from rippling clouds to river deltas, and in sand. At that time Jack Carmichael was visiting my mentor, statistical mechanic Terrell Hill, working on the basic mechanism of column chromatography. That’s a strange name, because in most chromatography techniques then and now, one sees no colors. But here’s the origin of the word from an online dictionary:

  • 1930s: from German Chromatographie. The name alludes to the earliest separations when the result was displayed as a number of colored bands or spots.

The sand was doing real color chromatography, on itself.

Jack moved on, and after my first postdoc he invited me to spend the summer of 1968 with him at the Department of Polymer Science & Engineering at the University of Massachusetts in Amherst. It was a great, if hot summer, because I also met Ryan Drum there, and launched my career in diatoms. But that is another story.

Jack, his student Frank Isackson and I built a plexiglass, 6 foot long, one dimensional flume. It was 8 inches tall, and just wide enough to hold white pellet gun plastic balls so we could see every one. We ran water through it from one end to the other, slow enough so the balls were not dislodged. Then we would add one ball and photograph its bouncing motion (called saltation) as it made its way driven by the current, using a strobe light to record its motion.

Saltation

I had done a lot of reading about how sand moves when driven by wind and water. Much of this literature was by Sir Ralph Bagnold, and I recall reading everything he wrote on the subject. While I was visiting Lewis Wolpert in London, UK in 1969, I took a train north to meet Bagnold at his country home, where he had retired, and spent a pleasant afternoon with him. He told me how he got interested in the motion of sand while in the English foreign legion in North Africa during World War II. He spoke of saltations so high during night sandstorms that one could see nothing horizontally, but could look up and see stars. I formulated the concept that it is important to meet the grand old men and women of science while they are still with us, and have frequently done so.

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The sand on the Oregon coast arranged into small dunes by the wind from the Pacific ocean. If you were to put your eye at ground level and look across sand in wind, you could watch individual grains saltating. (Dick Gordon)

I did a computer simulation of the bouncing balls, and we published the experimental and computer results in my one and only sandpaper:

acknowledging Bagnold too dryly “for discussions”. A couple of days ago I read that the Mars lander is now exploring the Bagnold Dunes  on Mars, a fitting tribute to a life well spent on shifting sands.

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Bagnold Dunes on Mars courtesy of NASA/JPL-Caltech/MSSS. This image, captured by NASA’s Mars Rover Curiosity on Sept 25, 2015 shows the dark Bagnold sand dunes in the middle distance.

 

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The Oregon Coast February 2013 (Dick Gordon)

 

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