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December 15, 2008

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Mr. Welland. I purchased your book through Amazon two weeks ago and am currently enjoying it very much and appreciate your insertion of literary references and analogies to complement the science descriptions. Recently told a friend on a naturalist hike in South Carolina about your section on the fascinating analysis of sand in forensics. The large number of phyla that occupy the spaces between grains is amazing and reminds us again how much diversity of life and matter resides beyond our everday human senses.

Are there any speculations on how those intriguing natural sand sculptures (Fig. 16)on page 64, especially the bottom, came about?

Thank you very much
a reader (Jules)

Jules - first of all, thanks for buying the book - I now know that I've sold three copies!

Pleased that you're enjoying the diversity in the same way I did while researching and writing - this blog is one way of satifying the frustration of all the stuff I had to leave out. And I fully agree with you comment on the diversity of life - every day there's more data that just demonstrates how much we don't know, but then that's what keeps science exciting.

With respect to the lower picture in Fig 16, it was submitted, by Martyn Gorman, to the New Scientist section where readers can ask questions (highlights have been compiled in to a couple of books along the lines of "do penguins' feet freeze?"). A few issues later, there was an answer that, to me, sort of explains it but not entirely - I'll leave that judgment up to you - here's the original question and the answer (interesting that it raises the controversy over water versus dry flows on Mars):

Can anybody help us explain what caused the phenomenon in this photograph? It was taken on the Sands of Forvie nature reserve in north-east Scotland. The weather was dry, though there had been rain the day before. The photograph shows the lip and face of a small mobile sand dune. The slope of the dune face was approximately 45 degrees and the sand was dry at the time the photograph was taken. The image shows a section about 1 metre wide. The whole pattern extended about 20 metres.

• Moisture from the rain retained by the striated slip face of the dune would have given it a firmer consistency than the sand on the top, which would have dried out more quickly. What happened then would have been quite startling for anyone lucky enough to witness it.

seen something quite startling

The loose dry sand on the dune top would have started to move, pushed by gentle winds. As it spilled over the edge, the sand cut this series of parallel gullies, creating the herringbone pattern. The uniform spacing of the gullies is related to the even flow of the wind dynamics on the edge of the dune. Gullies would not have been able to form in the dry loose sand on the top of the dune.

At the dune crest, erosion would be occurring along a hemispherical front (as you can see from the curved tops of dunes in a desert) as loose sand fell into the gullies below. This sand would have flowed down to the bottom of the slope to form a fan or ramp at the foot of each gully (visible at the base of the photograph). Once started, the whole process would have taken only a few minutes to complete. The gullies and ridges are very fragile and would soon be buried under sand as the dune face moved forward. The photographer was very lucky to see them.

I have seen this phenomenon on a grander scale in Arabian and African deserts where holes up to 6 metres deep have been dug in sandy soil. There, surface soil with some structure and a moderately hard consistency lies on top of poorly structured sand. The hard surface stops the face from collapsing but the whole system is inherently unstable and dangerous to observe from inside the pit.

A steady supply of drifting sand often blows over the rim of the pit, eroding the edge of the surface soil into intricate patterns, picking out minute differences in its constituents and etching out old roots and so on. The loose material produced by erosion feeds into a network of fragile gullies cut into the underlying sands. Where there are harder layers lower down, sand will flow down the first gully, cascade over the next hard layer as a "waterfall", race down another gully and then broaden out to form a fan at the base of the slope. Such a flow can be maintained for minutes on end.

This type of flow produced the pattern that is seen in the photograph, and is beginning to be recognised as of considerable significance in the geological record, according to Brian Turner of the University of Durham, UK, who has observed similar particle flows in sand ramp deposits in Jordan. Allan Treiman of the Lunar and Planetary Institute in Houston, Texas, has argued that similar examples on Mars are the result of "dry granular flows".

Gullies observed recently on Mars were attributed to the action of water (New Scientist, 15 January 2005, p 36, and 23 March 2006, p 19). I believe this is way off mark. Having seen the particle-flow process in action on many occasions, I believe the Mars gullies are far more likely to have been formed by dry granular flow closely related to that shown in the sand-dune photograph.

R. Neil Munro, Dirleton, East Lothian, UK

Mr Welland, thanks much for providing some of the possible explanations. Something to ponder and study further.

As you said, nature often poses many more questions for us than provides answers and indeed uncertainty is what keeps science ever stimulating. Nature, it appears has the ability to self-organize into beautiful and complex patterns(as interpreted by our brain's subjective appreciation) by conforming to the underlying laws of physics.

I hope that your well written and interesting book sells many more copies and probably will as more reviews and referrals are published. I am one who loves these type of books that explore sometimes obscure and esoteric subjects,that in our often frenetic,distracted and overly entertained culture some might consider mundane(like physics,weather,butterflies,other insects and birds,(including their songs)micro-organisms,lichens,dust,rocks(geology)and sand!)

My study of nature has made me more aware how our very existence is intimately tied to all the forces and organisms(many unseen and under appreciated)of this planet and the larger universe. Even plate tectonics may have had a integral part in the evolution of our species through the orogenesis of the Himalayas according to some theories.

A natural awe and curiosity about the universe is part of our best human qualities that I believe we are all born with, but unfortunately is often put aside by the other issues of our lives that seem to take priority. I think most scientists are the lucky ones who get to carry on with this awe and wonder through their adult lives(and get paid for it!).

Thanks for sharing your knowledge and enthusiasm for nature with us.

Seasons Greetings

Jules

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