I am presenting a poster at the IAG (8th IAG International Conference on Geomorphology – August 27th to 31st, 2013) in Paris next week. Eating lunch amongst humanities colleagues this week, the idea of a poster at a conference raised some chuckles and offers of Pritt Stick. This perhaps highlights some of the challenges of communicating how research is communicated in my field of geoscience (and in many other science disciplines) to other academics. So, where does this leave the much thornier issue of communicating science to the public?
Jon Tennant, who blogs at an EGU (European Geophysical Union) hosted blog GREEN TEA AND VELOCIRAPTORS, wrote (back in Oct 2012) about communicating research and knowledge to a wider public. This was orientated around ‘why bother’ and ‘what might the public audience already know’, which very effectively sets up an idea both of the motivation and the context to any endeavour to communicate geoscience research to the public (probably largely through blogging). Jon’s work was itself prompted by work by Prof Ian Steward and Ted Nield.
I have previously produced 1-page handouts (snippet in the picture) for land-owners at my sampling sites to give an idea of why I spent a few days digging holes into the sand in the heat of the desert.
So. The research I’m presenting next week, quite honestly didn’t start out as much. No pressing question set up in an academic paper, no large grant was awarded, rather it was an interesting view driving through the stunning Namibian landscape on the way to (another) conference, hosted at the Gobabeb Research Centre. After miles of mountainous terrane, and a descent down the hair-pin bends of the Gamsberg Pass, a very familiar colour of sediment to me was seen at the side of the road – red sand dunes (I’ve spent plenty of time digging holes into red sand dunes, sporting terrible fashion sense, both in the Kalahari, and the Namib Sand Sea, to the top of the latter we were travelling).
Drilling holes in sand dunes
I asked my travelling companion, a Namibian Geographer, if he knew where that beautiful red sand had come from, and he didn’t have an answer. Stopping for a cool drink at the lodge named after the red sands (Rooisand) it seemed they also weren’t completely sure, but that it was suggested the sand had blown over and down the mountain pass we had driven down, having starting off in the Kalahari, famous for it’s long, red, linear sand dunes. Once at the conference, I still couldn’t find the definitive answer I was looking for, with someone else suggesting the sand might have blown up north-east from the Namib Sand Sea (which would make it the most northerly part of the sand sea). So, on the way home, armed with some cutlery and sampling tubes, I decided to collect a bit of this sand for analysis from an exposure at the side of a dry river bed.
The exposure where samples were taken
… At this point it is worth asking you (the reader) whether asking ‘where the sand has come from?’ is an interesting enough question worthy of some geoscience research and effort? Maybe it is. However, much of my research field of Quaternary Science (go on, Google/ Wikipedia it) is about asking what piles of sediment (and other deposits like ice) can reveal to us about what the climate of the past was like. In this light, the question becomes when and by what process (wind deposition, water-deposition followed by wind deposition) did this loose sand accumulate here, and what was the climate like in order for this to occur? Today, the area is very dry, and only seasonally windy enough to move some of it around. Was this different in the past?
Rooisand from the air (via GoogleEarth)
So, now I had my sample, how was I going to settle the question of where this red sand came from? The term that’s used in geoscience for this is ‘provenance’. In addition, what might I be able to say about how long the red sand had been sitting there in the landscape for folks like me to catch a glimpse of as we travelled past on our way to the Namib Sand Sea or the coast (or how old the Rooisand deposit is)? A cool technique to establish this, is known as luminescence dating (making sand glow to establish how long it has been buried under other piles of sand, but that will have to be the topic of a separate blog post). My poster for next week is therefore imaginatively entitled ‘Age and provenance of the dunes of Rooisand’.
So, here beings my communication challenge. What has been done with those samples to answer my questions? (my methods). And, what do the results of these tell me, and my coauthors, that the answer is?
And a reminder of the possible answers about Rooisand provenance: from the Kalahari, from the Namib Sand Sea, or an alternative idea that it is very locally sourced (material eroded from the surrounding mountains).
When you take a handful, or even a fingerful, of the red sand and put it under a microscope it isn’t all red sand at all. Some of it is white, some milky-white, some translucent, some green, some shiny black, etc. etc. (I’ll try to source a picture, but it’s not quite as cool as the ocean sand pictures that have been doing the Twitter rounds, largely because it is not as full of old marine life). This microscope vision is not only pretty, but pretty useful for working out where the sand came from (provenance). In Italy, after some preparation, including putting grains onto slides, (to make it easier to tell exactly what these sand grains of different appearance are) Mara Limonta and Giovanni Vezzoli at the University di Milano-Bicocca counted and characterised a few hundred grains. They had been doing this for lots of other piles of sand collected from other sites in Namibia, some from river valleys, some from Kalahari, some from the Namib Sand Sea.
What all of this microscope work revealed is that samples from different locations contained different amounts of various minerals and heavy minerals (by this I mean an array of terms, some of which may be more familiar sounding than others – quartz, K-feldspar, plagioclase, muscovite, biotite, epidote, amphibole, zircon, rutile, tourmaline). Ultimately, the details of what the minerals are is not crucial to the story. What is, is that the hard-rocks at the surface of the earth (what we could call the bedrock geology, or consolidated hard rock material, as opposed to the soft sands at Rooisand) in different places contain different combinations and proportions of these minerals. In effect, the sediment (whether rock or loose sand) has a fingerprint. So, once a rock has been broken down by weathering into smaller grains of sand, and redeposited somewhere in the landscape (like at Rooisand), it is possible to use it’s fingerprint to work out where it came from. Similarly, the difference between sand sample fingerprints (from different river channels and areas of sand dunes) can be instructive.
It was a diagram plotting the difference between these sands that arrive in my inbox from Italy last month for presenting on the poster.
The plot from Italian colleagues
In this plot the squares represent river sands, the stars wind-blown dune material, and the straight coloured lines are a sneaky way of plotting lots and lots of information about what minerals are in the samples without being constrained to two simple axes: x (horizontal) and y (vertical) axis. In addition, the closer a box or star is to a line the more of that mineral (the coloured line) that sample contains. In addition, the closer the boxes and stars are to other boxes and stars, the more similar their fingerprint is (and therefore, they are very likely to have come from the same place and same bit of hard-rock geology). So, in short that plot shows me that the Rooisand sample (RS12/1) is most similar to samples from Rivers Gaub, and Kuiseb and closest to the coloured lines that represent heavy minerals such as garnet (and also apatite and amphibole) (all in the top left-hand box). The sample is very different to bottom right-hand box, where the sand samples from the Kalahari are plotted (so, I’m afraid I will have to tell the barman that served our cool drinks that the idea they have at the Rooisand lodge is wrong).
So, if the Rooisands are most similar to Kuiseb River sands and contain garnet, apatite and amphibole, what does this say about their provenance? Those suites of minerals are derived from a geological unit known as Damara metasediments (metasediments are sediments that some time after deposition, become subjected to heat and pressure, with changes to their properties, as mountains, like those in this part of the Namibian landscape are formed). These Damara metasediments form a band that runs through the Rooisand area, and so are very local.
To be able to answer the question about the age of (the last) sample burial event, I am awaiting one last piece of data (about something called dose rate, again this will have to be the subject of that other post on luminescence dating). What I can currently estimate is that this exposure close to the river bed is only a few hundred years old. It was deposited on that occasion by the wind. The average size of the grains is just over 300 microns (that’s 0.3 of one of those millimetre lines depicted on rulers), and this requires wind speeds of over 8 meters per second to move the sand. If all 10 meters of the exposure were deposited around a similar time in the past, then it would suggest that winds were over 8 meters per second sufficiently often during those years to move and then put back down 10 m of red sand. That’s a windier environment than today.
So here ends my first rehearsal of science communication, and as well as being slightly too long, it has revealed to me a more pressing question, why are the Rooisands, red sands (and not any other colour)? After all, that is what about them that caught my eye in the first place, and made the Rooisand lodge suggest the sand had travelled from the Kalahari. In short, they are coatings of iron oxides (just like rust). This rusting occurs in dry environments when the sediment and iron minerals are directly exposed to the atmosphere. The complicating factor is that it is possible the red coatings on these grain could have been inherited from the much-older geological hard-rock, or have accumulated since the soft sand sediments were deposited. This geoscience question currently remains unanswered.
Abi Stone 