Through The Sandglass

Sunday Sand: Unawatuna

Heralded as one of the finest beaches in the world, Unawatuna lies close to the southern tip of Sri Lanka. The sand contributes to the heralding – on every scale – but this sand must have tales to tell. The resort was devastated by the 2004 tsunami, and a quick search of the internet reveals harrowing stories typical of those from around the Indian Ocean that appalling day. The before and after images below do not begin to evoke the full extent of the catastrophe that hit the residents that day, but the Google Earth image (from before the tsunami) shows the complex way in which the shape of the coast refracts and focuses even normal ocean waves – the chaos of what this natural lens created when successive tsunami surges hit can only be imagined.

 

Many stretches of Sri Lanka’s beaches lost huge amounts of sand, but nature seems to have achieved effective beach nourishment and restoration. I can find no evidence of a human contribution to the re-supply of sand, only the opposite – extensive sand mining that reduced the coastal supply and inhibited the natural processes. So who knows exactly what stories these sand grains tell? In all likelihood some were sucked from the beach, only to be thrown back as the tsunami surged, joined probably by others that had been residing peacefully offshore, among the coral reefs whose fragments we see in the sand. But this is a spectacular and diverse sand: the ubiquitous quartz grains there, but overwhelmed by biogenic detritus. Sponge spicules, coral fragments, sea urchin spines, the inevitable forams, bits and pieces of shells as well as tiny complete ones, all testimony to the great organic engine of the tropical ocean. And what exactly that little beautiful blue and grey “cogwheel” is, I really don’t know.

All in all, a sand and a beach whose character belies their witness to chaos and tragedy.

 

[Thanks – once again – to Connie for collecting the sand. The immediate post-tsunami image is from Muddled Clarity, the tranquil beach scene from HolidayCheck.com]

The US role in the 21st Century: one to be proud of

At a time when there is a great deal of hand-wringing introspection, garishly coloured by the inevitable political posturing and empty but bombastic rhetoric, on what role the US will play as this century progresses, allow me to recommend one. Unfortunately, it’s one that is in complete conflict with the agenda of most of the rhetoricians.

Our world today would be a different place if it were not for the extraordinary contribution to society’s global knowledge by the US Government scientific agencies: the role that the USGS, NASA, NOAA, and others have played is, quite literally, unequalled by any other country. And the potential of their future contribution to our (shamefully imperfect) attempts to understand and manage our home planet is beyond value. The US is established as the world leader in providing open and comprehensive geoscience data (in the broadest sense), and has the capacity to build on that role in the future, to provide truly global benefits. And yet, in the bizarre political parallel universe of today, the support for the work of these agencies, never mind science in general, is already eroded and under further threat. 

To illustrate my grand claim of scientific leadership, the obvious headline is that of Curiosity and the stunning achievement of the mission so far. But in the excitement of that event, it has been easy to overlook another that, in many ways, is of greater significance to us and our own planet: the Landsat mission celebrated 40 years of continuous operations last month. Forty years of recording the changing surface of our planet, seven successive satellites, and an unparalleled body of earth imaging data whose multitude of applications have demonstrably made a difference to our world. There are, of course, many other satellites, from different agencies of different countries, circling the earth, each with its own sophisticated technology dedicated to specialist imaging. But none have equalled the collective contribution of Landsat.

 

There are several excellent resources celebrating Landsat’s anniversary and browsing them is inspiring: of course, the Goddard Space Center and the mission home page, plus an excellent series in Wired Science, and videos and other material via Google’s Earth Engine. The power of monitoring 40 years of change is evident in many of the time-lapse videos – probably the Aral Sea sequence is the most dramatically depressing - but all are fascinating – see NASA’s top ten. And then there is the the Earth as Art image gallery – the two images at the head of this post (Algerian dunes and the Mississippi, credit: NASA's Goddard Space Flight Center/USGS) are from the top five selected by popular vote:

Beyond the scientific information they supply, some Landsat images are simply striking to look at, presenting spectacular views of mountains, valleys, and islands as well as forests, grasslands, and agricultural patterns. By selecting certain features and coloring them from a digital palate, the U.S. Geological Survey has created a series of "Earth as Art" perspectives that demonstrate an artistic resonance in satellite land imagery and provide a special avenue of insight about the geography of each scene. We asked the public to vote on their favorite images from the more than 120 images in the online "Earth as Art" collection. We received over 14,000 votes and are happy to announce the top five winners.

 
However, this is a celebration that could have an unhappy ending. As reported in Wired Science in a separate piece - “Our View of Earth from Space Is in Danger” - earlier this year:

The nation’s Earth observing capability from space is beginning to wane as older missions fail and are not replaced,” according to a new National Research Council report, released May 2 as an update to a 2007 decadal report on Earth-observing capabilities.

While roughly 22 satellite or satellite systems run by NASA, NOAA, and the USGS are currently in orbit, that number could drop to only six by 2020. Of the 18 missions recommended in the original 2007 report, only two have specific launch dates.

This is a dire situation, considering that the U.S. relies on this network of satellites for weather forecasting, climate change data, and important geologic and oceanographic information – not to mention the thousands of amazing pictures of our home planet. Weather-related damage from wildfires, flooding, tornadoes, and heat waves resulted in nearly 600 fatalities and cost the economy approximately $50 billion in 2011, but this number would have been even greater without satellite observations.

There are many arenas in which the US can continue or develop a global leadership role as this century progresses, but to consciously abandon its leadership in acquiring and providing – free to every individual on the planet – the earth science data that we need if we are to have any hope of addressing issues that face us, would, in my humble view, be a crime against humanity.

 

 

Here, for those interested, is the (slightly edited) summary of the Landsat program from the USGS:

Landsat Turns 40

The Long View of Earth from Space

The world’s longest-running Earth-observing satellite program — Landsat — turns 40.

NASA — working in cooperation with the U.S. Department of the Interior (DOI) and its science agency, the USGS — launched the first Landsat satellite on July 23, 1972. The resulting 40-year archive of Earth observations from the Landsat fleet forms an impartial, comprehensive, and easily accessed register of human and natural changes on the land.

Remote-sensing satellites, such as the Landsat series, help scientists to observe the world beyond the power of human sight, to monitor changes, and to detect critical trends in the conditions of natural resources. Data supplied by Landsat supports the improvement of human and environmental health, energy and water management, urban planning, disaster recovery, and crop monitoring.

Through 40 years of continuous coverage, the Landsat series of Earth observation satellites has become a fundamental global reference for scientific issues related to land use and natural resources. Landsat is valued all over the world as the gold standard of land observation. No other satellite program, in our nation or in any other country, comes close to having the historical length and breadth, the continuity and the coverage, of the Landsat archive.

A Versatile Perspective

Landsat satellites can give us a view as broad as 12,000 square miles per scene while characterizing land cover in units the size of a baseball diamond. In one instant look from over 400 miles in space, a single Landsat scene can record the condition of hundreds of thousands of acres of grassland, agricultural crops, or forests.

A comparison of the images illustrates the significant growth in the greater D.C. area. Major urban development can be seen the surrounding communities of Rockville, Greenbelt, and Suitland, Maryland. The expanded Woodrow Wilson Bridge, connecting Springfield, Virginia, with Oxon Hill, Maryland, is evident. The record of surface change is used by urban planners and local officials to evaluate the rate and direction of growth in the area.

Landsat images from space are not just pictures. They contain many layers of data collected at different points along the visible and invisible light spectrum. Consequently, Landsat images can show where vegetation is thriving and where it is stressed, where droughts are occurring, where wildland fire is a danger, and where erosion has altered coastlines or river courses.

Landsat images reveal subtle, gradual changes, such as Wyoming rangelands greening up after a drought, as well as massive landscape changes that occur in rapidly growing urban areas. Landsat can also provide inexpensive assessments of sudden natural or human-induced disasters, such as the number of acres charred by a forest fire or the extent of tsunami inundation.

Impartial information freely available

The Department of the Interior’s policy of releasing the full Landsat archive at no cost allows everyone to have access to this important resource, allowing researchers in the private sector and at universities to generate even more data applications — applications that serve commercial endeavors in agriculture and forestry, that enable land managers in and out of government to work more efficiently, and that define and tackle critical environmental issues.

Landsat and innovation

Landsat has sparked innovation in Earth systems research and in commercial applications of the data from its inception in the mid-1960s.  Since 2008, when Landsat images were made available free of charge, there has been a remarkable burst of innovative science applications of the data.

For example, Landsat data played a central role in an award-winning type of mapping that tracks water use. Using Landsat imagery supplied by USGS in combination with ground-based water data, the Idaho Department of Water Resources and the University of Idaho developed a novel method to create water-use maps that are accurate to the scale of individual fields. Water-use maps help save taxpayer money by increasing the accuracy and effectiveness of public decisions involving water — for instance, in monitoring compliance with legal water rights. In 2009, the Kennedy School of Government at Harvard University cited Idaho’s original design for these maps as an outstanding innovation in American government.

The National Land Cover Database (NLCD 2006) produced by USGS and the federal interagency Multi‑Resolution Land Characteristics Consortium (MRLC) from Landsat imagery is a massive database that describes the surface condition of each 30-meter cell of land in the conterminous U.S. One such cell is approximately the area of a baseball diamond. The range and accuracy of the database enables land managers, urban planners, agricultural experts, and scientists with many different interests (for instance, climate change or invasive species) to identify critical characteristics of the land for a wide variety of investigations.

In the beginning

By the mid-1960s, some civilian geologists, geographers, and agronomists were familiar with imaging potential of classified Earth-observing satellites and had also studied the surprisingly detailed land-surface photos taken by early astronauts using hand-held cameras.

In 1966, with NASA still heavily committed to the Apollo Program in preparation for what would be a 1969 moon landing, the USGS convinced Interior Secretary Stewart Udall to hold a press conference announcing Interior’s new Project EROS, the acronym for Earth Resources Observation Satellites, and, furthermore, that Interior’s first satellite would launch in 1969!

In a statement that echoes true to this day, Udall said, “…the time is now right and urgent to apply space technology towards the solution of many pressing natural resources problems being compounded by population and industrial growth.” This bold announcement succeeded as a catalyst for what eventually became the world’s first civilian land-imaging satellite, developed by NASA and launched on July 23, 1972.

Six years earlier, Udall had said the satellite would be “…just the beginning of a great decade in land and resource analysis for a burgeoning population.”  Today we celebrate not one but four great decades in Earth science from space.

On the horizon

NASA is preparing to launch the next Landsat satellite, the Landsat Data Continuity Mission (LDCM), on February 11, 2013, from Vandenberg Air Force Base in California. LDCM will be the most technologically advanced satellite in the Landsat series. LDCM sensors take advantage of evolutionary advances in detector and sensor technologies to improve performance and increase reliability. Once it successfully achieves orbit, LDCM will join the Landsat 5 and Landsat 7 satellites as Landsat 8 to continue the Landsat data record.

An artist's impression becomes an astonishing reality

Countless words have been written – appropriately – over the last couple of weeks, in the blogosphere and the international press, about Curiosity. I have little to add, except for a personal note of awe and gratitude.

The landing was scheduled for about an hour before my flight landed in Singapore, and the first thing I did after disembarking was to hook up to Google News – and there it was, incredibly, awe-inspiringly, it had worked, and Curiosity was flexing its muscles on the surface of Mars. I will readily admit that I haven’t the faintest clue how this whole, mind-bogglingly complex, mission was planned and executed; I watched and relished the infectious celebrations in the control room with only a partial sense of the true emotions of every individual there.

And then – a picture is truly worth a thousand words – the images started coming in.

When I looked at that image, and understood that the hills in the distance were not on Curiosity’s fieldwork itinerary, my immediate reaction was “Well, why don’t I wander over there and have a look at that winding valley system, while you go off and do your stuff. We’ll meet back here this afternoon.” Curiosity feels, intimately, like a fellow field-geologist – because, of course, that’s exactly what the rover is. I now check out the mission site routinely to see what my friend has been up to, and to continue to celebrate this incredible achievement.

 

And, for me, the other cause for celebration is simply that, faced daily with the stories of the depravity, greed, and ignorance of our bizarre species, this provides a strong antidote, grounds for cautious, if perhaps fleeting, optimism. Thank you, NASA, JPL, Caltech, and everyone involved.

 

[All images courtesy of NASA/JPL-Caltech/MSSS]

The brass section

I do, on occasion – and to the great distress of anyone within earshot – quite literally blow my own trumpet. Or, to be precise, these days, a flugelhorn. It began in the early Pleistocene when I was in high school, playing second trumpet in the band and orchestra to the first, whose surname, gloriously, was “Tootle.” I graduated – to the great distress of anyone within earshot - to the tuba (a fine and much-maligned instrument), and my father always maintained, entirely erroneously, that this was simply because the size of the instrument required my being driven to school on rehearsal days. 

But enough of my instrumental aspirations (as anyone within earshot would agree). There’s always a great and immodest pleasure in finding oneself cited, and there have recently been several examples of this, to which I feel compelled to draw attention. First of all, Andrew Alden on About Geology kindly posted a reprise of his views on Sand, together with a link to the conversation he and I had a couple of years ago. Then Gary Hayes at Geotripper referred to “an excellent geo-blog based on sand” in his recent post, “Sand...Lots of Sand.”

And, just yesterday, Geoff Manaugh, of the acclaimed BLDBLOG, put up two successive posts directly related to topics that I have written about – the New York sand mines, and the Normandy beaches (see the posts, in addition to sections in the book, here, and here).

So thanks to all for the citations and the pleasure. I shall now sign off, without – to the relief of those within earshot – fanfare.

Update 14 August, breaking news! Thanks to Geoff Manaugh and BLDBLOG, I have now made it onto BOINGBOING. 

Perfecting your sandcastle

 

Before you head off to the beach, you might want to jot down the equation in the image above. Because this is good news for sandcastle builders. Had you been depressed by the fact that science can easily demonstrate that the maximum height of a sandcastle is 20 cms (assuming you believe that what’s going on is driven by capillary forces), then you should celebrate the news that new science now allows for sandcastles several meters high. But then again, your own kids have probable demonstrated that elevations of significantly more than 20 cms are no problem at all, never mind the stark evidence of the towering sand sculptures routinely constructed in events around the world. Those capillary guys really need to get out of the lab, look around occasionally at reality, and get a life.

A just-published report from Nature, playfully titled “How to construct the perfect sandcastle,” is a work of serious science, and one of those delightful international collaborations between researchers, in this case from Iran, the Netherlands, and France.

The challenges that dry granular materials pose to science are seemingly endless, and have been reported on this blog too often to link here (just put “granular” into the search box for a sampling). But wet granular materials represent depths still unchartered by physics, and the act of building a sandcastle is the quintessential illustration of this – just add water to dry sand, and it becomes an entirely new and different material. Add more water and everything changes yet again (no wonder that researchers are trying to develop phase diagrams – like those for ice, water, and steam – for granular stuff). This recent work has taken a simple, ground-upwards (so to speak) approach to the mechanisms of sandcastle stability:

To account for the (in)stability of sandcastles, we show here that it is sufficient to consider that the limit of instability is reached when a column of sand undergoes a buckling transition under its own weight. An elastic rod becomes elastically unstable and buckles under its own weight when exceeding a critical height.

This, of course, again reflects real experience – adding that last bucket of sand to the top of the castle causes the whole thing to collapse, tragically and infuriatingly. There’s a standard equation for the maximum height of a cylinder before it buckles under its own weight that incorporates its radius and density, gravity (inevitably), a rather esoteric term that, quite frankly I don’t understand, and, critically, the elastic modulus of the material. This latter characteristic is critical – also known as Young’s Modulus, it describes how strong a material is, how well it responds to strain. In this case the strain is its own weight, and the strength of wet sand comes entirely from the surface tension effects of just a little water between the grains.

I sometimes use a dramatic demonstration of the potency of surface tension – simply wet a number of ping-pong balls, cluster them together, and see how many you can drag across the surface of a table by just pulling one of them. It’s surface tension that allows us to build a sandcastle, that gives the wet sand its strength. For physicists, the reality of exactly what’s going on between the grains is somewhat more complex, but the authors of this paper have taken the model for the strength of wet granular matter and worked it to develop an equation for the optimum strength, or elastic modulus. Plug that back into the equation for the maximum height of a cylinder, and you end up with the wonderful expression for “h,” the maximum height of a sandcastle, in the image above. The researchers then tested this by making their own cylinders of sand with varying diameters, and found that reality correlated well with prediction:

"To verify this experimentally, beach sand with an average radius of 100 mm was mixed with a small amount of deionized water. Cylindrical ‘sandcastles’ were constructed using non-wetting PVC pipes of different diameters cut in half over the length of the tube. The two halves were assembled, and the wet sand was put in the tube standing on vertically on a surface. The wet sand was poured into the pipe in small portions and compacted by dropping a thumper into the pipe at least 70 times. This process was repeated until the pipe was filled with sand up to a certain height. The two halves of
the cylindrical tube were then carefully removed and if the sand column was stable, a new experiment was launched filling the tube to a larger height, until the column collapsed. Several experiments were done at each filling height to ensure the reproducibility of the results. Figure 1 shows two columns of sand with height 27 cm and 60 cm with diameters 2 cm and 7 cm. This procedure was followed for 8 pipes of diameter ranging between 0.5 and 7.5 centimeters."

As they note, the compaction is critical. Look at the equation in the image at the head of this post – in order to maximise the height, h, of your sandcastle, you don’t have a lot of options. You can increase the radius of the base (“R”), but can’t do much about gravity (“g”), the size of the grains (“a”), or the density of your mixture (“ρ”), but that mysterious little “α” is, as the authors remark, a “potent power.” And α is a measure of how strong the bonds are between the grains – compact the sand and this increases, and therefore, very importantly, so does the potential height of your castle. The sand sculptors of the world are very well aware of how critical compaction is to their art.

Larry Nelson is a sand sculptor based in Venice Beach, California, and his work is extraordinary. Larry was of enormous help to me when I was writing the Sand book, and he achieves forms with sand that seem impossible: fragile soaring arches, interlocking curves.To achieve these exquisite results, he has developed an intimate relationship with his material, and his description of the character of wet sand eloquently summarizes its magic – and its physics:

It doesn’t take long to learn that water mixed with sand changes both completely. Two fluids become a formable solid. It may be counterintuitive, but anyone who has spent time in the playground knows this in the fingers.

Water tends to pull in on itself. This makes raindrops, rainbows, and flying sparks from every sprinkler. Anything in contact with the water feels this pull, imparting a tiny tensile characteristic to damp sand. It sticks together.

This adhesion is the essence of sand sculpture. It’s also the bane, because damp sand stickily resists being compacted beyond a certain point, no matter how hard it’s hit. Granular materials naturally form arch structures, tiny but powerfully resistant to compaction. Smack it on top, and your pile simply spreads sideways.

Here is just a sample of Larry’s wonderful creations – and note the compacted layers:

 

So, take the equation to the beach, be inspired by Larry Nelson, look after your radius, and make sure you maximise your alpha. Oh, and I almost forgot – the researchers found that “the optimum strength is achieved at a very low liquid volume fraction of about 1%” – you need 99% sand and just a very little water.

 

[The paper from Nature: Pakpour, M., Habibi, M., Møller, P. & Bonn, D. How to construct the perfect sandcastle. Sci. Rep. 2, 549; DOI:10.1038/srep00549 (2012). Thank you, Jan Kirchner, for pointing me to it and to Andrew Dwyer, my fearless Outback leader, for bringing the article about it in the Australian Geographic to my attention. Sand sculpture image at the head of the post from the Sand Castle Days 2006 event on South Padre Island, photographed by Sam on the Poof’n’whiffs blog.]