credit: The Daily Mail

I blogged about this channel system in June 2009 and showed a similar, although much less colorful, image in this post.

The image above and the following quote are from this article in The Daily Mail.

The undersea river – the only active one to have been found so far – stems from salty water spilling through the Bosphorus Strait from the Mediterranean into the Black Sea, where the water has a lower salt content. This causes the dense water from the Mediterranean to flow like a river along the sea bed, carving a channel and deep bank.

The second sentence of that statement is a good one — it explains the mechanism for the origin of this submarine channel system (i.e., saline density currents that hug the sea bottom) and mentions it forms a geomorphic feature similar to a terrestrial river. But the first sentence causes my inner nerd to itch a bit. Firstly, submarine channels are not “undersea rivers” — at least, I’ve never heard anyone else who studies these features call them that. The quote from the researcher included in the piece is simply painting a picture for a general reader that the geomorphology is similar to a river. Secondly, what exactly is meant by “the only active one to have been found so far”? If they mean the active submarine channel systems then, no, this is not the only active one — there are numerous submarine canyon-channel systems that have transmitted density currents in recent decades (e.g. Monterey, Var, Hueneme, Congo, etc.). Perhaps they mean the only active system in which a saline current is the dominant agent? I’m not sure about that — maybe some of my readers could comment on that.

Don’t get me wrong, a discussion about what aspects of submarine channels are similar to rivers and what aspects are different from rivers is a discussion very much worth having. In fact, having that discussion helps us understand these features much better. But, I’m not ready to let the mainstream press and the general public simply call these ‘undersea rivers’ and be done with it — there’s still far too much to learn.

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* pointed out by @jeffersonite last week

Dust blowing from west Africa into the Atlantic Ocean (credit: NASA Earth Observatory)

Strong winds can pick up dust particles* from continents and carry them thousands of kilometers where they are deposited on the ocean floor. Deserts are especially important contributors of dust with the Sahara Desert of northern Africa being the single largest source of mineral dust in the world.  The occurrence of this process has been observed and deposits of dust have been documented in marine sediment cores for a long time, but what has been more difficult to determine is how this process changes over time.

Very recent changes in dust flux (since the 1970s) are well known and relatively well understood to be the result of recent drought conditions in the Sahel region. However, longer-term trends, at the scale of centuries and millennia, are not as well understood. A new paper by Mulitza et al., published in Nature last week, provides a robust record of dust deposition for the past 3,200 years. The sedimentary archive is from a marine site offshore northwest Africa, located in a prime position under one of the most active dust plumes.

The top three curves on the diagram at left are the dust fraction, terrigenous (i.e., continent-derived) fraction of a certain grain size, and dust flux, respectively (click on it for a bigger version). The curve at the bottom of the diagram is a δ18O record, which the authors use as a proxy for precipitation. Also note the arrows near the top of diagram denoting when various forms of agriculture became dominant in the region.

Essentially, the authors of this study are arguing that the dust deposition generally corresponds to the paleo-precipitation record until very recently. When the climate was drier, more dust was picked up from the continent and deposited in the ocean. The curves don’t match exactly, but I wouldn’t expect them to — there are numerous other factors at play here. But the general correspondence is compelling. The departure of the dust fraction and flux curves from the paleo-precipitation curve starts a few hundred years ago.

From the abstract, Mulitza et al. explain this departure:

With the help of our dust record and a proxy record for West African precipitation we find that, on the century scale, dust deposition is related to precipitation in tropical West Africa until the 17th century. At the beginning of the 19th century, a sharp increase in dust deposition parallels the advent of commercial agriculture in the Sahel region.

I find these millennial-scale records fascinating because they highlight the complex interaction of multiple controls on Earth surface processes and commonly, although not always, reveal the significant impact that human civilization has on these processes.

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* according to authors, ‘dust’ refers to airborne particles mostly within the very fine silt range (<10 microns) with some as coarse as fine sand (~200 microns)

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Mulitza, S., Heslop, D., Pittauerova, D., Fischer, H., Meyer, I., Stuut, J., Zabel, M., Mollenhauer, G., Collins, J., Kuhnert, H., & Schulz, M. (2010). Increase in African dust flux at the onset of commercial agriculture in the Sahel region Nature, 466 (7303), 226-228 DOI: 10.1038/nature09213

image from NASA’s Earth Observatory website [link]

Oxygen isotope curve for Cenozoic (Zachos et al., 2001; Science)

Paleoclimate records for the past ~50 million years show overall global cooling with higher-frequency fluctuations (see plot of δ¹⁸O measurements, a proxy for temperature, at left). The annotation on the right side of the figure denotes when researchers think continental glaciation was initiated — approximately 30 million years ago for Antarctica and 5-8 million years ago for the northern hemisphere.

What caused this long-term global cooling?

Some researchers have hypothesized that increased tectonic uplift (especially the Himalayas) and the increased weathering that came with it is one of the primary causes of this long-term global cooling*. That is, as more carbon dioxide was withdrawn from the atmosphere and naturally sequestered, the Earth cooled. One line of evidence geologists have used to infer changes in rates of erosion and weathering is the depositional record.

Sediment-dispersal systems transfer eroded material from mountainous uplands to sites of sediment accumulation in alluvial lowlands, coastal deltas, the continental shelf, and the deep sea. Because erosion in one location is balanced by deposition in another location, some geologists are using changes in deposition rates to infer changes in erosion rates. This seems like an elegant solution but, as usual, it’s not quite so simple.

I was delighted to see this paper by Willenbring and von Blanckenburg about late Cenozoic erosion/weathering rates come out in Nature last month. There’s a lot to say about this paper and its implications, too much to cover in this one blog post. I recommend this great review article by Yves Godderis, which highlights the global paleoclimate implications of the study nicely. Here, I will focus on one aspect I find fascinating: how erosion and deposition is recorded in the stratigraphic record.

Willenbring and von Blanckenburg revisit an inherent measurement bias demonstrated by Peter Sadler in his 1981 seminal paper “Sediment accumulation rates and the completeness of stratigraphic sections.” I’ve written about the ‘Sadler Effect’ before on this blog (read this post from 2007) but to make a long story short — the longer the measured time interval the smaller the sedimentation rates and vice versa.

Sediment accumulation rates and erosion rates as functions of geological time (Figure 2 from Willenbring & von Blanckenburg, 2010, Nature 465; doi:10.1038/nature09044

This phenomenon arises because the accumulation of sediment is unsteady — that is, at one location it varies over time. As longer durations are measured in a succession, more hiatuses, or periods of no deposition, are captured and, thus, the rate (thickness/time) is lower. Conversely, rates measured from very short durations can be quite high. Think about it — if you go out to a river mouth when it’s flooding and measure the thickness of sediment that piled up over a day and converted it to a yearly rate by simply multiplying by 365 you’d get a huge rate that wildly overestimates the actual yearly rate (unless, of course, that river is flooding every single day of the year). This is intuitive and few would attempt to make such a conversion, but this is essentially what is happening when comparing sedimentation rates that were measured from different time scales. Similarly, geomorphologists have discussed the unsteadiness of processes such as erosion and uplift^.

Willenbring and von Blanckenburg show this by plotting various process rates against time. The plots at right show, from top to bottom, (a) ocean-basin sediment accumulation rates, (b) volumetric erosion rates, (c) sediment accumulation rates in Asian offshore basins, and (d) global denudation rates. Note how all of them show a huge uptick in rates during younger time intervals. The point here is that this apparent increase in rates is an artifact of measuring unsteady processes — it isn’t real. The inset log-log plots of the same data show the Sadler Effect clear as day.

So, does this mean we can’t use measured rates of deposition to say something about the variability of processes in Earth history? I think we can but we need to significantly increase our understanding of rates of processes at multiple time scales. Careful documentation of sediment-dispersal systems with ever-improving geochronological tools is one approach to unraveling these complex temporal relationships. Numerical/physical experimental methodologies can be designed to address process rate questions as well. Ultimately, the integration of multiple approaches will lead to a better understanding of the complex temporal relationships of sediment erosion, transfer, and deposition and how we can utilize the stratigraphic record to reconstruct Earth history.

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Willenbring, J., & von Blanckenburg, F. (2010). Long-term stability of global erosion rates and weathering during late-Cenozoic cooling Nature, 465 (7295), 211-214 DOI: 10.1038/nature09044

* just one example is this Raymo and Ruddiman paper from 1992

^ Gardner et al. (1987); Geology

Canyon Lake Gorge (credit: http://www.canyongorge.org/about-the-canyon-gorge)

In 2002, flood waters from Canyon Lake dam reservoir in central Texas were diverted into an emergency spillway at nearly 200 times the normal flow rate. The resulting flood event, which lasted for six weeks, removed trees and sediment and excavated a 7 m deep and >1 km long canyon into the limestone bedrock.

A paper by Lamb & Fonstad called Rapid formation of a modern bedrock canyon by a single flood event published in Nature Geoscience this week documents the patterns left in the landscape and reconstructs the hydraulics involved in this catastrophic flood.

I encourage those interested in the details of sediment transport and bedrock incision to read the paper. But what I want to discuss in this post is an issue that will come up as a result of this study — an issue that I can almost feel bubbling up as I write this. In fact, I’m certain that someone, somewhere is abusing the results of this study in an attempt to claim that because significant change to the Earth’s surface can occur abruptly then it follows that all geologic change must be the result of abrupt and cataclysmic events. This is a false dichotomy pushed by neocatastrophists that are typically, but not always, associated with the viewpoint that the Earth is ~6,000 years old.

When the history of the science of geology is taught it commonly includes the classic uniformitarianism vs. catastrophism debates of the late 1700s-early 1800s. The uniformitarianists, so the story goes, argued that the changes we see in the geologic record were the result of minor and gradual processes that accumulated over time — from processes that we can see working on the landscape today. Catastrophists believed the same geologic products were the result of cataclysmic events that reshaped the land abruptly.

Studying this historical debate is thought-provoking and provides context for a novice geoscientist but the science has largely moved on from this false dichotomy. Geologists in the 1800s and early 1900s documented features that could only be explained by large-magnitude events*. Geologists realized that, of course, both gradual and catastrophic processes helped shape the landscape. The great paleontologist Stephen Jay Gould wrote a paper in the American Journal of Science in 1965 (he was 24 years old) called “Is Uniformitarianism Necessary?” that succinctly summed up where the science was regarding the concept of uniformitarianism. The incredible clarity of Gould’s writing forces me to quote the entire abstract:

Uniformitarianism is a dual concept. Substantive uniformitarianism (a testable theory of geologic change postulating uniformity of rates or material conditions) is false and stifling to hypothesis formation. Methodological uniformitarianism (a procedural principle asserting spatial and temporal invariance of natural laws) belongs to the definition of science and is not unique to geology. Methodological uniformitarianism enabled Lyell to exclude the miraculous from geologic explanation; its invocation today is anachronistic since the question of divine intervention is no longer and issue in science. Substantive uniformitarianism, and incorrect theory, should be abandoned. Methodological uniformitarianism, now a superfluous term, is best confined to the past history of geology.

In other words, the original notion of uniformitarianism — that there is uniformity in rates — is false. Although the science has discarded this erroneous concept, it is what modern catastrophists use as a straw man in their arguments. And, unfortunately, we see glimpses of it in mainstream science writing and reporting of geologic processes. The nuance of Gould’s paper from nearly 50 years ago is lost within the compelling story of pitting one absolute versus another.

I would argue that rapid and significant processes are included within our current understanding of processes. For example, I study the processes and deposits of turbidity currents, which are essentially submarine avalanches of sediment. The recurrence of such events varies but is typically on the order of hundreds to thousands of years. Moderate to large turbidity current events would surely be labeled “catastrophic” from our point of view. Yet, entire sedimentary basins are filled with the deposits of hundreds of thousands of individual catastrophic events. While each event may be short-lived and cataclysmic, they occur very regularly over time and incrementally stack to produce a stratigraphic succession. We might consider some volcanic systems similarly — each eruption event might be catastrophic, but over time this is how the volcano is incrementally constructed.

This doesn’t take away from the insights from Lamb & Fonstad’s study. What they document here is just how rapid significant Earth-surface modification can occur given a certain set of conditions. In this case, they explicitly make the point that characteristics of the bedrock are important within the context of their results:

We suspect that well developed vertical and horizontal joints at Canyon Lake Gorge define blocks of bedrock that have little interlocking along their boundaries, rendering their behavior similar to an alluvial bed when critical stress for mobility is surpassed. … Thus, it seems plausible that erosion of well-jointed rock by large floods might be extremely rapid, such that canyon formation is limited by the capacity of the flood to transport plucked blocks rather than by the plucking process itself.

In other words, the bedrock which was eroded during the flood was already slowly eroding through the formation of joints (a type of fracture) in the rock. The high-energy flood event took advantage of this weakness and literally plucked large boulders of bedrock from the floor and walls of the canyon. In this case, the slow and gradual processes of joint formation worked in concert with the catastrophic flood event to produce this result.

There will be some who will use this paper to attempt to tear down uniformitarianism. Not only will they fail to mention the nuances of this specific study but they will be tearing down an idea that has long since been discarded by geology.

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Lamb, M., & Fonstad, M. (2010). Rapid formation of a modern bedrock canyon by a single flood event Nature Geoscience DOI: 10.1038/ngeo894

Caltech press release: http://www.eurekalert.org/pub_releases/2010-06/ciot-cgi061810.php

Scientific American: http://www.scientificamerican.com/article.cfm?id=canyon-lake-flood

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* see this post at 4.5 Billion Years of Wonder for more commentary about this paper within the context of Bretz and the origin of the Channeled Scablands of Washington.

update: check out Geotripper’s post about a similar flood event involving the Tuolumne River of California in 1997; also check out before/after images of the event described above at Pathological Geomorphology

I wanted to highlight this video I came across showing  a jökulhlaup in process. A jökulhlaup is the Icelandic word for a glacial outburst flood that is commonly generated by subglacial melting during a volcanic eruption. I think the term is also used for similar magnitude flood events from glacial lakes when an ice (or debris) dam abruptly fails.

Absolutely amazing.

I also want to point out the train of waves from 0:46-0:57 seconds in the video. I’m not sure — don’t quote me on this — but those appear to be associated with supercritical flow (most are introduced to this concept discussing the formation of antidunes). Perhaps a train of hydraulic jumps or some kind of cyclic step process? A quick search came across this paper interpreting supercritical flow based on the sedimentary deposits from a jökulhlaup in 1918 in Iceland.

This AW is to share your latest discovery with all of us. Please let us in on your thoughts about your current work. What you are finding, what you are looking for. Any problems? Anything working out well?

Because I work in the private sector I do not (and will never) blog about the work I do on a daily basis in any detail. In fact, Clastic Detritus is designed to be completely disconnected just so there is no confusion. Read the disclaimer page for more.

What I do blog about, however, is my published research — this is the stuff that is out there for the scientific community to read and evaluate so I feel that this blog can be an additional venue for sharing it. And, although this work was submitted many months ago and maybe not the very latest, it is a good representation of my current research interests and activities.

As my research interests page states, in the most general sense I’m interested in utilizing the sedimentary record to investigate and understand past and present Earth conditions. The sedimentary record is a representation of Earth surface processes through time and, as such, can be analyzed to reconstruct ancient environments as they relate to tectonic activity, climatic and sea-level fluctuations, oceanic conditions, and intrinsic dynamics of depositional systems.

I specialize in the study of submarine channel and fan systems, which are some of the largest accumulations of detrital material on Earth (e.g., Bengal submarine fan). Sand, silt, and mud that is eroded from the continent and the continental margin is deposited out into the deep sea by submarine sediment gravity flows called turbidity currents. If you’ve been reading this blog for a while you are well aware of my love of all things turbidite related!

I’m mostly interested in using these deep-sea sedimentary records to answer questions about the volumes, rates, and distribution of detritus that is transferred across continental margins. Essentially, I want to use the patterns we observe and measure in the stratigraphic record and relate it to fundamental processes such as plate tectonics or paleo-environmental conditions. A very interesting debate in the stratigraphic community is how to (or even if we can) unravel the extrinsic vs. intrinsic controls on the observed patterns — more on that another time. To try and address these questions my colleagues and I are analyzing both ancient and modern systems.

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Ancient Deep-Sea Sedimentary Systems

In some cases the history of sedimentary basin development is followed by mountain-building processes, which results in the preservation of sediments deposited 10s to 100s of millions of years ago in outcrops now exposed on the Earth’s surface. The value of investigating outcrops is that the details of the system at the scale of individual beds (a few centimeters) to packaging of those beds (i.e., stratigraphy) at many kilometers is on full display. One such system that I spent several years working on (and am still working on) is the Magallanes sedimentary basin in southern Chile. These rocks were deposited in the Late Cretaceous (~70-80 million years ago) in a deep foreland basin that developed adjacent to the paleo-Andes.

Because I’m interested in understanding these systems at multiple scales — that is, what controls the character of the beds? what controls how multiple beds stack? what controls the distribution of detritus at the basin scale? — I looked at these strata at different scales. To get at some of the sedimentological details and stacking patterns at the outcrop scale I investigated a particularly well-exposed outcrop at a mountain called Cerro Divisadero. I’ve already blogged about this study, which was published in Sedimentology, so I won’t repeat it here.

So, that study looked at patterns from the centimeter- to kilometer-scale, but what about much larger patterns — for example, at the scale of the entire basin (10s to 100s of kilometers)? What’s cool about that question is that, in addition to integrating the mapping and characterization of the entire region, we looked at the microscopic level for answers. I published a paper in Basin Research (currently in the ‘early view’ here) that summarizes the results of analyzing the ages of zircon grains extracted from these sedimentary rocks. I’m still working on a blog post that discusses this work in more detail, but to make a long story short, the detrital zircon record help constrain the timing of significant tectonic activity in the adjacent mountain belt. This tectonic activity (in this case, the emplacement of thrust sheets) had a profound effect on the basin-scale stratigraphic patterns.

But not all ancient sedimentary basins are now uplifted into mountains — in fact, a lot are technically still sedimentary basins. That is, the ancient sediments are buried very deeply (sometimes up to several kilometers!) by younger deposits. Investigating the subsurface utilizes an entirely different suite of tools (e.g., seismic-reflection data), but the fundamental questions are the same.

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Modern Deep-Sea Sedimentary Systems

When discussing sedimentary systems from a stratigraphic point of view, ‘modern’ refers to those that are still actively receiving and distributing sediment and continuing to evolve. This commonly equates to systems active during the past glacial and current interglacial climate cycles — or, the past 10,000 to 30,000 years. In other words, even if a turbidity current hasn’t occurred for a several hundred years we will still refer to the system as ‘modern’ because the depositional patterns from geologically recent activity is still in place.

Because one of my goals is to understand how sedimentary systems respond to the myriad interacting factors that control them, investigating modern systems offers the chance to establish relationships that are impossible with ancient systems. For example, although geochronometric approaches continue to improve, I highly doubt it that we’ll be able to constrain the timing of individual depositional events at the scale of few hundred years for strata that are 100 million years old. Let’s put it another way — I challenge you geochronologists out there to accomplish that! :)

Context is also critical. Ancient sedimentary systems are only partially preserved — we have to make inferences and interpretations about the nature of source areas that have long since eroded. By comparison, modern sediment dispersal systems are laid out in all their glory for us to study. For example, when characterizing ancient deep-sea sediments we commonly make an interpretation that the deposits represent a submarine channel. Depending on data the degree of confidence of such an interpretation can be high or low. Well, with modern systems, we don’t have to interpret some of those fundamental aspects — we simply know if we are looking at a channel (as long as the bathymetric mapping is good enough, of course). Given this context we can then ask some more specific questions about the system.

I published a paper last fall in GSA Bulletin about the depositional history of a modern submarine fan system offshore southern California. We integrated high-resolution mapping of the fan with a sediment core from which we obtained radiocarbon dates. We were able to constrain the timing of sedimentation for the past 7,000 years very well and saw a nice relationship to independent records of paleoclimate in southern California. This is another study that I have a blog post in draft stage that I hope to finish soon. Stay tuned.

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Integration: Characterizing Sedimentary Systems from ‘Source to Sink’

In recent years researchers have been emphasizing ways to integrate observations and measurements from different segments of sedimentary systems — from erosion-dominated mountainous areas to deposition in rivers and floodplains and, ultimately, to sediment ‘sinks’ in coastal deltas or deep-sea basins. I wrote a post about this approach a couple years ago after reading a very nice essay by Allen in Nature, which I highly recommend.

Read that post and Allen’s essay for more, but what I’ll comment on here is some work that I am doing right now that fits nicely within the source-to-sink framework. One way to investigate how sediment source areas relate to the sediment sink areas is to look at rates of erosion and rates of deposition. Some relatively new methods of dating cosmogenic nuclides of exposed bedrock surfaces and/or sediments is helping geomorphologists constrain erosion rates. How this exactly works is something I am still learning myself (check out this article that explains it better than I could).

Some colleagues of mine did some preliminary work using cosmogenic-nuclide-derived erosion rates and compared them to deposition rates in offshore segments of the dispersal system. The preliminary results were promising so we decided to expand the dataset and we are currently awaiting the results.

I could go on but this post is already way longer than I planned and is mostly my stream-of-consciousness ramblings. I’m going to cut myself off here! I hope it’s not too confusing and if you’ve read this far you are either really interested in what I’m working on and/or are really bored!

What causes avulsion? This is a fundamental question — I have many colleagues and peers conducting research that address this question. In a simplified sense, if the downstream segment of a channel begins to back-fill with sediment (and, thus, reduce gradient along the reach), the upstream segment will respond by ‘seeking’ a new course to a lower site. Now, exactly where along the channel that happens, and when it occurs is what researchers would like to figure out. Another idea is that during a particularly large flood, or particularly large turbidity current, the flow simply breaches its natural levee, thus, creating a new course.

The example of avulsion I’m showing in this post, however, is the product of human engineering. The two images below are from a recent post on Earth Observatory that shows a series of images of the Huang He (Yellow River) delta in China.  I’m really loving NASA’s Earth Observatory site lately — it seems to be getting better and better.

Here’s an excerpt from the explanation of the series of images that show recent change in the delta morphology:

Between 1989 and 1995, the delta became longer and narrower along a southeast-bending arc. In 1996, however, Chinese engineers blocked the main channel and forced the river to veer northeast. By 1999, erosion and settling along the old channel caused the tip of the delta to retreat, while a new peninsula had formed to the north.

The two images below are from 1995 and 1999, respectively, and show this anthropogenic avulsion nicely.

Delta of the Yellow River in 1995 (credit: NASA Earth Observatory)

Delta of the Yellow River in 1999 (credit: NASA Earth Observatory)

Compare those two images and note the changes in the abandoned part of the delta after the avulsion. As the excerpt above mentions, the coastline of the abandoned part of the delta is receding. The supply of sediment, which is what constructs and builds the delta seaward, has been cut off. A combination of natural subsidence — a slow sinking as the underlying sediment compacts — with rising sea level is now eating away at that part of the delta. Also notice how the new channel is contributing to net-construction of the delta to the north.

About a year ago I posted similar images of the Huange He, also from Earth Observatory, that showed changes in the delta over a bit longer time scale and, more importantly, comparing before major human influence to after.

Note how significant the delta morphology is in the 1979 image — showing a much more rounded delta front, whereas the more recent morphology protrudes into Bohai Bay creating what delta researchers call a “bird’s foot” morphology. While the Chinese have been constructing levees along this river for a very long time I wonder if natural avulsions were able to occur at the lowermost reaches — the river mouth — until more recently.  [note: this paragraph edited from original version; see comments]

Management of delta regions is an increasingly important area of research, especially as we deal with rising sea levels. The example of the anthropogenic avulsion shown here will certainly be something to watch. A significant proportion of the Earth’s population lives on delta and coastal plain environments, so we will undoubtedly continue to geo-engineer these sedimentary environments. The more effort we put into researching their dynamics and processes, the better our strategies will be for doing smart engineering that takes advantage of the natural processes that shape and maintain the health of a delta.

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The other reason I love these images is because of the beautiful sediment plumes — I’m a sucker for sediment plume images (e.g., here, here, and here).

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Pick up a single grain from the beach, look at it through a magnifying glass, and you have embarked on a journey taken by poets, artists, and philosophers — not to mention geologists.
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I have to admit that when I found out there was a popular science book devoted to sand I got really excited. Not only am I geologist, but I am a sedimentary geologist … and not only am I a sedimentary geologist, but I specialize in clastic sediments — a lot of which is sand. So, perhaps it’s not a big surprise that I’m a fan of book all about sand. But, at the same time, because I’m a sand-lover (or an ‘arenophile’ as Welland calls us) I read this book not only for the enjoyment of the narrative but also for additional insights and specific facts about my field of study.

However, this book is not just for the specialist. The subtitle for the edition I have is ‘The Neverending Story’* and the clever narrative that Welland employs throughout much of the book is the journey a grain of sand takes from birth (weathering and liberation of sand-sized particles from rock) through transport, deposition and burial, and, if the geologic situation is right, lithification of those grains into sandstone, and potentially the breakdown of that sandstone back to sand again.

… sand is one of our planet’s most ubiquitous and fundamental materials and is both a medium and a tool for nature’s gigantic and ever-changing sculptures.

This narrative is woven into a book that’s filled with fascinating facts and stories about the role sand has played in both natural and human history. Thus, ‘Sand’ is a great read for anyone interested in the story of one of nature’s most important geologic agents.

Thankfully, Michael Welland, who is himself a geologist, addresses one of the misconceptions about sand in the first few pages of the book — that is, what makes sand sand is the size of the particle, not what it’s made out of.

Our sand grain, newly born, finds itself, together with a motley collection of other detritus, organic and inorganic, as part of a soil, the in situ accumulation from the physical, chemical, and biological processes at work in a particular place. The sand grain is anonymous, waiting for rain and wind to sweep it away on an endless journey, to demonstrate its durability while its weaker companions fall by the wayside. But it is called sand not because of what it is made of or its origins, but because of how big it is.

The first two chapters of ‘Sand’ introduce the basics of this material and discuss some important fundamentals related to the fascinating, and surprising, physics of granular materials (and not just transport but also how this material behaves when mixed, vibrated, dropped, and more).

‘Sand’ then returns the narrative of the journey a grain of sand takes with a series of chapters related to river transport, transport by wind, coastal processes, and finally, export of sand to the deep sea. There is enough fluid dynamics and details of particle transport within these sections to satisfy sedimentologists, yet it is also presented in such a way to be accessible to the non-specialist. In fact, if I were to ever teach a course in clastic sedimentology to novice geologists I would assign these sections of ‘Sand’ as required reading. Welland communicates many of the details within stories about pioneering sedimentologists, especially Ralph Bagnold, and how their research changed the science forever. To me, this is the mark of a successful popular science book — if I wanted straight-up sedimentology I could open a textbook — but, ‘Sand’ discusses these concepts within a story. In this case, a story about nature interwoven with stories about the people who study nature.

I also enjoy Welland’s writing style — some passages almost approach a rhythmic, even poetic style, but the writing manages to stay within a enjoyable and accessible style typical of non-fiction books. I’m not sure if my description is accurate from a literary point-of-view (I’m no expert), but here’s an example from the chapter on deserts:

When sand moves under a gathering desert wind, it seems to take on a life of its own, to become a different form of matter — like a gas, like liquid nitrogen spilling and spreading, following the ground surface. Spraying off the crest of a dune, shimmering in the light, veils of sand race and ripple, spread and vanish, their place continually taken by the next gossamer sheet, dancing, playing, celebrating. Are these jinns, the spirits of the desert? The sight is beautiful and hypnotizing in the evening sun, but if the wind gathers speed, beauty rapidly vanishes as the violence and menace of a sandstorm grows. Suddenly, it seems as if the entire mass of desert sand has sprung from the ground to hurtle with the wind. On the surface, everything is moving, even the largest grains, rolling, tumbling, kicking smaller grains into the rushing current. The sky disappears, and the howl of the wind seems amplified by its cargo of sand. The air is filled with flying sand, unbreathable.

There are many sections of ‘Sand’ that are able to communicate how dynamic and beautiful nature’s processes are. Another theme that is apparent throughout Welland’s writing is the concept of scale — both spatial and temporal — and how sand is so intimately connected with considerations of deep time and countless numbers.

In addition to stories of Earth’s geologic history that are revealed through sand, Welland devotes significant parts of the book to the seemingly countless ways in which sand intersects human civilization. This list is by no means meant to be exhaustive but will give you a flavor of some of the topics discussed in ‘Sand’:

• fundamental materials (building stone, glass, aggregates, etc.)
• the concept of sand as a powerful metaphor in thought and storytelling (e.g., very large numbers and very small things)
• importance of sand for the ecological health and safety of coastal areas
• utility of sand in forensics and crime-fighting
• reservoirs for important (and valuable) fluids
• threat of migrating sand dunes to villages/towns
• sand as an artistic medium –  for drawing, sculpting, painting, writing, and more
• microchips (and, electronics in general)
• how quicksand really works
• and much, much more …

If I had to pick one thing I didn’t like about ‘Sand’ it’s the chapter on the myriad uses of sand in our lives. It is organized as an A to Z list, which, when compared to the other chapters that read more like a story, comes across as encyclopedic and a bit out of place. That said, I don’t have any suggestions for a better way to do it. Sand truly is ubiquitous and its uses are literally everywhere — if the point of the chapter was to emphasize sand’s ubiquity through a comprehensive list then the point is well taken.

The closing chapter of ‘Sand’ addresses the presence and importance of this material beyond the confines of our planet. The fact that the Huygens probe documented sand when it landed on Titan is a poignant testament to how fundamental it is in our universe (nevermind that the sand is made out of hydrocarbon ice — remember, it’s the size that makes it sand).

I highly recommend picking up a copy of ‘Sand’ if you are an Earth scientist of any kind — go ahead and make it a must-read on your 2010 list. For my readers that aren’t Earth scientists but enjoy nature writing at its best, I think you’ll really like this book as well.

Finally, I’ll leave you with one more quote from ‘Sand’ — a quote that offers a clear and succinct answer to the question of why it is important to increase our knowledge of the dynamics and history of a material like sand:

On such details does the character and habitability of our planet depend.

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^ Make sure to check out Michael’s blog Through the Sandglass to read more fascinating stories about sand — some of which are included in the book, but many that are not.

* Michael Welland explains why there are two editions of ‘Sand’ with different subtitles on his blog here.

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UPDATE (2/3/2010): Michael Welland has been awarded The John Burroughs Medal for excellence in natural history writing. This is very well-deserved.

Several other geo-bloggers have been covering the conference (including AGU’s “official” blog,  Dave’s Landslide Blog, Harmonic Tremors, Musings of a Life-Long Scholar, Active Margin, and Andrew at geology.about.com). See the blogroll for a bunch more. And the Twitter feed (using #AGU09 tag) is extremely active and highly recommended for keeping up with it all.

I hope you’ve paced yourself and are still hungry for what I think are some great sessions. This is how I will be spending my time at the meeting:

Thursday AM

EP41A (Moscone South) — Dynamics and Processes of Deltas, Fans, and Their Distributary Channels I (Posters)

EP42A (2008 Moscone West) — Computational Modeling of Landscape and Seascapes: Models, Data Sets, and Applications I (Oral) — specifically, I’m going to try and check out the following in this session:

• EP42A-01: Modeling the complex dynamic interactions between surface processes, crustal deformation, and climate change (Braun et al.)
• EP42A-05: Reconstructing the Waipaoa sedimentary systems at the LGM (Upton et al.)
• EP42A-06: Community sediment-transport modeling system (CSTMS) (Sherwood et al.)
• EP42A-08: Computational investigation of turbidity currents and river outflows (Meiburg et al.)

Thursday PM

EP43D (Moscone South) — Computational Modeling of Landscape and Seascapes: Models, Data Sets, and Applications II (Posters) — I will check out all, but hope to get some good discussions going about this one:

• EP43D-0672: Flow dynamics and sediment entrainment in natural turbidity currents inferred from numerical modeling (Traer et al.)

EP43F (2008 Moscone West) — Dynamics and Processes of Deltas, Fans, and Their Distributary Channels I (Oral) — this whole session looks fantastic

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Friday AM

EP52A (2002 Moscone West) — Interpreting Allogenic and Autogenic Processes in the Stratigraphic Record I (Oral) — this session explores the interactions of external (or allogenic) forcings and intrinsic dynamics (or autogenic processes) on what is preserved in the stratigraphic record. I am giving a talk in this session that starts at 11:35am titled:

• EP52A-06: High-frequency allogenic forcings on the Holocene stratigraphy of  Santa Monica Basin, California

Friday PM

EP53A (Moscone South) — Interpreting Allogenic and Autogenic Processes in the Stratigraphic Record II (Posters) — this is the companion poster session to the morning oral session and has a bunch of awesome stuff. I really hope people stick around until Friday afternoon to argue about discuss what is actually being recorded in the stratigraphic record.

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I’m excited … now I need to finish preparing my talk.

I’m presenting a talk at the GSA meeting in Portland next month about some work I did for my Ph.D. looking at the tectonic influence of sedimentation in the Magallanes Basin in southern Chile. A paper for this work is now in press for Basin Research and should be out early 2010. This talk is in in this session on Tuesday afternoon. Here is the wordle.net word cloud for that abstract:

I was also invited to present at the AGU meeting in December (which is in San Francisco as always). This is going to be a very cool session focused on discussing how external (allogenic) factors and internal factors (autogenic) interact to produce the sedimentary record. Some work I did looking at a Holocene deep-marine record compared with paleoclimate records is out in GSA Bulletin this month (I hope to finish a blog post about it very soon). The program is not finalized yet, so check back for details of when the session is. Here is the wordle.net word cloud for that abstract:

I’m looking forward to sharing this work with others and checking out what others are doing!