Strange travels

Transport phenomena in highly heterogeneous media can be dramatically different from those in homogeneous media and therefore are of great fundamental and practical interest. Anomalous transport occurs in semiconductor physics, plasma physics, astrophysics, biology, and other areas. It plays an especially important role in hydrogeology because it may govern the rate of migration and degree of dispersion of groundwater contaminants from hazardous waste sites.

A series of four articles in Special Section: Nonclassical Transport of the November 2008 issue of Vadose Zone Journal is devoted to transport phenomena in heterogeneous media in the context of geologic disposal of radioactive waste. Guest Editors Leonid Bolshov and Peter Kondratenko (Nuclear Safety Institute, Russian Academy of Sciences) and Karsten Pruess (Lawrence Berkeley National Lab.) assembled the articles, which are the results of joint investigations performed at the Nuclear Safety Institute of the Russian Academy of Sciences and Lawrence Berkeley National Laboratory in California. The work was supported by the USDOE.

The problems addressed in this research involve a broad range of space and time scales and were approached using modern methods of theoretical and computational physics, such as scaling analysis and diagrammatic techniques used before in critical phenomena theory. Special attention is paid to concentration tails. This issue is exceptionally important for the reliability assessments of radioactive waste disposal because, depending on the structure of the tails, concentrations at large distances from the source can differ by many orders of magnitude.

The first paper of this special section presents an overview of field and laboratory observations that demonstrate nonclassical flow and transport behavior in geologic media, with an emphasis on the fractal geometry of natural fracture networks and the presence of contaminant traps. The second paper is devoted to the analysis of diffusion in heterogeneous media with sharply contrasting properties; the authors show that as time progresses, three different transport regimes can be realized. In the third paper, it is shown that the solute transport regime is determined by a competition of two mechanisms: random advection through a fracture network and trapping caused by sharply contrasting properties of the medium. In the fourth paper, the authors develop a model of anomalous diffusion to simulate solute transport in highly heterogeneous media, and the new model is shown to result in reasonable agreement with experimental data on solute transport in highly heterogeneous media.

Future snowmelt in West twice as early as expected; threatens ecosystems and water reserves





Timing of runoff
Timing of runoff

According to a new study, global warming could lead to larger changes in snowmelt in the western United States than was previously thought, possibly increasing wildfire risk and creating new water management challenges for agriculture, ecosystems and urban populations.



Researchers, including a Purdue University professor of earth and atmospheric sciences, discovered that a critical surface temperature feedback is twice as strong as what had been projected by earlier studies.



The high-resolution climate model used by the team was better able to reproduce the complex topography of the western United States and capture details of the effect of snow cover on the climate system, as well as the historical record of runoff.



The findings will be published in an upcoming issue of Geophysical Research Letters and are now available online at the journal’s Web site.



Noah Diffenbaugh, senior author of the paper and an associate professor of earth and atmospheric sciences at Purdue, said the influence of melting snow on regional climate is far greater than that of increased greenhouse gases alone.



“The heat trapping from elevated greenhouse gases triggers the warming, but the additional warming caused by the loss of snow is what really creates the big changes in surface runoff,” said Diffenbaugh, who also is a member of Purdue’s Climate Change Research Center. “Scientists have known about this general effect for years. The big surprise here is how much the complex topography plays a role, essentially doubling the threat to water resources in the West.”



Sara A. Rauscher, visiting scientist at the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy, and lead author on the paper, said the melting snow contributes to a feedback loop that accelerates warming.



“Because snow is more reflective than the ground or vegetation beneath it, it keeps the surface temperatures lower by reflecting energy from the sun,” Rauscher said. “When snow melts or does not accumulate in the first place, more solar energy is absorbed by the ground, warming the surface. A feedback loop is created because the warmer ground then makes it more difficult for snow to accumulate and perpetuates the effect.”



The amount and timing of the runoff from snowmelt is critical to the success of water management in the western United States. Water resources for the area are reliant on snow acting as a natural reservoir during the cold season that melts and releases water in the warm season.



Changes in this timing could create problems in meeting the increasing demand for water in large urban and agricultural areas during the hottest summer months, Diffenbaugh said.


“If the snow melts earlier or if it comes as rainfall instead, it would create a strain on infrastructure,” he said. “The current system relies on water being stored in the mountains as snow. So earlier runoff could mean too much water for the reservoirs early in the year and not enough available later in the year.”



Gregg M. Garfin, deputy director for science translation and outreach at the Institute for the Study of Planet Earth at the University of Arizona, said dry summers could lead to more severe wildfires and changes in the ecosystems of the West.



“Early snowmelt and warmer soil temperatures could result in further massive forest mortality and an increased risk of wildfire activity,” Garfin said. “If these projections become reality, then the ecosystems of the northern and central Rockies will undergo dramatic changes with ramifications for wildlife habitat, fire potential, soil erosion and tourism.”



The study suggests a substantial change in the runoff season, with the peak date more than two months earlier than today in some regions, Diffenbaugh said.



“During the past 50 years, the peak runoff time has moved 10 to 15 days earlier,” he said. “It is not surprising that as we look to the future, the projected changes are much greater than the historical changes. The increase in greenhouse gas emissions has been relatively small for the past 50 years compared with where we are headed over the next several decades if substantial changes in energy technology and population growth do not occur.”



The researchers also compared the climate model to historical records and found that it had a high level of agreement with historical data and observed trends.



“One of the most important contributions of this work is the remarkable agreement between the climate model and the observations of the recent past,” Diffenbaugh said. “This agreement should increase confidence not only in these particular projections of future changes, but also of climate model projections in general.”



Additional study co-authors are Jeremy S. Pal of Loyola Marymount University and Michael Benedetti of the University of North Carolina at Wilmington. The research was funded in part by grants from the National Science Foundation.



The Purdue Climate Change Research Center is affiliated with Purdue’s Discovery Park. The center promotes and organizes research and education on global climate change and studies its impact on agriculture, natural ecosystems and society. It was established in 2004 to support Purdue in research and education on regional-scale climate change, its impacts and mitigation, and adaptation strategies. The center serves as a hub for a range of activities beyond scientific research, including teaching, public education and the development of public policy recommendations.



The high-resolution climate model simulations were conducted using computing resources in Purdue’s Rosen Center for Advanced Computing. The Rosen Center is a research computing center named in memory of Saul Rosen, who served as director of Purdue’s Computing Center from 1968-87 and helped establish Purdue as a pioneering academic institution in high-performance computing. The Rosen Center is a part of Information Technology at Purdue, which is responsible for planning and coordinating the central computing and telecommunications systems on the West Lafayette campus.



The Abdus Salam International Centre for Theoretical Physics was founded in 1964 by Nobel Laureate Abdus Salam. The center operates under a tripartite agreement among the Italian Government and two U.N. agencies, UNESCO and IAEA. Its mission is to foster advanced studies and research, especially in developing countries. While the name of the center reflects its beginnings, its activities today include geophysical and environmental sciences.

Rocky water source


Water from rock, easier than blood from stone



Gypsum, a rocky mineral is abundant in desert regions where fresh water is usually in very short supply but oil and gas fields are common. Writing in International Journal of Global Environmental Issues, Peter van der Gaag of the Holland Innovation Team, in Rotterdam, The Netherlands, has hit on the idea of using the untapped energy from oil and gas flare-off to release the water locked in gypsum.



Fresh water resources are scarce and will be more so with the effects of global climate change. Finding alternative sources of water is an increasingly pressing issue for policy makers the world over. Gypsum, explains van der Gaag could be one such resource. He has discussed the technology with people in the Sahara who agree that the idea could help combat water shortages, improve irrigation, and even make some deserts fertile.



Chemically speaking, gypsum is calcium sulfate dihydrate, and has the chemical formula CaSO4.2H2O. In other words, for every unit of calcium sulfate in the mineral there are two water molecules, which means gypsum is 20% water by weight.


van der Gaag suggests that a large-scale, or macro, engineering project could be used to tap off this water from the vast deposits of gypsum found in desert regions, amounting to billions of cubic meters and representing trillions of liters of clean, drinking water.



The process would require energy, but this could be supplied using the energy from oil and gas fields that is usually wasted through flaring. Indeed, van der Gaag explains that it takes only moderate heating, compared with many chemical reactions, to temperatures of around 100 Celsius to liberate water from gypsum and turn the mineral residue into bassanite, the anhydrous form. “Such temperatures can be reached by small-scale solar power, or alternatively, the heat from flaring oil wells can be used,” he says. He adds that, “Dehydration under certain circumstances starts at 60 Celsius, goes faster at 85 Celsius, and faster still at 100 degrees. So in deserts – where there is abundant sunlight – it is very easy to do.”



van der Gaag points out that the dehydration of gypsum results in a material of much lower volume than the original mineral, so the very process of releasing water from the rock will cause local subsidence, which will then create a readymade reservoir for the water. Tests of the process itself have proved successful and the Holland Innovation Team is planning a pilot study in a desert location.



“The macro-engineering concept of dewatering gypsum deposits could solve the water shortage problem in many dry areas in the future, for drinking purposes as well as for drip irrigation,” concludes van der Gaag.



“Mining water from gypsum” in International Journal of Global Environmental Issues, 2008, 8, 274- 281

Geoengineering could slow down the global water cycle


As fossil fuel emissions continue to climb, reducing the amount of sunlight hitting the Earth would definitely have a cooling effect on surface temperatures.



However, a new study from Lawrence Livermore National Laboratory, led by atmospheric scientist Govindasamy Bala, shows that this intentional manipulation of solar radiation also could lead to a less intense global water cycle. Decreasing surface temperatures through “geoengineering” also could mean less rainfall.



The reduction in sunlight can be accomplished by geoengineering schemes. There are two classes: the so-called “sunshade” geoengineering scheme, which would mitigate climate change by intentionally manipulating the solar radiation on the earth’s surface; the other category removes atmospheric CO2 and sequesters it into the terrestrial vegetation, oceans or deep geologic formations.



In the new climate modeling study, which appears in the May 27-30 early online edition of the Proceedings of the National Academy of Sciences, Bala and his colleagues Karl Taylor and Philip Duffy demonstrate that the sunshade geoengineering scheme could slow down the global water cycle.



The sunshade schemes include placing reflectors in space, injecting sulfate or other reflective particles into the stratosphere, or enhancing the reflectivity of clouds by injecting cloud condensation nuclei in the troposphere. When CO2 is doubled as predicted in the future, a 2 percent reduction in sunlight is sufficient to counter the surface warming.



This new research investigated the sensitivity of the global mean precipitation to greenhouse and solar forcings separately to help understand the global water cycle in a geoengineered world.



While the surface temperature response is the same for CO2 and solar forcings, the rainfall response can be very different.


“We found that while climate sensitivity can be the same for different forcing mechanisms, the hydrological sensitivity is very different,” Bala said.



The global mean rainfall increased approximately 4 percent for a doubling of CO2 and decreases by 6 percent for a reduction in sunlight in his modeling study.



“Because the global water cycle is more sensitive to changes in solar radiation than to increases in CO2, geoengineering could lead to a decline in the intensity of the global water cycle” Bala said.



A recent study showed that there was a substantial decrease in rainfall over land and a record decrease in runoff and discharge into the ocean following the eruption of Mount Pinatubo in 1991. The ash emitted from Pinatubo masked some of the sunlight reaching the earth and therefore decreased surface temperatures slightly, but it also slowed down the global hydrologic cycle.



“Any research in geoengineering should explore the response of different components of the climate system to forcing mechanisms,” Bala said.



For instance, Bala said, sunshade geoengineering would not limit the amount of CO2 emissions. CO2 effects on ocean chemistry, specifically, could have harmful consequences for marine biota because of ocean acidification, which is not mitigated by geoengineering schemes.



“While geoengineering schemes would mitigate the surface warming, we still have to face the consequences of CO2 emissions on marine life, agriculture and the water cycle,” Bala said.

Continents loss to oceans boosts staying power


Study measures effects of chemical weathering on the composition of continents



New research suggests that the geological staying power of continents comes partly from their losing battle with the Earth’s oceans over magnesium. The research finds continents lose more than 20 percent of their initial mass via chemical reactions involving the Earth’s crust, water and atmosphere. Because much of the lost mass is dominated by magnesium and calcium, continents ultimately gain because the lighter, silicon-rich rock that’s left behind is buoyed up by denser rock beneath the Earth’s crust.



The Earth’s continents seem like fixtures, having changed little throughout recorded human history. But geologists know that continents have come and gone during the Earth’s 4.5 billion years. However, there are more theories than hard data about some of the key processes that govern continents’ lives.



“Continents are built by new rock that wells up from volcanoes in island arcs like Japan,” said lead author Cin-Ty Lee, assistant professor of Earth science at Rice University. “In addition to chemical weathering at the Earth’s surface, we know that some magnesium is also lost due to destabilizing convective forces beneath these arcs.”



Lee’s research, which appeared in the March 24 issue of the Proceedings of the National Academy of Science, marks the first attempt to precisely nail down how much magnesium is lost through two markedly different routes — destabilizing convective forces deep inside the Earth and chemical weathering reactions on its surface. Lee said the project might not have happened at all if it weren’t for some laboratory serendipity.



“I’d acquired some tourmaline samples in San Diego with my childhood mentor, Doug Morton,” Lee said. “We were adding to our rock collections, like kids, but when I got back to the lab, I was curious where the lithium, a major element in tourmaline, needed to make the tourmalines came from. I decided to measure the lithium content in the granitic rocks from the same area, and that’s where this started.”


In examining the lithium content in a variety of rocks, Lee realized that lithium tended to behave like the magnesium that was missing from continents. In fact, the correlation was so close, he realized that lithium could be used as a proxy to find out how much magnesium continents had lost due to chemical weathering.



Continents ride higher than oceans, partly because the Earth’s crust is thicker beneath continents than it is beneath the oceans. In addition, the rock beneath continents is made primarily of silicon-rich minerals like granite and quartz, which are less dense than the magnesium-rich basalt beneath the oceans.



Lee said he always assumed that processes deep in the Earth, beneath the volcanoes that feed continents, accounted for far more magnesium loss than weathering. In particular, a process called “delamination” occurs in subduction zones, places where one piece of the Earth’s crust slides beneath another and gets recycled into the Earth’s magma. As magma wells up beneath continent-feeding volcanoes, it often leaves behind a dense, magnesium-rich layer that ultimately founders back into the Earth’s interior.



In previous research, Lee found that about 40 percent of the magnesium in basaltic magma was lost to delamination. He said he was thus surprised to find that chemical weathering alone accounted for another 20 percent.



“Weathering occurs in just the top few meters or so of the Earth’s crust, and it’s driven by the hydrosphere, the water that moves between the air, land and oceans,” Lee said. “It appears that our planet has continents because we have an active hydrosphere, so if we want to find a hydrosphere on distant planets, perhaps we should look for continents.”



The research was sponsored by the National Science Foundation (NSF) and the Packard Foundation. Co-authors include Morton, of the U.S. Geological Survey (USGS) and the University of California-Riverside; the NSF’s William Leeman, professor emeritus of Earth science at Rice; Ronald Kistler of the USGS; former Rice postdoctorate Arnaud Agranier, now of the University of West Brittany in Brest, France; and former Rice undergraduate Ulyana Horodyskyj, now a graduate student at Brown University.

Using Ground Penetrating Radar to Observe Hidden Underground Water Processes


Researchers present applications of radar technology for exploring the properties and movement of water beneath our feet.



To meet the needs of a growing population and to provide it with a higher quality of life, increasing pressures are being placed on the environment through the development of agriculture, industry, and infrastructures.



Soil erosion, groundwater depletion, salinization, and pollution have been recognized for decades as major threats to ecosystems and human health. More recently, the progressive substitution of fossil fuels with biofuels for energy production have been recognized as potential threats to water resources and sustained agricultural productivity.



The top part of the earth between the surface and the water table is called the vadose zone. The vadose zone mediates many of the processes that govern water resources and quality, such as the partition of precipitation into infiltration and runoff, groundwater recharge, contaminant transport, plant growth, evaporation, and energy exchanges between the earth’s surface and its atmosphere. It also determines soil organic carbon sequestration and carbon-cycle feedbacks, which could substantially affect climate change.



The vadose zone’s inherent spatial variability and inaccessibility make direct observation of the important belowground (termed “subsurface”) processes difficult. Conventional soil sampling is destructive, laborious, expensive, and may not be representative of the actual variability over space and time. In a societal context where the development of sustainable and optimal environmental management strategies has become a priority, there is a strong prerequisite for the development of noninvasive characterization and monitoring techniques of the vadose zone.


In particular, approaches integrating water movement, geological, and physical principles (called hydrogeophysics) applied at relevant scales are required to appraise dynamic belowground phenomena and to develop optimal sustainability, exploitation, and remediation strategies.



Among existing geophysical techniques, ground-penetrating radar (GPR) technology is of particular interest for providing high-resolution subsurface images and specifically addressing water-related questions. GPR is based on the transmission and reception of electromagnetic waves into the ground, whose propagation velocity and signal strength is determined by the soil electromagnetic properties and spatial distribution. As the electric permittivity of water overwhelms the permittivity of other soil components, the presence of water in the soil principally governs GPR wave propagation. Therefore, GPR-derived dielectric permittivity is usually used as surrogate measure for soil water content.



In the areas of unsaturated zone hydrology and water resources, GPR has been used to identify soil layering, locate water tables, follow wetting front movement, estimate soil water content, assist in subsurface hydraulic parameter identification, assess soil salinity, and support the monitoring of contaminants.



The February 2008 issue of Vadose Zone Journal includes a special section that presents recent research advances and applications of GPR in hydrogeophysics. The studies presented deal with a wide range of surface and borehole GPR applications, including GPR sensitivity to contaminant plumes, new methods for soil water content determination, three-dimensional imaging of the subsurface, time-lapse monitoring of hydrodynamic events and processing techniques for soil hydraulic properties estimation, and joint interpretation of GPR data with other sources of information.



“GPR has known a rapid development over the last decade,” notes S├ębastien Lambot, who organized the special issue. “Yet, several challenges must still be overcome before we can benefit from the full potential of GPR. In particular, more exact GPR modeling procedures together with the integration of other sources of information, such as other sensors or process knowledge, are required to maximize quantitative and qualitative information retrieval capabilities of GPR. Once this is achieved, GPR will be established as a powerful tool to support the understanding of the vadose zone hydrological processes and the development of optimal environmental and agricultural management strategies for our soil and water resources.”



The full article is available for no charge for 30 days following the date of this summary. View the abstract at: vzj.scijournals.org

Lake Mead Could Be Dry by 2021





A map of the Colorado River basin.
A map of the Colorado River basin.

There is a 50 percent chance Lake Mead, a key source of water for millions of people in the southwestern United States, will be dry by 2021 if climate changes as expected and future water usage is not curtailed, according to a pair of researchers at Scripps Institution of Oceanography, UC San Diego.



Without Lake Mead and neighboring Lake Powell, the Colorado River system has no buffer to sustain the population of the Southwest through an unusually dry year, or worse, a sustained drought. In such an event, water deliveries would become highly unstable and variable, said research marine physicist Tim Barnett and climate scientist David Pierce.



Barnett and Pierce concluded that human demand, natural forces like evaporation, and human-induced climate change are creating a net deficit of nearly 1 million acre-feet of water per year from the Colorado River system that includes Lake Mead and Lake Powell. This amount of water can supply roughly 8 million people. Their analysis of Federal Bureau of Reclamation records of past water demand and calculations of scheduled water allocations and climate conditions indicate that the system could run dry even if mitigation measures now being proposed are implemented.



The paper, “When will Lake Mead go dry?,” has been accepted for publication in the peer-reviewed journal Water Resources Research, published by the American Geophysical Union (AGU), and is accessible via the AGU’s website (see instructions below).



“We were stunned at the magnitude of the problem and how fast it was coming at us,” said Barnett. “Make no mistake, this water problem is not a scientific abstraction, but rather one that will impact each and every one of us that live in the Southwest.”



“It’s likely to mean real changes to how we live and do business in this region,” Pierce added.



The Lake Mead/Lake Powell system includes the stretch of the Colorado River in northern Arizona. Aqueducts carry the water to Las Vegas, Los Angeles, San Diego, and other communities in the Southwest. Currently the system is only at half capacity because of a recent string of dry years, and the team estimates that the system has already entered an era of deficit.


“When expected changes due to global warming are included as well, currently scheduled depletions are simply not sustainable,” wrote Barnett and Pierce in the paper.



Barnett and Pierce note that a number of other studies in recent years have estimated that climate change will lead to reductions in runoff to the Colorado River system. Those analyses consistently forecast reductions of between 10 and 30 percent over the next 30 to 50 years, which could affect the water supply of between 12 and 36 million people.



The researchers estimated that there is a 10 percent chance that Lake Mead could be dry by 2014. They further predict that there is a 50 percent chance that reservoir levels will drop too low to allow hydroelectric power generation by 2017.



The researchers add that even if water agencies follow their current drought contingency plans, it might not be enough to counter natural forces, especially if the region enters a period of sustained drought and/or human-induced climate changes occur as currently predicted.



Barnett said that the researchers chose to go with conservative estimates of the situation in their analysis, though the water shortage is likely to be more dire in reality. The team based its findings on the premise that climate change effects only started in 2007, though most researchers consider human-caused changes in climate to have likely started decades earlier. They also based their river flow on averages over the past 100 years, even though it has dropped in recent decades. Over the past 500 years the average annual flow is even less.



“Today, we are at or beyond the sustainable limit of the Colorado system. The alternative to reasoned solutions to this coming water crisis is a major societal and economic disruption in the desert southwest; something that will affect each of us living in the region” the report concluded.



The research was supported under a joint program between UC San Diego and the Lawrence Livermore National Laboratory and by the California Energy Commission. The views expressed here do not necessarily represent the views of the California Energy Commission, its employees, or the state of California.

Water, water everywhere but is it sustainable?





Professor Malcolm Cox
Professor Malcolm Cox

While Brisbane is flush with underground water stores, more needs to be known about refill times to aquifers and the environmental effects of large-scale freshwater extraction to ensure their sustainable use.



Internationally recognised groundwater expert, UNESCO Professor Yongxin Xu is visiting Queensland University of Technology’s Institute for Sustainable Resources on Thursday to speak about the links between surface water and groundwater systems and how to model them.



QUT hydrogeologist Associate Professor Malcolm Cox said Professor Xu had developed models to assess the effect of changing rainfall patterns on the ability of groundwater systems to recharge.



He said Professor Xu’s work had many aspects that could be applied to South- East Queensland conditions to help understand how climate change was affecting our groundwater supplies.



“SEQ has a great variation in groundwater systems which need intensive study before it can be used with confidence as a long-term, sustainable resource,” Professor Cox said.


“Unlike Sydney, which is within a large basin of groundwater, we have groundwater stored in many different rock types with varying porosity and rates of recharge (refill times). Some of the SEQ groundwater may be thousands of years old, some might be only a few weeks.”



He urged caution in utilising South-East Queensland’s subsurface water supplies without fully understanding recharge times, how aquifer systems were linked and how they were connected to the surface.



“For example, The Lockyer Valley, which produces 30 per cent of Brisbane’s vegetables, has used its alluvial groundwater intensively for irrigation,” Professor Cox said.



“The alluvium (river gravel and sand) is not being recharged because rainfall has dropped. Normally it recharges very quickly from rainfall on mountains round the Valley.



Professor Cox said not enough was known about the environmental impact of extracting a lot of freshwater from the ground, especially in coastal areas.



“Stradbroke and Bribie islands, for example, are totally reliant on rainfall recharge for their groundwater supplies therefore groundwater extraction must be carefully monitored.”



Professor Cox said that in both these areas groundwater use must also consider potential problems such as the intrusion of saltwater to replace the fresh groundwater and the effects on ecosystems that rely on groundwater.



He said the Institute for Sustainable Resources had a key focus on water resources and was supporting a number of groundwater research projects in the region.

As waters clear, scientists seek to end a muddy debate





Schieber uses a camera to track the growth and movement of mud formations - Photo by: Chris Meyer
Schieber uses a camera to track the growth and movement of mud formations – Photo by: Chris Meyer

Geologists have long thought muds will only settle when waters are quiet, but new research by Indiana University Bloomington and Massachusetts Institute of Technology geologists shows muds will accumulate even when currents move swiftly. Their findings appear in this week’s Science.



This may seem a trifling matter at first, but understanding the deposition of mud could significantly impact a number of public and private endeavors, from harbor and canal engineering to oil reservoir management and fossil fuel prospecting.



“Mudstones make up two-thirds of the sedimentary geological record,” said IU Bloomington geologist Juergen Schieber, who led the study. “One thing we are very certain of is that our findings will influence how geologists and paleontologists reconstruct Earth’s past.”



Previously geologists had thought that constant, rapid water flow prevented mud’s constituents — silts and clays — from coalescing and gathering at the bottoms of rivers, lakes and oceans. This has led to a bias, Schieber explains, that wherever mudstones are encountered in the sedimentary rock record, they are generally interpreted as quiet water deposits.



“But we suspected this did not have to be the case,” Schieber said. “All you have to do is look around. After the creek on our university’s campus floods, you can see ripples on the sidewalks once the waters have subsided. Closely examined, these ripples consist of mud. Sedimentary geologists have assumed up until now that only sand can form ripples and that mud particles are too small and settle too slowly to do the same thing. We just needed to demonstrate it that it can actually happen under controlled conditions.”



Schieber and IU graduate student Kevin Thaisen used a specially designed “mud flume” to simulate mud deposition in natural flows. The oval-shaped apparatus resembles a race track. A motorized paddle belt keeps water moving in one direction at a pre-determined speed, say, 26 centimeters per second (about 0.6 miles per hour). The concentration of dispersed sediment, temperature, salinity, and a dozen other parameters can be controlled. M.I.T. veteran sedimentologist John Southard provided advice on the construction and operation of the mud flume used in the experiments.


For their experiments, the scientists used calcium montmorillonite and kaolinite, extremely fine clays that in dry form have the feel of facial powder. Most geologists would have predicted that these tiny mineral grains could not settle easily from rapidly moving water, but the flume experiments showed that mud was traveling on the bottom of the flume after a short time period. Experiments with natural lake muds showed the same results.



“We found that mud beds accumulate at flow velocities that are much higher than what anyone would have expected,” said Schieber, who, because of the white color of the clay suspensions, calls this ongoing work the “sedimentology of milk.”



The mud accumulates slowly at first, in the form of heart- or arrowhead-shaped ripples that point upstream. These ripples slowly move with the current while maintaining their overall shapes.



Understanding how and when muds deposit will aid engineers who build harbors and canals, Schieber says, by providing them with new information about the rates at which mud can accumulate from turbid waters. Taking into account local conditions, engineers can build waterways in a way that truly minimizes mud deposition by optimizing tidal and wave-driven water flow. Furthermore, Schieber explains, the knowledge that muds can deposit from moving waters could expand the possible places where oil companies prospect for oil and gas. Organic matter and muds are both sticky and are often found together.



“If anything, when organic matter is present in addition to mud, it enhances mud deposition from fast moving currents,” he said.



The finding feels like something of a vindication, Schieber says. He and his colleagues have (genially) argued about whether muds could deposit from rapidly flowing water. Schieber had posited the possibility after noting an apparent oddity in the sedimentary rock record.



“In many ancient mudstones, you see not only deposition, but also erosion and rapid re-deposition of mud — all in the same place,” Schieber said. “The erosive features are at odds with the notion that the waters must have been still all or most of the time. We needed a better explanation.”



This research was supported by a grant from the National Science Foundation.