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Supplementary material to “Interdisciplinary Research Produces Results in the Understanding of Planetary Dunes”
10 August 2010
Timothy N. Titus and Rosalyn K. Hayward, U.S. Geological Survey, Flagstaff, Arizona
Mary C. Bourke, Planetary Science Institute, Tucson, Arizona
Citation:
Titus, T. N., R. K. Hayward, and M. C. Bourke (2010), Interdisciplinary research produces results in the understanding of planetary dunes, Eos Trans. AGU, 91(32), 281. [Full Article (pdf)]
Second International Planetary Dunes Workshop: Planetary Analogs — Integrating Models, Remote Sensing, and Field Data.
Alamosa, CO, May 18–21, 2010
Landforms and deposits created by the dynamic interactions between granular material and airflow (aeolian processes) occur on several planetary bodies, including Earth, Mars, Titan, and Venus. The recognition of landforms on other planetary bodies requires use of terrestrial analogs in a well-established methodology for interpretation of landforms observed from orbital and lander platforms. Given the similarities between dune morphology on different planetary bodies, it is reasonable to assume that they are dynamically similar. Aeolian bedforms, therefore, can indicate surface processes and environments on unfamiliar extra-terrestrial landscapes, provided that the fundamentals of the landforms and processes are well-understood on Earth.
Dunes and other aeolian bedforms are a prominent part of landscapes shaped by wind action on several planetary bodies in our solar system. Despite the four decades of study, many questions regarding their composition, sediment sources, morphology, age and dynamics under present and past climatic conditions remain poorly understood. Recently acquired data from orbiters and rovers together with innovative approaches using terrestrial analogs and numerical models are beginning to provide new insights into Martian sand dunes, as well as aeolian bedforms on other terrestrial planetary bodies (e.g., Titan).
Dr. Timothy N. Titus of the U.S. Geological Survey (USGS), along with Dr. Lori Fenton (Carl Sagan Center), Dr. Nick Lancaster (Desert Research Institute), Andrew Valdez (National Park Service) and Rose Hayward (USGS) convened this workshop as a means of bringing together terrestrial and planetary researchers from diverse backgrounds with the goal of fostering collaborative interdisciplinary research. The small group setting facilitated intensive discussion of problems and issues associated with aeolian processes on Earth, Mars, and Titan.
The bedform activity sessions demonstrated that: 1) there are several features, in addition to dunes, that can track aeolian activity/ sediment transport, e.g. scours, ripples. 2) The use of automated change detection algorithms is promising in the search for active dunes and ripples. 3) Atmospheric models are improving in their ability to predict aeolian activity and are currently being used to interpret aeolian feature formation.
The session on the sources and transport of aeolian grains focused on three common themes: The first theme, sources of aeolian materials, varies with planetary body. River and stream sediment is a major source for the Earth. Bedrock and indurated ancient erg deposits comprise another source for Earth and probably Mars. The sources for Titan are yet to be determined, but a better understanding of the composition and transport pathways might help to identify possible sources. The second theme, methods for identifying sources and pathways, focused on the use of thermal infrared (TIR) and near-infrared (NIR) remote sensing. Many components of sand seas are better identified using TIR, especially on Earth. Windows in the methane absorption spectrum on Titan may allow some NIR spectroscopic investigation. The third theme was mineralogical maturity. On Earth, the mineralogical maturity of sediments is reflected by their quartz content. More study is needed to determine what mineralogical maturity means on Mars.
The session on dunes, water and ice focused on niveo-aeolian processes both on Earth and Mars. Niveo-aeolian processes refers to the incorporation of snow and ice in sand dunes either during or after deposition. A variety of observations suggest that the Mars polar erg contains water ice just below a thin surface covering of desiccated sand. However, the source and mobility of the ice remain outstanding questions. Two analogs for the polar erg were discussed. The Antarctic is dry and cold and therefore an excellent analog for processes. Iceland's dunes are basaltic and therefore and excellent analog for mineralogy.
The session on bedform morphology presented the results of numerical simulations, flume experiments and data collected from dunes on Mars, Titan and Earth analogues. The focus was on questions pertaining to the observed variability in dune planform, morphometry and wavelength. In particular, the papers explored how these attributes reflect a dependence on wind (direction and velocity) atmospheric density and sufficient time for bedform evolution. Subsequent discussions focused on how specific dune forms may be used to infer the nature of the formative environment.
The poster session spanned all topics of interest, ranging from terrestrial analogs to dune migration rates.
A significant portion of the workshop was dedicated to discussion. On the final day, participants compiled the following list to guide aeolian research.
Collaborations and Research Approaches:
1. Process-oriented research that includes all planetary bodies is valuable. Interdisciplinary research and collaborations are encouraged in order to advance the understanding of aeolian processes and form across all planetary bodies. The workshop was organized to encourage discussion of processes that are common to multiple bodies as opposed to planet-specific discussions. This approach proved to be highly successful and highlighted the need for research interactions based on common processes.
2. Dune fields do not form in isolation — but interact with topography and other processes, e.g. fluvial or lacustrine sand sources and cementing volatiles. In order to better understand dunes and dune fields, aeolian studies must include the effects from other types of processes.
Winds and Surface-Atmosphere Interactions:
3. There is an increased need to compare remotely-sensed and in-situ wind regime indicators (e.g. dune morphologies or convection patterns using clouds) to high resolution wind models (e.g. MRAMS). An example of this type of study resulted from the first planetary dune workshop (Hayward et al., 2009).
4. Numerical simulations that explore the link between dune form, wind direction and sediment supply have shown great promise in applications to Mars and Titan and should continue.
5. All future landers and rovers launched should be equipped with wind instrumentation, specifically an anemometer.
Composition and Age:
6. The concept of 'mineralogical maturity' is important in terrestrial dune research. It is likely to be significant on Mars as well. Research should be done to determine what 'mineralogical maturity' would be for the mafic minerals on Mars. This concept should be expanded to other planetary bodies as compositional data become available.
7. Given the antiquity, atmospheric composition and mineralogical composition of planetary surfaces, what absolute dating methods are appropriate to determine the age and time scales of evolution of aeolian forms?
8. Higher resolution images have made it possible to identify aeolianites in stratigraphic outcrops on Mars. The location, age and nature of the aeolianite record will help extend our understanding of the nature, timing and geomorphological importance of major phases of aeolian activity on Mars.
Aeolian Feature and Change Detection:
9. Higher resolution images have made it possible to detect changes in aeolian form during current missions (e.g., disappearing dunes and moving ripples). The development of automated methods of change detection may assist in this labor-intensive task.
10. In order to facilitate the development and testing of automated feature and change detection software, researchers should compile and make publically available databases of aeolian features that will provide 'ground truth.' Hayward et al. (2007) is an example of such a database. However, this database only contains dune fields of moderate to large size in the equatorial region of Mars.
Interactions with Volatiles:
11. Determine the composition of dune volatiles and the nature of volatile emplacement.
12. More physical experimental work is needed (e.g. aggregate transportation, physical weathering of aeolian grains and crust development in cold climates).
Field Work and Planetary Analogs:
13. There is a need for additional studies of relevant dune analogues. Field work can be expensive, but must be funded if progress in understanding aeolian processes is to continue. Relevant analogues:
a. Climate analogues: Antarctic (cold and hyperarid).
b. Mineralogical analogs: Hawaii, Iceland (also cold, but humid) plus other sites outlined in Edgett and Lancaster (1993).
c. Morphodynamic analogs: especially active hyper-arid deserts (e.g. Namib and Atacama Deserts).
Acknowledgments:
In addition to the organizing committee, we would like to recognize the contributions of the session co-chairs: Mark A. Bishop, Mary C. Bourke, Charles S. Bristow, Briony H. Horgan, Timothy I. Michaels, and Daniela Tirsch. Without their assistance, the workshop would not have been a success and these proceedings and recommendations could not have been written.
References:
Edgett, K. S., Lancaster, N., 1993 Volcaniclastic aeolian dunes:Terrestrial examples and application to martian sands. Journal of Arid Environments. 25, 271-297.
Hayward, Rosalyn K.; Mullins, Kevin F.; Fenton, Lori K.; Hare, Trent M.; Titus, Timothy N.; Bourke, Mary C.; Colaprete, Anthony; Christensen, Philip R. (2007) Mars Global Digital Dune Database and initial science results, Journal of Geophysical Research, Volume 112, Issue E11, CiteID E11007.
Hayward, R. K., T. N. Titus, T. I. Michaels, L. K. Fenton, A. Colaprete, and P. R. Christensen (2009), Aeolian dunes as ground truth for atmospheric modeling on Mars, J. Geophys. Res., 114, E11012, doi:10.1029/2009JE003428.