Ninth International Conference on Permafrost ... - IARC Research

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HiRISE Observations of Fractured Mounds in the Martian Mid-LatitudesColin M. DundasThe University of Arizona, Department of Planetary Sciences, Tucson, AZ, USAAlfred S. McEwenThe University of Arizona, Department of Planetary Sciences, Tucson, AZ, USAIntroductionThe planet Mars has widespread permafrost, muchof it ice-rich. Some ground ice features such as thermalcontraction cracks have been confidently identified basedon orbital imagery (e.g., Mellon 1997). The possibility ofother periglacial features has been considered; in particular,a number of authors have suggested various Martian featuresas pingos (Judson & Rossbacher 1979, Parker et al. 1993,Cabrol et al. 2000, Soare et al. 2005, Burr et al. 2005,Page & Murray 2006). However, low resolution of orbitalimagery made it difficult to assess detailed morphologies ofsuch features, and in several cases, later work has indicateddifferent formation mechanisms (Farrand et al. 2005,Martinez-Alonso et al. 2005, Jaeger et al. 2007). This hasleft the possibility of pingos on Mars an open question.The issue is of particular importance, since pingos wouldprovide information about the state and history of water onMars, with implications for the origins of other water-relatedfeatures such as young gullies (Malin et al. 2000).The High Resolution Imaging Science Experiment(HiRISE) camera on the Mars Reconnaissance Orbiter(MRO) spacecraft has returned several thousand images ofthe Martian surface with scale as small as 26 cm/pixel. Thisresolution allows assessment of fine-scale morphologies inmuch more detail than previously possible. Early imagesrevealed fractured mounds, similar to pingos on Earth insome respects, in both northern and southern mid-latitudes(Dundas et al. 2008). Dundas et al. (2008) also used lowerresolutionimages to examine the distribution of flat-toppedmounds (matching the approximate shape of some of theobserved features) and found that in the northern plainsregion of Utopia Planitia, the mounds occurred in thelatitudinal band where gullies are most common. This studyuses HiRISE images to examine the planet-wide distributionand range of morphologies in order to better compare thesemounds with pingos on Earth.polygonal cracks occurring as part of a widespread network(e.g., thermal contraction cracks).To date, 1350 HiRISE images have been incorporated intothis survey. All images obtained through orbit 2150 wereused; among images from subsequent orbits, only those fromlatitudes 20°–60° of each hemisphere were examined.Fractured mound morphologiesA wide range of morphologies fitting the loose definitionof fractured mound have been observed. Some are isolated,while others, typically smaller, are clustered. In severalinstances, roughly radial fracture patterns are observed,but in other cases the fractures are irregular. Mounds arefound in pits or small impact craters at several sites, oftenin association with other fractured features. The breadth ofthe definition also includes some anomalous forms, suchas irregular, few-hundred-meter scale raised plateaus withdistinct fracturing.This breadth prevents any feature from being truly typical,but several broad categories are observed. Fractured moundsin the Southern Hemisphere are generally found on thefloors of multi-kilometer diameter impact craters, often withgullied walls. This group includes both isolated mounds(e.g., Fig. 1) and clusters of fractured features. A groupof flat-topped mounds in Utopia Planitia displays distinctsummit fracturing, often radially oriented, and is often foundHiRISE ObservationsHiRISE surveyHiRISE images from across Mars were examined inorder to assess the distribution of fractured mounds. Thisis a non-genetic definition that could encompass a rangeof morphologies and origins, used here in order to ensurea comprehensive survey of possible pingos. We searchfor features where fracturing occurs only on the moundor is distinctly enhanced there, since much of the Martiansurface has fractures of various origins. We specificallyexclude outcrops of jointed rock and knobs with superposedFigure 1. Fractured mound in HiRISE image PSP_007522_1480.The mound is approximately 100 m across and lies on the floor ofan impact crater with gullied walls. Illumination is from the rightand north down in this non-map-projected image.67
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tin conjunction with irregular mounds in small craters. A thirdmajor class encompasses those mounds found on lineatedvalley fill. These are often irregular or degraded and, in somecases, may include remnants of a mantling deposit.Fractured mound distributionDespite the scope of the definition, the mounds exhibitnotable latitudinal control. They are generally found between30°–45° in each hemisphere. The distribution also exhibitssome longitudinal variation; fractured mounds are generallyabsent from the volcanic provinces of Tharsis and Elysium,although some portion of this variation may be due to biasesin HiRISE image coverage, which is concentrated overcertain areas.DiscussionFractured mounds are a broad category, which may includefeatures of multiple origins. The apparent latitudinal controlsuggests that these features have origins related to wateror ice activity, particularly since the latitude bands of themounds are also the locations of other water- or ice-relatedfeatures (e.g., Milliken et al. 2003).Several of the fractured mounds appear to be very goodmorphological analogues for terrestrial pingos, particularlythe isolated examples near the base of gullied slopes. Sincegullies may indicate shallow groundwater outflow (Mellon& Phillips 2001), these could be similar to hydraulic pingos.In other cases, a pingo-like origin is less likely: at least someof the mounds on lineated valley fill may be degraded impactcraters with inverted relief (Mangold 2003) or erodingmantling material. The mounds in Utopia Planitia aremorphologically similar to pingos in several ways, includingscale and (frequently) distinct radial fractures, but often havedistinctly trapezoidal profiles and are found in level terrainrather than in depressions or at the base of slopes.The possible effects of different Martian conditions onmorphology complicate interpretation. Different processescould produce similar resulting landforms, and Mars mayhave a different range of ground ice processes than Earth.However, the mounds discussed here include the bestmorphological analogues for pingos yet observed on Mars.Further coverage from HiRISE will clarify the range ofmorphologies and settings and allow more detailed analysisof formation mechanisms.AcknowledgmentsWe thank the HiRISE science and operations teams fortheir work in producing outstanding images and the MROproject for support.ReferencesBurr, D.M., Soare, R.J., Wan Bun Tseung, J.-M. & Emery, J.P.2005. Young (late Amazonian), near-surface, groundice features near the equator, Athabasca Valles, Mars.Icarus 178(1): 56-73.Cabrol, N.A., Grin, E.A. & Pollard, W.H. 2000. Possiblefrost mounds in an ancient Martian lake bed. Icarus145: 91-107.Dundas, C.M., Mellon, M.T., McEwen, A.S., Lefort,A., Keszthelyi, L.P. & Thomas, N. 2008. HiRISEObservations of fractured mounds: Possible Martianpingos. Geophysical Research Letters 35(4):L04201.Farrand, W.H., Gaddis, L.R. & Keszthelyi, L. 2005. Pittedcones and domes on Mars: Observations in AcidaliaPlanitia and Cydonia Mensae using MOC, THEMISand TES data. Journal of Geophysical Research(Planets) 110(E5): E05005.Jaeger, W.L., Keszthelyi, L.P., McEwen, A.S., Dundas, C.M.& Russell, P.S. 2007. Athabasca Valles, Mars: A lavadrapedchannel system. Science 317(5845): 1709-1711.Judson, S. & Rossbacher, L. 1979. Geomorphic role ofground ice on Mars. NASA Technical Memo 80339:229-231.Malin M.C. & Edgett, K.S. 2000. Evidence for recentgroundwater seepage and surface runoff on Mars.Science 288(5475): 2330-2335.Mangold, N. 2003. Geomorphic analysis of lobate debrisaprons on Mars at Mars Orbiter Camera scale:Evidence for sublimation initiated by fractures.Journal of Geophysical Research (Planets) 108(E4):CiteID 8021.Martinez-Alonso, S., Jakosky, B.M., Mellon, M.T. & Putzig,N.E. 2005. A volcanic interpretation of Gusev Cratersurface materials from thermophysical, spectral andmorphological evidence. Journal of GeophysicalResearch (Planets) 110(E1): CiteID E01003.Mellon, M.T. 1997. Small-scale polygonal features on Mars:Seasonal thermal contraction cracks in permafrost.Journal of Geophysical Research 102(E11): 25,617-25,628.Mellon, M.T. & Phillips, R.J. 2001. Recent gullies on Marsand the source of liquid water. Journal of GeophysicalResearch 106(E10): 23,165-23,180.Milliken, R., Mustard, J.F. & Goldsby, D.L. 2003. Viscousflow features on the surface of Mars: Observationsfrom high-resolution Mars Orbiter Camera (MOC)images. Journal of Geophysical Research (Planets)108(E6): CiteID 5057.Page, D.P. & Murray, J.B. 2006. Stratigraphical andmorphological evidence for pingo genesis in theCerberus plains. Icarus 183(1): 46-54.Parker, T.J., Gorsline, D.S., Saunders, R.S., Pieri, D.C. &Schneeberger, D.M. 1993. Coastal geomorphology ofthe Martian northern plains. Journal of GeophysicalResearch 98(E6): 11,061-11,078.Soare, R.J., Burr, D.M. & Wan Bun Tseung, J.-M. 2005.Possible pingos and a periglacial landscape innorthwest Utopia Planitia. Icarus 174(2): 373-382.68
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
Page 38 and 39: Time Series Analyses of Active Micr
Page 40 and 41: Impact of Permafrost Degradation on
Page 42 and 43: DC Resistivity Soundings Across a P
Page 44 and 45: Modeling Thermal and Moisture Regim
Page 46 and 47: A Provisional Permafrost Map of the
Page 48 and 49: Alpine Permafrost Distribution at M
Page 50 and 51: Cryogenic Formations of the Caucasu
Page 52 and 53: Modeling Potential Climatic Change
Page 54 and 55: A Hypothesis: A Condition of Growth
Page 56 and 57: Modeled Continual Surface Water Sto
Page 58 and 59: Freeze/Thaw Properties of Tundra So
Page 60 and 61: Discontinuous Permafrost Distributi
Page 62 and 63: Thermal Regime Within an Arctic Was
Page 64 and 65: Seasonal and Interannual Variabilit
Page 66 and 67: Twelve-Year Thaw Progression Data f
Page 68 and 69: Continued Permafrost Warming in Nor
Page 70 and 71: Landsliding Following Forest Fire o
Page 72 and 73: A Permafrost Model Incorporating Dy
Page 74 and 75: Seasonal Sources of Soil Respiratio
Page 76 and 77: Greenland Permafrost Temperature Si
Page 78 and 79: The Importance of Snow Cover Evolut
Page 80 and 81: The Account of Long-Term Air Temper
Page 82 and 83: The Combined Isotopic Analysis of L
Page 84 and 85: Adaptating and Managing Nunavik’s
Page 86 and 87: Human Experience of Cryospheric Cha
Page 90 and 91: A Soil Freeze-Thaw Model Through th
Page 92 and 93: Mapping and Modeling the Distributi
Page 94 and 95: First Results of Ground Surface Tem
Page 96 and 97: Historical Changes in the Seasonall
Page 98 and 99: Rock Glaciers in the Kåfjord Area,
Page 100 and 101: Snowpack Evolution on Permafrost, N
Page 102 and 103: Climate Change in Permafrost Region
Page 104 and 105: Maximizing Construction Season in a
Page 106 and 107: Pleistocene Sand-Wedge, Composite-W
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370Huang, B. 339Hugelius, G. 105, 1
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