Mathematics – Logic
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..659r&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Mathematics
Logic
Scientific paper
Martian gullies resemble terrestrial features formed by mass-wasting processes of a flowing mixture of clastic debris and water (debris flows). Their existence on Mars is interpreted to indicate liquid water in the recent past because of their pristine appearance, their stratigraphic relationships to young surface features, their lack of superimposed impact craters, and their distinct albedo relative to the surroundings, indicating limited dust cover [1]. The global distribution of gullies is limited to midand high-latitudes poleward of 30° in both hemispheres, with the highest frequency in the 30°- 50° latitude bands [1, 2]. Gullies occur preferentially on poleward-facing slopes [1, 2, 3, 4]. The most likely and physically most plausible medium to explain the gully morphology is liquid water [e.g., 1, 5]. Two main theories exist for the water source. One holds that water was released from the subsurface [1]. The other proposes that water is deposited as nearsurface ice or snow from the atmosphere and is subsequently melted by insolation [6, 7]. Debris flows found in Arctic climates on Earth could be an equitable analog for the Martian gullies. A comparative analysis might help to understand their formation mechanisms and the latitude-dependent, but clustered distribution as well as their specific orientations. The comparative analysis in the Arctic environment of Svalbard will be carried out in July/August of 2008. First results of the analog study of gullies will be presented at the conference. Debris flows on Svalbard Svalbard is located at 76°-81°N and 10°-35°E (Fig. 1), in the discontinuous zone of permafrost. Because the landscape of Svalbard is under the influence of the polar desert climate, it is a good analog for comparative Martian studies. These were performed in the last two years in the valley of Longyearbyen and on costal slopes of Isfjorden [8]. This study is complementary to the one described by Carlsson et al., 2008, this issue). Here we will focus on the regional distribution of gullies on the Hjorthfjellet and Adventtoppen mountain massif (Fig. 1, inset and Fig. 2), and detailed local studies of individual gullies on the same mountain massif are carried out as described by [8] and [9]. The Hjorthfjellet and Adventtoppen mountain massif consists of four stratigraphic units of sandstone and shales from the Tertiary and Mesozoic [10]. Several studies concerning talus slopes and debris flows on Svalbard have been performed in the last decades [e.g., 11, 12, 13, 14]. Regional studies of [14] using airborne imagery revealed that there are differences in the frequency and activity of debris flows on Svalbard between east- and west-facing slopes. Åkerman [14] suggested that differences in the solar radiation, the depth of the active layer and the amount of precipitation cause variances in the morphology and morphometry of the debris slopes as well as variances in the frequency and age of debris flows between east- and west-facing slopes. Studies and direct observations imply that debris flows on Svalbard are triggered by high intensity rainfall [e.g., 14, 15]. Gullies on mountains in Argyre basin, Mars For a comparative study on Mars we chose the Argyre region. Several isolated mountain massifs occur in the Nereidum and Charitum Montes (Fig. 3) with similar morphologies as the studied massif in Svalbard. A first data analysis with High Resolution Stereo Camera (HRSC) data revealed that gullies occur on the mountain slopes only at specific orientations. Fig. 4 shows an example of an isolated mountain, on which gullies only occur on west-facing slopes. Project Description The formation of gullies on Earth depends on several parameters, including rainfall and/or melting of snow, the presence of steep slopes, and sufficient amounts of fines/debris [e.g., 16]. As on Earth, the differences of slope angles and variabilities in bedrock and grain sizes influence the regional occurrence of gullies [17]. The main goals in both study regions on Earth and Mars are to classify different gully morphologies, map their distribution and orientations, gather information about bedrock, grain sizes and slopes and assess how all these parameters might influence the different gully morphologies, orientations, geological settings and their frequency. Airborne imagery from 1999 and a new, planned campaign in 2008 will be used to track the recent activity of debris flows in the last decade. In addition, a planned flight campaign with the High Resolution Stereo Camera (HRSC-AX) at the same time as the field trip might acquire high resolution image (10 cm/pxl) and topographic data (25 cm/pxl), if weather conditions are good. References [1] Malin, M.C. and Edgett K. S. (2000) Science, 288, 2330-2335. [2] Balme, M. et al. (2006) J. Geophys. Res. 111, E05001, doi:10.1029/2005JE002607. [3] Dickson, J.L. (2007) Icarus 188, 315-323. [4] Heldmann, J.L. and Mellon, M.T. (2004) Icarus, 168, 285-304. [5] Stewart, S.T. and Nimmo, F. (2002) J. Geophys. Res. 107, 5069, doi:10.1029/2000JE001465. [6] Costard, F. et al. (2002) Science 295, 110-113. [7] Christensen, P.R. (2003) Nature 422, 45-48. [8] Carlsson, E. et al. (2008) LPSC XXXIX, abstract 1852. [9] Carlsson, E. et al. (2008), this issue. [10] Dallmann et al. (2002) Norsk Polarinstitutt Temakart No. 33. [11] Rapp, A. (1957) Zeitschrift für Geomorphologie 1, 179-200. [12] Rapp, A. (1960) Norsk Polarinst. Skrifter 119, 1-96. [13] Larsson, S. (1982) Geografiska Annaler A64, 105-125. [14] Åkerman, J. (1984) Geografiska Annaler A66, 267-284. [15] Thiedig, F. and Kreling, A. (1973) Polarforschung 43, 40-49. [16] Costa, J.E. (1984) In: Developments and Applications of Geomorphology, Springer-Verlag, Berlin, 268-317. [17] Reiss et al. [2008] submitted to Planet. Space Sci.
Carlsson Erik
Fredriksson Sverker
Hauber Ernst
Heldmann Jennifer L.
Hiesinger Harald
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