Definition
A circular topographic depression that appears in a high-resolution topographic dataset but may not have a corresponding visual structure on the surface.
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Description
In the broad sense, all kinds of at least somewhat circular depressions in the gridded topographic dataset of Mars Orbiter Laser Altimeters or Lunar Orbiter Laser Altimeter are quasi-circular depressions (QCDs), visible or not. In a more strict sense, QCDs (or stealth/invisible QCDs) are only those evident depressions which have no structural representation in optical imagery, i.e., cannot be detected via photogeologic methods (Buczkowski 2007b) (Fig. 1). However, some stealth QCDs (sQCDs) are manifested as circular fractures (Ghent et al. 2012).
Quasicircular depressions near 50°N, 324°E (a) visible in MOLA data (arrows) and (b) invisible in Viking imagery (Buczkowsky 2007). Scale bar 20 km (NASA/JPL/MSSS)
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References
Buczkowski DL (2007) Comparing Quasi-Circular Depression (QCD) locations to Northern Lowland materials on Mars. Seventh International Conference on Mars # 3302
Buczkowski DL, McGill GE (2002) Topography within circular grabens: implications for polygon origin, Utopia Planitia, Mars. Geophys Res Lett 29(7):1155. doi:10.1029/2001GL014100
Buczkowsky DL (2007) Stealth quasi-circular depressions (sQCDs) in the northern lowlands of Mars. J Geophys Res 112:E09002. doi:10.1029/2006JE002836
Frey H (2008) Ages of very large impact basins on Mars: implications for the late heavy bombardment in the inner solar system. Geophys Res Lett 35:l13203. doi:10.1029/2008gl033515
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Frey HV (2011b) New candidate large lunar basins from Lola data. LPSC 42, #1190
Frey H, Sakimoto SEH, Roark JH (1999) Discovery of a 450 km diameter, multi-ring basin on Mars through analysis of MOLA topographic data. Geophys Res Lett 26(12):1657–1660
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Frey HV, Shockey KM, Frey EL, Roark JH, Sakimoto SEH (2001) A very large population of likely buried impact basins in the northern lowlands of Mars revealed by MOLA data. LPSC XXXII #1680
Frey HV, Roark JH, Shockey KM, Frey EL, Sakimoto SEH (2002) Ancient lowlands on Mars. Geophys Res Lett 29(10):1384. doi:10.1029/2001GL013832
Ghent RR, Anderson SW, Pithwala TM (2012) The formation of small cones in Isidis Planitia, Mars through mobilization of pyroclastic surge deposits. Icarus 217:169–183
Morrison SJ, Frey HV (2007) Crater densities in Noachis Terra: evidence for overlapping ejecta from Argyre and Hellas. LPSC XXXVIII #1355
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Edgar, L. (2014). Quasi-Circular Depression. In: Encyclopedia of Planetary Landforms. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-9213-9_288-1
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DOI: https://doi.org/10.1007/978-1-4614-9213-9_288-1
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