A distinct class of avalanche scars on Mars

We report observations of a set of surface features on Mars that form a distinct class of avalanche scars. These features have a horizontal scale of hundreds of meters, but a depth scale of meters distinguishes them from the shallower features known as slope streaks. The meters-thick avalanche scars have escaped previous attention because of weak contrast between the interiors of the scarred regions and their surroundings. Often the most visible feature is a shadow cast by the trough wall, a band 1–3 pixels wide in Mars Orbiter Camera narrow angle images, indicating maximum depths of 4–10 m. We investigate the morphology of more than 500 such features. Slopes upon which the avalanches occur average about 27°. Impact craters are seen at the heads of some avalanche scars; this subset exhibits statistically wider opening angles. The scars span an estimated several Ma in age. Those found so far occurred mainly in the Olympus Mons lower aureole. We compare shapes of slope streaks to shapes of meters-thick avalanches, and the results support the notion that the two classes are distinct. The newly-discovered avalanches resemble some terrestrial flows of loose, dry material such as dry snow and glass beads. On the basis of these analogs, we suggest a physical model.

[1]  Kenneth S. Edgett,et al.  New views of Mars eolian activity, materials, and surface properties : Three vignettes from the Mars Global Surveyor Mars Orbiter Camera , 2000 .

[2]  Ronald Greeley,et al.  Geologic map of the eastern equatorial region of Mars , 1987 .

[3]  D. Mcclung,et al.  The Avalanche Handbook , 1993 .

[4]  Kenneth S. Edgett,et al.  Mass movement slope streaks imaged by the Mars Orbiter Camera , 2001 .

[5]  G. Heiken,et al.  Volcanoes: Crucibles of Change , 1997 .

[6]  P. Christensen.  Regional dust deposits on Mars - Physical properties, age, and history , 1986 .

[7]  Richard W. Zurek,et al.  The martian dust cycle. , 1992 .

[8]  L. Fenton.  Aeolian processes on Mars: atmospheric modeling and GIS analysis , 2003 .

[9]  M E Davies,et al.  Early views of the martian surface from the Mars Orbiter Camera of Mars Global Surveyor. , 1998, Science.

[10]  Norbert Schorghofer,et al.  Slope streaks on Mars: Correlations with surface properties and the potential role of water , 2002 .

[11]  D. H. Scott,et al.  GEOLOGIC MAP OF THE WESTERN EQUATORIAL REGION OF MARS , 1986 .

[12]  W. Hartmann.  Martian cratering VI: Crater count isochrons and evidence for recent volcanism from Mars Global Surveyor , 1999 .

[13]  Stéphane Douady,et al.  Two types of avalanche behaviour in granular media , 1999, Nature.

[14]  W. Dietrich,et al.  Ice‐driven creep on Martian debris slopes , 2003 .

[15]  R. Jaumann,et al.  Recent debris flows on Mars: Seasonal observations of the Russell Crater dune field , 2003 .

[16]  M. Malin,et al.  Evidence for recent groundwater seepage and surface runoff on Mars. , 2000, Science.

[17]  M. Malin,et al.  Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission , 2001 .

[18]  Norbert Schorghofer,et al.  Slope streak formation and dust deposition rates on Mars , 2003 .

[19]  V. Jomelli,et al.  Comparing the characteristics of rockfall talus and snow avalanche landforms in an Alpine environment using a new methodological approach: Massif des Ecrins, French Alps , 2000 .

[20]  A. McEwen.  Secondary Cratering on Mars: Implications for Age Dating and Surface Properties , 2003 .