Outflow Channels

Although, the current Mars appears very dry, the Martian surface exhibits many features indicative for a formation by moving water, as either catastrophic floods or groundwater [Carr, 1979].

Mars exhibits giant outflow channels (Fig. 1). Outflow channels are supposed to be fluvially eroded landforms resulting from catastrophic release of water [Baker et al., 1992]. Many outflow channels emanate from chaotic terrain [Sharp, 1973], which is heavily collapsed terrain and assumed as their source region. Common features of outflow channels are eroded craters with teardrop-shaped tails, scour marks, and streamlined islands [Rodriguez et al., 2005]. They are found mainly on the younger surfaces of the northern lowlands. Outflow channels reflect a different Martian climate with respect to hydrological conditions during their formation in the Late Hesperian or Amazonian [Tanaka, 1986].

From Earth, outflow channels such as the Channeled Scablands of Washington are known (Fig. 1). These formed by breakout of water from the Pleistocene Lake Missoula comparable to Martian outflow channels. Since for Mars lake formation is rather unlikely due to current atmospheric conditions, groundwater-derived floods [Andrews-Hanna and Phillips, 2007; Andrews-Hanna et al., 2007] are considered as formation mechanisms for outflow channels.

 

Figure 1: (left) Satellite view of the Channeled Scablands/Washington, USA [www1]. (right) Kasei Vallis, the biggest outflow channel on Mars [www2]. It is 1.5 km deep and 100 km in diameter (image based on MGS/MOLA and MGS/MOC data).

Valley Networks

Channel systems of with filigree structure and a general tree-shaped or dendritic pattern of sinuous channels are called valley networks [Hartmann, 2003]. Earth, Mars and Saturn's moon Titan are the only planetary surfaces known to have widespread, branching, fluid-carved channels or valley networks. They are generally formed by the action of fluid flows. Whereas the channels on Earth (Fig. 1) and Mars (Fig. 2) were carved by flowing water [e.g. Pieri, 1980; Carr and Clow, 1981; Carr, 1996; Baker, 2001], Titan's valley networks (Fig. 3) are probably built by liquid hydrocarbons such as liquid ethane or liquid methane [e.g. Stofan et al., 2007; Brown et al., 2008; Lorenz et al., 2008].
The channels and valleys concerned here may not be mixed up with lava channels and collapes lava tupes which form relatively few sinuous valleys with few to no tributaries [Irwin et al., 2008].

Terrestrial valley networks have a wide range of morphologies and are represented by all fluvial channels carved by rivers and brooks. Thus they can be found almost globally distributed over Earth, especially in humid regions. Even hyperarid regions (i.e. deserts) exhibit drainage patterns of paleo rivers (sand covered) or sporadic flowing streams, so-called wadis (Fig. 1) [McCauley et al., 1982; Besler, 1992].

Figure 1: Fossil dendritic drainage pattern in the Republic of South Yemen, near the Rubh-al-Khali sand sea
Figure 1: Fossil dendritic drainage pattern in the Republic of South Yemen, near the Rubh-al-Khali sand sea

Martian valley networks are distributed mostly on the heavily crated highlands. Unlike the recent terrestrial channels the Martian valley networks are paleo-features because climatic conditions supporting flowing water are not present on Mars today. Water on Mars is currently stored as ice in the polar caps and ground ice in the crust. But the presence of the channels and the valley networks implies that the climate of Mars must have been warmer and wetter in the past [Pollack et al., 1987; Craddock and Howard, 2002].
Valley networks on Mars have widths of 10 km or less, and lengths of a few kilometres to nearly 1000 kilometres. They are characterized by theatre-like tributary heads, prominent structural control, low junction angles, quasi-parallel patterns, hanging tributary valleys, irregular widening and narrowing, and indistinct terminal areas [Komatsu, 2007]. The processes leading to the building of Martian valley networks are surface runoff [Malin and Edgett, 2000; Irwin et al., 2005] and groundwater sapping (or seepage erosion) [Lamb et al., 2006].

Figure 2: Drainage patterns on Mars, so called valley networks are less developed than typical terrestrial drainage systems.
Figure 2: Drainage patterns on Mars, so called valley networks are less developed than typical terrestrial drainage systems.
Figure 3: Valleys or channels (dark quasi-liner or sinuous features) discovered on Titan by the Huygens probe. Descent Imager/Spectral Radiometer (DISR) image mosaic. [image and caption by [Komatsu, 2007]; image credit: ESA/NASA/University of Arizona].
Figure 3: Valleys or channels (dark quasi-liner or sinuous features) discovered on Titan by the Huygens probe. Descent Imager/Spectral Radiometer (DISR) image mosaic. [image and caption by [Komatsu, 2007]; image credit: ESA/NASA/University of Arizona].

References

Outflow Channels:

  • Andrews-Hanna, J.C. and R.J. Phillips (2007): Hydrological modeling of outflow channels and chaos regions on Mars, JGR (Planets) 112, p. 08001.
  • Andrews-Hanna, J.C., R.J. Phillips, and M.T. Zuber (2007): Meridiani Planum and the global hydrology of Mars, Nature 446, pp. 163-166.
  • Baker, V.R., M.H. Carr, V.C. Gulick, C.R. Williams, and M.S. Marley (1992): Channels and valley networks, Mars, pp. 493-522.
  • Carr, M.H. (1979): Formation of Martian flood features by release of water from confined aquifers, JGR 84, pp. 2995-3007.
  • Rodriguez, J.A.P., S. Sasaki, R.O. Kuzmin, J.M. Dohm, K.L. Tanaka, H. Miyamoto, K. Kurita, G. Komatsu, A.G. Fairén, and J.C. Ferris (2005): Outflow channel sources, reactivation, and chaos formation, Xanthe Terra, Mars, Icarus 175, pp. 36-57.
  • Sharp, R.P. (1973): Mars: fretted and chaotic terrains, JGR 78, pp. 4073-4083.
  • Tanaka, K.L. (1986): The stratigraphy of Mars, JGR 91, p. 139.

Valley Networks:

  • Baker, V.R. (2001): Water and the Martian landscape, Nature, 412, 228-236.
  • Besler, H. (1992): Geomorphologie der ariden Gebiete, Wissenschfl. Buchgesellschft. , Darmstadt.
  • Brown, R. H., L. A. Soderblom, J. M. Soderblom, R. N. Clark, R. Jaumann, J. W. Barnes, C. Sotin, B. Buratti, K. H. Baines, and P. D. Nicholson (2008): The identification of liquid ethane in Titan's Ontario Lacus, Nature, 454, 607-610.
  • Carr, M. H. and G. D. Clow (1981): Martian channels and valleys - Their characteristics, distribution, and age, Icarus, 48, 91-117.
  • Craddock, R.A. and A.D. Howard (2002): The case for rainfall on a warm, wet early Mars, Journal of Geophysical Research (Planets), 107, 5111, doi:10.1029/2001JE001505.
  • Irwin, R. P., III , A.D. Howard, and R.A. Craddock (2008): Fluvial valley networks on Mars, in River Confluences, Tributaries and the Fluvial Network, edited by S. P. Rice, et al., JohnWiley & Sons, Ltd, Chichester, New York.
  • Irwin, R.P., A.D. Howard, R.A. Craddock, and J.M. Moore (2005): An intense terminal epoch of widespread fluvial activity on early Mars: 2. Increased runoff and paleolake development, Journal of Geophysical Research (Planets), 110.
  • Komatsu, G. (2007): Rivers in the Solar System: Water Is Not the Only Fluid Flow on Planetary Bodies, Geography Compass, 1 (3), 480–502, doi: 10.1111/j.1749-8198.2007.00029.x.
  • Lamb, M.P., A.D. Howard, J. Johnson, K.X. Whipple, W.E. Dietrich, and J. T. Perron (2006): Can springs cut canyons into rock?, Journal of Geophysical Research (Planets), 111, 07002.
  • Lorenz, R.D., R.M. Lopes, F. Paganelli, J.I. Lunine, R.L. Kirk, K.L. Mitchell, L.A. Soderblom, E.R. Stofan, G.G. Ori, M. Myers, H. Miyamoto, J. Radebaugh, B. Stiles, S.D. Wall, C. A. Wood, and the Cassini Radar Team (2008): Fluvial channels on Titan: Initial Cassini RADAR observations, Planetary and Space Science, 56, 1132-1144.
  • Malin, M.C. and K.S. Edgett (2000): Evidence for recent groundwater seepage and surface runoff on Mars, Science, 288, 2330–2335.
  • McCauley, J. F., G. G. Schaber, C. S. Breed, M. J. Grolier, C. V. Haynes, B. Issawi, C. Elachi, and R. Blom (1982): Subsurface Valleys and Geoarcheology of the Eastern Sahara Revealed by Shuttle Radar, Science, 218, 1004-1020.
  • Pieri, D.C. (1980): Martian valleys - Morphology, distribution, age, and origin, Science, 210, 895-897.
  • Pollack, J.B., J.F. Kasting, S.M. Richardson, and K. Poliakov (1987): The case for a wet, warm climate on early Mars, Icarus, 71, 203-224.
  • Stofan, E. R., C. Elachi, J. I. Lunine, R. D. Lorenz, B. Stiles, K. L. Mitchell, S. Ostro, L. Soderblom, C. Wood, H. Zebker, S. Wall, M. Janssen, R. Kirk, R. Lopes, F. Paganelli, J. Radebaugh, L. Wye, Y. Anderson, M. Allison, R. Boehmer, P. Callahan, P. Encrenaz, E. Flamini, G. Francescetti, Y. Gim, G. Hamilton, S. Hensley, W. T. K. Johnson, K. Kelleher, D. Muhleman, P. Paillou, G. Picardi, F. Posa, L. Roth, R. Seu, S. Shaffer, S. Vetrella, and R. West (2007): The lakes of Titan, Nature, 445, 61-64.

Links

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Last update: 07/06/2010 14:22