Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13e..02p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P13E-02
Other
[1815] Hydrology / Erosion, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes
Scientific paper
Mid-latitude valleys (MLVs) are important because they provide constraints on the Martian climate and hydrosphere during the middle of Mars' evolution. In order to assess the time and total sediment and water volumes involved in forming MLVs, we applied a numerical model of fluvial runoff and erosion under Martian gravity based on [1]. Based on the observed number (~10) and length (up to 75 km) of MLVs in Newton basin (40°S, 201°E), their braided or distributary channel morphology, and their valley width to meander wavelength ratios, a significant volume of liquid water must have been released near the basin rim during the late Hesperian to Early Amazonian (2 - 3 Gyr ago), and flowed into the interior - perhaps forming a lake [2]. Valleys incise into a background slope of 5° along the crater wall, and terminate in alluvial deposits at the basin floor, after which, a second set of valleys continue along the 1-2° slopes at the basin floor extending toward the basin center. We ran two simulations using a water-filled channel 1 m deep by 8 m wide, and another for a channel 10 cm deep and 3 m wide flowing over a surface which changes slope from 0.2° to 5° and again to 1° from the rim to the wall to the floor of an idealized crater. The simulations were run until the length of the alluvial fan reached 3 km - comparable to the observed fan extent. Our preliminary results indicate that roughly 4x107 m3 of sediment is contained within alluvial fans deposited by MLVs, and they would require 2 to 140 yrs to form under constant flow conditions for channel dimensions of 1 by 8 m and 0.1 by 3 m. These results are independent of sediment grain size as long as grains are finer than 1/50th the channel depth. Both of these simulations require 1 km3 of water giving a total volume of water of roughly 10 km3 for all of the drainage basins within Newton crater. About 400 km3 of water would be required to fill Newton basin to the elevation at which channels appear to terminate near the basin center, although degradation processes and coarse topographic data make determining the location of channel termination difficult. Assuming MLVs were carved by water sourced from a melting snow pack, then a 1 m thickness of ice would account for the water invoked by our model assuming a 1000 km2 area of each of the ~10 drainage catchments is covered with snow. However, more water would likely be required because we are neglecting losses due freezing, evaporation, and infiltration. For a 0.1 by 3 m channel, this snow pack would have to melt at 8 mm/yr to provide the necessary discharge rate, whereas a 65 cm/yr melting rate would be required to fill a 1 by 8m channel. Climate models suggest current melting rates of mid-latitude snow packs only reach 2 mm/yr [3], whereas rainfall rates of 2.5 m/yr lasting 2.7 yrs would follow an impact from 100 km diameter object [4]. [1] Parsons and Nimmo, 2010, J. of Geophys. Res., 115. [2] Howard and Moore 2011, J. of Geophys. Res.,116. [3] Williams et al, 2009, Icarus, 200, pp. 418-425. [4] Segura et al, 2008 J. of Geophys. Res., 113.
Howard Alan D.
Moore Jeffery M.
Parsons Robert
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