Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p13a0987h&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P13A-0987
Mathematics
Logic
6225 Mars, 1832 Groundwater Transport
Scientific paper
The large Martian outflow channels terminating in Chryse Planitia are remnants of Hesperian flooding events involving the localized discharge of millions of cubic kilometers of subsurface water. Given reasonable crustal porosities, such volumes cannot be stored in the regional aquifer and recharge is required. Initial results of dynamic groundwater models [1] demonstrated that snowpack or glaciers on the Tharsis rise, formed during periods of high obliquity when ice was stable at low latitudes, may have provided an efficient source of recharge and hydraulic head for the circum-Chryse outflow channels. Comparison of model results with Martian South Pole recharge simulations (based on the hypotheses of Clifford and Parker [2]) show that Tharsis recharge produces up to four times more discharge through the circum-Chryse outflow channels in a given time period. The Medusae Fossae formation may support the past existence of large low-latitude ice sheets as early as the Hesperian [3]. Ground ice may have been involved in the formation of rootless cones, the Olympus Mons aureoles, and glacial features on volcanic edifices. The U.S. Geological Survey MODFLOW-2000 groundwater code, which we have modified to simulate spherical geometry, is used to explore further two key aspects of Tharsis recharge: infiltration area and initial water table. In previous models we assumed an infiltration area equal to that estimated by other authors for recharge over the Martian South Pole. We present new models with the infiltration area extended to regions of Tharsis above a range of threshold elevations. Early Hesperian Tharsis recharge also depends on initial water table elevations determined by hydrologic conditions in the late Noachian. In previous models, we assumed that Noachian precipitation rates maintained a shallow water table that could be approximated by the Martian topography. The transition from unconfined to confined conditions in the late Noachian may, however, have resulted in some relaxation of the water table before Tharsis recharge commenced. We thus present models with alternative initial water tables representing varying degrees of relaxation, including the extreme case of constant elevation. [1] Harrison and Grimm, GRL, 31, DOI:10.1029/2004GL020502, 2004. [2] Clifford and Parker, Icarus, 154, 40-79, 2001. [3] Head and Kreslavsky, 35th LPSC, 1635, 2004.
Grimm Robert E.
Harrison Keith P.
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