Hydrology of early Mars: Valley network incision

Abstract

[1] Widespread occurrences of valley networks on Mars provide geomorphic evidence for an active hydrologic cycle. To constrain the climatic conditions capable of forming the valley networks, a hydrological model was used to analyze the valley incision depth and volume of eroded valleys. Because the absolute magnitudes of precipitation, runoff, and evaporation are uncertain, we have used the ratio of these quantities (the X-ratio) to express climatic conditions. The spatial distribution and strength of the correlations between (1) the estimated depth and volume of eroded material and (2) estimated flood magnitude and valley gradients were investigated as a function of the assumed X-ratio. We also conducted an analysis of conditions required to have appreciable discharge in selected valley networks, which provided the most definitive constraint on Martian paleoclimate. The other methods show a relatively weak dependency of incision depths and volumes upon the assumed X-ratio. The multiple regression analyses indicate that incision depth is strongly influenced by gradient and weakly related to modeled flood discharge. The factors determining relative depth of incision depend partly on the type of channel bed. However, postflow modification of the valley networks by mass wasting, cratering, aeolian infilling, and ice-related processes precludes direct determination of bed morphology. Our hydrological analyses suggest that climatic conditions on early Mars were at least as moist as those that occurred in the Great Basin region of the U.S. when large lakes were present during the Pleistocene in terms of the balance of runoff and lake evaporation.

Paleohydrology of Eberswalde crater, Mars

“…Valley networks hundreds of kilometers long, valley heads near topographic divides, locally dense dissection, overflowed basins, and a need for aquifer recharge to erode the measured volumes of valleys indicate an active hydrological cycle at times in the past (e.g., Grant, 2000;Craddock and Howard, 2002;Fassett and Head, 2008b;Irwin et al, 2008;Matsubara et al, 2011Matsubara et al, , 2013. Degradation of impact craters throughout the Noachian Period and into the Hesperian Period required a more effective geomorphic regime than is found currently on Mars (Craddock and Maxwell, 1993;Grant and Schultz, 1993a;Craddock et al, 1997;Forsberg-Taylor et al, 2004;Golombek et al, 2006).…”

Fluvial Landforms and the Post-Noachian Environment on Mars

“…To constrain the hydrologic regime associated with the formation of FSVs in our study area, we utilized the hydrologic routing model after Matsubara et al [2011Matsubara et al [ , 2013 water. Due to uncertainties associated with the absolute magnitudes of precipitation, runoff and evaporation, these variables are replaced by the "X-ratio," which serves as a proxy for climatic conditions [Matsubara et al, 2011[Matsubara et al, , 2013.…”

“…Due to uncertainties associated with the absolute magnitudes of precipitation, runoff and evaporation, these variables are replaced by the "X-ratio," which serves as a proxy for climatic conditions [Matsubara et al, 2011[Matsubara et al, , 2013. The X ratio is defined as:…”

“…As the X-ratio increases, the corresponding climate becomes more arid, fewer basins overflow and drainage networks become more fragmented. As explained in Matsubara et al [2013], the value of the X-ratio does not correspond to any one combination of precipitation, runoff and evaporation, such that that several combinations of values for these variables could result in the same X-ratio. Matsubara et al, 2013].…”

“…As explained in Matsubara et al [2013], the value of the X-ratio does not correspond to any one combination of precipitation, runoff and evaporation, such that that several combinations of values for these variables could result in the same X-ratio. Matsubara et al, 2013]. Several simulations were run using a range of X ratio values from -1 (runoffdominated) to 6 (evaporation-dominated with little runoff) to constrain how wet the environment had to be to match the location and morphology of FSVs preserved in the landscape, including overflow of inferred lakes embedded in long FSV systems.…”