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Fluvial valley networks are a key record of the geomorphic effects of past liquid water on the surface of Mars. Most valley networks formed early in Mars history (>3.5 Ga) during a period of increased surface water availability, and these landforms may preserve information on the nature and spatial heterogeneity of the ancient martian hydroclimate. Here we present work to constrain patterns of valley network geometry (length, depth, and volume), and assess how these factors are related to topography and landscape position. We find that valley depth is most strongly controlled by regional slope and landscape relief, with deeper valleys on steeper/higher relief terrains, likely driven by a slope control on the rate of fluvial erosion. In contrast, total valley length and volume are most controlled by slope orientation, with larger values on north-draining slopes, which we suggest is related to more efficient fluvial integration (i.e., inter-connection of valleys) on such slopes. At lower elevations and towards terminal basins (northern plains and Hellas), valley depth increases, while total valley length and volume decrease, consistent with the geometry expected as a branching valley system converges downstream into fewer, larger valleys. Finally, we show that patterns of total valley length and eroded volume peak about a previously proposed paleo-latitude band on a pre-Tharsis-driven true polar wander Mars. Valley depth increases from paleo-south to paleo-north in this pre-true polar wander framework, consistent with valley network development in a paleo-north direction. This is potentially consistent with syn/pre-Tharsis growth and true polar wander valley network incision; however, this signal is not unique and may be amplified by patterns of post-valley network incision resurfacing. • We analyze spatial patterns of Mars fluvial valley geometry (length, depth, volume). • Depth increases with steeper slopes, likely due to increased fluvial incision rate. • Total valley length/volume larger on northward slopes due to landscape integration. • All aspects of valley geometry show signatures of downstream network growth. • Observed pattern potentially consistent with syn/pre-Tharsis growth valley incision. [ABSTRACT FROM AUTHOR]

• Overlapping crater populations constrain the total era of martian valley formation. • Martian valleys may have formed intermittently over hundreds of millions of years. • Long-term erosion rates would have been similar to the modern Atacama Desert. A number of studies have constrained the cessation of martian valley network activity to around the Noachian-Hesperian boundary, but the total time period over which these features formed remains poorly constrained. Most attempts to ascertain valley network formative timescales rely on an intermittency factor that varies widely for terrestrial rivers and is unknown for Mars. In this contribution, superposition relationships are used to identify crater populations that pre- and postdate valley network incision, resulting in maximum cumulative valley formation times of ∼108 years. These timescales correspond with long-term erosion rates of ∼0.25 m/Myr, similar to those calculated for the Middle to Late Noachian as well as the central Atacama Desert since the Late Miocene. Assuming sediment transport rates previously calculated for other martian valley networks, this implies a minimum fluvial intermittency of ∼10−5, several orders of magnitude lower than modern day Earth rivers but similar to values independently calculated for some martian fluvial deposits. This low intermittency suggests that martian valley incision may have been significantly hindered by erosion into existing bedrock or by boulder armoring of the valley floor. Alternatively, unlike river valleys on Earth, runoff events driving martian valley network activity may have been non-seasonal, Milankovitch-like cycles, with long eras of quiescence between periods of intensified fluvial activity. [ABSTRACT FROM AUTHOR]

The interiors and exteriors of the >25 km diameter Batson, Nako, Salkhad, and Jori craters (and McCauley crater to a lesser degree) on the northeastern rim of Hellas basin, Mars, were extensively modified by glacio-fluvial and glacio-lacustrine activity during the Middle and Late Amazonian, from some time before 1.4 Ga to the present as revealed by CTX, HiRISE, and CaSSIS observations. This work presents extensive descriptions and discussions of individual candidate glacial and glaciofluvial landforms associated with cratered landscapes, as well as their spatial association. We also present absolute age dates and a relative sequence of events, followed by a possible environmental reconstruction, involving a regional ice cover, subglacial meltwater, and ice-covered lakes. On crater interiors, inferred glacial modification included dissection of interior rims, emplacement of depositional aprons with basinward scarps, remnant glaciers and associated fresh shallow valleys, supraglacial debris, and candidate moraines. On crater exterior rims and on the plateaus surrounding Batson crater we describe moderate incision and sedimentation, subglacial meltwater runoff through Navua A Valles, candidate eskers, valleys discordant with topography but concordant with inferred ice flow direction, and hummocky material, among others. Wet-based glaciation and subglacial runoff may have been favored due to a locally enhanced geothermal heating or strain heating on steep crater slopes. This work presents a comprehensive and detailed characterization of landforms interpreted as glacial in origin, which could be used to guide identifications of glacial landforms in other cratered regions of Mars. • Warm-based glacial erosion on Mars is mostly expressed through subglacial landforms. • Ice-covered and subglacial hydrology and water environments on Amazonian Mars. • Guidelines for the identification of glacial and subglacial landforms on Mars. • Role of glaciation in the modification, degradation and erosion of craters. • 1 Gya Amazonian warm based glaciation of Batson crater, north eastern Hellas. [ABSTRACT FROM AUTHOR]