Interior channels in Martian valley networks: Discharge and runoff production

Abstract

The highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on Mars Ͼ3.5 Ga. However, determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data. New orbital imaging reveals 21 late-stage channels within valley networks, which we use to estimate formative discharges and to evaluate water supply mechanisms. We find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief. For 15 narrow channels in basin-filling networks, likely episodic runoff production rates up to centimeters per day and first-order formative discharges of ϳ300-3000 m 3 /s are similar to terrestrial floods supplied by precipitation. Geothermal melting of ground ice would produce discharges ϳ100 times smaller per unit area and would require pulsed outbursts to form the channels. In four large valleys with few tributaries, wider channels may represent large subsurface outflows or paleolake overflows, as these four channels originate at breached basin divides and/or near source regions for the catastrophic outflow channels.

A lake in Uzboi Vallis and implications for Late Noachian–Early Hesperian climate on Mars

“…These observations point to a short-lived, abruptly ending, globally active hydrologic system in the Late Noachian (Fassett and Head, 2008;Howard et al, 2005;Irwin et al, 2005b;Moore and Howard, 2005;Wray et al, 2009), perhaps extending into the Hesperian, that may have been the last widespread period when water was available across broad areas of Mars (Bibring et al, 2006). Conditions during this period may have been relatively dry by terrestrial standards , with systems being transport-limited, but capable of producing runoff sourcing a wide range of alluvial and lacustrine systems.…”

“…1). The estimated discharge from Nirgal is on order of 4800 m 3 s À1 (Irwin et al, 2005b) and could have flooded Uzboi in as little as 20-30 years. The valley is graded approximately to the floor of Uzboi and emerges onto the floor $400 m below the high stand of the lake at À350 m, thereby suggesting incision of at least the lower reach occurred prior to formation of the lake.…”

Paleohydrology of Eberswalde crater, Mars

“…The discovery of paleochannels and inverted paleochannels allowed the first empirical constraints on channel-forming (dominant) discharge in past Martian rivers (Malin and Edgett, 2003;Moore et al, 2003;Fassett and Head, 2005;Irwin et al, 2005a;Jaumann et al, 2005). In alluvial channels on Earth, channel-forming discharge is approximately bankfull, controls certain channel dimensions, cumulatively transports more sediment than any other discharge, and has a recurrence interval of a year or two (e.g., Knighton, 1998).…”

The fluvial history of Mars

“…Where lakes were present, the lake levels may have fluctuated and so no delta formed. Despite their general absence, a few tens of deltas have been recognized [11,34]. Most are in local depressions such as craters but some that occur over a narrow elevation range along the dichotomy boundary have been interpreted as having formed where valleys debouch into a northern ocean [34].…”

“…Irwin et al [11] and Jaumann [12] have, however, identified a number of valleys with inner channels from which they were able to estimate stream discharges, which ranged from 300 to 5000 m 3 s −1 . The rates are comparable to terrestrial rates for similar drainage areas.…”