Stream Channels

There is some overlap of Earth and Mars surface conditions Worst of Mars Worst of Earth

BL Ehlmann et al. Nature 479, (2011) doi: /nature10582 Evolution of aqueous environments during the first billion years of Mars history.

BL Ehlmann et al. Nature 479, (2011) doi: /nature10582 Timeline of major processes in Mars history.

Stream Properties Stream Gradient – ground slope – Generally steeper at the HEAD – Very shallow at the MOUTH – Variable along the central length Affects water velocity and volume BASE LEVEL – lowest level of erosion DISCHARGE – volume x width x area Affects SEDIMENT LOAD – Amount of material being moved

Flowing Water Following rain events (melting events) – Overland flow / sheetwash – Streamflow – channels begin to form Streams – general passage for water flow – Rill, creek, stream, river – size-based – Channel – passage-way of water flow – Banks – side walls of channel

Rills, Gullies and Streams Sheetwash causes erosion Channels form and grow headward

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Water Drainage Ultimately, all water returns to the oceans Drainage systems –Basins – areas collecting water into one main channel –Drainage basins – geographic zones –Divides – high elevations separating basins –Continental divides – largest basins directing water to the oceans

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Evolution of a meandering stream system

Evidence for Past Water The current thin, cold atmosphere prohibits liquid water from being stable on the surface. However, there is ample evidence for past water 3 flavors of flowing surface water: 1) Valley Networks (really old) 2) Outflow Channels (pretty old) 3) Gullies (really young) 10 km 500 km Viking Orbiter image MOLA topography

Martian Gullies

Global Distribution of Valley Networks

Amazonian (<3 Ga) Valley Networks Implication: 90% of VNs formed in the 1 st billion years of the planet’s history.

How big?

Main evidence for a “warm and wet” ancient Mars Valley networks –clear evidence of erosion by water –there has been a long standing debate over the importance of surface runoff vs. groundwater processes –more recent works show that precipitation was required to form many of the features Widespread highland erosion (up to a km of crust lost) Recently identified chemically weathered components of the crust (TES and OMEGA instruments) –hematite deposits in limited locales –sulfate deposits seen in many settings on Mars –clays (phyllosilicates) also detected Mars Exploration Rovers show clear signs of groundwater interaction and possible signs of standing bodies of water

Outflow Channels of Mars Formed from catastrophic release of groundwater in mid to late martian history.

There are abundant channels on Mars

Some really convincing evidence of surface flow NE Holden Crater Delta MOC NA images

Ref: Owen and Bar-Nun, in R. M. Canup and K. Righter, eds., Origin of the Earth and Moon (2000), p. 463 Deuterium/hydrogen ratios show that Mars (and Venus) lost most all of their water to space. For Mars, the remaining water is tied up in the subsurface and polar caps Venus Where did all the water go?

* Higher stream order corresponds to more mature drainage systems and more contribution from surface runoff downslope Strahler [1958] stream order classification

blue = previously recognized valley networks by Carr [1995]

Additional valley networks seen in MGS data

Viking MDIM and Carr VN MGS data and newly recognized VN Comparison of old and new data

Previously mapped unconnected valleys (blue) are now recognized as an integrated drainage system (yellow). Carr VN on Viking base Newly recognized VN from MGS

Numerous VNs head near divides Centered near 1ºS, 22ºE

How long and when was Mars Humid? As it appears today Arid early on... Extended humidity

Fossil dendritic drainage channels

Outwash channel

Water flowing creates cross-bedded structures with sediment load Gusev Crater It is likely that there was some flowing water on Mars, at least early on in its history

older, degraded channel system different flow paths medial ridge

On the Titanian Coast...

Valley networks!

A channel on Titan...