Stream Channels. There is some overlap of Earth and Mars surface conditions Worst of Mars Worst of...

Stream Channels

There is some overlap of

Earthand Mars surface

conditions

Worst of Mars

Worst of Earth

BL Ehlmann et al. Nature 479, 53-60 (2011) doi:10.1038/nature10582

Evolution of aqueous environments during the first billion years of Mars history.

BL Ehlmann et al. Nature 479, 53-60 (2011) doi:10.1038/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 ameandering streamsystem

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 1st 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 Some really convincing convincing evidence of evidence of surface flowsurface 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?

1 1

1

11

1

12 22

23

3

* Higher stream order corresponds to more mature drainage systems and

more contribution from surface runoff

dow

nsl

op

eStrahler [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 near1ºS, 22ºE

How long andwhen was MarsHumid?

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 someflowing water on Mars, at least early on in its history

older, degraded channel system

older, degraded channel system

differentdifferentflow pathsflow paths

medial ridge

On the Titanian Coast...

Valley networks!

A channel on Titan...