Stream Channels. There is some overlap of Earth and Mars surface conditions Worst of Mars Worst of...
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Transcript of Stream Channels. There is some overlap of Earth and Mars surface conditions Worst of Mars Worst of...
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Stream Channels
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There is some overlap of
Earthand Mars surface
conditions
Worst of Mars
Worst of Earth
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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.
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BL Ehlmann et al. Nature 479, 53-60 (2011) doi:10.1038/nature10582
Timeline of major processes in Mars history.
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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
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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
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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
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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
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Martian Gullies
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Global Distribution of Valley Networks
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Amazonian (<3 Ga) Valley Networks
Implication: 90% of VNs formed in the 1st billion years of the planet’s history.
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How big?
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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
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Outflow Channels of Mars • Formed from catastrophic release of groundwater
in mid to late martian history.
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There are abundant channels on Mars
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Some really Some really convincing convincing evidence of evidence of surface flowsurface flow
NE Holden Crater Delta MOC NA images
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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?
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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
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blue = previously recognized valley networks by Carr [1995]
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Additional valley networks seen in MGS data
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Viking MDIM and Carr VN MGS data and newly recognized VN
Comparison of old and new data
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Previously mapped unconnected valleys (blue) are now recognized as an integrated drainage system (yellow).
Carr VN on Viking base Newly recognized VN from MGS
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Numerous VNs head near divides
Centered near1ºS, 22ºE
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How long andwhen was MarsHumid?
As it appears today
Arid early on...
Extended humidity
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Fossil dendritic drainage channels
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Outwash channel
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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
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older, degraded channel system
older, degraded channel system
differentdifferentflow pathsflow paths
medial ridge
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On the Titanian Coast...
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Valley networks!
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A channel on Titan...