Drainage basins and Channel incision on Mars Aharonson, Zuber, Rothman, Schorghofer, Whipple Robert...

Drainage basins and Channel incision on Mars

Aharonson, Zuber, Rothman, Schorghofer, Whipple

Robert I. Davies

San Francisco State University

Channels on Mars

Material squished out by impact

What are the evidences of Free water on Mars?

• Was there a climate on Mars that supported rainfall?

• How are channels formed?

• What is the hydrology of Mars?

Channel Incision Results from

• Surface Runoff• Groundwater sapping

– Erosion along the base of a cliff, and allowing the rocks above to fall in large blocks

– Erosion around a spring at the headwaters of a spring

– Undercutting along the headwall of a cirque, owing to frost action at the bottom of the bergschrund

Terrestrial Analog

• East & West arms of the Escalante River– East- Channel incision progressed via headward

erosion aided by seepage of groundwater at its base

– West - Tributaries evolved primarily by runoff

Comparison of Stream Profiles

Al-Qahria Vallis

Ma’adim Vallis

Browns Canyon

The geometry of the profile is characteristic of groundwater sapping, rather than overland flow.

S=A-tterresterial Marstheta = .07 theta = .02X value Km basin X value km basin

1 1 1 10.61557221 2 0.812252 20.46346306 3 0.719223 30.37892914 4 0.659754 40.32413132 5 0.617034 50.28529498 6 0.584191 60.25611285 7 0.55779 70.23325825 8 0.535887 8

0.214798 9 0.517282 90.19952623 10 0.501187 100.18664876 11 0.48706 110.17561966 12 0.47451 120.1660503 13 0.463252 13

0.15765595 14 0.453066 140.15022289 15 0.443785 150.14358729 16 0.435275 160.13762133 17 0.42743 170.13222368 18 0.420163 180.12731292 19 0.413403 19

CalculationsComparison of Streamgradients on Earth and Mars, given thatSA-

= .02 for Mars= .07 for Earth

0

5

10

15

20

0 0.5 1 1.5

Local slope

Area of basin in km 2

Concavity for terresterialFluvial Systems

Concavity for Mars

Graph comparing concavity of streams on Earth and Mars

Conclusions

• Slope-area relations show no evidence for fluvial sculpting

• Topographic measurements suggest that sapping is the primary method of channel incision

Question #6

What role does gravity play in all this?

Mars’ gravitational acceleration is only 3.745 m/s/s