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Lecture 10

GEO 330 Lecture Notes - Lecture 10: Aquifer, Valles Marineris, Gravity Current

Course Code
GEO 330
Timothy Glotch

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"Valley" describes any linear depression. They could be formed by water erosion, glaciation,
faulting, mass wasting, volcanism, or a combination of these processes.
"Channel" is a more restrictive term. It refers to the conduit within which a stream is confined
Most start full size and have no tributaries
Thought to have formed by huge "catastrophic" floods
10s to 100s of km across and most contain streamlined remnants of pre-existing
Outflow Channels
Can be 100s or 1000s of km in length
Thought to have formed by slow erosion of running water
Narrower than outflow channels, with individual valleys usually being 1-5km across
Valley Networks
Only found on steep slopes, and are 10s of meters wide and 100s of meters long
Origin is somewhat controversial, but water likely played some role in their
Smaller than both valley networks and outflow channels
On Mars, three types of linear, incised, and likely water-eroded features are distinguished:
Channels, Valleys, and Gullies
Teardrop shaped islands are common in most outflow channels
Shapes indicate direction of flow
Craters at the end of islands indicate that water flowed around pre-existing obstacles
Teardrop islands and scour features in Ares Vallis
Channels vary greatly in size and can be less than 1km across
Largest outflow channel, Kasei Vallis is 400km across at its mouth and 2.5km deep
Other ideas included CO2supported debris flows, lava, wind, glaciers, and slow fluvial
erosion over time
Most researchers agree that outflow channels were caused by large floods
Low sinuosity, and high width-depth ratios
Walls are streamlined and contain teardrop-shaped islands
Wide range of fluvial bedforms
Channels appear similar to those caused by large floods on Earth
Outflow Channels
Large channels imply huge volumes of water. How was so much water stored in the subsurface
and why was it released suddenly to form the channels?
If the channels formed by floods, then large bodies of water would have formed at the ends of the
channels. Where is that water (or ice) today?
What do the floods tell us about the climate at the time they formed? Did these events affect the
Outflow Channel Questions
Convergence of several channels results in 800km across region of scoured ground and
teardrop islands in southern Chryse Planitia
Largest region of outflow channels on the planet
Circum-Chyrse Outflow Channels
Water, Channels, Valleys, and Chaos Terrain
Thursday, March 1, 2018
1:07 PM
GEO 330 Page 1
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