Carving Mars: Rivers
In-Class Activity 1
Julia Kahmann-Robinson PhD, University of Utah Department of Geology & Geophysics
Observe the formation of fluvial channels, the effects associated with varying water velocity and changing base/level gradient, and the evidence for fluvial/alluvial environments on Mars.
- Acquire red/blue glasses to view HIRISE red-blue anaglyph images: http://www.rainbowsymphonystor e.com/maopandsproc.html
- Expose students to fluvial styles and fluvial processes (meandering vs. braided channels, base level fluctuation, changing stream gradient etc.) on Earth and how they are formed prior to conducting this In-Class Activity.
- Stream Table by Davidson Geology: meandering river- http://www.youtube.com/watch?v=YsQ7hW2fAEs&feature=related
- Eberswalde Delta-HIRISE: (context) http://hirise.lpl.arizona.edu/PSP_001534_1560 Image: http://hirise.lpl.arizona.edu/images/2007/details/cut/Eberswalde-delta-3x.jpg
- MOLA global map: http://www.google.com/mars/
- Meander Scar Image Source: ftp://eol.jsc.nasa.gov/EFS_highres_ISS022_ISS022-E-19513.JPG
- Water flows on Mars (choose the video under "Possible Water Flows on Mars"): http://mars.jpl.nasa.gov/mro/multimedia/videoarchive/
Watch the following You Tube Colorado River video: http://www.youtube.com/user/oarsweb?v=QYoBC0qIn_8
- Have students think about the following before showing the video:
- Relate student ideas to stream gradient, flow, channel formation [too fast to form meandering channels] etc.
- Where is the river fast? [Direct students to look to the middle or periphery of river.]
- Why did the large sandbar form (where the rafters camp)? [As the river cut, the slow section of the river deposited the sand bar.]
- Why do rapids form? [changes in river gradient, width of channel, drop in volume exposing more obstacles to flow]
- Why does the river form bends? [low gradient, slower stream velocity]
Davidson Geology stream table experiment:
Ask students to observe the experiment and sketch and label the timestamp associated with the following fluvial events [Multiple timestamps are possible; students can come up to the board to sketch, or you may move about the room to observe their sketches and correct when necessary]:
- Formation of a cut bank
- Formation of a point bar
- Stream avulsion
- Formation of multiple channels (at least more than 1)
- Cut bank [this is where the stream erodes and the current is most swift]
- Point Bar [where the stream is slow and allows bed load, finer grain sizes, to be deposited]
- Stream Avulsion [higher sediment input, increased flow, meander grows]
- Multiple channels [increased flow, higher gradient]
Exploring a HIRSE anaglyph image
Using red-blue glasses (blue filter over right eye), of the Eberswalde region of Mars have students think about the following questions: http://hirise.lpl.arizona.edu/images/2007/details/cut/Eberswalde-delta-3x.jpg
- Are any of the stream table sketches similar to what students are observing on Mars? Which one, if any?
- Explain the circumstances in which this surface geomorphology on Mars might have formed. [Surface water must be available either through precipitation, groundwater, or ice melt; the majority of which occurred early in Mars geologic history, the Noachian.]
Discussion of Terms (as needed)
- Cut bank [The concave bank of a winding stream that is maintained as a steep or even overhanging cliff].
- Point Bar [A low, curved ridge of sand and gravel along the inner bank of a meandering stream. Point bars form through the slow accumulation of sediment deposited by the stream when its velocity drops along the inner bank]
- Meandering vs. braided [Braided systems are characterized by lower sinuosity, the presence of many channels and small islands/bars, as well as a more coarse sediment load. Typically they occur in areas of high relief and have a very limited areal extent. Meandering systems have much greater sinuosity, single channel, lower gradients, and a finer sediment load (Boggs, 2001).]
Stream Styles on Earth
Identify areas on Earth where multi-stacked channel styles would be prevalent, do the same for single change styles. In doing so, discuss the following concepts
- Channel gradient
- Sediment input
Make a Mars global map available for students to view digitally or hardcopy: http://www.google.com/mars/
- Consider the landscape of Mars. In what regions, could water have flowed as braided channels? [Any steep gradient: crater walls, canyon mouth, flanks of “mountains”/volcanoes; from the southern highlands to the northern lowlands]
- Would meandering or braided fluvial styles be more common on Mars? How does this differ from Earth, or does it? [Variable answers, Earth has more variability in mountain ranges, but Mars has many sizeable craters both of which can be the sources for braided styles]
Have students use a Mars image or image they sketched from the stream table demonstration and ask:
- Where would it be safe to build a house?
- Where is deposition occurring? What about erosion?
- When students see the following scars:
Observe Figure 2: Rio Negro, Colonel Josefa Area, Flood plain
- Can you students discern which meanders are older and which are younger?
- Did students observe similar geomorphology on Mars?