Estimating Discharge from Ares Vallis Using Pathfinder Images and MOLA Topography

Eric B. Grosfils
Geology Department, Pomona College
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Students use Pathfinder lander images and MOLA topography, in combination with tools including a Hjulstrom diagram, ternary plot and a simple Manning equation, to estimate the discharge through Ares Vallis on Mars and compare their values with published estimates.

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Introductory Physical Geology course; possibly a Hydrogeology course

Skills and concepts that students must have mastered

The exercise follows a lab (using data from Earth), the relevant parts of which for this assignment have students: (a) learn about Hjulstrom diagrams and how water velocity is related to transport and deposit of detrital grains; (b) learn how to plot data on a ternary diagram. The students also have gained confidence about their quantitative problem-solving skills by this time in the semester and thus can expand into use of the Manning equation without direct instruction.

How the activity is situated in the course


Content/concepts goals for this activity

This exercise explores how images, topography, graphs and analytical equations can be combined to estimate discharge rates on Mars.

Higher order thinking skills goals for this activity

  • Analysis of images and topography
  • Ternary plots
  • Interpreting a complex graph
  • Quantitative reasoning and assessment of calculation results
  • Comparison with published data

Other skills goals for this activity

  • Locating supplemental data in journals and online
  • written presentation of a quantitative argument

Description of the activity/assignment

On July 4th, 1997, Mars Pathfinder landed at the mouth of Ares Vallis, a large channel that drains into the Chryse Planitia basin. While there remains a great deal to debate about the origin of the channels, one of the leading hypotheses at present is the idea that these features are the result of catastrophic flooding. If this is correct, then the plains where Pathfinder landed may be rich in debris eroded out of the Martian highlands across which the Ares Vallis channel passes, providing a golden combination—a relatively safe landing site which still provides access to a wide variety of different rock types. [If you would like to learn more about the many Pathfinder results, explore the April, 1999 and January, 2000 issues of the journal Journal of Geophysical Research—Planets (the green one) in the library.]

For the sake of this lab assignment you will hypothesize that the Ares Vallis and associated deposits were indeed produced by catastrophic flooding, and will use the information at your disposal to learn all you can about the putative flooding event.

Determining whether students have met the goals

A range of answers can be supported using the data provided. The assignment is graded paying more attention to internal self-consistency (within reason!) and logic than to the exact values obtained. Instructors, please feel free to contact me via email for my key to the assignment, or for the accompanying lab if desired.

More information about assessment tools and techniques.

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