Relative Age of Landforms and Sequencing of Processes
This lab has the following objectives:
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to introduce you to Mars Odyssey THEMIS-derived imagery
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to give you practice in inferring relative ages of Martian surfaces through
crater counting and assessment of crater condition
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to give you practice in applying superposition to infer the relative sequence
of processes creating Martian landforms
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to alert you to imagery flaws that could be misinterpreted as surface features
Background
The NASA Mars Odyssey orbiter (2001+) carries the Thermal Emission Imaging
System, or THEMIS. This is a multispectral imager that offers five visible
light bands (with 19 m pixels) and ten infrared bands (with 100 m pixels). In
the IR, THEMIS picks up the emitted re-radiation of solar energy absorbed
during the day. It creates images that resemble a lit landscape but it must
be remembered that the bright areas are not reflecting sunlight but strongly
emitting IR radiation based on absorption of sunlight).
For more information about THEMIS:
Christensen, P.R., N.S. Gorelick, G.L. Mehall, and K.C. Murray, THEMIS
Public Data Releases, Planetary Data System node, Arizona State
University, http://themis-
data.asu.edu.
Your data
You can download your target image from https://home.csulb.edu/~rodrigue/mars/labs/gangeschasma.jpg.
This depicts a section of Ganges Chasma on the eastern end of the Valles
Marineris system, roughly -8° and 48° W.
Interpreting the image
Think about which slopes (north facing or south facing) would be the adret or
ubac slopes (search those online if you don't remember what those are). On
Earth, which slopes are generally warmer: west-facing or east-facing? Why?
Use these ideas of warmer slope aspects to figure out the orientation of the
image.
Examine the different parts of this image: the flat terrain dominating the
top of the image, the scarp and large crater dominating the middle ground, and
the wide variety of deposits dominating the lower portion of the image.
Note
the varying density of craters found in each area and how fresh (sharp-edged
and cup-shaped) or softened (dulled edges and flatter floors) they appear.
The density and condition of the craters are related to the age of the various
surfaces.
What is the lumpy, blocky material at the base of the scarp? What are the
flatter, striated areas fanning out from those piles? You will probably need to look through your introductory
physical geography or general geology textbooks to figure out what those
features are and what the striations indicate.
Notice the superpositions of these fanned out deposits: They are a clue to
the sequence of events here. You might want to identify each of the lobes of
material by marking them with letters and then try to figure out which is
younger than which other(s) on the basis of superposition relationships.
Keep an eye out for artificial patterns that indicate camera or
data-transmission hiccups. Some are pretty obvious; one or two are really
subtle.
Lab report
Write a brief lab report interpreting this landscape, responding to the
following questions. You can deposit the report in the Dropbox for the course
in BeachBoard (Lab: Ganges Chasma).
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Which way is north (very generally)? Why do you think so?
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What is the oldest area (P, C, or L)? What makes you think so?
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Identify two examples of young craters and generally describe their location
within the image (right/left, up/down, center/edges). What makes you think
they are younger?
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Identify and describe the locations of two examples of older craters. What
convinces you they have been around a while?
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Which geomorphological process is creating the scarp? A key to answering this
is the very irregular, scalloped shape of the scarp.
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Which of the debris features is the youngest? Argue your case.
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Identify at least two of the same type of features that are older than this.
What makes you think so? (pay attention to superposition, striations, and how
eroded the scarp face above it is)
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What are those striations? How do they develop? (you may need to do some
Internet searching to figure this out)
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Identify (locate) at least two artifacts of the imaging process that could
lead to misinterpretation of the landscape: There are two data transmission
problems, another is probably dust on the lens, and another may be a post
processing marker.
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Brownie point: Using Google Mars,
try to figure out where this scarp/crater/plateau complex is. Once you think
you have it pinned down in Ganges Chasma, you can really zoom in at the ASU
Mars Space Flight Facility's MARS Global Data Sets at http://mars.asu.edu/data/: THEMIS Day IR
global mosaics. That might help affirm the answer you gave to "where is
north?" posed earlier on the basis on evidence internal to the image, given
its general location.
![[ image of Mars ]](https://home.csulb.edu/~rodrigue/mars/marsatlas.gif)