1. Arizona Space Grant Consortium
Small-Scale Morphologic Properties of Martian Gullies: Insights from Analysis of HiRISE Images
Carrie B. Welty
Department of Geosciences
University of Arizona
David A. Crown
Matthew R. Balme
Planetary Science Institute
Brief Introduction
Arizona Space Grant Consortium
Statewide Symposium
April 19, 2008

2. Objective
HiRISE subimage PSP_004988_ Full image centered at -71.2° S, 3.2°E; 0.50 meters/pixel. Image credit: NASA/
JPL/University of Arizona
gullies are significant . . .
geologically recent features discovered on Mars (in Mars Global Surveyor Mars Orbiter Camera images)
- The process(es) involved in gully formation may provide important insights into Martian geologic and volatile history.
Analyses of new high resolution Mars Reconnaissance Orbiter HiRISE images provide new insights into gully characteristics and formation processes.
This project has focused on documenting small-scale gully morphologies
Constructed a GIS, processed and input HiRISE images and MOLA topography… to make observations and analyses of small-scale gully features.
characterize small-scale gully features,
to explore the potential diversity of gully formation processes,
and to determine if small-scale gully morphology can be used to distinguish between the various mechanisms proposed on the basis of larger-scale characteristics
outline: features we focused on, methods, the significance….??
HiRISE subimage PSP_001684_ Full image centered at °S, °E; 0.25 meters/pixel.
Image credit: NASA/JPL/University of Arizona
HiRISE subimage PSP_004176_ Full image centered at °S, °E; .25 meters/pixel. Image credit: NASA/
JPL/University of Arizona

3. Morphologic Diversity
Analyses of HiRISE images have suggested a significant diversity in gully form:
Within and between clusters
Levels of maturity
Sizes and shapes
Channels incision and sinuosity
Development of tributary and distributary networks
Boulder abundances
Previous work has suggested diversity in Martian gullies. Our analyses…
Clusters (gullies tend to be found in clusters, primarily on walls of craters, pits and canyons).
Simple to complex planform shapes and a range of sizes
Diffuse streaks to deeply incised sinuous channels
variable levels of development of tributary and distributary networks in the gully alcove and apron (respectively)
in boulder abundances on gullied slopes…
HiRISE subimage PSP_004019_ Full image centered at °S, °E; 0.25 meters/pixel. Image credit: NASA/JPL/University of Arizona

4. Methods
A population of over 40 HiRISE images was examined in this study.
Qualitative observations and analysis:
General observations of gully features
Initiation morphologies
Boulder distributions
Quantitative measurements using ArcGIS and MOLA topography:
Gully dimensions (including totally gully system, alcove, channel, and apron sizes)
Channel sinuosity
Wall slope
Gully made up of 3 components…alcove, channel, apron…
Goal to qualitatively and quantitatively characterize small-scale gully morphologies
HiRISE subimage PSP_003890_1405. Full image centered at -39.4°S, 91.7°E; 0.25 meters/pixel. Image credit: NASA/
JPL/University of Arizona

5. Initiation Morphologies
Two different styles of initiation morphologies have been recognized in what are interpreted to be immature gully systems.
Discrete “pinholes” with a single channel or streak.
Small hollows with simple planform shapes at the tops of slopes with debris deposits immediately below.
HiRISE subimage PSP_003287_ Full image centered at -68.3°S, 1.2 °E; 0.50 meters/pixel. Image credit: NASA/JPL/
University of Arizona
Describe upslope – downslope in images, crater rim
HiRISE subimage PSP_004176_1405. Full image centered at -39.4°S, 202.7°E; 0.25 meters/pixel. Image credit: NASA/JPL/
University of Arizona

6. Boulder Distributions
Abundances were visually estimated for the alcove, channel, apron,
and surrounding hillslope.
HiRISE subimage PSP_003517_ Full image centered at -40.4°S, 196.9°E; 0.50 meters/pixel. Image credit: NASA/
JPL/University of Arizona.
Boulders are more densely concentrated in alcoves than surrounding hillslope.
Boulder concentrations decrease down-gully.
While boulder abundances can range from heavily bouldered gully systems and slopes to those containing fewer visible boulders, the primary pattern appears to be…(bullet points)

7. Gully Morphometry
Wall slope measured using ArcGIS and HiRISE (~1 meter/
pixel) overlain on MOLA Topography (~128 pixels/degree), calculated from slope profile.
Variety of measurements, won’t go into specifics…
HiRISE subimage PSP_003287_1115, slope profile graph created in ArcGIS. Full image centered at -68.3°S, 1.2 °E; 0.50 meters/pixel. image credit: NASA/JPL/University of Arizona

8. Patterns and Diversity in Gully Dimensions
The lack of strong correlations between parameters reflects observed morphologic diversity.
Trends indicate potential controls on gully system dimensions by alcove characteristics, suggesting eroded volume dependency.
Explored relationships between different parameters…
Stronger correlations found in:
Alcove length vs total gully length [shown] (longer gully systems have wider alcoves)
Alcove length vs alcove width (narrow alcoves are shorter)
Apron length vs apron width (narrower aprons are shorter)
Apron length vs alcove width (gullies with wider alcoves have longer aprons)

9. Conclusions Diversity in gully form.
The gully population examined includes different types and/or stages of maturity.
Morphometric measurements support qualitative observations of gully diversity.
Boulder abundances show regular patterns:
Greatest concentrations in alcoves
Progressively fewer boulders downslope.
A significant control on gully morphology is the eroded volume of the alcove, as suggested by trends between various morphometric measurements.
These results indicate possible starting points for further research.
…further research including:
Continuing to work on this, expand and separate the population…
Research involving gully dimensions through subdividing gullies into similar types
And through comparisons with terrestrial analogs.

10. Thank you
HiRISE subimage PSP_001684_ Full image centered at °S, °S; 0.25 cm/pixel. Image credit: NASA/JPL/University of Arizona