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

Objective HiRISE subimage PSP_004988_1085. 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_1410. Full image centered at -38.9 °S, 196.0 °E; 0.25 meters/pixel. Image credit: NASA/JPL/University of Arizona HiRISE subimage PSP_004176_1405. Full image centered at -39.4 °S, 202.7 °E; .25 meters/pixel. Image credit: NASA/ JPL/University of Arizona

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_1420. Full image centered at -37.9 °S, 169.6 °E; 0.25 meters/pixel. Image credit: NASA/JPL/University of Arizona

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

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_1115. 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

Boulder Distributions Abundances were visually estimated for the alcove, channel, apron, and surrounding hillslope. HiRISE subimage PSP_003517_1395. 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)

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

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)

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.

Thank you HiRISE subimage PSP_001684_1410. Full image centered at -38.9 °S, 196.0 °S; 0.25 cm/pixel. Image credit: NASA/JPL/University of Arizona