HR: 0800h
AN: P31B-0434    [Abstracts]
TI: Evidence of multiple flooding events or pulses from erosional features in Martian outflow channels
AU: Davatzes, A
EM: adavatzes@mail.arc.nasa.gov
AF: NASA Ames/ORAU, MS239-20 NASA Ames Research Center, Moffett Field, CA 94035, United States
AU: * Gulick, V
EM: vgulick@mail.arc.nasa.gov
AF: NASA Ames/SETI, MS239-20 NASA Ames Research Center, Moffett Field, CA 94035, United States
AU: Keszthelyi, L
EM: laz@usgs.gov
AF: USGS, Astrogeology Team 2255 N. Gemini Drive, Flagstaff, AZ 86001, United States
AU: HiRISE Team, M
AB: Cataracts, steep knickpoints in large outflow channels, were once large waterfalls on the martian surface. New images of cataracts in the Kasei, Ares, and Mangala Valles obtained by the High Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO) in conjunction with topography from the Mars Orbiter Laser Altimeter (MOLA) are used to further constrain channel outflow rates and durations. Both the morphology and geometry of these erosional features help us to further elucidate the history of these outflow channels. Morphologically, all of the cataract systems have horseshoe-shaped headcuts and longitudinal grooves. These morphological features are strikingly similar to terrestrial flood erosional features from the Missoula Flood, Jokulsa a Fjollum, and English Channel flood. Like terrestrial cataracts, the Martian cataracts have significantly lower width-to-depth ratios compared to the rest of the channel, consistent with erosion into bedrock. Knickpoint recession is also evident from these images. The Ares Valles cataract has migrated more than 35 km, an order of magnitude more than the terrestrial examples of catastrophic floods. Most estimates from Ares Vallis suggest similar discharge rates to the terrestrial floods, though some estimates of Martian flood discharge are significantly higher. High resolution imaging shows that nearly all of the cataract systems have multiple generations of erosion, with smaller subchannels within the cataract system. Based on the length of the recession and the morphological evidence, multiple flooding events are possible in most of these Martian channels, either by discrete events or pulses of flow. All of the terrestrial examples resulted from the breaching of a rock or ice dam, releasing a glacial flood. Most of the Martian outflow channel discharges likely came from the subsurface. DEM's of these cataracts from HiRISE and CTX stereo pairs will be input into a 2.5D hydraulic flood model to provide more precise discharge calculations. HiRISE stereo pairs have a vertical precision of better than 25 cm.
DE: 5415 Erosion and weathering
DE: 5419 Hydrology and fluvial processes
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting