HR: 1340h
AN: P23B-0189    [Abstracts]
TI: A Protracted, Complex, Period of Valley Formation on Hecates Tholus Volcano, Mars
AU: * Mouginis-Mark, P J
EM: pmm@higp.hawaii.edu
AF: University of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AB: Analysis of THEMIS VIS, HRSC and MOC images of Hecates Tholus volcano, Mars, reveals an extended time period over which the volcano's extensive valley network must have evolved, and hence constrains the origin and longevity of the hydrogeologic conditions under which the valleys formed. These image data, along with MOLA topographic data, permit the following valley attributes to be identified: (1) Some valleys on the southern flank of the volcano pre-date the emplacement of the lava flows from Elysium Mons, while other valleys post-date this volcanism; (2) Braided valleys on the E. flank formed on the shallower slopes, while deeper valleys formed on steeper slopes; (3) Valleys that flooded impact craters by breaching their rims did not create any deltaic deposits within the craters, indicating low sediment loads for the water; (4) Valleys are most well developed on the NW flank of the volcano; (5) Water discharge took place within the floor of at least one impact crater, while the rim of this crater was not eroded, indicating a ground water source; (6) Valleys originated within a few kilometers of the caldera rim; and (7) No valleys formed within the summit caldera. No source for the water that carved the valleys has yet been identified, but snow melt [Fassett and Head, 2004; Lunar Planet. Sci. XXXV, no. 1113] or the remobilization of volatiles released from the degassing volcano [Scott and Wilson, 1999; JGR 104, 27,079 - 27,089] appear to be the most likely. In either model, a hydrothermal system such as the one proposed by Gulick [1998; JGR 103, 19,365 - 19,389] could have remobilized the volatiles and carved the valleys. Explosive volcanism is, therefore, still a possible style of activity for Hecates Tholus (Mouginis-Mark et al., 1982; JGR 87, 9890 - 9904), but alternative explanations for the non-uniform distribution of sub-kilometer diameter impact craters on the volcano, including glacial erosion or the rotting of surface lava flows by an active hydrothermal system, need to be investigated.
DE: 5415 Erosion and weathering
DE: 5419 Hydrology and fluvial processes
DE: 5480 Volcanism (6063, 8148, 8450)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005