Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p13d..03f&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P13D-03
Astronomy and Astrophysics
Astrophysics
5415 Erosion And Weathering, 5419 Hydrology And Fluvial Processes, 5480 Volcanism (6063, 8148, 8450), 6225 Mars
Scientific paper
Most valley networks on Mars appear to have been formed during the Noachian. However, there are a few locations where valleys incise younger surfaces, including the Hesperian-aged volcanoes Ceraunius Tholus and Hecates Tholus (Gulick and Baker, 1990). Both of these volcanoes are characterized by numerous small radial valleys on their flanks (widths <~500 m). Ceraunius Tholus also has a set of large canyons on its north flank that appear qualitatively different from the smaller features (width ~2 km). The largest of these canyons originates near the lowest part of the caldera, continues 40 km down the north flank, and debauches into Rahe Crater (an oblique impact crater) where it formed a depositional fan. We have been exploring the origin of these relatively young valley features to help constrain valley formation mechanism on Mars. Recent study of climate change on Mars suggests that many low-latitude regions (especially large volcanic edifices) were periodically the sites of snow accumulation, likely triggered by variations in spin-axis/orbital parameters. As with earlier work on Hecates Tholus (Fassett and Head, 2006), numerical modeling suggests that conductive cooling from intrusions of plausible geometry within Ceraunius Tholus would provide sufficient surface heat flux to melt snowpack of a few hundred meters in thickness on these volcanoes. We interpret this process to have formed the radial valleys. Due to the geometry of the summit, meltwater would also have accumulated in the summit caldera, forming a caldera lake of significant volume. It appears that catastrophic drainage of this summit caldera lake may have formed the large canyons, in a manner most akin to terrestrial jökulhaups. The hypothesis that these canyons formed fluvially is supported by comes from the similarity in the volume of material removed from the valley and found in its depositional fan (both ~20 km3), consistent with its formation by a mechanism that was predominantly erosional. This similarity in volume is likely not what would be expected if these canyons formed from a volcanic process (e.g., Li and Robinson, 2001). The presence of both the large canyons and small radial valleys on Ceraunius Tholus may be related to confluence of two circumstances, summit snow deposition and volcanic activity, which may explain why valley formation was occurs only on some volcanoes during the Hesperian. References Fassett, C.I., Head, J.W., 2006. Valleys on Hecates Tholus, Mars: origin by basal melting of summit snowpack. Planet. Space Sci. 54, 370-378. Gulick, V.C., Baker, V.R., 1990. Origin and evolution of valleys on Martian volcanoes. J. Geophys. Res. 95, 14,325-14,344. Li, H., Robinson, M.S., 2002. Modeling Channel Formation on Ceraunius Tholus, Mars. AGU Spring Meeting, #P31A-13.
Fassett Caleb I.
Head James W.
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