Late Episodes of Fluvial Valleys Formation on Mars From HRSC/MEX Data

Details Late Episodes of Fluvial Valleys Formation on Mars From HRSC/MEX Data Late Episodes of Fluvial Valleys Formation on Mars From HRSC/MEX Data

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.h31g..04m&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #H31G-04

Mathematics

Logic

5415 Erosion And Weathering, 5419 Hydrology And Fluvial Processes, 6225 Mars

Scientific paper

Most valley systems on Mars formed in the Noachian period (> 3.6 Gy). They are usually considered to be of fluvial origin but many studies suggest alternative explanations such as subsurface flows. The identification of well preserved dendritic valleys on a Hesperian terrain (3.6- 2.9 Ga) in the Valles Marineris region using THEMIS imagery permitted to study of their geometry with good precision. The new HRSC images show more details that support a fluvial origin for these dendritic valleys. The most dendritic example has a Strahler order of 5 and a drainage density of 1.3 km-1. Several thousands of years are usually required on Earth to form such mature networks of valleys, but stratigraphical relationships suggest that the period of time required for the formation of these valleys is probably geologically reduced and likely episodic. The analysis of these images also shows that valleys are partially deleted from the surface by erosion. Additionally, DEMs (Digital Elevation Model) are constructed using the HRSC stereoscopic images. These DEMs show that the valleys are shallow, 100 m deep for the main tributary, and less than 50 m deep for secondary tributaries with many of them not visible throughout the DEM. Slopes along longitudinal profiles of main tributaries are consistent with terrestrial fluvial valley beds but the incision does not correspond to million years of liquid water activity. By comparison, Noachian valleys are dendritic but also deeper with more incision and volume of eroded material. Noachian valleys likely formed over periods of time much longer than the Hesperian valleys (see Ansan et al., this conference). Thus, the preliminary analysis of plateau valleys in Valles Marineris region using HRSC images confirms the formation of Hesperian aged valleys by sustained water flows but over periods much restricted in time than in the Noachian period. As a consequence, the climate in the Hesperian may have been drier than in the Noachian but with water still stable at the surface, at least episodically.

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