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The Formation of Fluvial Valleys on Alba Mons, Mars
Lehnigk, Karin Eva
Lehnigk, Karin Eva
Abstract
Fluvial channels occur on the central edifice and flanks of the Martian shield volcano Alba Mons along steeply sloped portions of the volcano. These fluvial channels are embayed by younger lava flows and disrupted by grabens, indicating they formed while the volcano was still active. Manual channel mapping reveals two morphologically distinct populations of channels. One population, located to the north of Alba’s caldera (Population 1), consists of dense channels with long low-order tributaries and wide junction angles. The other population, located to the northwest of the caldera and further downslope than those in the north (Population 2), consists of straight, parallel channels with short low-order tributaries that are bounded by ridges. Bifurcation ratios indicate that northern streams reached a higher degree of maturity than northwestern channels. Valley dimensions indicate that tributary beheading was more common in the northwest than in the north. These findings, along with a higher occurrence of volcanic features in the northwest than in the north, suggest that volcanic feature emplacement exerted a higher degree of topographic control on valley formation in the northwest, while valley incision was a dominant surface process in the north. Finally, mass wasting has altered valley slopes significantly since incision ceased, so efforts to determine slope-based flow characteristics would likely yield inaccurate results.
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2016-04-01
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Geology