Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.h33a0983d&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #H33A-0983
Physics
0700 Cryosphere (4540), 1600 Global Change, 1800 Hydrology, 1824 Geomorphology: General (1625), 8485 Remote Sensing Of Volcanoes
Scientific paper
A perennial challenge to terrestrial and planetary geologists is to understand remotely sensed features in terms of process and properties of the host lithologies. Among the geomorphic features common to Earth and Mars are yardangs; remnant wind-eroded aerodynamic ridges. On Mars, the nature of the host lithology of yardangs there has been of considerable debate. Resolution of the debate may rest on observations from appropriate terrestrial analogs. Through remote and field study of yardang morphologies in extensive regional ignimbrite sheets in the Central Andes, we have gained valuable insight into the process of yardang formation and the role that the variable material properties of the host lithology plays in their final form. Ignimbrites typically show two main facies: an upper massive, indurated and jointed facies, and a lower weak to poorly indurated, massive ash- and pumice-rich facies. These facies may locally have a welding profile superimposed on them. The two facies have quite different mechanical properties; the indurated facies behaves as strong rock, fails by block collapse and supports steep/vertical cliffs, while the non-indurated facies forms gentle slopes and subdued erosional forms. The two facies produce yardangs of quite different character. The presence of the indurated facies results in massive, extremely elongate, high aspect ratio (1:20 to 1:40) megayardangs, that form tall (100m), thin ridges with steep to vertical walls. Weakly indurated ignimbrites are carved into stubby and chaotic yardangs and demoiselles (hoodoos) with aspect ratios of 1:5 to 1:10 and heights rarely exceeding 20m. While the indurated facies is commonly pervasively jointed, jointing is off secondary importance and and a persistent strong unidirectional wind is the dominant parameter controlling yardang orientation. In many locations, we have found serrated margins that result from oblique intersections of jointing and yardangs or scarps of ignimbrite sheets. The form and environmental conditions of the yardangs in the ignimbrites in the Central Andes may be the most convincing analog to the extensive yardangs seen on the surface of Mars.
Bailey James E.
de Silva Shanaka L.
Mandt Kathleen E.
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