A Catalog of Sinuous Rilles on the Tharsis Montes Rift Aprons, Mars

Sinuous rilles observed on Venus, the Moon, and Mars, with lengths ranging from 10s to 1000s of kilometers, have been interpreted as either erosional or constructional features formed by flowing lava. Exotic lava compositions and high effusion rates have been proposed to explain these landforms. On Mars, the spatial distribution, morphology, and emplacement conditions of these channels are key to understanding its volcanic history, interior and surface evolution. The Tharsis volcanic province covers approximately a third of the planet’s surface and presents the largest volcanic region.  Numerous sinuous rilles are observed in the flanks of the Tharsis Montes, three large shield volcanoes trending NE-SW.  Specifically, each volcano displays a rift apron, a large wedge of effusive deposits postdating the formation of the main shield edifice. The aprons represent an understudied region with relatively young deposits.  We mapped and characterized sinuous rilles on the Tharsis Montes (Arsia, Pavonis, and Ascraeus) rift aprons.

We delineated rift apron subregions using previously published geologic maps and boundaries (e.g. Plescia 2004, Skinner et al. 2006). Using the Thermal Emission Imaging System (THEMIS) infrared [100m/px] and the Context Camera (CTX) a [~6 m/px], we have identified, to date, 162 sinuous rilles on the 6 rift aprons of the Tharsis Montes. On the Arsia Mons rift apron, we have identified 74 sinuous rilles, with lengths ranging from ~2 - 90 km with a mean length of ~19 km and a median length of ~13 km.  On Pavonis Mons, we have identified 27 sinuous rilles. Channels range in length from ~3 - 72 km with a mean and median of ~16 km and ~9 km, respectively. On Ascraeus Mons, we have identified 76 sinuous rilles, with lengths ranging from ~2 - 235 km, a with a mean length of ~27 km, and a median length of ~17 km.  The rilles are emplaced on regional slopes ranging from ~0.1 – 3°.  To date, we have calculated 76 of 169 (45%) rille widths with a mean width of 0.21 km.

These preliminary observations suggest that long-lived effusive eruptions capable of eroding the substrate were part of the later evolution of the Tharsis Montes.  Furthermore, the sinuous rilles formed contemporaneous with widespread tectonic and collapse features evident in crosscutting relationships.  Measured rille depths and sinuosity will provide further constraints on their formation.