PLATEAUS AND SINUOUS RIDGES AS EVIDENCE OF LAVA FLOW INFLATION IN THE THARSIS REGION OF MARS

The Tharsis Montes on Mars are among the Solar System’s largest basaltic volcanoes. Their main flanks have slopes of up to several degrees, and they include younger rift aprons composed of materials erupted from chaotic terrains on the NE and SW flank of each volcano. The rift aprons typically display slopes higher than one degree and transition into the adjacent Tharsis plains where slopes approach zero degrees. The main flanks display units interpreted to be channel- and tube-fed flow units. Interspersed with channels and tubes within the rift aprons are sinuous, sometimes branching channel systems that lack levees. Beyond the rift aprons, the plains units lack the sinuous channel systems but display sinuous ridges and plateaus among channels and tube-fed flows. Within the geologic context of the eastern Tharsis plains adjacent to Pavonis Mons, sinuous plains ridges that are linked with plateaus are consistent with a formation via slow and steady lava flow emplacement across low slope terrains through ample topographic obstacles (channel- and tube-fed flow margins and low shields) that acted to inhibit lateral flow field advance. Both plateaus and ridges are indicative of flow inflation either across broad sheets or topographically confined, narrow pathways. Because these units are linked with units on the rift apron of Pavonis Mons, we also conclude that those units share a volcanic origin, including sinuous and branching, non-leveed channel networks. Similar features occur in Hawaiʻi and New Mexico. These terrestrial examples show that lava interacting with a range of regional slopes and topographic obstacles can produce produce a variety of lava flow pathway structures and morphologies, all of which are consistent with the transition in lava flow structures observed on Mars.