Comparing the Late Stage Effusive Histories of Olympus, Pavonis, and Arsia Montes, Mars, Inferred From Lava flow Abundance Mapping of Mars Express HRSC Data

The abundances and temporal relationships between lava flow types provide insight into the most recent styles of effusive activity of a volcano, as they tend to form during different eruptive conditions. HRSC and THEMIS lava flow abundance mapping shows a high ratio of lava channels to tubes for Olympus Mons, with superposition relations indicating that channels are typically younger. This suggests that a change in eruptive style occurred from tube-forming (long-lived, steady effusions of lower viscosity lavas) to channel-forming (shorter-lived, unsteady effusions of higher viscosity lavas) eruptions. The southern flanks of Pavonis and Arsia Mons are typified by a lack of lava tubes. Highly subdued channels dominate their flanks, along with a mottled surface likely to be nearly completely buried channels. These results suggest that Pavonis and Arsia have likely completed the evolutionary trend from tube- to channel-forming eruptions as seen at Olympus, or never underwent conditions favorable for tube formation. Following main edifice formation, Pavonis and Arsia Mons formed similar northeast-trending rifts that acted as source regions for large lava aprons to the northeast and southwest. The aprons, which are lacking at Olympus Mons, are composed mostly of channel-fed flows. Arsia's southern apron appears to be the source for some long lava flows that extend into southern and western Tharsis. No detectable vents are present along the apron, and were likely buried by younger flows from the rift. Although Pavonis and Arsia Mons display similar flank morphologies, effusive styles on the aprons differ significantly. The rift style of eruption at Pavonis' south flank appears to have transitioned towards plains-style volcanism, typical of the Snake River Plains, Idaho. This area of the Pavonis apron is composed of >31 low shields and fissure-fed flow fields, covering the southeastern portion of the rift apron with lava tubes and sheets. Both aprons represent a change from major shield building to Tharsis plains formation. These results support previous Mariner and Viking era classifications of Tharsis shield building, but also suggest that main construct formation involves a change from tube- to channel-forming eruptions, while the advanced stages achieved by the Tharsis Montes are more complex than previously suspected.