Prodigious ash deposits near the summit of Arsia Mons volcano, Mars

[1] Mars Orbiter Camera images are used to identify widespread material interpreted to have formed via explosive volcanism on Arsia Mons volcano, Mars. This material crops out in cliff sections associated with pit craters in layers 45– 50 m thick. The large range of elevations where the material is found (6.2–17.5 km) suggests locally-derived materials, although extensive reworking has produced a wide variety of dune forms. Two possible styles of volcanism appear possible for generating this material: (1) explosive volcanism associated with pit crater formation due to the release of magmatic gases, or (2) the interaction between dikes and volatile-rich substrates. Although the best examples occur on Arsia Mons, pit craters on Ascraeus Mons also suggest explosive activity. The absence of comparable features on Olympus Mons indicates that the eruptive histories of the larger Tharsis shields were more diverse than has been inferred from Viking Orbiter images.