Images obtained by the THEMIS instrument on Mars Odyssey permit the identification of many new volcanic features on Mars. Several new types of vent systems, including fissure vents within the Tharsis region, flank vents on Olympus Mons and Ascraeus Mons, and lava shields on the floor of Arsia Mons have been found. The valley networks on Hecates Tholus are seen to be more complex than previously believed. Extending from the caldera rim to the base of Hecates Tholus volcano, individual valleys change width and depth in apparent response to local topography. Valley formation spanned the time period during which lava flows from Elysium Mons embayed the southern flank of Hecates Tholus, as demonstrated by the burial of some valleys by the lava flows and the formation of sediment fans on top of adjacent parts of the flows. THEMIS images now allow new constraints to be placed on the dynamics of lava flow emplacement, with the identification of flows with well-defined lava channels on the northern flank of Ascraeus Mons, as well as an enigmatic braided lava channel. Three previously unreported collapse events (3.7 to 4.3 km in diameter) are identified within the caldera of Ascraeus Mons. Details of the mode of formation of parts of the Olympus Mons aureole can also be identified, supporting the idea that the aureole had a landslide origin. THEMIS images show that parts of the aureole have been modified by water discharged to the east of Olympus Mons.