Satellite cones and vents at Tharsis Tholus, Mars

We describe satellite cones and vents at the northern flank of Tharsis Tholus.The cones have an elliptical outline and at their downslope portion, channels may emanate which can be t raced for several kilo metres.We interpret those cones as scoria cones formed during exp losive eruptions.The channels are likely formed by lava flo ws, indicating syn-eruptive effusive stage(s).A fissure eruption occurred at the base of the NW flank and is located within a graben.An explosive eruptive event is evident because it doubled the width of the graben.The associated fallout was deposited to the north and northwest and is clearly v isible in THEMIS infra-red n ight images.The erupted material is partially dark coloured and is exposed just outside the vent.We conclude this eruption was associated with a regional grabenforming tectonic event where mag ma was tapped and ascended along deep-reaching faults.Finally, we observed a conical edifice rising about 1160 m above the surrounding plain.Th is construct may represent a stratocone of alternating effusive and explosive volcanic rocks.