Ulysses Patera
This feature is an example of a class of volcanos that are considerably smaller than either the broad shield volcanos or Alba Patera. The summit consists of a single, very circular caldera with a smooth floor that predates the ejecta from two large impact craters. The lower flanks of the volcano, including portions of the impact craters, have been buried by the material that makes up the surrounding plains. This superpositional relationship indicates that the plains were emplaced subsequent to both the volcano and large impact craters on the volcano. The plains are probably made up of lava supplied from the Tharsis Montes that flowed down the sides of the broad uplift associated with the Tharsis shields. Both the plains and the volcano are cut by a graben (a paired set of linear faults), indicating tectonic activity subsequent to the emplacement of the plains.
This image was taken by NASA's Viking 2 orbiter in 1977.
