23. Apollinaris Patera
Elysium Planitia, Mars

Apollinaris Patera, Mars, is a complex shield volcano 180 × 280 kilometers across and 5 kilometers high. Shield volcanos are large volcanic cones with gently sloping flanks. Apollinaris features an unusually large complex summit caldera 85 kilometers across and 1 kilometer deep, and a basal scarp up to 1 kilometer high similar to that observed at Olympus Mons. The steep flank to the southeast (to left) is also unusual. A broad fan-shaped volcanic deposit formed on the southern flank of the volcano (to lower right) when lavas breached the southern rim of the caldera. The caldera itself formed when the roof of the underground magma chamber partially collapsed. The morphology of Apollinaris Patera is unusual, perhaps due to different lava composition or to the role of water/ice during eruption. Apollinaris Patera is located on the southern edge of the Elysium Planitia volcanic province and is perhaps more than 3.5 billion years old.

Viking 1 images 603A42, 639A92.
Location: 8.5 S, 186.0 W
Image Width: 410 kilometers
Vertical Exaggeration: 4× normal
Image Resolution: 600 meters/pixel

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