Figure 5. Mars Orbiter Camera image (false color) of Apollonaris Patera, an ancient Martian caldera (~70 km diameter) located in Elysium Basin–Terra Cimmeria region of Mars. Note chaos features and associated outflow channels especially abundant near base of volcano (lower left), which could have formed by melting of subsurface cryosphere. Proximity of chaos to volcano suggests possibility of prolonged hydrothermal activity (courtesy of NASA).