Hadriacus Mons by a contact between magma and groundwater. "Hadriaca Patera", a term formerly used for the entire edifice, is now only used for the central caldera, which is in diameter. Hadriacus Mons Hadriacus Mons is an ancient, low-relief volcanic mountain on the planet Mars, located in the southern hemisphere just northeast of the impact basin Hellas and southwest of the similar volcano Tyrrhenus Mons. Hadriacus Mons is in the Hellas quadrangle. It has a diameter of . The name was approved in 2007. The flanks of Hadriacus Mons have been eroded into gullies; its southern slopes are incised by the outflow
Tharsis Montes is about across and stands above the ocean floor. The Tharsis Montes volcanoes lie near the equator, along the crest of a vast volcanic plateau called the Tharsis region or Tharsis bulge. The Tharsis region is thousands of kilometers across and averages nearly above the mean elevation of the planet. Olympus Mons, the tallest known mountain in the Solar System, is located about northwest of the Tharsis Montes, at the edge of the Tharsis region. The Tharsis Montes were discovered by the Mariner 9 spacecraft in 1971. They were among the few surface features visible as the spacecraft entered orbit