Hadriacus Mons is an ancient, low-relief volcanic mountain on the planet Mars, located in the southern hemisphere just northeast of the impact basinHellas and southwest of the similar volcano Tyrrhenus Mons. It has a diameter of 450 kilometres (280 mi). The name was approved in 2007. The flanks of Hadriacus Mons have been eroded into gullies; its southern slopes are incised by the outflow channelDao Vallis. The large extent of volcanic deposits and the caldera size leads some researchers to suggest that these features were the result of an explosive event caused 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 66 kilometres (41 mi) in diameter.