Elysium Planitia

Elysium Planitia, located in the Elysium quadrangle, is the second largest volcanic region on Mars, after Tharsis. It is centered at 2°00′N 155°00′E / 2.0°N 155.0°E / 2.0; 155.0. The region includes volcanoes, from north to south, Hecates Tholus, Elysium Mons and Albor Tholus. Another large volcano, Apollinaris Mons, lies south of the others. Besides having large volcanoes, Elysium Planitia has several areas with long trenches, called fossa or fossae (plural) on Mars. They include Cerberus Fossae, Elysium Fossae, and Hephaestus Fossae.

A 2005 photo of Elysium Planitia by the Mars Express spacecraft shows what may be ash-covered water ice. The volume of ice is estimated to be 800 km (500 mi) by 900 km (560 mi) in size and 45 m (148 ft) deep, similar in size and depth to the North Sea. The ice is thought to be the remains of water floods and lava flows in the Cerberus Fossae fissures about 2 to 10 million years ago. The surface of the area is broken into 'plates' like broken ice floating on a lake. Impact crater counts show that the plates are up to 1 million years older than the gap material, showing that the area solidified much too slowly for the material to be basaltic lava.