The Phoenicis Lacus quadrangle covers the area from 90° to 135° west longitude and 0° to 30° south latitude on Mars. The Tharsus rise, which was formed from lava flows, occupies part of area. The volcanoes Pavonis Mons and Arsia Mons are believed to have once had glaciers on them. Glaciers may still exist under a thin layer of rocks. The ice can be a source of water for the possible future colonization of the planet. One of the most prominent features of this quadrangle is a large intersecting set of canyons called Noctis Labyrinthus. Other interesting features are lava channels, Dark slope streaks, pit crater chains, and large troughs (called fossae). Research published in the journal Icarus has found pits in Zumba Crater are caused by hot ejecta falling on ground containing ice. The pits are formed by heat forming steam that rushes out from groups of pits simultaneously, thereby blowing away from the pit ejecta.