Large amounts of water ice are believed to be present in the Martian subsurface. The interaction of ice with molten rock can produce distinct landforms. On Earth, when hot volcanic material comes into contact with surface ice, large amounts of liquid water and mud may form that flow catastrophically down slope as massive debris flows (lahars). Some channels in Martian volcanic areas, such as Hrad Vallis near Elysium Mons, may have been similarly carved or modified by lahars. Lava flowing over water-saturated ground can cause the water to erupt violently in an explosion of steam (see phreatic eruption), producing small volcano-like landforms called pseudocraters, or rootless cones. Features that resemble terrestrial rootless cones occur in Elysium, Amazonis, and Isidis and Chryse Planitiae. Also, phreatomagmatism produce tuff rings or tuff cones on Earth and existence of similar landforms on Mars is expected too. Their existence was suggested from Nepenthes/Amenthes region. Finally, when a volcano erupts under an ice sheet, it can form a distinct, mesa-like landform called a tuya or table mountain. Some researchers cite geomorphic evidence that many of the layered interior deposits in Valles Marineris may be the Martian equivalent of tuyas.