Vallis

Vallis (plural valles) is the Latin word for valley. It is used in planetary geology for the naming of landform features on other planets.

Vallis (plural valles) was used for old river valleys that were discovered on Mars, when probes were first sent to Mars. The Viking Orbiters caused a revolution in our ideas about water on Mars; huge river valleys were found in many areas. Space craft cameras showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Some valles on Mars (Mangala Vallis, Athabasca Vallis, Granicus Vallis, and Tinjar Valles) clearly begin at graben. On the other hand, some of the large outflow channels begin in rubble-filled low areas called chaos or chaotic terrain. It has been suggested that massive amounts of water were trapped under pressure beneath a thick cryosphere (layer of frozen ground), then the water was suddenly released, perhaps when the cryosphere was broken by a fault.

Read more about Vallis:  Nirgal Vallis and Sapping, Kasei Valles, Other Valles in The Lunae Palus Quadrangle, Valles in The Syrtis Major Quadrangle, Valles in The Hellas Quadrangle, Lineated Floor Deposits, Origin of Dao Vallis, Vallis in Elysium Quadrangle, Vallis in Oxia Palus Quadrangle, Vallis in Memnonia Quadrangle, Other Examples of Vallis