River Valleys and Chaos
Many large, ancient river valleys are found in this area; along with collapsed features, called Chaos. The Chaotic features may have collapsed when water came out of the surface. Martian rivers begin with a Chaos region. A chaotic region can be recognized by a rat's nest of mesas, buttes, and hills, chopped through with valleys which in places look almost patterned. Some parts of this chaotic area have not collapsed completely—they are still formed into large mesas, so they may still contain water ice. Chaotic terrain occurs in numerous locations on Mars, and always gives the strong impression that something abruptly disturbed the ground. More information and more examples of chaos can be found at Chaos terrain. Chaos regions formed long ago. By counting craters (more craters in any given area means an older surface) and by studying the valleys' relations with other geological features, scientists have concluded the channels formed 2.0 to 3.8 billion years ago.
One generally accepted view for the formation of large outflow channels is that they were formed by catastrophic floods of water released from giant groundwater reservoirs. Perhaps, the water started to come out of the ground due to faulting or volcanic activity. Sometimes hot magma just travels under the surface. If that is the case, the ground will be heated, but there may be no evidence of lava at the surface. After water escapes, the surface collapses. Moving across the surface, the water would have simultaneously froze and evaporated. Chunks of ice that would have rapidly formed may have enhanced the erosive power of the flood. Furthermore, the water may have frozen over at the surface, but continuing to flow underneath, eroding the ground as it moved along. Rivers in cold climates on the Earth often become ice-covered, yet continue to flow.
Such catastrophic floods have occurred on Earth. One commonly cited example is the Channeled Scabland of Washington State; it was formed by the breakout of water from the Pleistocene Lake Missoula. This region resembles the Martian outflow channels.
Read more about this topic: Oxia Palus Quadrangle
Famous quotes containing the words river, valleys and/or chaos:
“We approached the Indian Island through the narrow strait called “Cook.” He said, “I ‘xpect we take in some water there, river so high,—never see it so high at this season. Very rough water there, but short; swamp steamboat once. Don’t paddle till I tell you, then you paddle right along.” It was a very short rapid. When we were in the midst of it he shouted “paddle,” and we shot through without taking in a drop.”
—Henry David Thoreau (1817–1862)
“... often in the heat of noonday, leaning on a hoe, looking across valleys at the mountains, so blue, so close, my only conscious thought was, “How can I ever get away from here? How can I get to where they have books, where I can be educated?” I worked hard, always waiting for something to happen to change things. There came a time when I knew I must make them happen; that no one would do anything about it for me. And I did.”
—Belinda Jelliffe (1892–1979)
“To the indefinite, uncertain mind of the American radical the most contradictory ideas and methods are possible. The result is a sad chaos in the radical movement, a sort of intellectual hash, which has neither taste nor character.”
—Emma Goldman (1869–1940)