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:
“My favorite figure of the American author is that of a man who breeds a favorite dog, which he throws into the Mississippi River for the pleasure of making a splash. The river does not splash, but it drowns the dog.”
—Henry Brooks Adams (1838–1918)
“It was a comfort in those succeeding days to sit up and contemplate the majestic panorama of mountains and valleys spread out below us and eat ham and hard boiled eggs while our spiritual natures reveled alternately in rainbows, thunderstorms, and peerless sunsets. Nothing helps scenery like ham and eggs.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)
“To study history means submitting to chaos and nevertheless retaining faith in order and meaning. It is a very serious task, young man, and possibly a tragic one.”
—Hermann Hesse (1877–1962)