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:
“There is a river in Macedon, and there is moreover a river in Monmouth. It is called Wye at Monmouth, but it is out of my prains what is the name of the other river; but ‘tis all one, ‘tis alike as my fingers is to my fingers, and there is salmons in both.”
—William Shakespeare (1564–1616)
“The West is preparing to add its fables to those of the East. The valleys of the Ganges, the Nile, and the Rhine having yielded their crop, it remains to be seen what the valleys of the Amazon, the Plate, the Orinoco, the St. Lawrence, and the Mississippi will produce. Perchance, when, in the course of ages, American liberty has become a fiction of the past,—as it is to some extent a fiction of the present,—the poets of the world will be inspired by American mythology.”
—Henry David Thoreau (1817–1862)
“She comes! She comes! The sable throne behold
Of Night primaeval, and of Chaos old!”
—Alexander Pope (1688–1744)