No. 76: Jul-Aug 1991
Could that parched red planet seen in the Viking pictures have been the site of a colossal flood -- a wall of water greater than anything ever seen on earth?
Terrestrial geologists point to the Channeled Scablands in eastern Washington State as evidence of what the sudden release of a huge lake's water can do to the landscape. Everywhere in this part of Washington are deeply incised grooves and dry cataracts separated by water-streamlined bars. Exactly this sort of harsh, scoured topography can be found at Kasei Valles, Mars.
"The upper part of the channel system is typically less than 1 km deep and descends from Echus Chasma about 1 km over a distance of 1000 km; it then splits into north and south channels. On the basis of a stereomodel of Viking images, we have measured the geometry of a steep, constricted reach of the north channel that drops 900 m in only 100 km. A late-stage flood is hypothesized to have scoured the channel. If we assume that channel striations indicate water levels, then the flood had a minimum cross-sectional area of 3.12 x 107 m2 (the putative flood had a width of 83 km, an average depth of 373 m, and a maximum depth of 1280 m). These channel measurements suggest that flood vel ocities ranged from 32 to 75 m. s-1 and that discharge was greater than 1 km3. s-1 , values larger than those calculated for any other flood event on Mars or Earth."
That maximum flood velocity is equal to 170 miles/hour! The erosion features included a ¼-mile-deep pothole. Some temporary lake was likely the source of the flood, although no one sees any surface water on Mars today. (Robinson, Mark S., and Tanaka, Kenneth L.; "Magnitude of a Catastrophic Flood Event at Kasei Valles, Mars," Geology, 18:902, 1990.)
Reference. Our catalog: The Moon and the Planets contains a section on the Martian "channels" (AEM1). For ordering information, visit: here.