The Paradox: After rushing down the "flood" channels and debouching into the lowlands, either in the Northern Plains or in southern impact basins, what happened to the volatiles that carried the debris? There is a big volumetric problem if water were the working fluid. For a start, a significant proportion of the water would freeze to ice on emerging from depth and being exposed to the frigid thin atmosphere of Mars. This can be reduced,but not totally avoided if the waters emerge hot, from geothermal sources. The ice thus formed and the debris that we see eroded from the chaos zones and the channels, and transported into the lowlands must be carried by the remaining water. In order to flow as a flood, not a slurry, then about 5:1 water to debris load must be available, so large volumes of water are involved. Remember that repeated "floods" emerged down each channel, and there are many seperate channels.

One conventional solution - Oceans: The proponents of a Northern Ocean use this large volume to suggest that there must have been an ocean at the terminus, but their evidence is weak. Whenever potential shorelines are inspected, they do not look like terrestrial shorelines at all. The distribution of polygonal ground textures that implies subsurface volatiles is not centred on the deepest part of the ocean basin, but instead covers the inflow channels suggesting that the volatiles did not arrive in the middle of the basin, but stalled on their way in. This does not, of itself, rule out water as the active agent. it just suggests that the flows generally froze up before filling an ocean. See Head et al.'s recent Science paper based on MOLA results, and in particular, this figure.

Another conventional solution: the Polecaps: The volumetric issue remains. In order for the flows to have been water-based, then the northern plains should consist of 80% water ice. Craters in them do not suggest anything like this amount of ice. One way round this is to suggest that the water ice slowly sublimed into Mars' thin atmosphere and was added to the polecaps each winter. In this way, over geological time, the entire water inventory of the floods could have been removed from the plains. The trouble is, that water is no longer in the pole caps. Perhaps it has been lost to space? The D/H isotope ratios suggest that a volume 10 times that of the active water inventory has been lost to space. If the active water inventory is the polecaps, then this more or less balances. The trouble is it then suggests that Mars is volatile poor at the present day, despite plenty of signs to the contrary.

The White Mars solution to the Paradox: Since the working fluid is a gas, rather than a liquid, the volumetric issue becomes much reduced. Just as the chaos zones can source the volatiles from within their own solid volume, so can the CO2 condense in polar regions as part of the Polar Layered terrain. The debris of the density flows is deposited in the northern plains as volatile-depleted sheets, then volatile-rich layers are deposited from atmospheric condensation - a repeat of the layering process from early Mars, except this time no impacts are involved. There is no volumetric problem, no ocean, and no paradox.
 

      Created: May 2002
      Last modified: May 2002
      Authorised by:  Head, Earth Sciences

      Maintained by: Nick Hoffman
      Email: nhoffman@unimelb.edu.au