Amemeba wrote:hydrology_joe wrote:In this case, the simple answer described previously in this thread is actually more applicable to the formation of epikarst, not cave passage formation. That is exactly why I provided the KISS description of mixing water corrosion.
Wrongo, Hydro, "epikarst" is but an aspect of poor hydrologic circulation.
The dissolution effects of renewed acidity by a recharging liberation of CO2 through mixed waters is dwarfed by the effects of a time enhanced hydrologic flow. A directional flow through time is paramount to linear cave developement.
Ain't it the truth?
I don't know how I was wrong as I never claimed that epikarst wasn't an aspect of poor hydrologic flow nor did I claim that time wasn't a factor... but for further clarification:
Epikarst is formed as a result of poor hydrologic flow and results is the formation of perched epikarstic watertables. Because of this, the water becomes saturated with calcite at its pCO2 near the surface and loses its corrosivity long before it can form caves.
from Ford and Williams, Karst geomorphology and hydrology, 1994:
Recharge from rainfall will be relatively diffuse, depending on soil cover, and percolating water will accomplish 50-80% of its solutional work within about 10 m of the surface. Hence fissures that are considerably widened by corrosion beneath the soil close rapidly with depth. As a result, infiltration into the top of this highly corroded subcutaneous zone is much easier than drainage out of it.The bottleneck effect results in much storage of water in this zone after heavy rain, constituting a perched epikarstic aquifer with a base that is essentially a leaky capillary barrier. Because of initial spatial variability in fissure frequency and permeability arising from tectonic and lithological influences, preferred (low resistance) vertical leakage paths develop down connected pipes at the base of this aquifer. These paths are enlarged by solution with the result that a depression develops in the overlying subcutaneous water table similar to the cone of depression around a pumped well. Flow paths then adjust in the epikarst aquifer to converge on the dominant leakage route. The extra flow encourages more solution and with it the enhancement of vertical permeability.
The mixing water corrosion that occurs below the water table as I described previously is enhanced by time. As with the old racing addage "there's no replacement for displacement"; there is no replacement for time. The longer the time-span the process is allowed to take place over, the more dissolution will occur assuming continued input & discharge of water. Flow alone cannot replace the chemistry required to dissolve the limestone. Increased flow can began physical erosion, but the initial flow paths need to be developed through dissolution first (unless we're getting into tectonic caves).