<PRE>
water flow water flow
-----------------\down up /--surface-----
\--------surface------------/
-------------------\ /-------------------
\-----------------------/
\ /
----------------------\ /---------------------
\-----------------/
\ porous layer /
porous layer \ water flow> /
--------------------------\ /-------------------
\---------/
^
|
heat conduction
---------------------------
/ cooled rind of batholith \
/ -------------------- \
/ / liquid magma \ \
</PRE>
Drawing slightly modified from figure 4 of White,
The liquid magma as it cools will initially produce a solid rind which will
separate the water from the actual heat source, the magma. Thus conduction,
must at least be the prime mechanism of heat loss through the rind, and is
most likely the prime mechanism up to a point near the surface.
The temperatures of water found in geothermal sites generally are in the range
of 250-500 degrees C. (see Otte and Kruger) Since the magma is at a
temperature of 1200 deg. C the coolness of the water is an indication that
the water did not get that close to the magma body. This fact further
supports the concept that conduction from the magma chamber to the level of
the mobile water is due to conduction.
Since the recharge rate for geothermal energy is from rainfall, the amount of
energy removed is related to what enters into the groundwater flow. Only
about 10% of the rainfall is recharged into the groundwater and 40% of that
is discharged by local flow systems.(see Willet and Chapman) This leaves
6% of the rainfall actually going into the deep ground and into a
geothermal system. If a region, like California has 50 cm of precipitation
only 3 centimeters per year enter the basin. Assuming a straight down and
back up flow, this represents a minor removal system. Assuming that the
waters start at 25 deg. C and at depth are heated to 300 deg C, A 1 cal/gm
specific heat for the water, this represents the removal of 825 calories
per sq. cm.
I can't find the heat of fusion for basalt, but it should be in the realm of
20 calories per gram. Basalt weighs 2.75 grams/cc so to solidify 1 cc you
need 55 calories removed. Thus this rate of removal can solidify 15 cm of
the basalt per year.From that point on that 15 cm will loose heat at the
rate of .2 cal/gm/deg. But the magma must now loose heat by conduction
through the 15 cm solid rind. Year after year as the rind grows,
conduction plays a larger and larger role in the cooling and the cooling
gets slower and slower.
While I agree that a hydrothermal system will cool the batholith more
rapidly, it is not of sufficient magnitude to cool these things as rapidly
as the 1 year flood advocates require for their view.
references
Carel Otte, and Paul Kruger, ""Worldwide Status of Geothermal Resources
Development," in Paul Kruger and Carel Otte, editor, Geothermal Energy,
Stanford, Stanford University Press, 1973, p., 24
Donald E. White, "Characteristics of Geothermal Systems", in Paul Kruger and
Carel Otte, editor, Geothermal Energy, Stanford, Stanford University Press,
1973, p.,76
S.D. Willett, and D.S. Chapman, "Temperatures, Fluid Flow and the Thermal
History of the Uinta Basin," in B.Doligez ed. Migration of Hydrocarbons in
Sedimentary Basins, (2nd IFP Exploration Research Conference," Carcans,
France, June 15-19, 1987 Paris, Editions Technip, 1987), p. 544
glenn
Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm