Jökull - 01.12.1976, Page 58

about 80% N2, 20% C02 (B. Árnasoji, pers.
comm. 1973) bubbled from the drill hole dis-
charge. (
As mentioned above, the water discharging
through the drill hole loses heat to the sur-
rounding rock. Model calculations, using an
equation given by Bödvarsson (1950) and ignor-
ing any effect of the casing, yield an equation
of temperature T as function of depth x of the
form
the hole to reach fairly steady thermal condi-
tion after a step change in inflow is several
days, in agreement with the temperature-pres-
sure lag mentioned above. The computations
also show that after a discharge of four months,
the surroundings of the hole have been heated
appreciably to a radius of 2 meters or so and
that stagnant water in the hole would subse-
quently take several months to cool again, in
agreement with the observations.
T(x) = gx +
gqc
27rKA(t)
(1 - exp (— 27rKA(t) (h - x)/qc))
where g is the undisturbed temperature gradi-
ent, q the discharge from the hole (in kg/sec),
c the specific heat of the water, Iv the thermal
conductivity of the rock, h the depth of inflow
and A(t) a lieat transfer function (Carslaw and
Jaeger, 1959, section 13.5). The function
A changes rapidly during the first day, but is
essentially constant after a few days. Approxi-
mate computations indicate that the time for
It is possible that some of the observed heat-
ing is caused directly by an increase in tem-
perature in the aquifers due to convection in
the ground water. This convection, in turn,
would be due to direct heating of water near
the fissure or by the passage of diffusing hot
gases. Gas seepage in the town of Vestmanna-
eyjar, between the fissure and the drillhole
(later, even to the west of the hole) was first
UTSTREYMISHRAPI A GASI
GAS SPEED VESTM. 1973
«'4

'll'M | K.
y't n
w \'Vi
pf*
V
tí
l'Vrt

? í V
\ / v
V A
AÖ / \
\i\f'
m \
5} "
-h/

\
'K
mi
V
O HRAUN
• REYKIR
□ GR/ENAHLÍÐ 4
V ISFELAGIÐ
A HRADFRYSTJST.
▼ VALLARGATA
+ HVÍTINGAVEGUR 8
X URÐARVEGUR
H HOTEL H.BEN.
L LÖGR.ST.
V VESTURV.
-j- HÚS UNDIR HRAUN
;/>
íw\i\
AO/ V \|l/ if £
Pi 11 V—V
/ 1 I, s' '
\\ \i
\ +-" vs
\
I \
i j \ ^
I V'\ 7
1 \ A í
V V
,/\ /\
\/ \

v~r_
' x \
V- \
X
v.
y3
DAGUR
3A
DATE
3%
Fig. 5. Speed of gas issuing from 2" basement drains in buildings at various points in Vest-
mannaeyjar town in 1973. Measured with a “Wallac” thermo-anemometer. | indicates that a
building has been overrun by lava.
Mynd 5. Útstreymishraði á gasi í niðurföllum nokkurra húsa í Vestmannaeyjum 1973.
56 JÖKULL 26. ÁR