Jökull - 01.12.1976, Side 43

Fig. 1.
Types of glacier water
reservoirs. Cross-section.
a) A subglacial water cu-
pola beneath a glacier
surface clepression
b) A stable subglacial
water reservoir beneath
a convex glacier sur-
face
c) An illustration of
Grímsvötn (Björnsson
1974, 1975)
d) A glacier-margin lake
e) A lake which may be
created by subglacial
volcanic eruption
f) A glacier-surface lake
Mynd 1.
Hinar ýmsu gerðir
jökullóna. Snið.
a) Vatnsgeymir undir
dcsld i jökulyfirborði
b) Vatnsgeymir í skál
undir jökulbungu
c) Grímsvötn
d) Jaðarlón
e) Lón, sem gœti myndast
við eldgos undir jökli
f) Lón á yfirborði jökuls
in whicli zw is the elevation of the top surface
of a subglacial water layer, zs is the glacier sur-
face elevation, p^ and pw are the densities of
ice and water, respectively. Further, the water
flow in a permeable glacier can be described
for a cross-section by a family of equipotential
curves <p (x, z, t) = C = constant which are
given by
Pi C
z = z —------------(z — z ) + — (2)
Pw - Pi g
in whicli z0 is an arbitrary datum level and g
is the acceleration of gravity. Choosing z0 =
zw + (zs - zw) (pi/pw) the curve cp = 0 marks
the surface of the water reservoir.
Figs. la and b illustrate the two fundamental
types of subglacial water reservoirs. Fig. Ib
shows a stable reservoir which is situated in a
bedrock depression beneath a convex glacier
surface. The reservoir in Fig. la rises above the
glacier bed as a result of a glacier surface de-
JÖKULL 26. ÁR 41