Jökull - 01.01.2001, Side 12

Helgi Björnsson et al.
Figure 8. Calving rate ( 
) versus water depth (  )
at the calving front of Breiðamerkurjökull. a)
 at
the central flow line, and b) width–averaged
 
. Red
dots show the observed calving rate marked with the
year of observation, and the blue line is a linear least-
squares fit to the data. – Hraði kelfingar á sporði
Breiðamerkurjökuls sem fall af dýpi Jökulsárlóns.
The mass balance of a vertical column of length in the flow direction can be described by the fol-
lowing equation of continuity:

   
 
   (8)
where

is the thickness of the glacier at the flow
line,

is the surface width of the actual glacier
cross section, the area of which is equivalent to that
of a square of

, where

is the width of that
square (Figure 11),

is the mass balance rate on the
glacier surface,  is the average horizontal velocity
through the cross section and

is a coordinate mea-
sured downglacier from the ice divide along the flow
line.
Figure 9. Reconstructed values of mass balance at the
terminus of Breiðamerkurjökull 1903–1998. Terms
as in equation (1). a) Average velocity at the cross
section above the lake (  ). b) Area of the cross sec-
tion above the lake ( ). c) Ice flow through the cross
section above the lake ( !#" ). d) Mass change due to
surface elevation changes at the terminus ( !%$ );  $ is
the average thinning of the glacier. e) Mass changes
due to the retreat at the calving front of Jökulsárlón
( !'& ). f) Surface mass balance at the terminus ( !)( ). g)
Calving flux at the glacier front at Jökulsárlón ( !
).
– Afkoma sporðs Breiðamerkurjökuls við Jökulsárlón
1903–1998.
12 JÖKULL No. 50