Jökull - 01.12.1970, Page 57

TABLE2 - TAFLA 2
The Recession of Breidamerkurjökull in the years 1894—1968
Rýrnun Breiðamerkurjökuls á árunum 1894—1968
Time intervals
Timabil
Retreat Loss in area1) Decrease in Volume2) Thinning in water Increase in discharge
Hopun Flatarmáls- Rúmmáls- equivalent Þynning Aukning
rýrnun rýrnun vatnsg. i afrennsli
m m km2 km2 km3 106 m3 m cm 103 gl kl/sec
year/ári year/ári year / ári year/ári
1894-1904 120 12 3,0 0.3 2,8 280 2 20 2,5 8
1904-1945 1130 28 23,5 0,6 21,2 520 16 40 19,1 15
1945—19683) . .. . 1046 45 25,3 1,1 25,0 1190 20 85 22,5 31
1894-1968 .. 2296 31 51,8 0,7 49,0 660 38 51 44,1 19
1) These measurements of deglaciated area include only that part of the glacier lobe, which
is below 450 meters above sea level.
2) fn the calculations of the reduction in volume, the thinning of the glacier for different
periods of time is assumed to be proportional to the loss in area of the glacier snout.
3) The loss in area and decrease in volume for the years 1965—1968 are assumed to be pro-
portional to the retreat.
These measurements were initiated in 1932 but
the previous retreat of the glacier front was
obtained by measurements on maps. The re-
treat is shown graphically in Fig. 6. The retreat
after 1932 is given separately east (F.) and west
(W) of Jökulsá. Fig. 7 shows four different
stages of the position of the front of Breida-
merkurjökull from its maximum extent in 1894
up to the year 1965. The changes in area are
given in Table 2, but they could not be mea-
sured except for the lowest part of the glacier
up to 450 m height, due to the fact that the
map from 1965 covers only the lowest part of
the glacier and also due to the inaccuracy of
the maps of the Geodaetic Institute. The re-
duction in glacierized area given in Table 2
is therefore restricted to the map of 1965. The
total deglaciation can be estimated to have
been at least 10—20% greater thus approaching
5—6% of the total area of Breidamerkurjökull.
The reduction in volume of the glacier
(Table 2) was computed from the values for
its lowering as given in Table 3. The thinning
of the glacier lobe was found by drawing three
longitudinal sections of the glacier and three
cross sections of its lobe according to the maps.
TABLE 3 - TAFLA 3
The thinning of Breidamerkurjökull in each
100 m altitude interval in the years 1894—1968
Þynning Breiðamerkurjökuls á hverju 100 m
hœðarbili á árunurn 1894—1968
Elevation Thinning, m
m y. s. Þynning, m
20- 100 57
100- 200 155
200- 300 206
300- 400 95
400- 500 69
500- 600 40
600- 700 45
700- 800 55
800- 900 40
900-1000 35
1000-1100 30
1100-1200 30
1200-1300 30
1300-1400 30
1400-1500 30
1500-1600 15
> 1600 0
JÖKULL 20. ÁR 55