Jökull - 01.12.1982, Page 43

TABLE 1. Jökulsárlón. Selected morphometric parameters. TAFLA 1. Ýmsar mœlistœrbir sem lýsa J'ókulsárlóni.
Maximum length Mesta lengd Lm 4.11 km
Maximum Width Mesta breidd wm 2.92 km
Direction of major axes Lm S69° W
Stefna meginása wm £ co
Area Flatarmál A0 7.87 km2
Mean width Meðalbreidd II BrL> 1.92 km
Maximum depth Mesta dypi dm 152 m
Mean depth Meðaldýpi d=f A0 63.6 m
Ratio of mean: maximum depth Hlutfall meðaldýpis og mesta dýpis Z- zm 0.42
Volume Rúmmál V 500.7 x 106 x m3 500.7 GL
Development of volume D dm 1.26
Shoreline circumference Ummál strandlínu L 11.30 km
Ice front length, 1975 Lengd ísjaðars Li 3.00 km
Development of shoreline Dl _ L /- 2\AlrA 1.14
Breidamerkurjökull probably reached its Little
Ice Age maximum extent in 1894 (Thorarinsson
1943). During its subsequent retreat, in 1932, the
lake Jökulsárlón first began to appear. Since then it
has been progressively exposed during glacier re-
treat (Fig. 4 and Table 2), which was at its most
rapid during the years 1951 - 1965, during which
period, unfortunately, we have no survey dataof the
ice margin position.
There is strong evidence that Jökulsárlón did not
exist prior to the maximum Little Ice Age advance
of Breidarmerkurjökull in the eighteenth and nine-
teenth centuries. Knopfs map of 1735 shows the
river Jökulsá ílowing from “Breida Merkur Jökull”
to the sea over a broad sandur, from which Thorar-
insson (1943) calculated that the distance from the
glacier to the sea, then in the vicinity of the present
Jökulsá, was 9 km, with no indication of a lake on
the surface. Similarly, Sveinn Pálsson’s mapof 1794
shows “Jökulsá á Breidamerkursandi” with no in-
dication of lakes in the 7.5 km which Thorarinsson
(1943) suggested separated the glacier from the sea
at this time.
Thus, it would appear that the basin ofjökulsár-
lónhasbeen produced in between 130and 175years
at most, a removal of 500 x 1(f m3 of material, or
erosion of64 m averaged over the whole lake area, at
a minimum rate of 0.37 m/year. These are extra-
ordinary values by any standard.
Derhyshire (1974) suggested that the lake lies in a
JÖKULL 32. ÁR 39