Glaciological investigations in Johan Dahl Land 1980, South Greenland

Glaciological investigations in Johan Dahl Land, southern West Greenland, were started in 1977 by GGU in connection with the proposal for a hydroelectric project in the Nordbosø basin (ACG/VBB, 1975). The Nordbogletscher with an area of 208 km 2 covers 68 per cent of the basin area and is the most important water source. The work of the GGU has therefore concentrated on the Nordbogletscher and the relation between its mass balance and dimate, while the Greenland Technical Organization (GTO) is measuring runoff from the Nordbosø as well as making engineering studies. Results from GGU's fieldwork are published in annual reports, e.g. Olesen & Weidick (1978) and Clement (1980).


Glaciological investigations in Johan Dahl Land 1980, South Greenland Poul Clement
Glaciological investigations in Johan Dahl Land, southern West Greenland, were started in 1977 by GGU in connection with the proposal for a hydroelectric project in the Nordbosø basin (ACG/VBB, 1975). The Nordbogletscher with an area of 208 km 2 covers 68 per cent of the basin area and is the most important water source. The work of the GGU has therefore concentrated on the Nordbogletscher and the relation between its mass balance and dimate, while the Greenland Technical Organization (GTO) is measuring runoff from the Nordbosø as well as making engineering studies. Results from GGU's fieldwork are published in annual reports, e.g. Olesen & Weidick (1978) and Clement (1980). Nordbogletscher 1979Nordbogletscher -1980 During 1980, the field programme was extended to indude measurements in the accumulation area so that the total mass balance of the Nordbogletscher can be determined for the first time. The results are summarized in fig. 22 and in Table 7.

Mass balance of
The winter balance was measured at the end of May in snowpits and by depth soundings at points scattered over the whole glacier area. The total winter balance was calculated to be + 103 x 10 6 m 3 of water, corresponding to a mean specific winter balance of +0.49 m of water equivalent. The established accumulation pattern appears to be rather uniform over the whole glacier and there is no strong variation with altitude. The summer balance was determined in the middle of September by measurements within a network of stakes drilled into the glacier. The total summer balance was -163 x 10 6 m 3 of water and the specific summer balance shows a marked increase with elevation.
The net balance for 1979/1980 is -60 x 10 6 m 3 which represents a large net mass loss. The corresponding elevation of the equilibrium line was dose to 1550 m, i.e. an accumula-700 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 +0.5 Metres water equivalent  tion area ratio of about 50 per cent. As this is the first time that the complete mass balance has been measured, it is not possibie to compare 1979/1980 with previous years directly. However, from ablation measurements made on the glacier tongue in 1978 and 1979, it appears that the 1979/1980 mass balance is the most negative one since studies started in 1977.

Other investigations
Detailed ablation measurements were made on the tongue of Nordbogletscher on a daily-weekly basis as in previous years. At the same time, c!imatological elements were recorded at two weather stations; one at base camp beside the glader and one at the same altitude on the glader itself. Results show that the main controion ablation variations is due to temperature while sunshine duration shows suprisingly no effect.
A number of ice-dammed lakes were kept under observation. In particular, water-level variations and infiow were continuously recorded for a lake immediately beside the Nordbogletscher at 850 m elevation, which taps every year under the glader. The results will permit estimation of the water quantities involved in the tapping.
Observations were also made on a number of glacier fronts. The glaciers in the area are growing. For example, Nordgletscher which lies 10 km east of Nordbogletscher has advanced 400 msince 1969.
In August 1980 a special survey programme using an airgun system was made on Nordbosø to measure water depth and thickness of bottom sediments.
Studies in Johan Dahl Land will be continued in the coming year.