Náttúrufræðingurinn

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Náttúrufræðingurinn - 1990, Qupperneq 16

Náttúrufræðingurinn - 1990, Qupperneq 16
Hofsjökli horfnum gætu þó smáfannir lifað af sum sumur og speglast í nýju öskjuvatni. ÞAKKIR Landsvirkjun kostaði íssjármælingar á Hofsjökli og úrvinnslu þeirra. Finnur Páls- son vann að tölvuteikningu korta og Krist- offer J. Kristiansen að útlitshönnun og frágangi. HEIMILDIR Helgi Björnsson, 1977. Könnun á jöklum með rafseaulbvlgjum. Náttúrufrœðine- urinn, 47, 184-194. Helgi Björnsson, 1987. Könnun jökla með rafsegulbylgjum. Bls. 279-292 í í hlutar- ins eðli (Ritstj. Þorsteinn I. Sigfússon). Bókaútgáfa Menningarsjóðs. Reykjavík, bls. 279-292. Helgi Björnsson, 1988. Hydrology of ice caps in volcanic regions. Vísindafélag Is- lendinga, Rit 45. 139 bls.+ 21 kort í öskju. Markús Á. Einarsoon, 1976. Veðurfar á íslandi. Iðunn, Reykjavík, 150 bls. Sigurjón Rist, 1990. Vatns er þörf. Bóka- útgáfa Menningarsjóðs. Reykjavík. 248 bls. SUMMARY Hofsjökull: topography, storage and drainage of ice and water by Helgi Björnsson Science Institute University of Iceland Dunltaga 5 IS-107 REYKJAVÍK lceland In 1983 the surface and bedrock topo- graphy of Hofsjökull (923 km2) was mapped by radio echo soundings and pre- cision barometric altimetry. The highest part of the ice cap forms a circular plateau at an elevation of about 1800 m. An ice ridge strikes northeast from this centre and ice flows southeast and northwest from this main ice divide. The most prom- inent landform beneath the ice cap is a large circular volcano with a 200 km2 base at 1000 m elevation. The mountain rises up to rims at 1500-1600 m that surround a 650 m deep caldera. The elevation of the caldera bottom is about 980 m. About 2/3 of the bedrock is above 1000 m and 1/9 of it is above 1300 m. The total volume of ice on Hofsjökull is 208 km3 and the average thickness only 225 m. The maximum ice thickness, about 750 m, is found in the caldera. Hofsjökull is made up of 22 ice catchment basins. The ice cap drains meltwater into four main glacial river systems. The water drainage basin of the river Þjórsá is 433 km2 and contains 101 km3 of ice, of the Jökulkvísl 51 km2 and 8 km3, of the Blanda 226 km2 and 51 km3, of the Vestari-Jökulsá 94 km2 and 22 km3, and of the Austari-Jökulsá 116 km2 and 24 km3. The total volume of the ice cap equals 200 times the annual net balance in the ac- cumulation area (which is 550 km2). If the whole ice cap were to melt over the next 200 years due to CO, induced warming, mean runoff would increase by 30 m3/s. This would be a 60% increase in the pre- sent runoff from Hofsjökull, estimated to be of the order of 50 m3/s. Assuming no increase in accumulation, an increase in air temperature by 2°C, would raise the equilibrium line by the order of 300 m, to a 1400-1500 m elevation, and Hofsjökull would shrink to a small ice cap covering the caldera. Il' the temperature increased by 3°C the ice cap would disappear alto- gether. 126

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