Náttúrufræðingurinn

Volume

Náttúrufræðingurinn - 1983, Page 115

Náttúrufræðingurinn - 1983, Page 115
Pálssonar, dagbækur og ritgerðir 1791 — 1797. — Snælandsútgáfan, Reykjavík: 813 bls. Wigner, J. H. 1905. The Vatnajökuli traversed from N. E. to S. W. - Alpine Journal 22: 436—448. Þorleifur Einarsson. 1968. Jarðfræði. Saga bergs og lands. — Mál og menning, Reykjavík: 335 bls. Þorvaldur Thoroddsen, 1914. Ferðabók. 3. bindi. - Hið íslenzka fræðafélag, Kaupmannahöfn: 360 bls. SUMMARY The Graenalón region in Vestur-Skaftafellssýsla, South Iceland by Haukur Jóhannesson, Icelandic Museum of Natural History, P. O. Box 5320, Reykjavík, Iceland. A historical review of Lake Grænalón and Mt. Grænafjall in the pre-1900 literature is presented. The Lake Grænalón is first mentioned around 1700 and frequently since, but usually under the name Gríms- vötn, and later as Núpsárvatn, Græna- fjallslón and Grænalón. Mt. Grænafjall is first mentioned in the year 1793. Two Brit- ish travellers were the first men to reach Mt. Grænafjall and it occurred as late as 1904. The Skeiðarárjökull glacier flows along the Skeiðarárdalur valley and dams a tributary valley on its western side forming the Lake Grænalón. The Lake Grænalón has been emptied repeatedly or its water- level lowered drastically in the course of the water forcing its way beneath the gla- cier, causing floodings on the Skeiðarár- sandur plain (glacial burst, jökulhlaups). Prior to 1935 the lake had an outlet to the Núpsá river through a mountain pass at 635 m a. s. 1. Pronounced shore-line indi- cates the former high waterlevel of the lake. The geology of the region is outlined. The rocks are all volcanic in origin and supposed to be erupted during the early Matuyama epoch, 1.6 to 2.0 million years ago. The sequence is about 500—700 m thick and is characterized by subglacial basic hyaloclastites and interglacial basalt lava flows. The section indicates three glaciations and three interglacial periods, respectively. In the region are two recent basalt lava flows, Bergvatnsár flows, which are about 4000 years old and believed to be formed in the same eruption. The eruption sites are at present covered by the Vatnajökull glacier which is supposed to have been considerably smaller in the early part of the Holocene. The flows cover an area of about 10.7 km2 off the glacier and their volume is about 0.07 km'. Newly discovered cold mineral springs on Mt. Grænafjall are described and evi- dence for high temperature geothermal field in the Þórðarhyrna area in the Vatna- jökull glacier is presented. Þórðarhyrna is an active central volcano and the Berg- vatnsár lava flows may be erupted from a fissure swarm presently subglacial, stretch- ing towards southwest from the main volcano. 101
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