Jökull


Jökull - 01.12.1953, Síða 39

Jökull - 01.12.1953, Síða 39
ANCHORED STONE POLYGONS AT LOW LEVELS WITHIN THE ICELAND BASALT REGIONS In a preliminary paper of a compilatory nature I arrived at the following main clas- sification of Iceland in respect of polygons: „Low level coastal areas and valley bottoms: All polygons shallow („floating"), with gravel margins, usual dimeters 20—80 cm. Well assorted throughout. Gradually merg- ing into Inland plateaux at 400—800 m levels: Polygons usually relatively shallow and assorted, with gravel margins. Usual dia- meters 60—200 cm, tending to incraese with altitude. The basalt plateaux at about 600—1000 m levels: Polygons usually deep („anchored") and assorted, with block margins. Usual dia- Swedish-Icelandic Investigations 1936—37—38. Geografiska Annaler, Stockholm 1937—1940. 1943. Lewis, W. V., in Discussion on the origin of glacial drift. The Journal of Glaciology, Vol. I. London 1950. Thorarinsson, Sigurdur, Uber anomale Glet- scherschwankungen. Geologiska Föreningens i Stockholm Förhandlingar. 1938. Thoroddsen, Th., Island, Grundriss der Geo- graphie und Geologie. Pet. Mitt. Erg. Heft 152/53. Gotha 1905-06. Todtmann, E. M., Im Gletscherriickzugsgebiet des Vatnajökull auf Island, 1951. Neues Jb. Geol. Palaontol. Stuttgart 1952. ÁGRIP: Dr. E. M. Todtmann, jarðfrœöingur frá Hamborg hefur oft liomið hingað til lands til jöklarannsókna. Síðastliðið sumar dvaldi hún 10 daga við Eyjabakkajökul. I ofanritaðri grein lýsir hún svœðinu framan við jökulinn og rekur lengdarbreytingar hans, frá því er hann gekli fram árið 1890. Styðst hún við flugmyndir og við athuganir Sigurðar Þórarinssonar, sem dvaldist á þessum slóðum sumarið 1935. Jökullinn geklt nokltuð fram árið 1931 og sömuleiðis 1938, en heildarlega hefur jökullinn hörfað til baka um 1300 m síðan 1890. meters 2—10 m.“ (Notes on Patterned Ground in Iceland. Geografiska Annaler 1951, p. 147). Since I compiled this paper I have paid more attention to patterned ground during my travels in Iceland without, however, having had oppor- tunity to study these interesting phenomena systematically. To the above-mentioned classi- fication I should now like to add the following remarks: During my travels in the tertiary basalt re- gions in N and E Iceland the two last summers I have found anchored polygons with block margins even on low level coastal areas and valley bottoms. Three examples may be mentioned: 1. On a rather plain area SW of Skógafjall in Hrútafjörður, N Iceland (8 km W of Ivjörseyri) in ab. 250 m height I ob- served rather regular anchored polygons with block margins. The diameter of the polygons was 2 á 3 m, and the diam. of the blocks in the margins 10—35 cm. This type of polygons seems to be common on the ridges between Hrútafjörður and Gils- fjörður, and may probably be found at lower levels than 250 m. 2. In Búlandsdalur, S of Búlandstindur, E. Iceland, I found on the valley bottom in ab. 150 m height stone polygons of the same type and size as in Hrútafjörður. This was the only type of polygons observed in that valley. 3. N of the mouth of Búlandsdalur the river Búlandsá has formed very nice gravel ter- races in ab. 50 and ab. 22 m height respect- ively. On these terraces are found small floating gravel polygons and rings 30—50 cm in diam. The same type of floating polygons, with diameter varying between 30 and 80 cm, is common on gravel plains near the farm Teigarhorn in ab. 20 m height, but in that height one can also find rather irregular, anchored stone poly- gons, and one can find both types of polygons on the same place such as shown 37

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