Náttúrufræðingurinn

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Náttúrufræðingurinn - 01.02.1966, Blaðsíða 1

Náttúrufræðingurinn - 01.02.1966, Blaðsíða 1
________________ NATTURUFRÆÐINGURINN_________________179 því eru útlínur eyjarinnar stöðugum breytingum háðar, svo sem sjá má af 7. mynd, sem teiknuð er eftir ljósmyndum Landmælinga ís- lands af Surtsey á ýmsum tímum. Vindrof er einnig mikið í eynni á stundum, svo að vart er verandi þar fyrir sandfoki. Vatnsrof er töluvert í rigningum og skriðuföll tíð, einkum þó þar, sem brim sker sig inn í gjallhamrana. Það er þegar orðið ærið fjölbreytilegt og tilkomumikið landslagið á þessari ungu ey (Pl. III b), sem er og verður sannkallað óskaland landmótunarfræðinga. SUMMARY Some Facts about the Surtsey Eruption by S. Thorarinsson Departmeni og Geology and Geography, Museum af Natural History, lieykjavik. The history of the Surtsey eruption is brielly outlined. It can be divided in i'our main phases. 1. Explosive (phreatic) activity which started visibly Nov. 14, 1963, írom a 300—400 m long íissure running N35°E—S35°W, situated 3 naut. miles WSW o[ Geirfuglasker, the southernmost o£ the Westman Islands (Vest- mannaeyjar). It may be regarded as likely that the eruption broke through the sea floor at about 130 m depth about a week before it became visible. The island Surtsey was born Nov. 15. On January 31, 1964, the eruption ceased in the vent (Surtur Senior) active until then, but broke out the following day in a fissure (Surtur Junior) on the NW side of Surtsey. The explosive phase ended April 4, 1964. 2. Purely effusive Hawaiian type activity in Surtsey from April 4, 1964, to May 17, 1965. This activity built up a lava shield of the Hawaiian-Ice- Iandic type. 3. Explosive activity 0.6 km ENE of Surtsey (Figs. 1 and 3), starting visibly May 22, 1965, and ending about Oct. 20, 1965. This activity built up the island Syrtlingur which reached a max. height of about 70 m and a max. area of about 0.15 km2. This island was completely washed away by the breakers during a stormy week Oct. 17 to 24, 1965. 4. Explosive activity 0.9 km SW of Surtsey (Fig. 4) starting visibly Des. 26, 1965, and still going on in early March 1966. A small island had by then been repeatedly built up and destroyed. Between Dec. 28, 1963, and Jan. 6, 1964, submarine activity was visible 2.5 km ENE of Surtsey (The Surtla activity, cf. Fig. 1). A submarine ridge was built up to more than 100 m height but did not reach the surface. The distance between this ridge and the active vents SW of Surtsey is about 5 km, direction N65°E-S65°W. Although eruption has broken out in at least five separate fissures the pre- sent writer is inclined to regard the entire activity in the Surtsey area since its

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