Náttúrufræðingurinn

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Náttúrufræðingurinn - 1974, Side 45

Náttúrufræðingurinn - 1974, Side 45
NÁTTÚRUFRÆÐINGURINN 39 Stephensen, Magnús, 1785: Kort Beskrivelse over den nye Vulkans Ildsprud- ning i Vester-Skaptafields-Syssel paa Island i Aaret 1783. Kopenhagen 1785. Talwani, MWindisch, C. C. ir Langseth, M. G., 1971: Reykjanes Ridge crest: A detailed geophysical study. f. Geopliys. Res. 76: 473—517. Thoroddsen, Þorvaldur, 1915: Die Geschichte der Islándischen Vulkane. D. Kgl. Danske Vid. Selsk. Skr., Naturv. og Mat. Afd., 8. R. IX; 458 p. Þórarinsson, Sigurður, 1965: Neðansjávargos við ísland. Náttúrufr. 35: 49—74. S U M M A R Y Volcanic eruptions at Eldeyjarbodi, the Reykjanes Ridge, by Sveinn Jakobsson Museum of Natural History, Reykjavik. Dredge hauls collected on the crest of the Reykjanes Ridge by the USNS Lynch in June 1971 and October 1973 are briefly described. A total ol’ 235 kg of fresh basalts were obtained at 12 stations between 63° 17.6' N and 63° 45.7' W (Fig. 1). Petrology of dredged rocks collected in 1971 has previously been discussed (Brooks, Jakobsson & Campsie 1974). The rocks are all tholeiitic basalts, forrned in situ and derive mostly from submarine breccias and pillow lavas, but a few pices of tuff were also found, proltably formed in near-surface phreatic eruptions. The samples are fresh and free of icerafted debris and are therefore thought to be recent (post-glacial). The dredge L 71-19 which was taken in June 1971 SW of tlie breaker Eldeyjarbodi prooved to be extremely fresh and without any sign of biological growth (Fig. 2). The dredges L 73-42 and L 73-41 collected in Oct. 1973 are petrologically very similar to L 71-19 and probably all three derive from the same eruption (Fig. 3). These rocks are inferred to be very recent and possibly formed in a volcanic eruption in 1970 or 1971. There are no known witnessess to this inferred eruption but air pilots reported a small eruption in 1966 at this location. Other volcanic erup- tions on the Reykjanes Ridge, known to have occurred during the last 200 years are discussed and localized (Fig. 4). The Reykjanes Ridge between 63° 10' and 63° 48' N consists of flat-topped seamounts arranged en ecliclon. Their trend changes frorn N 20° E in the southern part to N 37° E close to land. It is suggested that the seamounts are submarine expressions of fissure swarms comparable to those found on the Reykjanes Peninsula, live such swarms can tentatively be localized on the northernmost Reykjanes Ridge. Elongated seamounts are explained as formecl in fissure eruptions but tuyas in single-vent eruptions (Fig. 5), like the subglacial móberg ridges and tuyas (stapis) on
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