Náttúrufræðingurinn - 1974, Page 45

NÁTTÚRUFRÆÐINGURINN
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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