Náttúrufræðingurinn - 1966, Page 33

NÁTTÚ RU FRÆÐI N GU R1 N N
179
því eru útlínur eyjarinnar stöðugum breytingum liáðar, svo sem sjá
má af 7. mynd, sem teiknuð er eftir ljósmyndum Landmælinga Is-
lands af Surtsey á ýmsum tímum. Vindrof er einnig mikið í eynni
á stundum, svo að vart er verandi þar fyrir sandfoki. Vatnsrof er
tciluvert í rigningum og skriðuföll tíð, einkum þó þar, sem brim
sker sig inn í gjallhamrana. Það er jregar orðið ærið fjölbreytilegt
og tilkomumikið landslagið á þessari ungu ey (Pl. III b), sem er
og verður sannkallað óskaland landinótunarfræðinga.
SUMMARY
Some Facts about the Surtsey Eruption
by S. Thorarinsson
Depnrtment og Geology and Geography, Museum af Natural History, lleykjavik.
The history ol the Surtsey eruption is briefly outlined. It can be divided
in four main phases.
1. Explosive (phreatic) activity which started visiblv Nov. 14, 1963, from a
300—400 m long fissure running N35°E—S35°W, situated 3 naut. miles
WSW of Geirfuglasker, the southernmost of 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 tlien, 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 efíusive Hawaiian type activity in Surtsey from April 4, 1964, to
May 17, 1965. This activity built up a lava shield of the Hawaiian-Ice-
landic 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 reachcd 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 stortny 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.
Hetween 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 lias broken out in at least l'ive separate íissures the pre-
sent writer is inciined to regard the entire activity in the Surtsey area since its