Jökull - 01.12.1999, Blaðsíða 96

such bodies, but suggests that they are not present in
the uppermost kilometer under the center of the is-
land. However, since the data coverage is limited to
the island itself, the existence of more extensive
anomalous bodies in the upper crust under the island
cannot be ruled out. A longer profile, extending over
the sea on both sides, would be required to study any
anomalies due to such bodies.
The first model (Fig. 5a) is the simplest, based
mainly on the drill core results of Jakobsson and
Moore (1982). The units of the model are tephra, pil-
low breccias and subaerial lava. The gravity field cal-
Fig. 5. Forward gravity models of Surtsey. Densities, in 103 kg/m3 (g/cm3) given above the models, and half-strike lengths of
the bodies (T = tephra, L = lava, PB = pillow breccia, PL = pillow lava, CF = crater filling, S = sediments) are given in Table
2. The vertical line near the center of the island is the location of the drill hole. a) A model with the center of the island under-
lain by tephra, no core of pillow lava. b) A model with a large core of pillow lava. c) A model with a small pillow lava core and
a high density plug under the crater. d) A model with no core of pillows but with relatively high density sediments making up
the northem peninsula. - Líkön af byggingu Surtseyjar samkvœmt þyngdarmœlingum. Eölismassar í g/cm^ og lengdir skrokka
hornrétt á snið eru í 2. töflu (T = gjóska, L = hraun, PB = bólstrabrotaberg, PL = bólstraberg, CF = gígfylling, S = set). Lóð-
rétta línan nœrri miðri eyjunni sýnir legu borholunnar. a) Líkan þar sem ekki gert ráðfyrir neinu bólstrabergi undir eynni. b)
Líkan með stórum kjarna af bólstrabergi. c) Líkan með litlum kjarna af bólstrabergi og gígfyllingu. d) Líkan án bólstrabergs
en gert er ráð fyrirfremur háum eðlismassa sets í norðurtanganum.
94
JÖKULL, No. 47, 1999