Jökull - 01.12.1999, Page 93

forward an alternative model where no pillow lava is
present in the root of the island. Finally, Cameron et
al. (1992) presented results of gravity modeling of the
island (Fig. 3). They proposed that chimneys of very
high porosity extended from beneath the tuff cones to
considerable depth under the island, well into the pre-
eruption sea-floor. They further suggested that these
might be the remnants of volcanic conduits. The
model has dense bodies (p = 2600 kg/m3) flanking the
chimney that were not found in the coring of 1979. In-
stead the region of one of these dense bodies was
found to be composed of palagonite and altered tephra
with a mean density close to 2000 kg/m3 (Jakobsson
and Moore, 1982). A potential problem with the inter-
pretation of Cameron et al. (1992) is that no consider-
ation was given to density variations above sea level.
Such an approach must be regarded as questionable
when dealing with a volcanic edifice known to contain
spatially separate units with significantly different
densities such as subaerial lava and tephra.
Fig. 2. Surtsey as mapped in 1994 (Einarsson et al., 1994), bathymetry as measured in 1989 (from Norrman and Erlingsson, 1992)
and from Sjómælingar íslands (1977). The contour interval is 10 m. Also shown are the two eroded islands, Jólnir and Syrtlingur,
the two craters, Surtur I and II, the location of the drill hole and the profile AA'. The region of Fig. 4 is shown as a box. - Kort af
Surtsey samkvœmt mœlingum 1994 (Einarsson et al, 1994) en dýptarlínur erufrá 1989 (Normann og Erlingsson, 1992) og
1977 (Sjómœlingar Islands).
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