Jökull - 01.01.2012, Page 149

Öræfajökull central volcano, SE-Iceland
Figure 12. The bedrock topography for the centre part of Öræfajökull along with the outlines of Öræfajökull
caldera (broken red line), a potential inner caldera formation (broken yellow line) and a possible older eroded
caldera formation north of the present caldera (broken green line) within the accumulation area of Svínafells-
jökull. – Botnlandslag undir hæsta hluta Öræfajökuls. Brotalínur sýna Öræfajökulsöskjuna (rautt), líklega
innri öskjumyndun (gult) og mögulega eldri og rofna öskjumyndun undir upptökum Svínafellsjökuls (grænt).
fore be expected for an eruption vent located below
this elevation. The corresponding water table for an
open cauldron within the Virkisá part of the caldera
(Figure 11), would be ∼1610 m a.s.l. The basal water
pressure maintained by a water level at 1610 m a.s.l.
would not hydrostatically lift up the ∼130 m ice block
covering the pass underneath Kvíárjökull. Propaga-
tion of floodwater through an ice tunnel, melted by
warm water, east towards Kvíá should however not be
ruled out.
The topography of the mountain outside the
caldera is much more complex than within it, with
many ridges propagating radially from the Öræfajök-
ull centre. It is not trivial to distinguish between to-
pographic features formed initially by volcanic activ-
ity and forms solely produced by glacier erosion, but
many of these ridges were probably initially formed
by flank eruptions from Öræfajökull. The valley stor-
ing the accumulation area of Svínafellsjökull north of
the Öræfajökull caldera is a topographic feature where
such a separation is difficult (Figure 12). It may have
been formed entirely by glacier erosion. However,
the feature looks very much like an old caldera, of
similar size to the present caldera, eroded down to-
wards west by the glaciers. A caldera at this loca-
tion would be in agreement with geophysical studies
JÖKULL No. 62, 2012 147