Jökull - 01.01.2015, Page 68

Sigurðardóttir et al.
lava edges or ledges that may be presented could not
be estimated. These profiles could be reflecting a
stack of several different lava lobes or flows beneath
the sand. Due to lack of exposure it is not possible
to establish connections between the assumed buried
lava bodies with known lava flows in the area such
as the Eldgjá (934 AD) and Hólmsá lava (7700 years
old) flows or the Kriki hyaloclastite flow. The Kriki
hyaloclastite flow disappears beneath the sand a few
hundred meters northwest of the profiles and no edges
are visible on the surface. It is therefore possible that
the Kriki flow extends far enough to the east to be the
source of some of the anomalies seen in these profiles.
Possibly all the lava flows previously mentioned could
be located at the profiles and are thus all influencing
the measurements.
Area and volume estimations
The location of the Eldgjá lava edge beneath Mýrdals-
sandur, estimated in this study, was used to re-evaluate
the size of the Eldgjá lava flow. The area of the lava
flow found in this study, not included in previous vol-
ume estimates is 64 km2. No magnetic profiling took
part in the southernmost part of Mýrdalssandur, near
the sea. As a result this estimate of the area has con-
siderable uncertainty.
The thickness of the lava flow is 18–25 m accord-
ing to borehole data (Vegagerðin, 2013). Taking into
account considerable uncertainty in area and assum-
ing that the lava flow thickness of the buried part is
the same as in the area where the drilling took place,
the additional volume estimated in this study adds
1.4±0.5 km3 to previous estimates of the Eldgjá lava.
Figure 7. Cross section model from Hafursey hyaloclastite mountain and the Eldgjá lava along profile 4. The
black dots in the sandur indicate assumed thickness according to the VES soundings (Thórarinsson and Guð-
mundsson, 1979). The total thickness of sediments to the west of the lava field is highly uncertain but probably
not less than 100 m. – Þverskurðarlíkan frá Hafursey í vestri til Eldgjárhrauns í austri eftir sniði 4. Svörtu
punktarnir á sandinum austan við Hafursey sýna þykktarmat samkvæmt viðnámsmælingum. Þykkt sandsins
vestan við hraunbrúnina er varla minni en 100 m en óvissa í þykkt er mikil.
68 JÖKULL No. 65, 2015