Jökull - 01.12.1973, Qupperneq 9

ERTS-1 Image of Vatnajökull: Analysis of Giaciological,
Structural, and Volcanic Features1
SIGURDUR THORARI NSSON
SCIENCE INSTITUTE, UNIVERSITY OF ICELAND
KRISTJÁN SÆMUNDSSON,
NATIONAL ENERGY AUTHORITY, REYKJAVÍK
RICHARD S. WILLIAMS, JR.
U. S. GEOLOGICAL SURVEY, RESTON, VIRGINIA
abstract
An ERTS-1 image of the snow-covered Vatna-
jökull area, Iceland, acquired at 7° sun angle,
reveals large stnictural and volcanic features
which are partly or wholly buried under the ice-
cap. Some of these features were previously un-
known or only suspected. The morphology of
Bárdarbunga, an area east of Hamarinn, and
Esjufjöll suggest buried central volcanoes Two
elliptical features, one at Kverkfjöll and an-
other at Esjufjöll are recognized as probable
subglacial calderas. A line of depressions be-
tween Hamarinn and Grimsvötn is related to
subglacial geothermal or volcanic activity. The
easternmost depression is related to an August
1972 jökulhlaup on the Skaftá river. A chain
°f shallow depressions E to SSE of Grímsfjall
may show the subglacial course of floodwater
from the March 1972 jökulhlaup from Grims-
vötn.
Two prominent volcano-tectonic lineaments
can be traced across the image. One strikes N.
E. for at least 80 km along a line of nuna-
taks and subglacial volcanoes, calderas, and geo-
thermal areas. Tlie other volcano-tectonic line
strikes N. 35° W. along Vatnajökull’s southern
rnargm, cutting across the other alignment. This
lcitter structural feature separat.es two markedly
different tectonic regimes. On tlie southwest is
an area dominated by volcanic fissures, faidts,
1) Publication authorized by the Director, U. S.
Geological Survey.
hyaloclastite ridges, and crater rows of unusual
length and linearity. Northeast of this line,
mostly within, but also just beyond the margin
of Vatnajökull, is an area dominated by central
volcano complexes.
INTRODUCTION
The previous paper was devoted to a general
discussion of the ERTS-1 image of the Vatna-
jökull area (See the cover picture), how it and
other imagery of Iceland are being acquired by
the first Earth Resources Technology Satellite
(ERTS-1), and a few comments on some of the
prominent glacial features (eg., moraines). This
paper, however, is directed at an analysis of
the glaciological, structural, and volcanic fea-
tures within the confines of Vatnajökull and
the area around it. Of particular importance
is the relationship between the three kinds of
features and to the tectonic setting of Iceland.
In fact, the glaciological, structural, and vol-
canic features are very closely interrelated. As
will be seen there are important structural fea-
tures visible on the ERTS-1 image of Vatna-
jökull, some previously unknown or only sus-
pected from other evidence, which may explain
the very great difference in outpouring of vol-
canic material and the unique concentration of
specific volcanic landforms in the area now
known as Vatnajökull. It is this highland area,
of course, upon which the Vatnajökull icecap
JÖKULL 23. ÁR 7