Jökull - 01.12.1989, Blaðsíða 108

Book Review
HYDROLOGY OFICE CAPS IN VOLCANIC REGIONS
by
Helgi Bjömsson
Science Institute, University oflceland
Glaciers and ice caps (collectively named "gla-
ciers" in this review) are a prominent feature of the
landscape of Iceland, covering almost 11% of the
country’s surface. While most people, content with
viewing these from a distance, may consider them to
be simply static masses of snow, others have real-
ized that there are important scientiíic questions to
be answered about the dynamics of glaciers and
about their effects upon the environment. In the last
couple of million years, glaciation was much more
extensive than now, and it played a role in creating
many of the geological and geographical features of
Iceland. At the present time the glaciers influence
the climate of parts of the island as well as the flow
of the major rivers, which in tum affects the nation's
agricultural, energy and communications situation.
Some of the glaciers also represent a hazard to the
population, mostly through the effects of subglacial
volcanic activity.
The results of observations on Icelandic glaciers
are somewhat scattered, and no comprehensive
treatise describing them is yet available. What has
been missing in particular from our knowledge of
the glaciers is the "third dimension", namely their
intemal stmcture and the subglacial landscape.
Seismic sounding efforts on Vatnajökull in the early
1950’s have not been followed up subsequently, and
only a single deep drilling has been carried out, in
1972.
New possibilities in the study of glaciers in Ice-
land were opened up in 1976 with a successful
attempt at radio-echo sounding, by a joint U.K.-
Icelandic expedition to Vatnajökull. As has been the
case in many other fields of research, Icelandic
scientists were quick to develop further the ideas
and equipment brought from abroad: an improved
sounder was built at the Science Institute of the
University of Iceland and tested in the following
summer. Since then, two large areas in Vatnajökull
have been surveyed in detail, as well as essentially
all of Hofsjökull, mostly by continuous measure-
ments at 1-km line spacing. The radio wavelength
used is (in ice) about 40 m, and random errors in
ice-thickness determinations are generally less t’nan
20 m. The survey equipment and processing capa-
bilities has been steadily upgraded, and the very
strenuous work of each field season has been
rewarded by exciting discoveries.
Helgi Bjömsson has been the key person in these
developments, which followed logically from his
previous research interests in fields such as glacial
hydrology, jökulhlaups, and subglacial volcanism.
He has been ably assisted by technical staff of the
University and by members of the Iceland Glacio-
logical Society.
Helgi has now summarized the results of these
surveys up through 1987 in a book accompanied by
a collection of 21 very detailed and accurately sur-
veyed maps. One is an index map of Vatnajökull in
scale 1: 500 000, the others are in 1: 200 000 scale.
Ten of these are multicolor maps of glacier surface
elevations (which incorporate many improvements
upon previous topographic maps), glacier
thicknesses, bedrock surfaces, and ice/water
divides. The other ten (black and white) maps show
data sources, ice flowlines and water potential con-
tours.
The book consists of eight chapters. The first
106 JÖKULL, No. 39, 1989