Jökull - 01.12.1989, Blaðsíða 109

chapter reviews briefly earlier efforts in glacier map-
ping and glacial hydrology in Iceland. Chapter 2
outlines theoretical concepts (to be applied later in
the book) on subglacial drainage including
specifically Icelandic subjects such as the interac-
tion of the glacier with geothermal activity and
subglacial eruptions. Chapter 3 describes surface
topography and radio-echo sounding results from
Vatnajökull and Hofsjökull. The sounding lines total
4500 km in length and cover about 3400 km2 in
detail. To a hard-rock person like myself, the single
most remarkable feature of these results may be the
mapping of large caldera structures in the basement.
Chapter 4 deals with the ice catchment basins on the
two glaciers, and Chapter 5 discusses subglacial
lakes in westem Vatnajökull, including the geother-
mal Grímsvötn lake and its discharge through the
Skeiðará river. Chapter 6 treats Grímsvötn in more
detail, using conservation equations for water mass,
energy and solute content to infer the magnitudes of
the main heat sources (totalling 4-5 GW on average)
for this unique lake. Other observational data is also
used to constrain the possible mechanisms for hla-
ups from Grímsvötn. Chapter 7 delineates water
drainage basins in the glacier areas so far investi-
gated; the divides between these do not always coin-
cide with the corresponding ice divides. This topic is
especially of interest for the main sponsor of the
echo sounding project, the National Power Com-
pany. The final chapter presents the main conclu-
stons of the book, including the important result that
at least in Iceland — the water pressure at the
glacier bed appears to be approximately equal to the
ice overburden pressure rather than to atmospheric
pressure ; this has long been a disputed subject
among glaciologists.
It is difficult to find anything to criticize in this
work. The book is very well written and legible, and
the accompanying maps are beautifully produced.
There are some errors of typographical nature in the
text and the list of references; many of these are of
the inconsequential but stubbom kind for which an
author tends to blame the printers or, more recently,
his word-processor. In b/w photographs of distant
glacier scenes (such as some of those in Chapter 1),
I have difficulties in distinguishing between glacier,
snow, rock or even clouds, but this may not be a
problem to more seasoned readers. In the interesting
computer-drawn perspective plots of the subglacial
landscapes in Chapter 3, inclusion of a coordinate
grid or index map would have been helpful.
Presentation of the radio-echo sounding method,
equipment and signal processing, only takes up a
few pages in the book. One would have liked to see
a more extensive discussion of the feasibilities and
limitations (e.g., resolution, sources of errors and
artifacts) of the method based on the author’s
experience, as he has indeed done recently in Ice-
landic in the festschrift "í hlutarins eðli" (1987). In
this paper he mentions that the sounding records
sometimes show evidence of layering within the ice,
such as may be caused e.g. by thick ash deposits.
This work, for which Helgi Bjömsson was
awarded the dr. philos. degree by the University of
Oslo in Dec. 1988, is a major landmark in glaciolog-
ical research in Iceland. It has both fundamental
value in the scientific understanding of glaciers and
subglacial volcanism, and economical value for
projects hamessing the glacial rivers for electricity
generation or other purposes. One must hope that it
reaches the large intemational circulation that it
deserves; unfortunately much original research in
Icelandic geoscience, including not only the glacio-
logical contributions of Þórður Þorkelsson and
Sveinn Pálsson in past centuries but also quite
recent work, has remained relatively unknown due
to difficulties in getting its results distributed to the
scientific community. The many glacier enthusiasts
in Iceland will no doubt look forward to a continua-
tion of the radio echo sounding activities, as well as
to other surveys of the glaciers of Iceland that build
on these successes.
Leó Kristjánsson
The book "Hydrology of Ice Caps in Volcanic
Regions" (Societas Scientiarum Islandica, Rit
(Monograph) 45, Reykjavík 1988, viii +139 pp. and
21 maps, $55) may be ordered from the University
Bookstore, University oflceland, 101 Reykjavík.
JÖKULL, No. 39, 1989 107