Jökull - 01.12.1983, Side 11

three Landsat images (1392-12191; August 19,
1973; 1426-12070; September 22, 1973; and 1446-
12180; October 12, 1973) to document advance and
recession of the ice cap margin and termini of
several outlet glaciers. He also used Landsat images
to define the soaked zone from the percolation/dry
snow zone of the accumulation zone facies and
noted the ambiguity in determining exact position
of the termini of outlet glaciers when covered with
surface debris.
Subglacial volcanic and geothermal activity is
manifested on Landsat images as collapse caul-
drons of various diameters and related features.
The January 31, 1973,image (1192-12084) and an
enhanced September 22, 1973, image (1426-12064)
of Vatnajökull have been analyzed for a number of
investigations. An extension of geothermal activity
south into Vatnajökull from Hveradalur in the
Kverkfjöll area was discussed by Thorarinsson et al.
(1974). Jökulhlaups on Skaftá are related to the two
collapse cauldrons east of Hamarinn in westem
Vatnajökull (Williams et al., 1974; Thorarinsson et al.,
1974; Williams, 1976). Thorarinsson et al. (1974) and
Bjömsson (1975) discussed a line of cauldrons north
of Skeidarárjökull which are related to the March
1972 jökulhlaup from Grímsvötn. Tómasson (1975)
published a map of the path of this jökulhlaup based
on the Landsat image. Rist (1974), in his discussion
of the August 1973 jökulhlaup from Graenalón, a
glacier-dammed lake in southwestem Vatnajökull,
used successive Landsat images to calculate a 175
G1 reduction in vclume ofGraenalón after the jökul-
hlaup.
Landsat images have also been used eis substitut-
es for conventional line maps (U.S. GeologicalSurvey,
1976 and 1977) and as illustrations for scientific
articles: Steinthórsson (1978), in showing Bárdar-
bunga, an ice-core drilling site in northwestem
Vatnajökull; and Bjömsson (1980a), to illustrate his
summary paper on the glaciers of Iceland. Thor-
arinsson (1974a) used a Landsat MSS color com-
posite of Skeidarárjökull and environs as a dust-
jacket cover and as an illustration in his historical
review of Skeidarárhlaups and volcanic eruptions
from Grímsvötn. He (Thorarinsson 1974b) also
used the low sun angle image of Vatnajökull in his
discussion of the morphology of Lakagígar and the
móberg ridges southwest of Vatnajökull, Sugden and
John (1976) in their textbook, Glaciers and Landscape:
A Geomorphological Approach used a Landsat MSS
color composite on the cover and two other black
and white images of Iceland as illustrations in the
text. The cover of Science (v. 207, no. 4434, February
29, 1980) showed a computer-enhanced image
(1426-12070) of Vatnajökull. The cover of Jökull in
1978 (v. 28) carried a specially enhanced image
(1392-12185) of Hofsjökull, showing the prominent
subglacial volcanic landform in the southwestem
quadrant of this ice cap. Bjömsson (1978) used a
Landsat image of Vatnajökull to show the traverse
line of his radio-echosounding survey between
Tungnárjökull and Grímsfjall and for comparison
with the cross-section showing ice thickness and
subglacier topography. Hoppe (1982) used the
computer-enhanced image of Vatnajökull (1426-
12070) in his discussion of studying the Earth from
space.
Unenhanced and specially enhanced Landsat
images have been used by various scientists for
analysis of geomorphic, structural, and tectonic
features concealed by Iceland’s glaciers (Williams et
al., 1973; Williams and Thorarinsson, 1974; Thorarins-
son et al., 1974). Williams et al. (1977) discussed how
the interpretability of the September 22, 1973,
Landsat image of Vatnajökull could be markedly
improved by computer-enhancement techniques
with computer-compatible tapes (GC-I'‘s). Soha etal.
(1976) had applied a similar technique to the same
image of Vatnajökull to delineate reflectivity vari-
ations on the surface of Vatnajökull. These re-
flectivity variations were considered by Williams et
al. (1979) to portray the accumulation zone -
ablation zone facies (bare glacial ice, superposed
ice, saturated snow or slush, and wet snow) on
Vatnajökull. Delineation of the snowlines on Hofs-
jökull, Langjökull, Mýrdalsjökull, and Eyjafjalla-
jökull was discussed by Williams (1976a). Miinzer
and Bodechtel (1980) used digital image processing
techniques ofCCT’s to analyze the subglacial top>o-
graphy of and to map lineaments on Vatnajökull.
Bodechtel et al. (1979) compared Landsat and Seasat
synthetic aperture radar (SAR) images of Iceland,
including its glaciers, in their analysis of
morphologic and tectonic features. Hunting
Surveys Ltd. constructed a 1:500,000 - scale Seasat-
1 radar mosaic of most of Iceland which delineates
the glaciers of Iceland (Hunting Geology and Geo-
physics, Ltd. n.d.).
Contorted medial moraines or tephra layers in
Skeidarárjökull visible on successive Landsat
images have been used to calculate the speed offlow
of this outlet glacier east of Graenalón. During an
11-month interval, between October 14, 1972
(1083-12023) and September 22, 1973 (1426-
JÖKULL 33. ÁR 9