Jökull - 01.12.1972, Síða 39

INTERPRETATION
OF INERARED IMAGES
AND AERIAL PEIOTOGRAPHS
Kverkfjöll vestri:
Hveradalur a,nd Jökullón
The dominant feature of the 1966 and 1968
infrared images of Kverkfjöll vestri is the part-
ly subglacial, linear thermal area of Hvera-
dalur (Figs. 4 ancl 6) trending north-northeast
for 3.2 kilometers (64°38'4P N; 16°40'44' W).
More than 120 distinct individual or coale-
scent thermal points are identifiable on high-
amplitude level slices of Hveradalur (Fig. 7C).
The thermal features extend northeastward
beginning on the southwest, from thermally
emitting single and double ice-perforation
features, several of which were clescribed from
ground observations in 1953 by Thorarinsson
(1953, p. 20, Fig. 11) to the partly ice-covered
glacial lake (Jökullón) and then along the
narrow solfatara valley (Hveradalur) at about
1620-meter elevation, to a broader thermal
area leading to a breach in the ice margin on
the north, and finally to a linear series of
punctate ice performations (Fig. 3), each the
focal point of thermal emission (Figs. 4, 5,
ancl 6).
Based on the 1968 Infrarecl Ektachrome ancl
Plus X photographs, the thermal area of
Hveradalur (excluding the ice cauldron) is
about 500 meters wide at the glacial lake,
Jökullón (Fig. 8), ancl 700 meters at its widest
northeast of the steam vent named Gámur
(Thorarinsson 1953, p. 20, Fig. 11), which is
located at a constricted part ol the valley. At
the northeasternmost ice perforation feature the
thermal area may be only 50 meters wide. The
Hveradalur thermal area clearly extends under
the lake. Thorarinsson (1953) has described
hot springs high in silica, occasionally visible
in the lake basin, but the extent and depth
of the lake varies considerably. On 12 March
1944 it was at least 500 meters long, but on
9 July 1946 no lake was present at all (Thor-
arinsson 1953, p. 21).
Measurements made on the unrectified aerial
photographs (significant error may be greater
than five per cent) indicate that tlie open part
of Jökullón containing floating ice bits was
410 meters long and 130 meters wicle (Fig. 8)
in August 1968. The maximum dimensions of
the water-filled and ice-covered lake basin were
560 X 290 meters, but strand line features
suggest the existence of a slightly larger lake
in the past. The hot springs rich in silica were
not visible and may now be sublacustrine,
contributing to the volume of the melt-water
lake.
The infrared imagery of 1966 (Fig. 4) in-
dicates that the largest group of thermal points
is located north-northeast of Jökullón at the
widest part of the valley. Northwest-flowing
thermal surface drainage through a wide
breach in the glacier margin is clearly revealed
by the imagery; however, U. S. Air F’orce aerial
photographs of 28 August 1960 (Fig. 31 show
that this outflow area was still partly ice
covered at that time, although northwest-flow-
ing streams emanating from ice perforation
features were identifiable. By 1968 the north-
western margin of the ice in the area of the
breach had receded 200—300 meters farther to
the southeast than its position of 1960 (Fig. 8).
This part of Hveradalur has thus been opened
up considerably since 19601). Considerable ice
melting over the thermal features of Kverk-
fjöll vestri must thus liave occurred in recent
years.
A second grouping of thermal points, identi-
fiable but not outstanding on the 1966 irnag-
ery, occurs on the southeastern slope of a hill
within an ice amphitheater immediately south-
east of Jökullón. Here, on 24 May 1968 a
vapor column 300—400 meters high was ob-
served emanating from a new powerful steam
vent. On 9 June 1968 Thorarinsson visited the
area. This steam vent was then still the largest
in the group of solfataras and continued to
be so in August 1969.
Signal amplitude level slices of the magne-
tically taped infrared imagery of 26 August
1968 show intensity of thermal emission in
several steps (Fig. 7). Using this technique, two
major coalescent groups of high intensity
thermal features were recorded: 1) southeast ol’
Jökullón, coincident with the steam vent and
1) 1914 topographic mapping by Trautz
(1919) suggests, liowever, that in parts of Kverk-
fjöll vestri near Hveradalur, the ice margin
then was farther upslope than in 1960.
JÖKULL 22. ÁR 37