AFA-TE 100 was within * 12 m. Topographic maps were used
for the comparison, when aerial photos were not available. The
studies have resulted in several interesting findings.
1. The theory of present glacial retreat in FJL first introduced
by V. Sukhodrovskiy in 1934 and developed by M.Grosswald in
1973 was proved to be correct in general. We found nearly 50
ice sheets and caps showing drastic withdrawal of their borders
(up to several hundreds of meters) during the past 40 years,
several of them have totally disappeared. The most significant
retreat of glacial termini occurs at fronts of outlet glaciers
because of marine abrasion and calving. Thus, big - more than
500 meter long - frontier parts of tidal glaciers on Prince
George Land, Jackson, Karl Alexander, McClintock and
Salisbury islands were broken off and shorelines have changed
significantly. Large tabular icebergs found close to those new
glacial fronts indicate that this destruction happened nearly
simultaneously in all places, and probably not long ago. The
maximum retreat of ice shores was detected to be 2-4 km at
Rough Bay on Hall Island. According to our planimetric
assessment glacial retreat on Hall Island amounts to 3.296 in the
course of the past 40 years.
2. Several new islands attached to the larger lands by glaciers
have appeared in FJL due to glacial retreat. So, Littrow Island
(65 km?), specified as a peninsula in contemporary maps, was -
for the second time after the American Wellman polar
expedition - discovered to be separated from Hall Island by the
Nordenskjóld Channel (Kostka, Sharov 1996). One new, as yet
uncharted islet close to the southern ice shore of Ziegler Island
was first discovered in the lab by means of SAR image data,
which revealed small terrains free of glacier ice with better
contrast, but only if the surrounding water surface is smooth. It
was also discovered that Mother-of-pearl Island with a total
area of 1.5 km? and a maximum height of 22 m asl, shown on
all topographic maps as entirely covered by the ice cap, does
not exist any more. We assume it was a temporarily grounded
icy island.
3. A very interesting exception to the common glacial retreat in
FJL was recognized in spaceborne imagery: the greatest outlet
glaciers have advanced offshore by several hundreds of meters.
The front of Eastern Glacier at Salisbury Island has flowed
about 500 meters into the Rhodes Channel; Impetuous and
Famous glaciers in Wilczek Land have advanced by 600 meters
in several parts since May 1958. This phenomenon has yet to be
explained, but together with other data on glacial dynamics, it
supports a hypothesis about the presence of floating or partly
grounded ice shelves in the archipelago that has been mistrusted
by some explorers until today (Dowdeswell 1994).
4. Ice-free coastal areas also underwent essential changes,
especially in the areas with gentle slopes (beaches, low-lands).
With the exception of some insignificant advances, which could
be caused by fluvioglacial and wave processes, all such areas
investigated in the central part of the archipelago have shown a
retreat of coastlines. The largest rates of retreat can be observed
at the coast of Littrow (between 20 and 80 meters),
Komsomolskiy (30-100 m) and Fersman (130-190 m) islands.
One example of changing coastlines at Lake Cape is given in
Figure 2 showing an "old" aerial photograph with the "new"
position of the shoreline overprinted. Such coastal changes
could not be explained by occasional variations in the sea level,
which was close to the mean value during spaceborne survey
(see Figure 1,D - first columns). In satellite images we could
not observe any advancement of the delta of the Romantics
River, the largest river of the archipelago, with its delta
advancing toward the sea at a rate of 2-3 mm per year (cited
from Barr 1995). Field observations were necessary to interpret
all these findings which contradict some existing hypotheses.
COASTLINES AT LAKE CAPE
3-1993 ’
600 — 900
x A enn
D Geodetic signal s
^ . Photogrammetric point
Coastline in August, 1993 |B
g : MASSEN
Figure 2. Sketch map showing changes of shorelines at Lake
Cape
4. RESULTS OF FIELD OBSERVATIONS
Terrestrial observations and geodetic measurements were
carried out during two field campaigns in FJL in August 1994
and July 1995 in order to perform ground control surveys, to
check the datum governing the vertical control and to complete
obscured areas and phenomena that were not readily
understood. A helicopter and motorboat were effectively used to
reach distant places of interest, and a number of additional
terrestrial and aerial photographs were taken. Some toponymic
investigations were performed to verify and present geographic
names in the new maps. Specific interpretation of typical sites
appearing on aerial and spaceborne images was carried out on
17 large islands of the archipelago. Main emphasis was put on
the registration of hydrographic features and areas of pioneer
vegetation. In the course of the investigations, we did not find
any examples of an increase in the erosion rate testifying to à
. current uplift in those lands.
472
Planimetric differential coordinates of 71 ground control points
were measured for subsequent mapping by means of two
identical "Trimble-Navigation" GPS receivers, and elevations
above sea level were determined by "Thommen" and "Avocet'
barometric altimeters. The existence of the new small island
Malyshok (Midget) in Rhodes Channel very close to the ice
shore of Ziegler Island was proved and its coordinates Were
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
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