Jökull - 01.12.1982, Blaðsíða 35

vances were recorded in 1942/43, 1949/50 and
1953/54. The largest was 133 m in 1953/54 which
took the ice edge back to its 1949/50 position. In the
west, the only readvance recorded was in 1953/54
which amounted to 7 m.
SEDIMENTS AND LANDFORMS
IN THE PROGLACIAL AREA
The retreat of Breidamerkurjökull over the past
ninety years has resulted in the accumulation of
vast quantities ofglacial and fluvioglacial sediments
and the creation of an intricate landform assembl-
age which contains classic examples of most of the
principle landforms associated with glacial and ílu-
vioglacial deposition. There can be few proglacial
areas in the world where such a wide variety of
features can be studied within an area of about 60
square km. Little is known about the sediments
which have accumulated prior to the last advance of
the glacier. Boulton (1977), by means ofa geophysi-
cal traverse of Jökulsárlón has identified a “lower-
till” which he suggests pre-dates the Holocene clim-
atic optimum. It is likely that the valley now occupi-
ed by Breidamerkurjökull and its proglacial area is
underlain by many hundreds of metres of sediment
accumulated during the many and sometimes very
rapid advances and retreats oftheglacierduring the
Quaternary climatic oscillations.The very recent
sediments (post-1890) have been mapped and exa-
mined indetail (Fig. l).Therearelargeareascover-
ed by glacial till, the surface of which is often “flut-
ed” (Howarth 1968, Price 1969, 1970, Boulton\9T6,
Boulton and Dent 1974, Boultonet al 1974). There are
also many well-developed moraine ridges 10-20 m
high (Howarth 1968, Price 1969). and numerous
small “wash-board” and “annual” moraines (Price
1970). The present distribution of “ground mor-
aine” and moraine ridges is largely the result of the
lack of meltwater erosion in the areas where they
exist. The large and migrating meltwater rivers
have removed large areas ofground moraine and of
segments of the moraine ridge system.
The most extensive surface material in the pro-
glacial area is fluvioglacial sand and gravel. Mass-
>ve sandar have been built up by the numerous
anastomosing meltwater streams issuing along the
ice front. These sandar can be divided into two
groups. Firstly, the sandar beyond the 1890 mor-
atne were mainly developed in the early years ofthis
century and although major streams still crossed
the western half of the system in 1951 (Price and
Howarth 1970), the concentration of meltwater dis-
charge into the Stemma, Jökulsá and Fjallsá rivers
meant that the proximal parts of the older sandar
became incised by these rivers and little sediment
was added to these sandar surfaces after 1945.
Secondly, the sandar inside the 1890 moraine are
smaller and more complex in their development.
Many of them were related to englacial and sub-
glacial streams so that esker ridges are now seen
leading into the proximal parts ofsandar. Extensive
areas of fluvioglacial sedimentation took place
against or on top of glacier ice so that when the
buried ice eventually melted, extensive areas be-
came pitted with kettle holes. The availability of
good quality aerial photography since 1945, taken
on 7 occasions, has allowed the detailed study of the
evolution of the sandar, eskers and drainage syst-
ems (Howarth 1968, Price 1969, Price 1971). The rate
of change of landforms in this low altitude, wet and
relatively warm proglacial area consequent upon
the melting ofburied ice has been quite remarkable.
Smooth sandar surfaces have become extensively
pitted with little of the original surface remaining
within 10 to 15 years.
The detailed photogrammetric maps and ground
surveys of the proglacial area near the Máva-
byggdarönd medial moraine (Figs. 4 and 5), have
permitted the study of the evolution of one esker (E5
of Price 1969) between 1965 and 1977. Maps and
profiles of this esker have been made on four occas-
ions (Price 1969, Pennington 1978). Altitudinal
changes in the profile (Fig. 4) reveal continuous
loweri.ig of the esker crest of some 8 m at the distal
end between 1965 and 1977 and of 20 - 25 m at the
proximal end. The base of theesker has been lower-
ed by some 2 m at the distal end and by 10 — 15 m at
the proximal end over the same period. It is remark-
able that an englacial esker with an ice core has
survived such rapid lowering and has been preserv-
ed as a distinct gravel ridge 4 — 10 m high. Other
eskers have been studied (Howarth 1971) and new
eskers have emerged in the area to the north of the
Stemmulón during the last few years.
PROGLACIAL RIVERS AND L/\KES
The evolution of the drainage system in front of
Breidamerkurjökull between 1904 and 1965 has
been described by Price and Howarth and a des-
cription of the proglacial lake basins has been pro-
JÖKULL 32. ÁR 31