Antarctic Science 13 (1): 75-78 (2001) 0 British Antarctic Survey Printed in the United Kingdom Geomorphological sketch map of the Fossil Bluff area (Alexander Island, Antarctica) mapped from aerial photographs MARIA CRlSTlNA SALVATORE Dipartimento di Scienre della Terra, Universita "LaSapienra ", P le A Moro 5, 00185 Rome, Itab Abstract: A geomorphological sketch map of the Fossil Bluff area, showing the main morphological characteristicswas prepared from aerial photographs taken by the British Antarctic Survey in 1995. Landforms and deposits mapped include those related to glaciers and the local hydrography,periglacial and nival activity, and wind and gravity action. Data mapped originally at a scale of 1: 12 500 and simplified for presentation here at a scale of about 1:30 000, have been digitized as vectors using a GIs. In this way these data may easily be integrated with other environmental data for future research. Received 27 August 1998, accepted 1 December ZOO0 Key words: Aerial photographs, Antarctic Peninsula, Fossil Bluff, geomorphological map Introduction by periodic northward extensions of anticyclonic systems Aerial photographs were used to prepare a geomorphological from West Antarctica (Clapperton & Sudgen 1982). An sketch map of the Fossil Bluff area at a scale of 1:30 000, and analysis of a 34-year surface air temperature record for Fossil to interpret the geomorphological features present. The Bluff by Harangozo et al. (1997) documented the climate investigationof landforms, particularly those of glacial origin, regime as being 'continental', rather than 'maritime' as is the and of the glacial cover can provide an important contribution case farther north; the mean air temperatures in the warmest to the reconstruction of climatic change, as well as to the and coldest months are -1.2"C and -17.3'C, respectively. compilation of thematic maps. The studied area (Fig. 1) Fossil Bluff is one of several small ice-free areas present covers about 46 km2of the eastern coast of Alexander Island along the eastern margin of Alexander Island near George VI (Antarcticpeninsula)behveenlatitude 7 1"18'and71'21'52"S Sound, a trench of tectonic origin, located between Alexander and longitude 68'13' and 68"23'W. It faces George VI Ice Island and Palmer Land. The sound is now occupied by an ice Shelf to the east and is bounded to the north by Eros Glacier, shelf 500 km long, 20-60 km wide and 100-500 m thick, fed to the south by Uranus Glacier, and to the West by LeMay by outlet glaciers flowing from the Palmer Land ice cap Range. (Swithinbank 1968). Unlike most ice shelves, George VI Ice Shelf flows in two directions from an ice divide (Swithinbank 1988). More precisely, the southern extremity flows mainly Methodology towards Ronne Entrance (Bellingshausen Sea) between The elements described and shown on the sketch map were Monteverdi Peninsula and DeAtley Island, the part north of interpreted from aerial photographs by analysing differences approximately 70'40's flows northward into Marguerite Bay in tone, texture, structure, dimension, etc. The work was and most of the ice in the central section flows across the sound based on the interpretation of three different sets of black and although with a slight northerly component (Swithinbank white panchromatic stereoscopicaerial photographs taken by 1968, Pearson & Rose 1983). The flow lines are detectable as British Antarctic Survey during 1995 (BASl2195, frames ridge and furrow features on the surface of the ice shelf, on 069472; BAS /4/95, frames 148-170; BAS/5/95, frames Landsat (Sugden & Clapperton 1981) and radar images. 205-253). About 76 vertical aerial photographs were used. George VI Sound trench separates the mainly plutonic, and They have approximate scales of 1:20 000 and 1:6000 with a volcanic rocks ofthe AntarcticPeninsula from the sedimentaq ground resolution of less than 1 in. The photointerpreted data rocks of eastern, central and southern Alexander Island (Bell were superimposed on a 1:12 500 topographic map (British 1975). In the Fossil Bluff area, rock exposures consist Antarctic Survey 2000) and digitized as vectors using a GIs essentially of mudstones with lesser amounts of sandstone, package (ARCIINFO software). conglomerate and rarer volcaniclastic deposits including penecontemporaneousvolcanic rocks, such as lava, tuffs and agglomerate (Grlkurov 1978, Taylor et al. 1982). The strata Climatic and geological settings have been affected by folding and thrusting associated with The present climate of the area is strongly influenced by a tectonic compression (Bell 1975). cyclonic pressure system moving to the east, and subordinately 75 Downloaded from https://www.cambridge.org/core. Open University Library, on 28 Jan 2020 at 06:31:33, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102001000116 76 MARIA CRlSTlNA SALVATORE Fig. 1. Geomorphological sketch map ofthe Fossil Bluff area. The, 1:12 500 scale BAS SCISTAMAP Series, Sheet 2, compiled by A.J. Fox was used as a topographic base. For Key see opposite page. Downloaded from https://www.cambridge.org/core. Open University Library, on 28 Jan 2020 at 06:31:33, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102001000116 GEOMORPHOLOGICAL SKETCH MAP, FOSSIL BLUFF 77 they have unstable slopes. In the proglacial area is a glacial Photo-interpretation of the Fossil Bluff area deposit, close to the glacier front (an ice apron), which, along The Fossil Bluff area has elevations no higher than 920 m. Its with big erratic boulders, seem to represent the youngest rocks have sub-horizontalbedding; in some places this results deposits in the area. On the north side of the glacier terminus in a landscape with a tabular or mesa-like structure, whereas and along the foot ofthe southern slope, lateral moraine ridges elsewhere an alpine-like morphology with well-developed are visible on the photographs; they seem to be ice-free and cirques hosting the heads of local glaciers, is developed. have stable slopes. Supraglacialdebris is widespread and dlfferentiated on the Three debris units have been recognized by map into “supraglacial debris”, where the cover is complete, photointerpretation. and “scattered supraglacial debris” where the ice surface is The first debris unit is located on the floor of a U-shaped incompletely covered. The debris may be former englacial ice-free valley about 2 km north of Fossil Bluff field debris, brought to the surface by ablation, with a subordinate station. The upper part of the valley is now occupied by contribution from the adjacent slopes as rockfall. Ice-cored the front of an alpine glacier with supraglacial moraine moraine ridges are common on supraglacial debris, as well as and ice-cored moraine ridges on its terminal part. ice-cored dirt cones and kettle holes. Considering that photogeological analysis permits the West of Fossil Bluff field station, is an easterly flowing distinction, on the basis of differences in tone, texture valley glacier 1700 m long and 500 m wide. Supraglacial and structure, of the debris unit from slope deposits, and debris is present on its terminal part and there is a lateral considering the morphology of the valley, this unit may moraine close to the foot of the southern margin. Ice-cored be interpreted as a glacial dra. moraine ridges are also present on that drift; they have sharp crests, and the presence of local debris slides suggests that b) The second debris unit is located about 2 hi south-west Downloaded from https://www.cambridge.org/core. Open University Library, on 28 Jan 2020 at 06:31:33, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102001000116 78 MARIA CRlSTlNA SALVATORE of Khdu Peak at an elevation of 320400 m a.s.1. It lies Among hydrographicfeatures, meltwater streams (bediere) on a low-gradient slope. and melt-water lakes are common on the surface of glaciers; cryconitic holes are probably also present on the glacier south c) The third is located south of Fossil Bluff field station in of Giza Peak and between the two wide supraglacial moraines a W-E trending valley, about 1.6 km long, between located to the south. KhduPeak and Giza Peak: thsvalley is partially occupied The data interpreted from the aerial photographs were by snow and probably also by a snow-covered glacier. mapped originally at a scale of 1:12 500 and are simplified The debris occurs along the medial part of the valley here to a scale of about 1:30 000; it is hoped that the resulting between 400 m and 370 m a.s.l., whereas between 370 m preliminary geomorphologicalmap will provide a framework and 300 m it extends also to the left slope of the valley, for more detailed ground surveys in the future. where it appears to be moulded in small ridges; large sandstoneboulders are present there, as well as at higher elevations. It may be interpreted as a glacial deposit. Acknowledgements Although the main morphogeilic processes are of glacial This work is the result of a collaborative project between the origin, nevertheless periglacial processes play an important British Antarctic Survey andtheoperativeunit GLA23 ofthe role in the morphological evolution of the area. Periglacial Italian Antarctic Research Programme (PNRA), in the featurcs, such as gelifluction terraces, blockfields, avalanche frameworkoftheItalianNational Council (CNR) short mobility cones and tracks, are widespread. Talus slopes, debris cones program. I thank the referee, Dr M. Bentley, whose comments and debris coverage are common, especially on the steepest helped me in the redrafting of this paper. slopes. Because the detrital release mechanism is mainly the result of freeze-thaw cycles, talus slopes and debris cones References may be regarded as periglacial processes with a subordinately iiffluencefroin gravitation, as observed also by Lopez-Martinez BELL,C.M.