Landslides and Relict Ice Margin Landforms in Adventdalen, Central Spitsbergen, Svalbard
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Landslides and relict ice margin landforms in Adventdalen, central Spitsbergen, Svalbard TAKANOBU SAWAGAKI and TAKASHI KOAZE Sawagaki, T. & Koaze, T. 1996: Landslides and relict ice margin landforms in Adventdalen, central Spitsbergen, Svalbard. Polar Research 15(2), 139-152. Two characteristic landforms, landslide blocks and drainage channels, were investigated in Adventdalen, central Spitsbergen. The landslides in the middle reaches of Adventdalen comprise large-scale bedrock slumps which form a hummocky surface on the south slope of Arctowskifjellet. The fourteen recognised landslide blocks are divided into upper and lower sections, according to altitude. The drainage channels consist of tributary rivers to Adventelva which flow in two distinct directions, either parallel with or oblique to the direction of the main river. Glacial deposits were found to cover the ridges between these tributary channels. The upper and lower landslide divisions may indicate former positions of the ice surface, and the channels appear to have originated during the existence of lateral moraine ridges with high ice content. These geomorphological findings have allowed reconstruction of former ice marginal positions, and they strongly suggest the existence of stagnant ice or minor re-advance phases during the course of deglaciation in Adventdalen. Tukanobu Sawagaki, Laboratory of Geoecology, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, 060, Jupan. Takashi Koaze, Department of Geography, Meiji University, Kanda, Surugadai, Chiyoda-ku, Tokyo, Japan. Introduction fluctuations and absolute ages for moraines and glacial deposits have prevented studies in the In the large valleys of central Spitsbergen, such as inland area up to now. Adventdalen, Reindalen and Sassendalen, distinct The Japanese Geomorphological Expedition to moraines delineating the pattern of deglaciation Svalbard carried out field work in 1988 and 1989 have not previously been recognised except for a (Ono et al. 1991) and was followed by the complex series of moraines outside of the mouth Japanese Svalbard Expedition in 1990. As part of of Isfjorden (Ohta 1982; Mangerud et al. 1992). the latter expedition, a geomorphological study Additionally, it has been stated that Younger was carried out in August 1990 and in the period Dryas moraines seem to be completely absent in of June-August 1991 to identify the geomorpho- Svalbard (Salvigsen 1979) and that the ice logical evidence for glacial fluctuations in Ad- dissipated rapidly in the warming climate of the ventdalen, an inland area of central Spitsbergen. early Holocene age (Feyling-Hanssen 1955, 1965; The investigated area is situated between the ice Forman 1989; Mangerud et al. 1992). As most of margin of Dr~nbreenand the junction of Foxdalen the studies on the Quaternary glaciation in and Adventdalen. Svalbard are based on research along the coastal Two characteristic landforms, landslides and areas, where glacial till and uplifted former drainage channels were investigated. The causes shorelines are easily found (e.g. Boulton 1979; and times of failure for the landslides were Troitsky et al. 1979; Mangerud et al. 1987; evaluated. Regarding the drainage channels, this Forman 1989; Miller et al. 1989; Mangerud & study shows how the distribution of till and Svendsen 1990; Salvigsen et al. 1981; Mangerud channels allow reconstruction of the former ice et al. 1992), the Quaternary history of the inland margin landforms in the Adventdalen area. area is less well understood. It is difficult to find As large-scale topographic maps suitable for thick glacial till layers due partly to the possible the purpose of this study are not available, two presence of former cold-based, non-scouring ice. basic maps on the scale of 1:10,000 and 1:25,000 In addition, the lack of historical record of glacial with a contour interval of 10 m were drawn, using 140 T. Sawagaki & T. Koaze Fig. 1. Location map of Adventdalen, Spitsbergen. Present glaciers are shaded. Inner squares indicate the sites of Figs. 2, 6, 8 and 13. the. Analytical Photogrammetric System (Wild largest glacier, occupies the valley head, and other Aviolyt BC 2) of the National Institute of Polar small glaciers terminate in the tributary valleys. Research, Japan. Data on morphometry were Adventelva, the main stream of this valley, obtained by interpretation of air photographs in drains westward from DrQnbreen into Adventfjor- the scale of 1:15,000 taken by the Norwegian den. It has formed braided channels and an Polar Institute in August 1990. outwash plain in front of Dranbreen. From the upper reaches to the middle reaches of the valley, the river has dissected Late Quaternary sediments and the underlying Jurassic shale bedrock to form terraces about 10m high which dominate the The study area valley bottom. In the lower reaches of the river, the stream spreads out to form complicated Adventdalen is an ESE-WNW trending glacial braided channels. In the investigated area, three valley which terminates in Adventfjorden, a large tributaries in Helvetiadalen, Janssondalen tributary to Isfjorden, central Spitsbergen, Sval- and Foxdalen flow into Adventelva. Wide alluvial bard (Fig. 1). The valley is approximately 45 km fans have formed at their confluent points. long and 4 km wide. The upper reaches of the Polygons of various sizes have developed both valley are connected with Sassendalen to the on river terraces along Adventelva and on the hill northeast and Reindalen to the south through low slopes. Ice wedges were found beneath some of passes at altitudes of about 400 m a.s.l., forming a the polygons (Svensson 1988; Ono et al. 1991) network of interconnected valleys. The valley is and some pingos were present on the riverbed. surrounded by ice-capped mountains ranging in Few direct measurements of the permafrost altitude from 1000 to 1100 m. The highest summit thickness have been made in this area. According is that of Mt. Skolten (1128 m). Dr~nbreen,the to the measurements reported by Liestgl (1975), Landslides and relict ice margin landforms 141 ,100d Contour line / Fault Dipstrike lan I Fig. 2. Distribution of the landslide blocks on the southern slope of Arctowskifjellet (cf. Fig. 1). the permafrost thickness on the southern side of Helvetiafjellet Formation consists of a lower Adventdalen was 450 m. In summer, a seasonal Festningen Member and an upper Glitrefjellet thawed layer 40-100 cm thick was observed, and Member (Parker 1967). The Festningen Member the active layer saturated by water collapsed in is a light-gray, fine- to coarse-grained sandstone many places on the valley slopes. As this type of forming distinctive cliffs. The Glitrefjellet Mem- failure is limited to the surface, it is not discussed ber is a medium- to coarse-grained sandstone in this article. interbedded with shale and siltstone. The Caro- The bedrock geology of Adventdalen is shown linefjellet Formation consists of shallow marine on a 1:100,000 map (Major & Nagy 1972). A sediments with alternating beds of sandstone and major part of the investigated area is underlain by shale (Major & Nagy 1972). Jurassic and Cretaceous sedimentary rocks which The most characteristic structures in the studied dip gently towards the southwest. Progressively area are two north-south trending anticlines, the older rocks are exposed from south to north. Skolten Anticline and the Tronfjellet Anticline, These deposits are lithologically divided into the which are separated by Dronbreen Syncline Janusfjellet, Helvetiafjellet and Carolinefjellet (Major & Nagy 1972; Haremo et al. 1990). The Formations in ascending order. Skolten Anticline in this area has a trend of about The Janusfjellet Formation consists predomi- N160"E and a plunge of less than S'SSE (Haremo nantly of dark-gray shale and siltstone. The et al. 1990, fig. 6). In a river section along 142 T. Sawagaki & T. Koaze Fig. 3. Landslide block location (No. 14) on the west of Arctowskifjellet. Fig. 4. Idealised sketch of the internal structure and features of the landslide blocks. Adventelva, the upper part of a duplex structure Landslides with a northward fold axis crops out (Haremo et al. 1990). Normal faults with minor (0.1-1 m) Identification of the landslides offset have been identified in the Janusfjellet Formation. Haremo et al. (1990) suggest these as According to the geological map of the Advent- young faults associated with landslides. They note dalen area (Major & Nagy 1972), a multitude of that cleavage and joints are generally not smaller and larger landslides termed ‘landslips’ characteristic deformation structures and that joint had occurred in areas where the mountain slopes orientation is highly variable in this area (Haremo were comprised of a combination of the Janusfjel- et al. 1990). let and Helvetiafjellet formations. These slopes Landslides and relict ice margin landforms 143 Table 1. Features of the landslide blocks. No. area orientation length width base top height old new dH dL (~10~~’)(m) (m) (m a.s.1.) (m a.s.1.) (m) (m a.s.1.) (m ad.) (m) (m) 1 12.61 S46E 400 400 430 572 142 600 550 50 215 2 6.15 S64E 280 200 380 480 100 600 480 120 62.5 3 7.03 S30E 370 150 300 450 150 600 450 150 675 4 15.12 S06E 550 275 210 390 180 600 390 210 1000 5 7.77 S06W 55 150 230 390 160 600 390 210 825 6 34.42 S08E 730 500 430 623 193 600 500 100 325 7 20.12 S08W 270 675 400 450 50 500 450 50 300 8 16.06 slow 440 475 250 373 123 - - - - 9 48.84 S46W 1010 600 380 587 207 540 450 90 325 10 6.28 W 320 200 410 520 110 - - - - 11 20.11 W 550 425 360 480 120 520 450 70 200 12 15.56 S72W 470 450 250 360 110 - - - - 13 21.19 S72W 670 350 270 410 140 540 400 140 700 14 48.02 S58W 730 780 230 380 150 540 360 180 875 No = Number of each block.