Marginal Moraines Research Articles

Glacier fluctuations, equilibrium-line altitudes and palaeoclimate in Lyngen, northern Norway, during the Lateglacial and Holocene

Based on lacustrine and morpho-stratigraphical evidence from Lyngen in Troms, northern Norway, 13 marginal moraines have been mapped in front of Lenangsbreene in Strupskardet. Moraines M1-M13 are inferred to represent glacier halts or advance/readvance taking place during the Lateglacial and Holocene. The presence of collapse depressions suggests that some of them were ice cored (M1-M3). A chronological framework, taking into account a combination of former shorelines and related glacier-meltwater channels, lichenometry and AMS radiocarbon-dated lacustrine sediments spanning the last 20 000 cal. yr BP, has been established. The distal glacier-fed lake Aspvatnet was isolated from the sea c 10 300 cal. yr BP, and the lacustrine sediments have been investigated by use of loss-on-ignition (LOI) magnetic susceptibility, water content, wet and dry bulk density (DBD), and the magnetic parameters anhysteretic remanent magnetization (ARM) and saturation remanent magnetization (SIRM). There is, in general, good agreement between physical sediment parameters and magnetic parameters. DBD, a combination of medium and fine silt and the two statistical parameters ‘sorting’ and ‘mean’ have been used to construct a high-resolution glacier-fluctuation curve for the last 3800 cal. yr BP. Based on an accumulation-area ratio (AAR) of 0.6 and an ablation-accumulation balance ratio (ABR) approach, a continuous temperature-precipitation-wind equilibrium-line altitude (TPW-ELA) curve for the last 20000 cal. yr BP has been constructed. Using an established exponential relationship between mean ablation-season temperature and mean annual solid precipitation at the ELA of Norwegian glaciers, variations in mean winter precipitation (snow) are quantified using an independent proxy for summer temperature. Mean annual winter precipitation varied from 500 to 5000 mm water equivalent, and on average, Holocene estimates are c. 50% higher than similar figures from the Lateglacial. The two driest periods occurred during Heinrich events 1 (HI) (17 500-16 500) and 0 (HO) (13 000-12 200), whereas freshwater pulses to the North Atlantic had apparently no systematic impact on mean winter precipitation. Based on the winter precipitation curve from Lyngen, the atmospheric circulation responded to the sea surface temperature (SST) lowering associated with HI and HO. The dry and cold climate during the events led to formation of talus-derived rock glaciers at sea level.

The Vestfjorden-Trænadjupet palaeo-ice stream drainage system, mid-Norwegian continental shelf

An ice stream in the Vestfjorden-Trænadjupet depressions off northern Norway transported glacial debris to the shelf edge and into the deep sea during the last glaciation. Our interpretation is based mainly on regional and detailed bathymetry, and 2D and 3D seismic data. This palaeo-ice stream was approximately 400 km long and covered an area of ∼20,000 km 2. Including a complex system of tributary fjords and valleys in Nordland county, the drainage basin had an area of ca. 150,000 km 2 within the Fennoscandian Ice Sheet (FIS) during the Last Glacial Maximum (LGM). The location of the palaeo-ice stream prevented large ice masses from reaching the montainous areas of Lofoten and Vesterålen. A local ice dome was established in these areas. The palaeo-ice stream eroded extensively into both Mesozoic and Cenozoic sedimentary rocks, and Quaternary sediments. A pattern of well-developed, subglacial, sedimentary bedforms was produced (e.g., mega-scale lineations, drumlins). Ice-stream shear margin moraines are located on both sides of Trænadjupet, defining the width of the palaeo-ice stream (∼ 90 km at the shelf edge). These moraines are commonly 10–20 m high, a few kilometres wide, and reach several tens of kilometres in length. A large recessional moraine (the Tennholmen Ridge) has been mapped in Vestfjorden. It is 80 m high, 20 km wide and 60 km long. We have interpreted this ridge as a grounding-line moraine, formed during a halt or a readvance of the ice stream during the last deglaciation. The large transport of glacial debris towards the grounding line occurred during this stage. Northeast of the Tennholmen Ridge, several smaller moraine ridges were developed at still-stands during deglaciation.

Lateglacial and early Holocene palaeoclimatic reconstruction based on glacier fluctuations and equilibrium‐line altitudes at northern Folgefonna, Hardanger, western Norway

AbstractNorthern Folgefonna (c. 23 km2), is a nearly circular maritime ice cap located on the Folgefonna Peninsula in Hardanger, western Norway. By combining the position of marginal moraines with AMS radiocarbon dated glacier‐meltwater induced sediments in proglacial lakes draining northern Folgefonna, a continuous high‐resolution record of variations in glacier size and equilibrium‐line altitudes (ELAs) during the Lateglacial and early Holocene has been obtained. After the termination of the Younger Dryas (c. 11 500 cal. yr BP), a short‐lived (100–150 years) climatically induced glacier readvance termed the ‘Jondal Event 1’ occurred within the ‘Preboreal Oscillation’ (PBO) c. 11 100 cal. yr BP. Bracketed to 10 550–10 450 cal. yr BP, a second glacier readvance is named the ‘Jondal Event 2’. A third readvance occurred about 10 000 cal. yr BP and corresponds with the ‘Erdalen Event 1’ recorded at Jostedalsbreen. An exponential relationship between mean solid winter precipitation and ablation‐season temperature at the ELA of Norwegian glaciers is used to reconstruct former variations in winter precipitation based on the corresponding ELA and an independent proxy for summer temperature. Compared to the present, the Younger Dryas was much colder and drier, the ‘Jondal Event 1’/PBO was colder and somewhat drier, and the ‘Jondal Event 2’ was much wetter. The ‘Erdalen Event 1’ started as rather dry and terminated as somewhat wetter. Variations in glacier magnitude/ELAs and corresponding palaeoclimatic reconstructions at northern Folgefonna suggest that low‐altitude cirque glaciers (lowest altitude of marginal moraines 290 m) in the area existed for the last time during the Younger Dryas. These low‐altitude cirque glaciers of suggested Younger Dryas age do not fit into the previous reconstructions of the Younger Dryas ice sheet in Hardanger. Copyright © 2005 John Wiley & Sons, Ltd.

Ice stream shear margin moraines

AbstractThe distribution and pattern of subglacial bedforms provides valuable insights into the configuration and behaviour of former ice sheets and recent work has begun to address the landform assemblages of palaeo‐ice streams. In this paper, we focus on subglacially formed ice stream shear margin moraines; these landforms are thought to form in the shear zone between fast‐flowing stream‐ice and slow‐moving sheet‐ice. Using satellite imagery and aerial photographs, we identify four ice stream shear margin moraines associated with the former M'Clintock Channel Palaeo‐Ice Stream, Victoria Island, Arctic Canada. The moraines range in length from 11 to 22 km, maintain fairly constant widths of around 500 m, and range in height from 10 to 50 m above the surrounding terrain. They are composed of carbonate drift of a similar composition as the ice stream bedforms and have been laid down irrespective of local and regional topography. Two of the moraines display a lateral offset and are thought to reflect minor migrations of the ice stream margin. We explore their possible mode of formation and suggest that they occur when erosion at the ice stream margin provides a surplus of sediment which is ‘smeared out’ in the downstream direction. The identification of other palaeo‐ice stream shear margin moraines has probably been hampered by their interrupted continuity which can only be appreciated at the large scale. It is hoped that the descriptions presented in this paper will help to identify these landforms and increased detection of palaeo‐ice streams will reveal other ice stream shear margin moraines. Copyright © 2002 John Wiley & Sons, Ltd.

Timing, equilibrium-line altitudes and climatic implications of two early-Holocene glacier readvances during the Erdalen Event at Jostedalsbreen, western Norway

Following the Younger Dryas, the first evidence of glacial activity in southern Norway in response to climatic change occurred during the early Holocene, when terminal moraines from the Erdalen Event formed beyond the position of later ‘Little Ice Age’ moraines. In front of present outlet glaciers on both sides of the Jostedalsbreen ice cap, sets of pre-‘Little Ice Age’ marginal moraines have been morphostratigraphically corre lated with the Erdalen Event. The lithostratigraphy in a peat bog at Hellemyrane in Jostedalen, western Norway, provides firm evidence for a two-phase Erdalen Event associated with two glacier readvances of Nigardsbreen at the Preboreal/Boreal transition. Radiocarbon dates from the peat bog give age estimates for the two phases: the first Erdalen Event readvance took place between 10 100 and 10 050 cal. BP, while the second occurred close to 9700 cal. BP. The lowering of the equilibrium-line altitude (ELA) during these readvances is estimated using the ‘Little Ice Age’ ratio (LR) approach to be about 230 m and 215 m, respectively. The first readvance is attributed to an increase in winter precipitation, while the second readvance may have been primarily caused by a marked drop in summer temperature which reactivated already existing ice masses.

Early and Middle Valdaian glaciations, ice-dammed lakes and periglacial interstadials in northwest Russia: new evidence from the Pyoza River area

The Pyoza River area in the Arkhangelsk district exposes sedimentary sequences suitable for study of the interaction between consecutive Valdaian ice sheets in Northern Russia. Lithostratigraphic investigations combined with luminescence dating have revealed new evidence on the Late Pleistocene history of the area. Overlying glacigenic deposits of the Moscowian (Saalian) glaciation marine deposits previously confined to three separate transgression phases have all been connected to the Mikulinian (Eemian) interglacial. Early Valdaian (E. Weichselian) proglacial, lacustrine and fluvial deposits indicate glaciation to the east or north and consequently glacier damming and meltwater run-off in the Pyoza area around 90–110 ka BP. Interstadial conditions with forest-steppe tundra vegetation and lacustrine and fluvial deposition prevailed at the end of the Early Valdaian around 75–95 ka BP. A terrestrial-based glaciation from easterly uplands reached the Pyoza area at the Early to Middle Valdaian transition around 65–75 ka BP and deposited glaciofluvial strata and subglacial till (Yolkino Till). During deglaciation, laterally extensive glaciolacustrine sediments were deposited in ice-dammed lakes in the early Middle Valdaian around 55–75 ka BP. The Barents–Kara Sea ice sheet deposited the Viryuga Till on the lower Pyoza from northerly directions. The ice sheet formed the Pyoza marginal moraines, which can be correlated with the Markhida moraines further east, and proglacial lacustrine deposition persisted in the area during the first part of the Middle Valdaian. Glacio-isostatic uplift caused erosion followed by pedogenesis and the formation of a deflation horizon in the Middle Valdaian. Widely dispersed periglacial river plains were formed during the Late Valdaian around 10–20 ka BP. Thus, the evidence of a terrestrial-based ice sheet from easterly uplands in the Pyoza area suggests that local piedmont glaciers situated in highlands such as the Timan Ridge or the Urals could have developed into larger, regionally confined ice sheets. Two phases of ice damming and development of proglacial lakes occurred during the Early and Middle Valdaian. The region did not experience glaciation during the Late Valdaian.

Timing and east–west correlation of south Swedish ice marginal lines during the Late Weichselian

The retreat of the Late Weichselian ice sheet over the southern part of Sweden is marked along the southwest coast by distinct marginal moraine ridges. Their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines. Along the southeastern side of the peninsula, the ice recession has been reconstructed based on a combination of clay-varve chronology, pollen and radiocarbon stratigraphy. A morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west-coast moraines cannot be followed through the central part of the peninsula towards the east coast. This paper is an attempt to reconstruct an age-equivalent west–east extension of the ice-recession lines on the basis of existing data sets. For our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon-dated clay-varve chronology on the east coast. We conclude that the two oldest moraines on the west coast formed at ∼18,000–16,000 and ∼15,400–14,500 cal yr BP, respectively. During the following rapid deglaciation, which may have coincided with the beginning of the Bølling pollen zone, large parts of southernmost Sweden became ice free, except for higher elevated areas, where stagnant ice remained for another 400–500 yr. A best guess is that the formation of the next younger ice marginal lines may have occurred at ∼14,400–14,200, ∼14,200 and ∼13,400 cal yr BP and during the Younger Dryas cold event.

Saalian to Weichselian stratigraphy and sedimentation along the Lågjæren - Høgjæren escarpment, southwest Norway

Quaternary sediments along a profile crossing the southern part of the Jæren escarpment, southwestern Norway, have been investigated with regard to their glacial history and sea-level variations. Deposits from at least three glaciations and two ice-free periods between Oxygen Isotope Stage 6 and the Late Weichselian have been identified. Subglacial till directly overlain by a glaciomarine regressional succession indicates a deglaciation, and amino acid ratios in Elphidium excavatum between 0.083 and 0.118 date this event to Oxygen Isotope Stage 6. Sea-level dropped from 130 to below 110 m a.s.l. Subsequently, a short-lived ice advance deposited a marginal moraine and a sandur locally on the escarpment. Stratigraphical position and luminescence dates around 148 ka BP suggest deposition during the final stage 6 deglaciation. A Late Weichselian till covers most of the surface of Jæren. In addition to a well documented westerly ice flow, glaciotectonic indications of ice flow towards the north have been found. Ice flow directions and a hiatus between Oxygen Isotope Stage 6 and the Weichselian indicate enhanced erosion along the escarpment and the influence of a Norwegian Channel ice-stream. Copyright © 1999 John Wiley & Sons, Ltd.

Saalian to Weichselian stratigraphy and sedimentation along the Lågjæren – Høgjæren escarpment, southwest Norway

Quaternary sediments along a profile crossing the southern part of the Jæren escarpment, southwestern Norway, have been investigated with regard to their glacial history and sea-level variations. Deposits from at least three glaciations and two ice-free periods between Oxygen Isotope Stage 6 and the Late Weichselian have been identified. Subglacial till directly overlain by a glaciomarine regressional succession indicates a deglaciation, and amino acid ratios in Elphidium excavatum between 0.083 and 0.118 date this event to Oxygen Isotope Stage 6. Sea-level dropped from 130 to below 110 m a.s.l. Subsequently, a short-lived ice advance deposited a marginal moraine and a sandur locally on the escarpment. Stratigraphical position and luminescence dates around 148 ka BP suggest deposition during the final stage 6 deglaciation. A Late Weichselian till covers most of the surface of Jæren. In addition to a well documented westerly ice flow, glaciotectonic indications of ice flow towards the north have been found. Ice flow directions and a hiatus between Oxygen Isotope Stage 6 and the Weichselian indicate enhanced erosion along the escarpment and the influence of a Norwegian Channel ice-stream. Copyright © 1999 John Wiley & Sons, Ltd.

Younger Dryas glaciation in the lfoten area, western Norway; evidence from lake sediments and marginal moraines

During the Younger Dryas, the Ålfoten area was covered by ice caps separated from the continental Scandinavian inland ice. The local Younger Dryas glacier margins of two coalescing plateau glaciers, Ålfotbreen and Davikbreen, have been reconstructed on the basis of marginal moraines, lacustrine sediments and radiocarbon age estimates. The Younger Dryas glaciation was more extensive in this area than previously postulated. Ålfotbreen advanced to its maximum position during the early/middle Younger Dryas, before the deposition of the Vedde Ash tephra layer ca. 10,300 yr BP.

Directions of ice flow during the last glaciation in counties Meath, Westmeath and Cavan

Ice How direction indicators in north-west County Meath and adjacent parts of Westmeath and Cavan are described. Drumlins, striae, roche moutonnees, and other streamlined features, as well as till fabrics, suggest a general flow during glacial maximum of north-west to south-east when combined with erratic carriage data. Analysis of the configuration of ice marginal moraines and subglacially deposited esker ridges deposited during glacial retreat, as well as till fabric analysis of deglacial sediments, suggest a more complicated retreat of ice. with margins oriented South-west to north-east prevailing in the south and cast of the study area. Further to the west and south-west there seems to be an element of retreat towards the west, with a north-south trending ice margin. This is suggested as providing evidence for a decoupling of Ihe ice into separate lobes in that area.

Evidence for Heinrich event 1 in the British Isles

In the north Irish Sea basin (ISB), sedimentary successions constrained by AMS 14C dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle. (i) Marine muds (Cooley Point Interstadial) dated to between 16.7 and 14.7 14C kyr BP record a major deglaciation of the ISB following the Late Glacial Maximum (LGM). (ii) Terminal outwash and ice-contact landforms (Killard Point Stadial) were deposited during an extensive ice readvance, which occurred after 14.7 14C kyr BP and reached a maximum extent at ca.14 14C kyr BP. At this time the lowlands surrounding the north ISB were drumlinised. Coeval flowlines reconstructed from these bedforms end at prominent moraines (Killard Point, Bride, St Bees) and indicate contemporaneity of drumlinisation from separate ice dispersal centres, substrate erosion by fast ice flow, and subglacial sediment transfer to ice-sheet margins. In north central Ireland bed reorganisation associated with this fast ice-flow phase involved overprinting and drumlinisation of earlier transverse ridges (Rogen-type moraines) by headward erosion along ice streams that exited through tidewater ice margins. This is the first direct terrestrial evidence that the British Ice Sheet (BIS) participated in Heinrich event 1 (H1). (iii) Regional mud drapes, directly overlying drumlins, record high relative sea-level (RSL) with stagnation zone retreat after 13.7 14C kyr BP (Rough Island Interstadial). Elsewhere in lowland areas of northern Britain ice-marginal sediments and morainic belts record millennial-scale oscillations of the BIS, which post-date the LGM advance on to the continental shelf, and pre-date the Loch Lomond Stadial (Younger Dryas) advance in the highlands of western Scotland (ca. 11–10 14C kyr BP). In western, northwestern and northern Ireland, Killard Point Stadial (H1) ice limits are reconstructed from ice-flow lines that are coeval with those in the north ISB and end at prominent moraines. On the Scottish continental shelf possible H1-age ice limits are reconstructed from dated marine muds and associated ice marginal moraines. It is argued that the last major offshore ice expansion from the Scottish mountains post-dated ca. 15 14C kyr BP and is therefore part of the H1 event. In eastern England the stratigraphic significance of the Dimlington silts is re-evaluated because evidence shows that there was only one major ice oscillation post-dating ca.18 14C kyr BP in these lowlands. In a wider context the sequence of deglacial events in the ISB (widespread deglaciation of southern part of the BIS → major readvance during H1 → ice sheet collapse) is similar to records of ice sheet variability from the southern margins of the Laurentide Ice Sheet (LIS). Well-dated ice-marginal records, however, show that during the Killard Point readvance the BIS was at its maximum position when retreat of the LIS was well underway. This phasing relationship supports the idea that the BIS readvance was a response to North Atlantic cooling induced by collapse of the LIS. © 1998 John Wiley & Sons, Ltd.

Seismic facies and architecture of ice‐contact submarine fans in high‐relief fjords, Troms, Northern Norway

During the Late Weichselian, large marginal moraines were deposited in the Norwegian fjords. In Troms County these features are termed the Skarpnes and Tromsø‐Lyngen moraines, respectively, and have been mapped from land into the marine environment where they were formed as ice‐contact submarine fans. High‐resolution seismic data from several fjords have been studied and reveal a typical sediment thickness of 150–320 m for these ice‐contact systems. All of the ice‐contact submarine fans were formed under similar climatic conditions, but display wide variation in geometry, architecture and seismic pattern. This variation is related to differences in sediment supply, the nature of the subsurface of the fan (e.g. position of thresholds), basin geometry and basin depth. Based on interpretation of the different seismic facies and the architecture of the fans, former ice‐front positions have been suggested and a model has been presented for the formation of different types of ice‐contact submarine fans dependent upon variation in local basin condition.

Cirque glaciers as morphological evidence for a thin Younger Dryas ice sheet in east‐central southern Norway

Three localities with marginal moraines deposited by former cirque glaciers are investigated in east‐central southern Norway. The wet‐based (erosive) cirque glaciers with aspects towards S‐SW and N‐NE are mapped at altitudes above 1100 m, and have a mean equilibrium‐line altitude of 1275 m. With a suggested mean annual winter precipitation close to the average for the modern accumulation season (1 October‐30 April) when the cirque glaciers existed, the mean air‐temperature depression during the ablation season (1 May‐30 September) is calculated to be 6–7°C lower than at present. The high‐altitude cirques of central Rondane were still covered by ice when the low‐altitude cirque glaciers developed in distal position for this massif in eastern Rondane and on isolated mountains. Hence, the cirque glaciers are suggested to have existed during the deglaciation after the Late Weichselian maximum, and most likely during the Younger Dryas (11000–10000 BP). The cirque glaciers indicate a downwasting ice‐sheet surface well below an altitude of 1100 m prior to the Younger Dryas, and this supports a limited (small) vertical extent for the Late Weichselian ice sheet in this region. With the contemporaneous level for instantaneous glacierization (glaciation threshold) just below the highest elevated peaks in east‐central southern Norway, this fits with the idea of a continuous downwasting of the Late Weichselian ice sheet since the ‘first’ nunataks appeared. The occurrence of the cirque glaciers indicates a multidomed Scandinavian ice‐sheet geometry during the Late Weichselian.

Genesis of an elongated ridge at jæren, southwest norway: drumlin or marginal moraine?

Southeast‐northwest trending longitudinal ridges are conspicuous morphological features at Lågjæaren, southwest Norway. They have been interpreted as either marginal push‐moraines, deposited by a southwesterly flowing glacier, or drumlins, which originated during advance of a northwesterly flowing glacier. The paper presents results of morphological, sedimentological and glaciotectonic analyses of one of these ridges at Obrestad. It is suggested that the ridge has been formed by drumlinization of outwash deposits by a glacier advancing towards the northwest and subsequently deformed by a southwesterly flowing glacier.

Genesis of an Elongated Ridge at Jaeren, Southwest Norway: Drumlin or Marginal Moraine?

Genesis of an Elongated Ridge at Jaeren, Southwest Norway: Drumlin or Marginal Moraine?

Topographic control of equilibrium-line altitude depression on reconstructed 'Little Ice Age' glaciers, Grovabreen, western Norway

'Little Ice Age' marginal moraines in the Grovabreen area, inner Sunnfjord, are mapped and described. The modem and 'Little Ice Age' (mid-eighteenth century) equilibrium-line altitude (ELA) of the plateau glacier Grovabreen is calculated by the use of an accumulation-area ratio (AAR) of 0.6, giving a 'Little Ice Age' ELA depression of 125 m. AAR-ELA depression of the 'Little Ice Age' glaciers is also calculated for northern and southern outlet glaciers. Different estimates are considered to be the result of topographic differences. Other methods, such as the mean elevation of glaciers (MEG) and the toe-to-headwall altitude ratio (THAR), gave ELA depressions of 260 m and 315 m, respectively. These differences, due to topographic conditions, indicate that only glaciers with a uniform slope should be used to calculate the regional ELA of former glaciers.

The influence of englacial drainage on sediment-transport pathways and till texture of temperate valley glaciers

Field studies at Mueller and Tasman Glaciers in New Zealand and in Iceland have revealed extensive ice-marginal moraine sequences fed by a series of debris bands containing characteristic rounded debris. We interpret these debris bands as meltwater deposits from relict conduits. The process of sediment accumulation described requires that debris undergoing basal or high-level ice transport is entrained by running water, becoming comminuted and rounded before being returned to high-level ice transport and eventual deposition in marginal moraines. Tins sequence of events suggests a link between glacier hydrology and ice-marginal sedimentation, possible mechanisms for which are explored. Pronounced moraines with rounded debris can be expected if (a) large quantity of debris is carried within the englacial drainage network; (b) there is a tendency for this debris to be abandoned within the ice; and (c) ice-flow trajectories and ablation ensure that this debris congregates at the ice surface. Streams which flow at high level within the ice can intercept and entrain englacial debris derived from rock fall. However, debris sources at Gigjökull and Steinholtsjökull in Iceland are restricted to the glacier bed, suggesting that, in certain cases, the presence of a basal overdeepening acts as a key factor controlling the accumulation of these moraines. Water pressure rises as channels encounter an overdeepening, forcing debris-laden streams to leave the bed and take an englacial route. That debris may pass from ice to water and back into ice before deposition has gone largely unrecognised in accounts of glacial process systems, yet it provides an explanation of how temperate alpine glaciers can include water-worked debris in their marginal depositional facies.

The influence of englacial drainage on sediment-transport pathways and till texture of temperate valley glaciers

Field studies at Mueller and Tasman Glaciers in New Zealand and in Iceland have revealed extensive ice-marginal moraine sequences fed by a series of debris bands containing characteristic rounded debris. We interpret these debris bands as meltwater deposits from relict conduits. The process of sediment accumulation described requires that debris undergoing basal or high-level ice transport is entrained by running water, becoming comminuted and rounded before being returned to high-level ice transport and eventual deposition in marginal moraines. Tins sequence of events suggests a link between glacier hydrology and ice-marginal sedimentation, possible mechanisms for which are explored. Pronounced moraines with rounded debris can be expected if (a) large quantity of debris is carried within the englacial drainage network; (b) there is a tendency for this debris to be abandoned within the ice; and (c) ice-flow trajectories and ablation ensure that this debris congregates at the ice surface. Streams which flow at high level within the ice can intercept and entrain englacial debris derived from rock fall. However, debris sources at Gigjökull and Steinholtsjökull in Iceland are restricted to the glacier bed, suggesting that, in certain cases, the presence of a basal overdeepening acts as a key factor controlling the accumulation of these moraines. Water pressure rises as channels encounter an overdeepening, forcing debris-laden streams to leave the bed and take an englacial route. That debris may pass from ice to water and back into ice before deposition has gone largely unrecognised in accounts of glacial process systems, yet it provides an explanation of how temperate alpine glaciers can include water-worked debris in their marginal depositional facies.

Seismic stratigraphy of Quaternary deposits in the north-western Baltic Proper — A pilot study

Abstract This investigation is a seismic reflection survey carried out in order to investigate the possible submarine Younger Dryas marginal moraines in the North-Western Baltic Proper. The records do not show any indications of distinct marginal moraines in the northern part of the investigated area south of Stockholm. In the southern part of the area there are indications of marginal deposits, though. The distance between the profiling lines is too spacious to allow detection of the direction of these morphological features. The age of the formation of the morphological features in the southern part of the investigated area is presently unknown. The beginning of Younger Dryas is likely, but Allerod and the end of Older Dryas should also be considered possible. Two seismic till units were discovered in one section in the south-eastern part of the investigated area. An erosional channel was found in the same section, which may indicate a stillstand of unknown age of the ice margin.