Moraine Ridges Research Articles

The Glacial Geomorphology and Surficial Geology of the South-West English Lake District

Please click here to download the map associated with this article. The glacial geomorphology of the south-west Lake District has been mapped over 98 km using 1:10,000 aerial photography, Google Earth images and a high resolution digital elevation model (NEXTMap). The area is subdivided into two map sheets (eastern and western) and includes Upper Eskdale, the Langdales, the valleys surrounding Wastwater and the neighbouring valley of Ennerdale. The maps include 9 surficial geology units in addition to the various geomorphological features. Suites of arcuate moraine ridges record the sequential retreat of topographically-controlled glaciers. Flutings, which may relate to radial outflow of ice from the central fells during the Late Devensian, are also present. ‘Paraglacially modified sediments and scree’ is the largest of the map units, reflecting the extensive occurrence of ancient and present-day hillslope processes in the region. More recent palaeo-glaciological reconstructions of the Younger Dryas (12.7—11.5 ka BP) ice extent in the Lake District remain spatially restricted, with many covering only small areas of the Lake District. Furthermore, these reconstructions suggest substantially different ice configurations. In particular, the south-west Lake District remains a key area of uncertainty. We use the geomorphological maps presented in this paper to produce new reconstructions of Younger Dryas ice extent in the south-west Lake District. We combine this with previously published reconstructions from across the whole Lake District to provide a complete regional Younger Dryas ice reconstruction.

Modelling a cohesive‐frictional debris flow: an experimental, theoretical, and field‐based study

AbstractThe rheology of debris flows is difficult to characterize owing to the varied composition and to the uneven distribution of the components that may range from clay to large boulders, in addition to water. Few studies have addressed debris flow rheology from observational, experimental, and theoretical viewpoints in conjunction. We present a coupled rheological‐numerical model to characterize the debris flows in which cohesive and frictional materials are both present. As a first step, we consider small‐scale artificial debris flows in a flume with variable percentages of clay versus sand, and measure separately the rheological properties of sand–clay mixtures. A comparison with the predictions of a modified version of the numerical model BING shows a reasonable agreement between measurements and simulations.As application to a field case, we analyse a recent debris flow that occurred in Fjærland (Western Norway) for which much information is now available. The event was caused by a glacial lake outburst flood (GLOF) originating from the failure of a moraine ridge. In a previous contribution (Breien et al., Landslides, 2008, 5: 271–280) we focused on the hydrological and geomorphological aspects. In particular we documented the marked erosion and reported the change in sediment transport during the event. In contrast to the laboratory debris flows, the presence of large boulders and the higher normal pressure inside the natural debris flow requires the introduction of a novel rheological model that distinguishes between mud‐to–clast supported material. We present simulations with a modified BING model with the new cohesive‐frictional rheology. To account for the severe erosion operated by the debris flow on the colluvial deposits of Fjærland, we also suggest a simple model for erosion and bulking along the slope path. Numerical simulations suggest that a self‐sustaining mechanism could partly explain the extreme growth of debris flows running on a soft terrain.

Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina

At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49°S, 72°W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide ( 10 Be) exposure ages ( n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ± 1.7 ka, 22.4 ± 2.3 ka, 34.4 ± 3.4 ka to 37.6 ± 3.4 ka (and possibly 60 ± 3.5 ka), and 99 ± 11 ka (1 σ). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on 14C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.

Geomorphic implications of the retreat of Breiðamerkurjökull in the southern part of the Skálabjörg ridge, Esjufjöll, Iceland

The Skálabjörg nunatak, one of the summits of the Esjufjöll central volcano (SE Iceland), has been glacially eroded by the Breiðamerkurjökull outlet glacier for thousands of years. Since the end of the Little Ice Age, six to eight lateral moraine ridges have formed on the slopes of Skálabjörg. Ice-dammed lakes have also developed in the southernmost part of Skálabjörg and in Fossadalur. The highest and largest moraine ridge is situated 85–98 m above the contemporary glacier margin. Dating based on lichenometry, cartographic and photographic documentation indicates that the initial exposure of the highest moraine ridge occurred between AD 1896 and 1930 along its eastern margin and between AD 1915 and 1930 along its southwestern margin, giving an average glacier surface lowering rate of 0.8–1.3 m/yr in the southern hills of Skálabjörg. Hills above the highest moraine ridge bear imprints of earlier glaciation, most notably glacially abraded rock outcrops and transported boulders. Small active solifluction tongues and lobes with stone-armoured fronts cover the surface above the LIA limit. Small-scale and large-scale stripes exhibiting sorting down to c. 15 cm are abundant. The uppermost parts of the Skálabjörg nunatak are heavily frost-weathered bedrock outcrops, and can be classified as a typical periglacial domain.

Plant adaptive responses during primary succession are associated with functional adaptations in ground beetles on deglaciated terrain

Little is known of how changes in plant function may influence adaptive traits amongst animals further up the food chain. We addressed the hypothesis that shifts in plant functional traits are associated with the adaptive function of animal species which have an indirect trophic link. We compared community characteristics and functional traits of two trophically detached biotic groups (vascular plants and carabid beetles) along a primary succession on terrain at the Cedec glacier in the Alps, where deglaciation events following post-Little Ice Age climate warmings are marked by moraine ridges. Morphofunctional traits were recorded: canopy height (CH), leaf dry matter content (LDMC), leaf dry weight (LDW) and specific leaf area (SLA) (for plants) and the number of brachypterous, autumn-breeding and predator species, and average body length (for carabid beetles). We found that vegetation cover and plant species richness gradually increased throughout early succession, with an abrupt increase between 40 and 150 years after deglaciation. At the early stages of the succession plant traits were typical of ruderal species (high SLA, lowCH, LDW) whilst a shift in traits towards stress-tolerance (low SLA) occurred >150 years. Carabid communities and traits changed alongside changes in plant species richness and cover, with late successional vegetation hosting larger, more diverse, less mobile carabid species with longer larval development. Thus, ruderal plant strategies are the main contributors during vegetation development, determining vegetation quantity, and probably have the greatest impact on changes in carabid assemblages by regulating resource availability. Plants then require greater stress-tolerance to survive in stable vegetation, which supports high carabid diversity. This suggests that different plant strategies may affect ground beetle communities via contrasting mechanisms: both quantities (biomass, species richness) and qualities (functional traits, adaptive strategies) should be taken into account during studies of plant-animal interactions within ecosystems.

Early to middle Holocene valley glaciations on northernmost Greenland

This paper presents the glacial stratigraphy and palaeoenvironmental evolution around Constable Bugt, Johannes V. Jensen Land, located on the north coast of Greenland. This is a land of extreme climate: polar desert conditions and a coast bound by a permanent sea ice cover. Our data covers the period from the Last Glacial Maximum (LGM, 18–22 cal ka BP) into the Holocene. It records the history of a shelf-based glaciation with ice flowing eastward along the coast as well as two local valley glacier advances from the south during the Holocene. With ice on the coastal plain during the LGM, glaciolacustrine basins formed in marginal positions and in ice-dammed valleys to the south into the mountainous area of Peary Land. With the break-up of shelf-based ice there was a gradual marine inundation at which the marine limit formed at ∼45 m a.s.l. This initial early Holocene ice advance from the south formed prominent valley mouth moraines, especially in Sifs valley. Here, both glaciolacustrine and marine sediments were remoulded and/or dislocated as thrust blocks into a moraine ridge spanning more than 1 km in width and >60 m in height. Radiocarbon ages of sediments incorporated in this moraine, as well as from on-lapping sediments, suggest that the moraine formed between 9.6 and 6.3 cal ka BP. Based on 14C dating results, the youngest ice advance phase can be narrowed down to 14C ages between ∼5.5–5.0 cal ka BP. The recorded ice advances took place during the Holocene Thermal Maximum (HTM) for North Greenland, the last one close to the beginning of the Neoglacial cooling. During the HTM we have recorded a period of ∼2500 years during which the north coast of Greenland – as opposed to today – experienced an absence to very restricted occurrence of land-fast or multi-year sea ice. This observation can be explained by the altitudinal and temporal distribution of beach-ridge complexes that must have formed by wave action and thus requiring at least partial open-water conditions. With a moisture source at hand, we propose that this lead to enhanced precipitation in the near-coastal areas which, coupled to documented HTM cold reversals, caused a lowered glaciation limit, and led to a positive mass balance and subsequent ice advance.

Schmidt-hammer exposure-age dating (SHD): application to early Holocene moraines and a reappraisal of the reliability of terrestrial cosmogenic-nuclide dating (TCND) at Austanbotnbreen, Jotunheimen, Norway

Matthews, J. A. & Winkler, S. 2010: Schmidt-hammer exposure-age dating (SHD): application to early Holocene moraines and a reappraisal of the reliability of terrestrial cosmogenic-nuclide dating (TCND) at Austanbotnbreen, Jotunheimen, Norway. Boreas, 10.1111/j.1502-3885.2010.00178.x. ISSN 0300-9483. Schmidt-hammer exposure-age dating (SHD) and terrestrial cosmogenic-nuclide dating (TCND) are complementary techniques that can be used for mutual testing. SHD is low-cost but requires local control points of known age and may be affected by local geological variation and other environmental factors that influence weathering rates. TCND is vulnerable to the occurrence of anomalous boulders, other geomorphological uncertainties and the effects of snow-shielding at high altitudes. Both techniques are sensitive to post-depositional disturbances if other than solid bedrock is sampled. SHD was applied to two moraine ridges beyond the Little Ice Age limit of Austanbotnbreen in the Hurrungane massif, southern Norway. Independent regional and experimental local age-calibration curves were used to reappraise previous TCND results. Neither the two boulder surfaces nor their proximal bedrock surfaces could be differentiated statistically in terms of SHD exposure ages or their mean R-values (±95% confidence intervals), which ranged from 40.73±1.72 to 43.34±0.69. The best of the independent regional-calibration curves produced SHD exposure ages of 9413±723 and 9304±602 years, which are consistent with moraine formation early (c. 10.2 ka) and late (c. 9.7 ka) within the late-Preboreal Erdalen Event. The current precision of SHD, as reflected in 95% confidence intervals of ±500–900 years, enables rejection of a Finse Event (c. 8.2 ka) age for either moraine. Results are consistent with a retracted Austanbotnbreen between the Erdalen Event and the Little Ice Age, and a modified model of Neoglaciation.

Changing glaciers in a changing climate: how vanishing geomorphosites have been driving deep changes in mountain landscapes and environments

The retreat of glaciers worldwide, from the Alpine areas to Antarctica, in the course of the last few decades, is frequently mentioned as a clear and unambiguous sign of global warming. In the Alps, although the warming experienced since the early 1980s is synchronous with warming at the global scale, nevertheless its amplitude is greater and it represents roughly a two-fold amplification of the global climate signal. As a result of this rapid climate change, many small glaciers could disappear in the next few decades. These small glaciers, common in the Alps, are also important in terms of environmental and economic systems. The rapid “disintegration” of Alpine glaciers has already been discussed in previous studies ; less attention, however, has been paid to their role as changing and potentially vanishing geomorphosites. Most Alpine glaciers, in fact, subject to rapid change driven by climate, are now responsible for unexpected environmental impacts, which in the Italian Alps have only been partially investigated. This paper analyses and discusses features and evolution in two representative glacier geomorphosites included in the official “Geosites Inventory” of the Lombardy region (Italy). In Lombardy (Italian Alps) 348 glaciers covered an area of about 92 km2 in 2003. They were found to have decreased in area by about 21 % in the period 1990-2003. The geomorphosites analysed are the Forni Glacier, the largest valley glacier in the Italian Alps, and the Val Viola glacierised basin, where various small glaciers with well-preserved moraine ridges (dating from the upper Holocene to the present) can be found. Both the geosites are located in areas identified as “Sites of Community Importance” (SCI) under directive 92/43/EEC ; furthermore, the Forni Glacier is also located in a protected area, the Stelvio National Park. These glacier geomorphosites represent well the variations affecting all Alpine glaciers ; these variations are not only driving significant changes in the morphology and ecology of the present mountain landscape, but at the same time are shaping newly formed morphologies, which may develop into smaller geomorphosites with significant value from a scientific and cultural point of view. The changes include thermokarst features such as kettles and supraglacial lakes, debris-covered glacier tongues frequently without any direct connections with the actual glacier, rounded rock outcrops emerging from the glacier surface which increase ice melting and accelerate glacier shrinkage, ice contact and moraine-dammed lakes where calving phenomena occur and icebergs drift loose, moraines affected by ice core melting with subsequent collapse and generation of mud and debris flows.

Little Ice Age advance and retreat sediment budgets for an outlet glacier in western Norway

Burki, V., Hansen, L., Fredin, O., Andersen, T. A., Beylich, A. A., Jaboyedoff, M., Larsen, E. & Tønnesen, J.‐ F. 2009: Little Ice Age advance and retreat sediment budgets for an outlet glacier in western Norway. Boreas, Vol. 39, pp. 551–566. 10.1111/j.1502‐3885.2009.00133.x. ISSN 0300‐9483Bødalsbreen is an outlet glacier of the Jostedalsbreen Ice Field in western Norway. Nine moraine ridges formed during and after the maximum extent of the Little Ice Age (LIA). The stratigraphy of proglacial sediments in the Bødalen basin inside the LIA moraines is examined, and corresponding sediment volumes are calculated based on georadar surveys and seismic profiling. The total erosion rates (etot) by the glacier are determined for the periods AD 1650–1930 and AD 1930–2005 as 0.8 ± 0.4 mm/yr and 0.7 ± 0.3 mm/yr, respectively. These rates are based on the total amount of sediment delivered to the glacier margin. The values are almost one order of magnitude higher than total erosion rates previously calculated for Norwegian glaciers. This is explained by the large amount of pre‐existing sediment that was recycled by Bødalsbreen. Thus, the total erosion rate must be considered as a composite of eroded bedrock and of removed pre‐existing sediments. The total erosion rate is likely to vary with time owing to a decreasing volume of easily erodible, unconsolidated sediment and till under the glacier. A slight increase in the subglacial bedrock erosion is expected owing to the gradually increasing bedrock surface area exposed to subglacial erosion.

Last Glacial Maximum and deglaciation of Sierra de Gredos, central Iberian Peninsula

The study area is located in the Sierra de Gredos, a portion of the Sistema Central range of central Spain, specifically in the Gredos Gorge, on the north side of Pico Almanzor (2596 masl), where glacial forms are present down to an altitude of 1410 m, 10 km from the headwall. This paper presents cosmogenic 36Cl surface exposure dates of four closely spaced lateral moraine ridges within the area of maximum advance of the ancient glacier, 8 km from the headwall; and two glacially polished bedrock thresholds 3 and 5 km from the headwall. The dates are overall coherent and indicate a maximum advance at 26–24 ka. Subsequently the glacier front stabilized around its maximum position for ∼3 ka, with small scale fluctuations resulting in small, closely spaced moraines ridges. Glacier recession began after 21 ka, accelerating sharply by ∼16 ka. The glacier had probably disappeared from the Gredos Gorge by 15 ka. There are no traces of older or more recent moraines than those dated in this study. These results are in agreement with the well known late Pleistocene climatic evolution of the Northern Atlantic and with the glacial chronology of the Alps and other Mediterranean mountains. However, the Gredos Gorge has no geomorphic evidence of the Younger Dryas cold event, probably because of the low altitude and southern character of these mountains.

Glacial advance and stagnation caused by rock avalanches

New model results show that a glacier advance caused by deposition of a rock avalanche on the ice will be followed by stagnation of the advanced ice lobe, producing distributed, hummocky deposits quite different from the single moraine ridges typically dated in paleoclimatic reconstructions. We obtain these results using a numerical flow-line glacier model with superimposed rock debris. In particular, our results imply that the single moraine ridge known as the Waiho Loop of the Franz Josef Glacier, New Zealand, is not the result of an advance triggered by a rock avalanche, else there would be a widespread, hummocky, glacial stagnation deposit associated with it.

Establishing lichenometric ages for nineteenth‐ and twentieth‐century glacier fluctuations on south georgia (south atlantic)

.Glaciers in small mountain cirques on South Georgia respond rapidly and sensitively to changes in South Atlantic climate. The timing and rate of their deglaciation can be used to examine the impact that nineteenth‐ and twentieth‐century climate change has had on the glacial dynamics and terrestrial ecosystems of South Georgia. As part of a reconnaissance study in Prince Olav Harbour (POH), South Georgia, we measured the size of lichens (Rhizocarpon Ram. em Th. Fr. subgenus. Rhizocarpon group) on ice‐free moraine ridges around two small mountain cirques. Our aims were twofold: first, to provide age estimates for lichen colonization, and hence, deglaciation of the moraine ridges, and second, to examine the potential of applying lichenometry more widely to provide deglacial age constraints on South Georgia. In the absence of lichen age‐size (dating) curves for South Georgia, we use long‐term Rhizocarpon lichen growth‐rates from recent studies on sub‐Antarctic Islands and the western Antarctic Peninsula to calculate likely age estimates. These data suggest ice retreat from the two outermost moraines occurred between the end of the ‘Little Ice Age’ (post c. 1870) and the early twentieth century on South Georgia. Lichen colonization of the innermost moraines is probably related to glacier retreat during the second half of the twentieth century, which has been linked to a well‐defined warming trend since c. 1950. Patterns of possible nineteenth‐ and twentieth‐century glacial retreat identified in POH need to be tested further by establishing species‐ and site‐specific lichen age‐size (dating) curves for South Georgia, and by applying lichenometry to other mountain cirques across South Georgia.

Depositional processes within the frontal ice-cored moraine system, Ragnar glacier, Svalbard

Depositional processes within the frontal ice-cored moraine system, Ragnar glacier, Svalbard The marginal zone of the Ragnar glacier has been divided into four zones: ice surface, proglacial lake, lateral moraine and frontal moraine complex. Detailed researches were carried out in the last one - frontal moraine complex consisting of three subzones: (1) outer moraine ridge, (2) culmination moraine ridge and (3) inner moraine plateau. The frontal moraine complex of the Ragnar glacier shows large variability of lithofacies and depositional processes. The aim of this study was to reconstruct the intensity and variability of depositional processes from early stage of the frontal ice-cored moraines creation till present situation. Debris flow processes, glaciofluvial and glaciolacustrine sedimentation as well as aeolian activity and down- and backwasting are identified as most important processes. Intensity of these processes has varied through the time. Presently the frontal ice-cored moraine complex of the Ragnar glacier is relatively stable, except few areas affected by the river or streams.

Morainic ridges on the floor of the Irish Sea

Morainic ridges on the floor of the Irish Sea

Morphodynamic evolution of Kongsfjorden-Krossfjorden, Svalbard, during the Late Weichselian and Holocene

Abstract We present a combination of fjord bathymetry and shallow seismic data from Kongsfjorden and Krossfjorden, Svalbard, to characterize and analyse change in the fjord coastal environment physiography and the glaciosedimentary processes since the Last Glacial Maximum. Swath bathymetry reveals a series of several styles of landform, frequently superimposed upon each other, permitting the reconstruction of the relative timings of deposition of each landform with the oldest successively overlain and cross-cut by younger landforms and erosional processes. Large transverse ridges interpreted as recessional moraines are overlain by streamlined lineations formed subglacially during a subsequent ice advance. A complex of recessional morainal ridges occurring within the central fjord are incised by glacial lineations and meltwater channels from younger glacial events.

Satujökull glacial landsystem, Iceland

Please click here to download the map associated with this article. A surficial geology and geomorphology map of the Satujökull foreland of the northern Hofsjökull ice cap in central Iceland provides a clear signature of spatial and temporal change in glacial landsystem signatures as a result of complex glacier behaviour in the historical period. Landsystem 1, indicative of polythermal conditions, comprises a wide arc of ice-cored moraine and controlled moraine ridges lying outside a fluted and drumlinized terrain and demarcates the historical Little Ice Age maximum limit. Landsystem 2 contains most of the diagnostic criteria for the surging glacier landsystem and records two separate surges by the western margin of Satujökull in the period since the attainment of the Little Ice Age maximum advance.

Little Ice Age glaciers in the Balkans: low altitude glaciation enabled by cooler temperatures and local topoclimatic controls

AbstractMoraine ridges are present in the highest cirques of the Durmitor massif in Montenegro and post‐date the widespread Pleistocene moraines of this area. Lichenometry suggests that at least eight glaciers were present in the 19th century and correlate with the culmination of the Little Ice Age in the European Alps. Cooler temperatures combined with local topoclimatic controls, including windblown and avalanching snow as well as shading, were crucial for the formation and survival of these glaciers below the regional equilibrium–line altitude. The resultant regional equilibrium line altitude (ELA) was positioned close to the highest peaks between 2400 and 2500 m, with local controls such as avalanche, windblown snow and shading depressing the ELA in the northern cirques to 2130–2210 m. This ELA position was very low for this latitude and lower than for most glaciers in the European Alps at any time during the Holocene, and even equivalent to many Alpine glaciers during the Younger Dryas. Today, one glacier still survives in Montenegro, in a deep northeast‐facing cirque characterized by the largest combined areas of potential avalanche and windblown snow. Copyright © 2009 John Wiley & Sons, Ltd.

Melt-out till and ribbed moraine formation, a case study from south Sweden

Hummocky moraine with dispersed agglomerations of ribbed moraine – here named ‘Åsnen-type ribbed moraine’ – forms a 20–40 km wide zone over Småland, south Sweden, terminated to the north by a sharp boundary to streamlined terrain. The hummocky/ribbed moraine zone can be geomorphologically linked to the subaqueous Göteborg Moraine, formed at an oscillation/stand-still phase during the deglaciation of the Swedish west coast. Based on detailed sedimentological and structural investigations of ribbed moraine ridges it is concluded that diamict sequences and associated sorted sediment were deposited due to passive melt-out from stagnant, debris-rich ice with synsedimentary deposition of sorted sediments, preferentially at a melting ice/bed interface. To accommodate for the geomorphological expression, such an interpretation further implies that debris-rich ice formed in an intermediate adfreezing zone between ice at the pressure-melting point and a frontal frozen zone at deglaciation. Basal debris-rich ice was stacked into transversally arranged zones (controlled moraine), forming ribbed moraine ‘embryos’, the active phase of ridge formation. The stacked sequences of debris-rich ice eventually melted out beneath a stable and melt-retarding supraglacial ablation complex to form the final moraine ridges, the passive phase of ridge formation. In areas with no stable supraglacial ablation complex, the resulting landform after final de-icing was a hummocky moraine landscape. Internal composition of moraine hummocks suggests that most of them are composed of sediment gravity flow sediments, intercalated with stream-deposited sediments, all resting on a platform of subglacial melt-out till. De-icing of the zone now occupied by hummocky and ribbed moraine took a considerable time; deglacial 14C age differences from lake basins on either side of the geomorphic boundary to the streamlined terrain indicate a separation between active and stagnant ice along that boundary, and that it took another 200–300 yr for the stagnant ice zone to melt during the final formation of present-day landforms.

The 1890 surge end moraine at Eyjabakkajökull, Iceland: a re-assessment of a classic glaciotectonic locality

The glaciotectonic architecture and sequential evolution of the Eyjabakkajökull 1890 surge end moraines in Iceland were studied for understanding better the formation and evolution of glaciotectonic end moraines and their relation to glacier dynamics. Based on morphological, geological and geophysical data from terrain cross-profiles, cross-sections and ground penetrating radar profiles, we demonstrate that three different qualitative and conceptual models are required to explain the genesis of the Eyjabakkajökull moraines. Firstly, a narrow, single-crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport. Secondly, large lobate end moraine ridges with multiple, closely spaced, narrow asymmetric crests formed by proglacial piggy-back thrusting. Thirdly, a new model shows that moraine ridges with different morphologies may reflect different members of an end moraine continuum. This is true for the eastern and western parts of the Eyjabakkajökull moraines as they show similar morphological and structural styles which developed to different degrees. The former represents an intermediate member with décollement at 4–5 m depth and 27–33% shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface. The latter represents an end member with décollement at about 27 m depth and 39% horizontal shortening through multiple high amplitude, overturned and overthrusted anticlines, appearing as broadly spaced symmetric crests. We propose that the opposite end member would be a moraine of multiple symmetric, wide open anticlinal crests of low amplitude. Our data suggest that the glacier coupled to the foreland to initiate the end moraine formation when it had surged to within 70–190 m of its terminal position. This indicates a time frame of 2–6 days for the formation of the end moraines.

Observations on terminal moraine-ridge formation during recent advances of southern Norwegian glaciers

Abstract The formation of terminal moraines dating from glacier advances during the A.D. 1990s was investigated at six temperate glaciers in the Jostedalsbreen and Jotunheimen regions of southern Norway. Morphological and sedimentological information was analysed and combined with detailed observations, photographic evidence, and length variation measurements. Bulldozing (pushing) of proglacial sediments was the predominant process at the low-lying glacier termini of the debris-free outlets of the Jostedalsbreen ice cap. Evidence for bulldozing includes the relocation and rotation of boulders and the presence of lichen-covered boulders in the distal slopes of moraines. Differences in moraine sedimentology between the individual sites are attributed to variations in the pre-existing material pushed up, rather than to specific processes. In Jotunheimen, several modes of moraine-ridge formation were active: dumping of supraglacial debris and the marginal freezing-on and subsequent melting-out of subglacial sediment slabs were more important than bulldozing at some sites and in some years. Low air temperatures in winter at the higher altitude glacier termini enabled freezing-on to occur. However, the forelands are below the lower limit of discontinuous permafrost and evidence of thrusting is absent. Whereas discrete terminal moraine ridges at Jostedalsbreen are related to (seasonal) advances, the less dynamic glaciers of Jotunheimen allow the accretion of successive ridges during consecutive years. No single regional mode of moraine formation is characteristic for southern Norway: several processes are involved depending on individual glacier morphology and dynamics, the glaciological regime, and environmental conditions (especially climate) on the glacier forelands. The importance of specific processes varies within and between glacier forelands. Thus, spatial and temporal variation and local individuality has to be taken into account in the interpretation of moraine-ridge formation. Similar variability is likely to have been characteristic of terminal moraines deposited during the “Little Ice Age” and earlier in the Quaternary.