Moraine Formation Research Articles

Post-sedimentary transformation of lateral moraines

The Kviarjokull, a southern outlet glacier of the Vatnajokull, is confined in the mountain foreland by lateral moraines measuring a height of up to 150 in. Each of the lateral moraines shows considerable breaches with deviations of the main moraine ridges. The paper discusses the possible origins of these modifications of the lateral moraines as result of: 1) ice overlappings during glacier advances and subsequent breaches of the lateral moraine, 2) bifurcations of the Kviarjokull glacier tongue triggered by the preglacial relief conditions and the prehistorical moraine landscape leading to afflux conditions, 3) drainage of ice-marginal glacier lakes and 4. volcanic activities, such as lava flows and volcanic-induced jokulhlaups. A historic-genetic model of the formation of the lateral moraines is presented considering the breaches in the lateral moraines as result from glacier bifurcations and therefore as former tributary tongue basins. Such breaches in the lateral moraines are also common landscape features at glaciers outside of Iceland and are from wider importance for the paleoreconstruction of former glacier stages. The knowledge of their development is essential for an adequate relative age classification of individual moraine ridges. In regard to the origin of the debris supply areas of the large-sized Kviarjokull moraines, the resedimentation of prehistoric till deposits by younger glacier advances plays a role in the formation of the lateral moraines apart from englacial and supraglacial sediment transfer processes.

A Basin Analysis of the Wabigoon Area of Lake Agassiz, a Quaternary Clay Basin in Northwerstern Ontario

Information from a wide range of sources is integrated in a basin analysis of the Wabigoon Basin, a Quaternary clay basin located on the Canadian Shield in northwestern Ontario. The basin sediments were deposited between 10.9 ka and 9.5 ka, along the margin of the Rainy Lobe of the Laurentide Ice Sheet, which formed the northern boundary of proglacial Lake Agassiz. The basin architecture is dominated by four major elements: end moraines, eskers, kames and a clay plain, all of which overlie irregular bedrock topography. End moraines, eskers and kames are composed mainly of a fining upward sequence of gravels and sands. The geometry of these sedimentary units, and their sedimentary structures indicates they were deposited mainly by high and low-density turbidity currents, on ice-marginal subaqueous outwash fans. Eskers contain a core of coarse gravel and sand deposited within subglacial meltwater conduits, overlain by subaqueous fan sediments deposited at the conduit mouth. Esker ridges were formed during conduit filling events and flanking deposits were formed when a conduit remained in use during ice-marginal retreat. Where conduits were shortlived, isolated subaqueous fans (kames) were formed. A depositional model is proposed which relates moraine formation to catastrophic releases of subglacial meltwater and sediment simultaneously along the entire margin of the Rainy Lobe. The clay plain forms a broad blanket of fine-grained, rhythmically-bedded sediment which obscures bedrock topography, and often buries esker and kame deposits. Seismic profiles and overburden drilling reveal deep (50-70 m) bedrock lows beneath the clay plain. These lows, oriented sub-parallel to the ice margin, acted as sediment traps, and were infilled by the deposits of underflows generated at the ice margin.

Cirque infills in the Khibiny Mountains, Kola Peninsula, Russia — palaeoglaciological interpretations and modern analogues in East Antarctica

AbstractWe report here on cirque infills mapped in the Khibiny Mountains, Kola Peninsula, Russia. Cirque infills are morainic deposits located near the headwalls of valleys and cirques. Their location and shape, often with concave margins towards the valley side, indicate that they were deposited by ice flowing up‐valley, into the mountains, rather than by local glaciers. We suggest that they formed during the last deglaciation, when Khibiny was a nunatak and Fennoscandian ice sheet lobes extended into valleys and cirques of the massif. The formation of cirque infills is probably more related to ice sheet dynamic factors, occurring when the ice margin retreated from the cirques, than to climate‐driven interruption in the ice‐marginal retreat. Glacial conditions similar to those prevalent when the Khibiny cirque infills were formed, occur today in Antarctica where the ice sheets engulf nunatak ranges. In Heimefrontfjella, Antarctica, the formation of supraglacial moraines at the head of cirques are linked to blue‐ice conditions, indicating locally low accumulation rates, a dry continental climate and sublimation dominated ablation. We suggest that these Antarctic moraines are modern analogues of cirque infills on the Kola Peninsula, and possibly, that the cirque infills may be used as palaeoenvironmental indicators. Copyright © 2007 John Wiley & Sons, Ltd.

Ribbed moraine formed by subglacial folding, thrust stacking and lee‐side cavity infill

Transverse‐to‐iceflow ribbed moraine occurs in abundance in the coastal zone of northern Sweden, particularly in areas below the highest shoreline (200–230 m a.s.l.), but occasionally also slightly above. Based on detailed sedimentological and structural investigations of machine‐dug sections across five ribbed moraine ridges, it is concluded that these vertically and distally prograding moraine ridges were formed as a result of subglacial folding/thrust stacking and lee‐side cavity deposition. The proximal part of the moraines (Proximal Element) was formed by subglacial folding and thrust stacking of sequences of pre‐existing sediments, whereas the distal part (Distal Element) was formed by glaciofluvial and gravity‐flow deposition in lee‐side cavities. The initial thrusting and folding is suggested to be a result of differences in bed rheology at the ice‐marginal zone during the early or late melt season, and that generated a compressive zone transverse to ice flow as a result of a more mobile bed up‐glacier compared to a less mobile bed down‐glacier. It is considered that the lee‐side cavities were formed as a result of ice‐bed separation on the distal slope of the thrust/fold‐created obstruction. The lee‐side cavities formed an integral part of a subglacial linked‐cavity drainage network regulated in their degree of interconnection, size and shape by fluctuations in basal meltwater pressure/discharge and basal iceflow velocity. The proximal and distal elements of the ribbed moraine ridges are erosively cut and/or draped with a consistently more homogeneous deforming bed till (Draping Element) marking the final phase of ribbed moraine formation considered to be contemporaneous with De Geer moraine formation further down‐flow at the receding ice‐sheet margin.

Early-Holocene glacier fluctuations in Krundalen, south central Norway: palaeoglacier dynamics and palaeoclimate

Krundalen, a valley occupied by three eastern outlet glaciers of the Jostedalsbre ice cap, contains three groups of moraines, two of which are outside the dated neoglacial (`Little Ice Age', LIA) limits. Exposures in the outermost moraine ridge display three sedimentary units. Detailed sedimentological analyses reveal that the lower two units formed during a temporary stillstand of the ice margin inferred to have occurred because of a topographically controlled stabilization of the ice margin during glacier retreat following the Younger Dryas. A climatically controlled readvance during which the upper unit was deposited, partly eroding pre-existing sediments, followed. Continuation of this readvance led to the whole sequence being pushed up to form the present moraine. The sedimentological results including clast shape measurements imply a temperate glacier thermal regime at the time of moraine formation. The glacial palaeoenvironment was characterized by frequent oscillations and an abundant supply of glaciogenic sediment. The age of this landform can at present not be determined by numerical dating. However, the moraine is likely to have been formed in the early Holocene, during Jondal Event 2 (JE) from c. 10 550—10 450 cal. yr BP. The average equilibrium-line altitude lowering calculated for this event is c. 440 m, 340 m for the Erdalen Event 1 (EE, 10 100—10 050 cal. yr BP) moraines and c. 190 m for the LIA moraines farther upvalley. Precipitation calculated for these stages compared with present values is 160—175% (JE), 165—175% (EE) and 110% (LIA). Summer air temperatures were slightly higher than today's during the JE, much higher during the EE and are indistinguishable from present values during the LIA. The existence of a potential JE-equivalent and the extent of the EE are reported and used for glacier reconstruction for the first time in Krundalen. The sedimentological data implies that the JE did not simply consist of a single readvance but was more complex. It is argued that glacial sedimentology linked with methods of glacier reconstruction provides a powerful tool to gain insights into the dynamics and functioning of formerly glaciated areas.

Submarine push moraine formation during the early Fennoscandian Ice Sheet deglaciation

The glacial history in the topographically confined paleo-ice stream drainage route of Vestfjorden, North Norway, was analysed based on bathymetric data, high-resolution seismology and 14C AMS-dated gravity cores. The inner part of the fjord is characterised by axial-parallel mega-scale lineations whereas the outer part is dominated by two marginal morainal bank systems. The Værøy (inner) and Røst (outer) marginal moraine systems comprise several transverse, zigzag-shaped ridges. Seismic records show thrusted and folded sediment blocks within the ridges. The landforms are inferred to reflect basal processes and the transition from warm-based (inner fjord) to cold-based (outer fjord) conditions, i.e. fast flow followed by basal freeze-on, sediment deformation and morainal bank formation. The moraines formed during the final part of two paleo-ice sheet re-advances. 14C AMS dating indicates a maximum age of 13.7 14C ka BP (16.2 cal ka BP) for the Røst system whereas the Værøy system is inferred to be slightly older than 12.5 14C ka BP (14.5 cal ka BP). This demonstrates that the northern part of the Fennoscandian Ice Sheet behaved in a much more dynamic way during the early deglaciation than previously assumed.

Distinguishing glaciogenic deposits in southern Finnish Lapland: implications for exploration

In glaciated terrains, the knowledge of Quaternary geology is essential for successful exploration. In Finland, the bedrock is almost completely covered by till of variable composition, thickness and stratigraphy, as well as various types of moraine formations from recent glaciations. In this study, the morphological, stratigraphical and compositional investigations of till and moraines in southern Finnish Lapland were combined with heavy mineral and geochemical studies to trace mineralised sources in the bedrock. In the study area, the glacial morphology is composed of an assemblage of transversal ribbed moraines and longitudinal drumlins and flutings with gently undulating till cover in between. In places, weathered bedrock remnants are preserved beneath the till cover and can be useful sampling media for exploration. The ribbed moraine ridges are the most favourable moraine type for exploration. Short glacial transportation of debris and boulders in the upper till and surface of the ridges is advantageous for tracing the ore indicators. Local bedrock indication is another aspect that makes sampling easy and minimises costs. In the areas of drumlins, flutings and thin till cover, transport distances are usually long and the possibility of complex glacial transportation increases. If weathered bedrock material is mixed in the till, it makes an interpretation of till geochemical data difficult; background values are usually elevated and anomalous values coming from fresh bedrock sources might be obscured. However, the sampling of the weathered bedrock provides indications of the local geochemical features in the bedrock.

Formation of glaciolacustrine Late Pleistocene end moraines in the Tasman Valley, New Zealand

Detailed examination of the Tekapo Formation in the Tasman Valley, New Zealand has identified 20 facies, and five facies associations. These associations are delta foresets and bottomsets, sediment density flows, ice-contact lake sediments with ice-rafted debris and resedimentation deposits, and outwash gravels. Interpretation of the sediment-landform associations informed by observations at modern glacier termini suggests that the Late Pleistocene Tekapo Formation moraines have been formed by downwasting of a more expanded Tasman Glacier. During the early stages of glacier retreat, ponds on the glacier surface develop into thermokarst lakes which enlarge and coalesce to form a large supraglacial lake. Continued downwasting causes the lake outlet river to entrench into the impounding latero-frontal ice-cored moraine, lowering the lake level. This exposes lake-bottom sediments and forms shorelines on the proximal slopes of the ice-cored moraine. As the ice-cored moraine melts, these lake sediments are deformed and deposited against the Mt. John moraine. The observations and interpretations reported here suggest the Late Pleistocene end moraine is a constructional feature not a structural (glaciotectonic) feature as suggested by previous studies.

The Lake Superior varve stratigraphy and implications for eastern Lake Agassiz outflow from 10,700 to 8900 cal ybp (9.5–8.0 14C ka)

Glaciolacustrine rhythmites within sediment cores from Lake Superior record the regional recession of the Laurentide Ice Sheet (LIS) from 10,700 to 8900 cal ybp [ca. 9.5–8.0 14C ka]. LIS retreat from Superior opened eastern Lake Agassiz outlets so that the rhythmites reflect the combined impacts of sediment-laden meltwater and Lake Agassiz discharge. Multiple rhythmite stratigraphies, a time series analysis of the thickness measurements, and high-resolution inorganic carbonate data demonstrate that this is an annual record (varved). The varve thickness records primarily document regional ice margin dynamics; correlative thick varve sequences at 9100 cal ybp [∼ 8.1 14C ka] and 10,400–10,200 cal ybp [∼ 9.2–9.0 14C ka] record two periods of enhanced glaciofluvial discharge, most likely moraine formation (the Nakina and Nipigon). General varve cessation is associated with the circumvention of Lake Agassiz and glacial meltwater into Lake Ojibway at 9040 cal ybp [∼ 8.1 14C ka], although adjacent to the inlets from Lake Nipigon, rhythmic sedimentation persisted for 200 years. Positively identifying Lake Agassiz catastrophic discharge events remains speculative but seems feasible. Following retreat of Marquette ice that had re-advanced to fill the basin, the initial influx of Lake Agassiz water is expected at around 10,600 cal ybp [∼ 9.4 14C ka], but at this time, most of northeastern Lake Superior was covered by ice. Three sets of thick–thin varves in western Lake Superior perhaps record influxes of Lake Agassiz at around 10,630, 10,600, and 10,570 cal ybp [∼ 9.4 14C ka]. Varve formation in Superior coincides with high lake levels in Lake Huron, suggesting that high lake levels in Huron correspond to periods of high Agassiz and/or meltwater flow into Lake Superior.

'A test of the englacial thrusting hypothesis of "hummocky" moraine formation: case studies from the northwest Highlands, Scotland': Comments

'A test of the englacial thrusting hypothesis of "hummocky" moraine formation: case studies from the northwest Highlands, Scotland': Comments

'A test of the englacial thrusting hypothesis of "hummocky" moraine formation: case studies from the northwest Highlands, Scotland': Reply to comments

'A test of the englacial thrusting hypothesis of "hummocky" moraine formation: case studies from the northwest Highlands, Scotland': Reply to comments

‘A test of the englacial thrusting hypothesis of “hummocky” moraine formation: case studies from the northwest Highlands, Scotland’: Reply to comments

‘A test of the englacial thrusting hypothesis of “hummocky” moraine formation: case studies from the northwest Highlands, Scotland’: Reply to comments

‘A test of the englacial thrusting hypothesis of “hummocky” moraine formation: case studies from the northwest Highlands, Scotland’: Comments

Areas of apparently chaotically organised moraine mounds and ridges are commonly associated with British Younger Dryas glaciers, and are also found at many contemporary glacier margins (Boulton & Eyles 1979; Benn 1992; Bennett & Boulton 1993b; Hambrey et al. 1997). Particularly in the British context, such landforms have commonly been referred to as ‘hummocky’ moraine. Whilst this term is undoubtedly an apt description of their morphology, genetic connotations have become attached to it, with some authors using it exclusively to refer to sediment-landform associations associated with wasting ice (e.g. Benn & Evans 1998: p. 483). Work undertaken over the last two decades has demonstrated that British Younger Dryas ‘hummocky’ moraine only rarely formed in association with stagnant ice, and it is now clear that they are polygenetic in origin (e.g. Benn 1992; Bennett & Boulton 1993b). For this reason the non-genetic, and similarly descriptive, ‘moraine-mound complex’ has been proposed for features of undetermined origin (Bennett et al. 1996b), and this term is adopted here.

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

Morphology, distribution and formation of relict marginal moraines in the swedish mountains

Relict marginal moraines are commonly used landforms in palaeoglaciological reconstructions. In the Swedish mountains, a large number of relict marginal moraines of variable morphology and origin occur. In this study, we have mapped 234 relict marginal moraines distributed all along the Swedish mountains and classified them into four morphological classes: cirque‐and‐valley moraines, valley‐side moraines, complex moraines and cross‐valley moraines. Of these, 46 moraines have been reclassified or are here mapped for the first time. A vast majority of the relict moraines are shown to have formed during deglaciation of an ice‐sheet, rather than by local mountain glaciers as suggested in earlier studies. The relict marginal moraines generally indicate that deglaciation throughout the mountains was characterised by a retreating ice‐sheet, successively damming glacial lakes, and downwasting around mountains. The general lack of moraines indicating valley and cirque glaciers during deglaciation suggests that climatic conditions were unfavourable for local glaciation during the last phase of the Weichselian. This interpretation contrasts with some earlier studies that have reconstructed the formation of local glaciers in the higher parts of the Swedish mountains during deglaciation.

Retreat dynamics of Younger Dryas glaciers in the far NW Scottish Highlands reconstructed from moraine sequences

Knowledge about moraine sequences produced by former glaciers can reveal much about the interaction between glaciers and palaeoclimate. In the far NW Highlands of Scotland, detailed records of deglaciation during the Younger Dryas (Loch Lomond Stadial) are preserved in sequences of ‘hummocky moraines’, consisting of arcuate chains of ridges and mounds, marking successive palaeo‐ice fronts. Reconstructed ice‐front positions are here used to construct ‘barcode patterns’ along former flowlines, allowing retreat patterns to be compared and frequency of moraine formation to be assessed. Since Younger Dryas glaciers in Scotland probably began to retreat around 12.1 ka and had disappeared by the early Holocene (11.5 ka), we assume time spans of 600–1200 years to calculate glacier retreat rates and to gain an understanding of marginal response to climate warming during the second half of the Younger Dryas. The calculations indicate that moraines formed every 3–23 years, depending, amongst other factors, on glacier size and basin topography. Retreat distances and the frequency of moraine formation have to be regarded as minimum values since sedimentological studies have shown that readvances were commonplace, i.e. two‐thirds of the ice‐marginal positions were occupied twice. Annual moraines might be present along short stretches, but are unlikely to occur throughout larger areas. This evidence indicates a palaeo‐environment dominated by very active glaciers with short margin response times similar to modern glaciers in maritime areas such as Norway or Iceland. Together, this evidence corresponds well with published data on the Younger Dryas palaeo‐environment in the far NW Scottish Highlands and in other areas such as the Isle of Skye and the central Grampian Highlands. The presented approach might help to fill gaps in the understanding of glacier dynamics in formerly glaciated areas elsewhere.

Retreat dynamics of Younger Dryas glaciers in the far NW Scottish Highlands reconstructed from moraine sequences

Abstract Knowledge about moraine sequences produced by former glaciers can reveal much about the interaction between glaciers and palaeoclimate. In the far NW Highlands of Scotland, detailed records of deglaciation during the Younger Dryas (Loch Lomond Stadial) are preserved in sequences of ‘hummocky moraines’, consisting of arcuate chains of ridges and mounds, marking successive palaeo‐ice fronts. Reconstructed ice‐front positions are here used to construct ‘barcode patterns’ along former flowlines, allowing retreat patterns to be compared and frequency of moraine formation to be assessed. Since Younger Dryas glaciers in Scotland probably began to retreat around 12.1 ka and had disappeared by the early Holocene (11.5 ka), we assume time spans of 600–1200 years to calculate glacier retreat rates and to gain an understanding of marginal response to climate warming during the second half of the Younger Dryas. The calculations indicate that moraines formed every 3–23 years, depending, amongst other factors, on glacier size and basin topography. Retreat distances and the frequency of moraine formation have to be regarded as minimum values since sedimentological studies have shown that readvances were commonplace, i.e. two‐thirds of the ice‐marginal positions were occupied twice. Annual moraines might be present along short stretches, but are unlikely to occur throughout larger areas. This evidence indicates a palaeo‐environment dominated by very active glaciers with short margin response times similar to modern glaciers in maritime areas such as Norway or Iceland. Together, this evidence corresponds well with published data on the Younger Dryas palaeo‐environment in the far NW Scottish Highlands and in other areas such as the Isle of Skye and the central Grampian Highlands. The presented approach might help to fill gaps in the understanding of glacier dynamics in formerly glaciated areas elsewhere.

Ribbed moraine stratigraphy and formation in southern Finnish Lapland

AbstractCharacteristics of ribbed moraines, the dominating moraine type in southern Finnish Lapland, have been studied in detail. The ridges are composed of several till units, of which the bottommost units consist of mature basal tills and the surficial parts are enriched with local, short‐transport rock fragments and boulders in till and at the surface of ridges. As a result of this re‐examination a two‐step model of the formation process of ribbed moraines is presented. In the first stage, while cold‐based conditions prevailed, both the bottommost part of the ice sheet and the frozen, substrate fractured under compressive ice flow. Following glacial transport of fractured blocks and formation of the transverse ridge morphology, erosion between the ridges continued owing to freeze–thaw process under variable pressure conditions. In the areas with a low pre‐existing till sheet, the process caused quarrying of the bedrock surface and subsequent deposition of rock fragments and boulders under high pressure on the next ridge. The most suitable conditions for ribbed moraine formation existed during Late Weichselian deglaciation, after the Younger Dryas when the climate warmed very quickly, leading to an imbalance between a warm glacier surface and a cold base. Copyright © 2006 John Wiley & Sons, Ltd.

Tree-ring evidence of ‘Little Ice Age’ glacier advances in southern Tibet

The history of late Holocene glacier fluctuations in eastern Tibet was studied by determining the ages of trees growing on glacier deposits. Maximum tree ages yield minimum ages of AD 1760 and 1780 for moraine formation at the maximum extent of the ‘Little Ice Age’ glacier advances in two glacier forefields. Subsequent moraines could be dated to the beginning of the nineteenth and the beginning of the twentieth century. Larch trees from a third glacier forefield in southeastern Tibet show evidence of glacier activity from 1580 to 1590, from the end of the eighteenth to the beginning of the nineteenth century and from 1860 to 1880. One glacier at Mt Gyalaperi recently advanced in both 1951 and 1987. Periods of glacier advances can partly be correlated with periods of growth reductions in chronologies of total ring width and maximum latewood density derived from trees growing on slopes above the glacier valleys. Correlation functions with meteorological data suggest that maximum latewood density of subalpine Picea balfouriana, Larix griffithii and Abies delavayi var. motouensis is positively correlated with summer temperature, while ring width of these species and of subalpine Juniperus tibetica is also sensitive to winter conditions prior to the growing season.

Geomorphological Map of Ribbed Moraines on the Dubawnt Lake Palaeo-Ice Stream Bed: A Signature of Ice Stream Shut-down?

Please click here to download the map associated with this article. The beds of active ice streams in Greenland and Antarctica are largely inaccessible, hindering a full understanding of the processes that initiate, sustain and inhibit fast ice flow in ice sheets. Detailed mapping of the glacial geomorphology of palaeo-ice stream tracks is, therefore, a valuable tool for exploring the basal processes that control their behaviour. In this paper we present a map that shows detailed glacial geomorphology from a part of the Dubawnt Lake Palaeo-Ice Stream bed on the north-western Canadian Shield (Northwest Territories), which operated at the end of the last glacial cycle. The map (centred on 63° 55″ 42′N, 102° 29″ 11′W, approximate scale 1:90,000) was compiled from digital Landsat Enhanced Thematic Mapper Plus satellite imagery and digital and hard-copy stereo-aerial photographs. The ice stream bed is dominated by parallel mega-scale glacial lineations (MGSL), whose lengths exceed several kilometres but the map also reveals that they have, in places, been superimposed with transverse ridges known as ribbed moraines. The ribbed moraines lie on top of the MSGL and appear to have segmented the individual lineaments. This indicates that formation of the ribbed moraines post-date the formation of the MSGL. The presence of ribbed moraine in the onset zone of another palaeo-ice stream has been linked to oscillations between cold and warm-based ice and/or a patchwork of cold-based areas which led to acceleration and deceleration of ice velocity. Our hypothesis is that the ribbed moraines on the Dubawnt Lake Ice Stream bed are a manifestation of the process that led to ice stream shut-down and may be associated with the process of basal freeze-on. The precise formation of ribbed moraines, however, remains open to debate and field observation of their structure will provide valuable data for formal testing of models of their formation.