Glacial Landforms Research Articles

Internal structure and water routing of an ice-debris landform assemblage using multiple geophysical methods in the semiarid Andes

Rock glaciers are the most abundant (peri) glacial landform in the semiarid Andes (SA, 29–34°S), covering about three times the area of mountain glaciers. Recent studies suggest they may play an important hydrological role, including generating, storing and routing water. However, processes governing these roles are still poorly known especially for glacier complex units, i.e., where there is a juxtaposition or continuity of different (peri) glacial landforms, which are common in semiarid Andean and Himalayan areas. This study aims to understand how the internal structure of an ice-debris landform assemblage controls hydrological routing. To address this aim, we used a combination of three geophysical techniques to qualitatively determine the internal structure and favourable water routing and storage zones at the Tapado glacier complex (30°S), Chile. The Tapado glacier complex consists of an assemblage of a debris-free glacier, a debris-covered glacier and two rock glaciers. For the purpose of this study, we focused on the debris-covered and active rock glacier connection. At this site, the debris-covered glacier has a relatively thin debris-cover that increases thickness downglacier. This debris cover connects to the active rock glacier and forms the active layer. The rock glacier contains a heterogenous internal structure consisting of debris with water or segregated ice filling the voids, which likely derives from the massive ice of the debris-covered glacier. The superficial debris layer of the ice-debris landforms may act as a transmissive medium by routing water downstream above the massive ice of the debris-covered glacier, but also into deeper areas, as intra-permafrost flow, in the rock glacier. The rock glacier likely has a higher capacity to transmit vertical and horizontal flows, thereby enhancing infiltration processes. This study reinforces the value of geophysical methods to determine the internal structure of ice-debris landforms, particularly in the transition between landforms, and highlights how a warming climate and consequent paraglacial processes will impact the hydrological system not only in terms of water storage, but also water transfer.

Sea-level rise in Southwest Greenland as a contributor to Viking abandonment

The first records of Greenland Vikings date to 985 CE. Archaeological evidence yields insight into how Vikings lived, yet drivers of their disappearance in the 15th century remain enigmatic. Research suggests a combination of environmental and socioeconomic factors, and the climatic shift from the Medieval Warm Period (~900 to 1250 CE) to the Little Ice Age (~1250 to 1900 CE) may have forced them to abandon Greenland. Glacial geomorphology and paleoclimate research suggest that the Southern Greenland Ice Sheet readvanced during Viking occupation, peaking in the Little Ice Age. Counterintuitively, the readvance caused sea-level rise near the ice margin due to increased gravitational attraction toward the ice sheet and crustal subsidence. We estimate ice growth in Southwestern Greenland using geomorphological indicators and lake core data from previous literature. We calculate the effect of ice growth on regional sea level by applying our ice history to a geophysical model of sea level with a resolution of ~1 km across Southwestern Greenland and compare the results to archaeological evidence. The results indicate that sea level rose up to ~3.3 m outside the glaciation zone during Viking settlement, producing shoreline retreat of hundreds of meters. Sea-level rise was progressive and encompassed the entire Eastern Settlement. Moreover, pervasive flooding would have forced abandonment of many coastal sites. These processes likely contributed to the suite of vulnerabilities that led to Viking abandonment of Greenland. Sea-level change thus represents an integral, missing element of the Viking story.

The impact of natural and anthropogenic factors on the landforms and landscapes of mountains and their forelands

This paper is an introduction to a collection of nine studies that are intended to fill the gap in the literature associated with landform development and landscape changes related to natural forces and human activities in the Central European Mountains and their close forelands. The papers are grouped into four general categories that describe the influence of climate on glacial landforms and snow avalanches, the evolution of slopes in high mountains, the development of mid-mountain relief, and changes in fluvial systems in mountains and their forelands. This paper summarises the contributions of these studies to this special issue and attempts to outline possible avenues of future research on landforms and landscapes in mountainous areas.

Late Pleistocene glaciation in the headwaters of the Ceremuşul Alb valley (Maramureş Mountains, Romania)

The Late Pleistocene Jupania palaeoglacier (area 0.85 km2 , 1.7 km long) was reconstructed in the headwaters of the Ceremuşul Alb/Bilyj Cheremosh valley (Maramureş Mountains). The study area represents one of the most inaccessible natural areas in the Romanian part of the Eastern Carpathians where the legacy of the Pleistocene glaciation has recently been discovered. Based on mapping of glacial landforms and deposits, we reconstruct glacier dimension and ice-surface geometry, as well as estimate equilibrium line altitude (ELA) during the maximal ice extent (MIE). Well-preserved terminal moraines mark the extent of glacier front at ~1400 m a.s.l. Sedimentological analysis documents that the lateral moraines are sometimes overbuilt by 1-1.5 m thick colluvial deposits. The ELA for the Jupania palaeoglacier calculated with the Area-AltitudeBalance-Ratio (AABR) 1.6 was 1630 m. However, the gentle-sloping mountain-top could serve as an important snow contribution area to glacier mass balance; therefore, the ELA could potentially exist even higher at 1676 m. The resulting climatic ELA (1630-1676 m) in the south-eastern part of the Maramureş Mountains fits well with the rising trend of ELA towards the southeast observed between Chornohora (ELA = 1516 m) and Rodna Mountains (ELA = 1697 m). The SE rising trend of the ELA corresponds well with the dominant palaeowind direction suggested in the Carpathian region and supports the prevalence of zonal circulation pattern in Central Eastern Europe during the culumination of the last glaciation.

Geomorphological evolution and mapping of the littoral of Asturias and Cantabria (Northern Spain) in the area of El Pindal Cave: relations between coastline and karstic morphologies

ABSTRACT Along the northern littoral of the Iberian Peninsula, from Cuerres (Asturias) to Oyambre (Cantabria) there are caves, such as El Pindal (World Heritage List). Two geomorphologic maps have been prepared: a general scaled 1:25000, and a detail one of the cave, with erosional and depositional landforms geomorphologic units. A relative Quaternary chronology for the depositional landforms, uses colour spots. Marine morphologies suitable for determining past sea-level positions were surveyed to identify the elevation of past high-stands and reconstructing paleo-shorelines. As a result, the study of seven erosional surfaces (rasas) in quartzites and six on limestones led to reconstructing a general sequence between 275–120 m and 90–1 m above sea level (a.s.l.) respectively. Around the El Pindal cave there are four rasas cut on quartzites (171–160 m) and four cut on limestone (65–32 m). Other additional indicators of paleoshorelines are: 24–25 m entrance to the El Pindal cave, 20–21 m lower Pindal, 15–17 m marine terrace, 9–10 m shelter, 2–3 m notches and 0–1 m present rasa.Considering the elevation rates for the various rasas, an estimated value of 0.066 mm/y as the most probable, it is concluded that the beginning of Quaternary lays at 172 m a.s.l.

Reconstructing terrestrial ice sheet retreat dynamics from hummocky topography using multiscale evidence: An example from central Ireland

The research reported here combines high-resolution digital elevation models (DEMs) derived from airborne LiDAR with ground-penetrating radar (GPR) surveys and macro- and micro-scale sedimentological analyses to study the geomorphology and internal structure and composition of ridges and mounds within an area of hummocky topography in the Brosna basin, central Ireland. Our evidence indicates that much of the hummocky topography consists of fragmented mega-scale glacial lineations (MSGLs) indicating a phase of accelerated ice flow, overlain by groups of small ridges composed of subglacially derived till and sediment gravity flow deposits. Subtle differences in ridge morphology indicate they may be multi-genetic and formed both ice-marginally as moraines and subglacially as small ribbed moraine. We interpret MSGL-ridge associations as a subglacial bedform continuum reflecting the evolution from a deforming bed to brittle deformation, due to changing thermal and hydrological conditions at the ice-bed interface during ice sheet retreat. Adjacent glaciofluvial landforms indicate initial en- and supra-glacial meltwater drainage, possibly directly related to changing basal thermal/hydrological characteristics and subglacial ridge formation. Subsequently a subglacial conduit system evolved, and later retreat involved formation of ice-marginal ridges. The partially preserved landsystem reflects formation at a polythermal to active temperate ice marginal zone, rather than the stagnating temperate margin previously assumed for this area. Our work demonstrates the usefulness of hummocky topography in identifying changes in ice sheet bed thermal/hydrological characteristics during deglaciation and the importance of combining multiple evidence strands in reconstructing the processes involved in glacial landform construction.

Late Quaternary modeling and paleoclimate evolution of the Mount Taibai glacier (Qinling Mountains, China) constrained by cosmogenic radionuclide exposure dating

Glacial landforms on Mount Taibai, the main peak of the Qinling Mountains, China, are investigated to improve understanding of Quaternary palaeoclimate evolution in this key region of China's geographical north and south junction. Cosmogenic radionuclide 10Be exposure dating and glacier-climate modeling are used to reconstruct glacier evolution during the last glaciation in the Eryehai Valley, on the slopes of Mount Taibai. Chronological results indicate that the earliest initiation of the Mount Taibai glaciation was earlier than the global Last Glacial Maximum (gLGM). The glacier subsequently advanced further reaching its greatest extent during the gLGM between ∼23.50 ka and 21.76 ka. After this time, the glacier receded rapidly, before disappearing completely between ∼17.9 ka and 17.7 ka. We also analyzed a compilation of 229 recalculated 10Be exposure ages from the mountain ranges on the eastern Tibetan Plateau (TP), as well as in the Jaggang Mountains on the south-central TP, and found that a few mountain ranges on the eastern TP experienced two distinct millennial-scale moraine building events during the gLGM. Using glacier-climate modeling, temperature was calculated to have fallen from between ∼9.0 and 9.4 °C during the gLGM, with precipitation being 60–80% of the present-day value. If precipitation during the rapid retreat of the glacier between ∼21.76 ka and 18.10 ka were to be consistent with present trends, then the temperature would have needed to increase by a total of ∼1.3 °C during this period, with a mean rate of increase of 0.4 °C/ka. Combining our findings with other paleoclimate proxies, we infer that the main reason that there was no further glacial advance after the gLGM on Mount Taibai was the lower altitude of its peak relative to the Equilibrium-line Altitude (ELA). Our results provide the paleoclimatic conditions of the last glaciation in this critical area of China's geographical north and south junction, and deepen the understanding of how the East Asian Summer Monsoon (EASM) influences glaciers on the TP.

Offshore murtoos indicate warm-based Fennoscandian ice-sheet conditions during the Bølling warming in the northern Gulf of Riga, Baltic Sea

Glacial landforms provide invaluable information on the dynamics and extent of past ice sheets. In planform view, murtoos are triangular-shaped subglacial landforms that have recently been described from areas previously covered by the Fennoscandian Ice Sheet and whose formation has been linked to meltwater activity. We document the first occurrence of offshore murtoos and associated eskers in a high-resolution multibeam and sub-bottom profile dataset from the northern Gulf of Riga, Baltic Sea. In this study area, the murtoos appear to be longer (range 43–748 m), narrower (range 12–394 m) and less high (range 0.5–7.8 m), on average, compared to those previously reported on land, although this may be partly due to post-glacial sediments that smooth the present-day seafloor topography and may have buried smaller murtoos. The direction of murtoo longitudinal axes suggests a local NNE–SSW paleo-ice stream direction. In sub-bottom boomer profiles, the murtoos are characterized by moderate amplitude, sub-parallel discontinuous internal reflectors, indicating a varying sandy diamicton and sand composition, which is compatible with the previously interpreted mode of deposition by pulsed subglacial meltwater flow. Eskers that are found in close association with the murtoos are shorter (mean length 538 m) and more curved than their counterparts on nearby land areas, and they lack a general alignment. In boomer profiles, the eskers are characterized by low-amplitude, sub-parallel continuous reflectors, suggesting a better-sorted sandy composition. The curved and poorly aligned external form of the eskers suggests deposition under restricted subglacial drainage conditions. We conclude that murtoos and related landforms in the northern Gulf of Riga were formed during the Bølling warming at ca. 14.5–14.1 cal kyr BP, when large amounts of meltwater were delivered to the ice-sheet bed.

Timing and extent of late Quaternary glaciations on Karlik Mountain, eastern Tianshan range, China

Glacial landforms formed by multiple glaciations are well-preserved in the valleys around Karlik Mountain in the easternmost Tianshan range, Central Asia. These landforms are direct imprints of palaeoglaciers and represent important archives of past climatic and environmental conditions. Dating these landforms contributes to understanding the spatiotemporal variations of past glaciers and provides key information for reconstructing the palaeoclimate and palaeoenvironment in Central Asia. In this study, thirty-two boulder and bedrock samples were collected from two glaciated valleys on the southern slope of Karlik Mountain for terrestrial in situ cosmogenic nuclides (TCN) 10Be surface exposure dating. Based on the geomorphic relationships and dating results, the innermost MS1 moraine complex was deposited during the Little Ice Age (LIA); the MS2 moraine complex was formed during the Lateglacial; the MS3 moraine complex was deposited during the global Last Glacial Maximum (LGMG); the MS4 moraine complex, which is the largest moraine complex, is marine oxygen isotope stage (MIS) 4 in ages; and the MS5 moraine complex, which is only preserved at the interfluve ridges, has a similar age to MS4. The age of MS4 demonstrates that the largest local last glacial maximum (LGML) occurred during the early part of the last glacial cycle rather than during the LGMG. The MS4 and MS5 glacial complexes imply that a large ice cap with outlet valley glaciers developed on the whole of Karlik Mountain during MIS 4. These ages, combined with previous landform mapping and dating on the northern slope of the mountain, show that glacial advances since MIS 4 in this mountainous area were restricted to the valleys, rather than large ice cap scale, which is consistent with moraine records in the other valleys across the Tianshan range. The pattern and nearly synchronous timing of palaeoglacier fluctuations during the last glaciation in arid Central Asia imply that the main determinant for glacier fluctuations in this region has been changes in precipitation brought by the westerlies during periods of low temperature.

Comprehensive Radar Mapping of Malaspina Glacier (Sít' Tlein), Alaska—The World's Largest Piedmont Glacier—Reveals Potential for Instability

AbstractMalaspina Glacier, located on the coast of southern Alaska, is the world's largest piedmont glacier. A narrow ice‐cored foreland zone undergoing rapid thermokarst erosion separates the glacier from the relatively warm waters of the Gulf of Alaska. Glacier‐wide thinning rates for Malaspina are greater than 1 m/yr, and previous geophysical investigations indicated that bed elevation exceeds 300 m below sea level in some places. These observations together give rise to the question of glacial stability. To address this question, glacier evolution models are dependent upon detailed observations of Malaspina's subglacial topography. Here, we map 2,000 line‐km of the glacier's bed using airborne radar sounding data collected by NASA's Operation IceBridge. When compared to gridded radar measurements, we find that glaciological models overestimate Malaspina's volume by more than 30%. While we report a mean bed elevation 100 m greater than previous models, we find that Malaspina inhabits a broad basin largely grounded below sea level. Several subglacial channels dissect the glacier's bed: the most prominent of these channels extends at least 35 km up‐glacier from the terminus toward the throat of Seward Glacier. Provided continued foreland erosion, an ice‐ocean connection may promote rapid retreat along these overdeepened subglacial channels, with a global sea‐level rise potential of 1.4 mm.

Glacial geomorphology of the northwest Laurentide Ice Sheet on the northern Interior Plains and western Canadian Shield, Canada

ABSTRACT The majority of the Northwest Territories of mainland Canada was covered by the Laurentide Ice Sheet during the Last Glacial Maximum. The increasing coverage of high resolution remotely sensed data provides new opportunities to map the glacial geomorphology and study the glacial history of this remote location. Here we present a comprehensive map of glacial landforms within the northern Interior Plains and adjacent areas of the Canadian Shield, comprising around 6% of the Laurentide Ice Sheet bed. Twelve landform types were mapped from the high resolution ArcticDEM: ice flow parallel lineations, subglacial ribs, crevasse-squeeze ridges, major and minor moraine crests, hummocky terrain complexes and ridges, shear margin moraines, major, minor and lateral and submarginal meltwater channels, esker ridges and complexes, glaciofluvial complexes, perched deltas, raised shorelines and aeolian dunes. Together, these landforms provide a record of the highly dynamic behaviour of the northwest sector of the Laurentide Ice Sheet.

Holocene glacial oscillations in the Tyroler Valley (NE Greenland)

AbstractAlthough the spatiotemporal oscillations of the Greenland Ice Sheet (GrIS) during the last millennia have played a prominent role in global environmental changes, its glacial response to the natural variability still needs to be better constrained. Here, we focused on the reconstruction of the glacial behavior and deglaciation process along the Tyroler Valley (74° N, 22° E), within the Northeast Greenland National Park. This NW‐SE valley connects with the GrIS via the Pasterze Glacier and divides two ice caps (A.P. Olsen Land and Payer Land), this last one feeding two piedmont glaciers (Copeland and Kløft glaciers). For this study, we combined the interpretation of the spatial pattern of geomorphological features and the chronological framework defined by a new dataset of 15 10Be cosmic‐ray exposure (CRE) ages from glacially polished bedrock surfaces and moraine boulders together with one optically stimulated luminescence (OSL) age of a glaciolacustrine deposit. CRE ages indicate that the deglaciation of the lowest parts of the valley and the exposure of the highest slopes took place during the Early Holocene, at ca. 10–8.5 ka (ka = thousand year [BP]). Furthermore, this ice thinning also favored the disconnection of the valley tributary glaciers. Samples from the moraines of the two tributary glaciers indicate that the deglaciation was not continuous, but it was interrupted by at least three phases of glacial advance during the Neoglacial cooling (before ca. 5.9 ka), and the Little Ice Age (LIA, 0.6, and 0.3 ka). The larger piedmont glacier (Copeland Glacier) occupied the valley floor during these major advances, damming the river and allowing the formation of a proglacial glacial lake upvalley, as confirmed by the OSL date of lacustrine sediments that yielded an age of 0.53 ± 0.06 ka. In short, our study provides new evidence of the relative stability of GrIS and the regional ice caps in the area, in which glacial fronts have been rather stable since their advances during the Neoglacial and the LIA.

Geoarchaeology of the Cornia river coastal plain (Piombino, southern Tuscany, Italy)

ABSTRACT This paper presents a 1:20,000 scale Geoarchaeological map of the Cornia river coastal plain in southern Tuscany. The Geoarchaeological map integrates a comprehensive dataset of geomorphological and archaeological features. The spatial relationships between landforms and archaeological records show that the settlement pattern from the VII century BC to the V century AD was mostly influenced by the presence of several depositional landforms which formed before the period under consideration. Integrating the outputs of geomorphological and topographical analyses with archaeological databases is also helpful for land planning, especially in areas where present-day anthropic exploitation needs predictive and valid tools to assess the archaeological hazard.

Glacial geomorphology and Pleistocene glacier reconstruction in the Demänovská Valley, Low Tatra Mountains, Slovakia

In the Western Carpathians, clear evidence of the Pleistocene glaciations only occurs in two mountain massifs – the Tatra and Low Tatra Mountains. The Low Tatra Mountains (2043 m a.s.l.), contrary to the higher and more strongly glaciated Tatra Mountains (2654 m a.s.l.), have previously been much less attractive for scientific research. Hence, in these mountains, both glacial landforms and chronology, together with a detailed reconstruction of glacier geometry and resulted equilibrium line altitude (ELA), are poorly documented. The aim of this paper is to characterize the glacial relief and reconstruction of geometry and ELA of the Zadná voda glacier in the Demänovská Valley system which belongs to the category of the largest Pleistocene glaciers on the northern slope of the Low Tatra Mountains. The mapping results show that a freshly shaped, massive terminal moraine of maximal ice extent (MIE, likely formed during the global Last Glacial Maximum – LGM) occurs 4.3 km distance down-valley from the glacial cirque backwalls. There is no evidence of deposits from older glaciations beyond the terminal moraine down the valley. The terminal zone of the MIE features a fresh morainic landscape with hummocky topography with kettle hollows and the only known morainic lake in the Low Tatra Mountains – Vrbické pleso. During the MIE, the Zadná voda glacier covered 7 km2 of the area and featured a mean thickness of 48 m. The ELA of this glacier was 1433 m, determined by the area-altitude balance ratio (AABR) 1.6 method, which is a similar value to the LGM ELA calculated in the Western Tatra Mountains. The recessional stages were only recognized in the cirques area, where one or two generations of debris-covered glaciers and rock glaciers mark the final deglaciation of the study area.

The Extent of Glaciation in the Pechora Sea, Eurasian Arctic, Based on Submarine Glacial Landforms

The Pechora Sea is optimally located for studying the coalescence of a glacial and periglacial continental shelf zone in the high Arctic. Here, we present data acquired during cruises of the RV Akademik Nikolaj Strakhov in 2018–2021, revealing the distribution of submarine glacial landforms in the central part of the Pechora shelf area. Based on moraines and the distribution of glacial lineations, the extent of the ice sheet during the Last Glacial Maximum (LGM) is proposed. The crests of the moraine ridges and the slopes of their sides express a variation in morphology, and the ridges combine into irregular complexes. The moraines are primarily composed of coarse cobble-sized material with an addition of coarse sand and other sedimentary fractions. The mapped glacial landforms clearly indicate that an ice sheet extended over the area, while the Pechora basin, at the same time, was comprised of lowland characterized by a cryogenic subaerial landscape. Based on the result from this study, the extent and ice-flow pattern of the Barents-Kara Ice Sheet during the LGM were determined.

Late Pleistocene glaciation in the Eastern Carpathians – a regional overview

The Eastern Carpathians are the northeasternmost sector of the European Alpine Mountain system and comprise 14 formerly glaciated massifs that stretch over 300 km into the territories of Ukraine and Romania. In this study we provide a regional overview on Late Pleistocene glaciation in the Eastern Carpathians integrating recently published and new geomorphological data which include mapped glacial landforms and glacier reconstruction of the maximal ice extent (MIE) which is assigned to the global Last Glacial Maximum (LGM). Thus we obtain a complete inventory of glaciation in the Eastern Carpathians, including the documentation of 214 glacial cirques and 147 small mountain glaciers with a total area of 153.2 km2. The estimated LGM equilibrium line altitude (ELA) shows a strong rise of 2.4 m/km from the northwest (1270 m asl) to the southeast (1870 m asl), as well as a consistent eastward rise on several W-E transects (2–3.4 m/km). Similar patterns are shown by the palaeoglaciation level and the cirque floor altitude trend, which mimic the pattern of modern temperature-precipitation ELA (tpELA) in the region. Reconstructed palaeoglacial trends reflect dominant W-NW precipitation-wind regime and an enhanced zonal North Atlantic circulation pattern in the far interior of Europe in full glacial climate. This is consistent with both regonal palaeoclimatic simulations and wind regime proxies which indicate that the pattern of LGM circulation was similar to the present circulation, although the magnitude may have increased during glacial conditions. Additionally, based on the wide array of glacial landscapes inventoried in this study, ranging from traces of small niche/cirques to about 7 km long valley glaciers, we propose a quantitative approach to define the distinct stages of glacial landscape development based on the relationship between the Pleistocene ELA and mountain hypsometry.

Distribution of Devensian glacial erratics and related evidence elucidate complex ice flow changes across a former ice divide: Northern England

The Lune Gorge and the uplands of the southern Shap Fells represent a key area in developing an understanding of the dynamics of the Late Devensian glaciation (Dimlington Stadial) of northern England. Here ice masses emanating from southern Scotland, the Lake District and the Howgill Fells interacted in the area of the upper Lune valley. Glacial landforms are recorded and tills noted. The dispersal pattern of Shap granite (Sg) erratics is mapped as these clasts are an important tracer of regional ice movements and local ice dynamics. This new information is synthesised with existing literature to provide an understanding of ice dynamics in an area of complex ice flow history. In particular, the ice flow interactions over an area of the western Pennines and the southern Shap Fells have been defined.Early Dimlington ice flow in the vicinity of the upper Lune valley was easterly. Later a northerly shift in the position of a regionally significant west–east aligned ice divide led to topographic steering of southerly basal ice flows, resulting in the development of a western ice stream (Mint Sg plume) and an eastern ice stream (Lune Sg plume); both flowing south around the massif of the southern Shap Fells. At that time, southerly flow of basal ice over the highest ridges of the Grayrigg massif in the southern Shap Fells was relatively weak. Whereas the western stream extended into the Lancashire lowlands, the eastern ice stream was impeded in the Lune Gorge by ice emanating from Borrowdale which forced northern ice to the eastern side of the Lune Gorge where it was blocked by western flowing Howgill ice; the latter extending as far as just east of Kendal.During the late Dimlington, the ice masses over the Mint valley and the southern Shap Fells largely thinned and retreated to the north and west, with a surge in northerly ice movement within the upper Lune valley that did not override the western Pennines. Local ice dynamics are well-illustrated in the western margin of the Pennines (Crosby Ravensworth Fell Gaythorne Plain), where the disposition of erratics reflects local late west-to-east weak down-wasting ice flow and the presence of subglacial meltwater drainage channels. However, ice ultimately decayed in situ on Crosby Ravensworth Fell Gaythorne Plain. Similarly, after complex variable easterly and southerly ice flow during the early Dimlington, there was weak northerly ice flow in the later phase over Birkbeck Fells Common before ice thinned and retreated from Grayrigg Forest. An extensive ice stream, fed by ice emanating from an ice dispersal centre in the eastern Lake District, occupied the large trough of Borrowdale that transverses the southern Shap Fells, but its extension and recession dynamics remain enigmatic.“Glacial Theory …, in its application to the transport of blocks across Stainmoor, involves such obvious mechanical absurdities that the author considers it totally unworthy of the attention of the Society.” William Hopkins, 1842

CAGE20-3 Cruise Report: Geochemical and Sedimentological Investigation into Ingøydjupet, Håkon Mosby Mud Volcano and the Sorvestnaget Sand Waves

This expedition ran between July 28 and August 3 2020, targeting three sites in the Barents Sea, an area of glacial landforms in Ingøydjupet trough, the Håkon Mosby Mud Volcano and the Sorvestnaget Sand Wave area. Our short but productive expedition gave three post-doctoral researchers the opportunity to follow a research hypothesis from conception through planning and data collection aboard the research vessel, as well as plan and lead a research expedition. At the Ingøydjupet and Håkon Mosby Mud Volcano study areas, our objectives were to collect cores for geochemical analyses of the area and bathymetry data for geophysical analyses while the objectives at the sand waves are were to collect a time-lapse multibeam survey and grab samples for sedimentological analysis
 The cruise may be known as: CAGE20_3

Effect of Dam Emplacement and Water Level Changes on Sublacustrine Geomorphology and Recent Sedimentation in Jackson Lake, Grand Teton National Park (Wyoming, United States)

Dam installation on a deep hydrologically open lake provides the experimental framework necessary to study the influence of outlet engineering and changing base levels on limnogeological processes. Here, high-resolution seismic reflection profiles, sediment cores, and historical water level elevation datasets were employed to assess the recent depositional history of Jackson Lake, a dammed glacial lake located adjacent to the Teton fault in western Wyoming (USA). Prograding clinoforms imaged in the shallow stratigraphy indicate a recent lake-wide episode of delta abandonment. Submerged ∼11–12 m below the lake surface, these Gilbert-type paleo-deltas represent extensive submerged coarse-grained deposits along the axial and lateral margins of Jackson Lake that resulted from shoreline transgression following dam construction in the early 20th century. Other paleo-lake margin environments, including delta plain, shoreline, and glacial (drumlins, moraines) landforms were likewise inundated following dam installation, and now form prominent features on the lake floor. In deepwater, a detailed chronology was established using137Cs,210Pb, and reservoir-corrected14C for a sediment core that spans ∼1654–2019 Common Era (CE). Dam emplacement (1908–1916 CE) correlates with a nearly five-fold acceleration in accumulation rates and a depositional shift towards carbonaceous sediments. Interbedded organic-rich black diatomaceous oozes and tan silts track changes in reservoir water level elevation, which oscillated in response to regional climate and downstream water needs between 1908 and 2019 CE. Chemostratigraphic patterns of carbon, phosphorus, and sulfur are consistent with a change in nutrient status and productivity, controlled initially by transgression-driven flooding of supralittoral soils and vegetation, and subsequently with water level changes. A thin gravity flow deposit punctuates the deepwater strata and provides a benchmark for turbidite characterization driven by hydroclimate change. Because the Teton fault is a major seismic hazard, end-member characterization of turbidites is a critical first step for accurate discrimination of mass transport deposits controlled by earthquakes in more ancient Jackson Lake strata. Results from this study illustrate the influence of dam installation on sublacustrine geomorphology and sedimentation, which has implications for lake management and ecosystem services. Further, this study demonstrates that Jackson Lake contains an expanded, untapped sedimentary archive recording environmental changes in the American West.

Retreat and stabilization of a marine-based ice margin along a high arctic fjord-cross-shelf trough system

Multibeam bathymetric and seismostratigraphic data collected in the Clyde fjord-cross-shelf trough system (eastern Baffin Island, Canadian Arctic Archipelago) display glacial landforms and depositional assemblages that enable the identification of the maximal extent of the Laurentide Ice Sheet (LIS) margin and delineating the patterns and controls on its subsequent retreat. Additionally, 10 new sediment cores – from which seven radiocarbon ages were acquired – allow the recognition of depositional processes. Results show that, during the Last Glacial Maximum, the LIS margin extended almost to the edge of the continental shelf. Early deglaciation of the trough was marked by an initial ice-shelf collapse and rapid retreat of the ice stream, as evidenced by the absence of ice marginal landforms and the presence of extensive iceberg ploughmarks across a large portion of the outer trough. It was followed by a slow retreat and successive stabilizations of the ice margin that led to the deposition of recessional moraines and grounding-zone wedges (GZWs). Deglaciation of the fjord in the early Holocene occurred in an episodic style, whereby rapid retreat was punctuated by relatively long standstills that enabled major moraine formation. Long-term stabilizations of the ice margin in the Clyde fjord-cross-shelf trough system are interpreted to coincide with major climatic cooling events, such as the Younger Dryas and early Holocene cold reversals. Ages derived from sediment cores and previous work suggest that higher retreat rates correspond with periods of significant global sea level rise, suggesting that oceanic forcing exerted a minor control on the deglaciation. GZWs and large moraine ridges are observed at pinning points in the trough and fjord, indicating that the location of ice margin stabilizations was influenced by topography. The reconstruction of the deglaciation of the Clyde fjord-cross-shelf trough system allows us to refine deglacial models for similar systems of northeastern Baffin Island, in particular beyond the coast and along the steeper section of the fjord where chronological gaps remained.