Landform Assemblages Research Articles

Geomorphological and historical records of the surge-type behaviour of Hansbreen (Svalbard)

Abstract This paper presents geomorphological and historical records of the surge-type behaviour of Hansbreen, one of the most studied tidewater glaciers in Svalbard. The surge-type behaviour of the glacier has not been considered before due to the lack of evidence of this phenomenon. We integrate geomorphological mapping of the terrestrial and submarine forefields with historical data from the 19th and 20th centuries to reconstruct the glacier dynamics and identify the possible timing of surging. Landform assemblages are representative of the surging glacier landsystem, including crevasse-squeeze ridges (CSRs) and submarine streamlined glacial lineations. Abundant CSRs in the outer part of the terrestrial forefield were also documented in the 1980s, but most have been obliterated since then. We suggest the identified surge landsystem was produced during a surge of Hansbreen detected from photographs taken during the Austro-Hungarian expedition in 1872. Historical photogrammetric photos from the Norwegian expedition in 1918 revealed surge-diagnostic features in the glacier surface, including a folded medial moraine and a dense, complex network of crevasses. A potential next surge remains questionable in the following decades due to the low-lying accumulation area of the main stream hindering the mass build-up, but potential surges of the tributary glaciers should not be excluded.

Unravelling the fragmented sediment–landform assemblage in an area of thick Quaternary sediment, western Hudson Bay Lowland, Canada

Laurentide Ice Sheet (LIS) reconstructions beyond the last glacial maximum (LGM) are difficult due to the incomplete stratigraphic record that has largely been eroded by the most recent glaciation. The Hudson Bay Lowland (HBL) is a key region to understanding the long-term evolution of the LIS, as it contains an extensive pre-LGM stratigraphic record of glacial and nonglacial events. This study uses a hybrid lithostratigraphy–allostratigraphy approach to decipher the stratigraphic record in the Kaskattama highland region of the western HBL, Manitoba, Canada. We identify five glacial (till) units and three nonglacial (sorted sediment) units that were deposited during at least three glacial–interglacial cycles, which are constrained by radiocarbon and optical ages. The provenance of till units is identified using clast-lithology and detrital hornblende 40Ar/39Ar ages and supported by matrix geochemistry. The new stratigraphic framework for this western HBL region indicates that the ice emanating from the Quebec–Labrador dome advanced into the region at the start of the last two glaciations, suggesting accelerated early growth of the Quebec–Labrador dome relative to the Keewatin Dome.

Younger Dryas and Early Holocene ice‐margin dynamics in northwest Russia

Younger Dryas and Early Holocene ice‐margin dynamics in northwest Russia

Glacial geomorphology of the Notsarula and Chanchakhi river valleys, Georgian Caucasus

ABSTRACT Detailed glacial geomorphological maps are valuable for identifying target sites for palaeoglaciological reconstructions and thus for palaeoclimate inferences. In this study, we present the first detailed glacial geomorphological mapping of the landform assemblages produced by the former glaciers in the Notsarula (42°45′44″N 43°38′29″E) and Chanchakhi (42°42′5″N 43°40′42″E) river valleys, Georgian Caucasus. Our goal is to create a high-resolution (1:33,000 scale) glacial geomorphological map of this area (237 km2) and provide a detailed and accurate distribution of glacier-related features (see Main Map). Several field investigations between 2010 and 2022 along with detailed remote sensing surveys have been conducted for this glacial geomorphological mapping. The mapped landforms indicate multiple readvance or stillstands of valley glaciers across the study area. The largest and complex glacier body likely existed in the Bubistskali River gorge (42°43′16″N 43°43′32″E). Well-preserved moraine landforms in this valley suggest at least five large and several relatively small glacier readvances or stillstands occurred during the Late Quaternary. The simple-valley-type (without branches) glaciers were also probably present in other tributary valleys of the Chanchakhi River basin at that time. This map can be used for further geomorphological investigation as well as to support future geochronological work in the Greater Caucasus.

Gneissic tors in the central European upland: Complex Late Pleistocene forms?

Bedrock outcrops punctuating regolith-covered surfaces in the summit/upper slope and hillside positions (tors and crags) have long been a subject of inquiry in geomorphology for their evolutionary trajectories and now also as valuable geoheritage sites. Methodological advances in research, such as DTM-based geomorphological analysis and terrestrial cosmogenic nuclide inventories, create new perspectives to decipher the spatial and temporal context of tor emergence and decay. The shape, structural controls, 10Be inventories and relation to surrounding medium-scale landforms were studied at thirteen conspicuous bedrock outcrops developed in metamorphic and sedimentary lithologies in the Bohemian-Moravian Highland, Czechia. The shapes of studied bedrock outcrops indicate significant litho-structural controls. The general outline is mainly governed by (sub)vertical joints, whereas the inclination of foliation or bedding planes dictates summit and cliff morphology. Some of the tors described in this study developed in exceptionally densely foliated and jointed gneiss, which does not comply with the generally accepted view of tors as massive rock compartments resisting weathering. A series of rock hardness measurements performed at three gneissic tors using Schmidt hammer show statistically significant within-tor variability of R-values, indicating different exposure times to subaerial weathering. The complexity of landform assemblages, within which studied tors/crags are developed, varies from isolated bedrock outcrops surrounded by smooth slopes covered with debris-rich soils to outcrops accompanied by low rock cliffs, debris-covered steps, slope benches, boulder fields and isolated large blocks. The 10Be inventories reveal ages mostly from the Late Pleistocene and rarely from the Holocene. Summit/upper slope tors and hillside crags show considerable variability in maximum denudation rates ranging from 6.4 ± 0.2 to 105.6 ± 4.8 m/Ma. Paired samples from the summits and cliffs of eight outcrops indicate three possible post-emergence evolutionary scenarios with summit downwearing while keeping the outcrop outline, balanced cliff and summit degradation rate, and backwearing as the dominant degradation process.

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.

Active temperate glacial landsystem evolution in association with outwash head/depositional overdeepenings

AbstractThe response of temperate glaciers to rapid climate warming is reflected in the geomorphology (landsystem) resulting from snout recession. This paper develops a locally diverse process‐form model of active temperate glaciers through mapping and quantification of historical landscape change on the Fjallsjökull‐Hrútárjökull foreland, SE Iceland. Quantification of volumetric and areal changes on the foreland are based on time series of archival aerial images for the period 1945–1998, high‐resolution satellite imagery for 2014 and digital elevation models of differences derived from time series of UAV imagery for the years 2014, 2016, 2018, 2019 and 2022. Landscape change and glacier snout behaviour since 1945 highlights the importance of azonal and potentially intrazonal signatures in temperate glacial landsystems, particularly: (1) the development and collapse of partially supraglacial outwash fans to produce outwash heads fronting depositional overdeepenings; and (2) the emergence of ice‐cored eskers that record the evolution of englacial drainage networks operating over overdeepenings. Such landform assemblages are manifested as substantial ice‐cored/hummocky terrains, a characteristic of deglaciating forelands that is likely to be widely replicated wherever ice‐contact glacifluvial assemblages create outwash heads that act as depositional overdeepenings. Due to its significantly greater supraglacial debris cover, complete de‐icing of the Hrútárjökull snout in response to post‐1945 warming was delayed until around 2014. This constitutes a prime example of incremental stagnation, which in a rapidly warming climate has resulted in significant landscape change (land surface elevation collapse of 0.8 m a−1) over the last 8 years.

Subglacial catastrophic-flood origin of linear and curvilinear flat-rimmed pit chains on Mars: Evidence from geomorphological mapping and detailed landsystem analysis

Flat-rimmed pits lacking emanating flow-like features on pit margins are typically clustered as linear or curvilinear chains on Mars. Their formation has been attributed to faulting, volcanism, or roof collapse of subsurface voids. Here we test these end-member models by conducting landform analysis and systematic geomorphological mapping in the central Tharsis region. Our work shows that the mapped flat-rimmed pit chains were formed on a lava-plain landscape that is mantled by a surficial meter-sized boulder layer. The flat-rimmed pit chains are closely associated with a landform assemblage consisting of localized pit-linking/terminating dendritic networks of gullies, U-shaped troughs, isolated sinuous channels, sinuous round-topped boulder-bearing ridges, and rampart craters. The absence of pit-bounding and pit-cutting faults rules out the faulting origin, while the lack of rubble-filled pit floors and erupting flow-like landforms does not favor the volcanic and roof-collapse mechanisms. When viewed together, the mapped flat-rimmed pit chains and their closely associated landform assemblage can be explained by a glacial-landsystem model: (1) pits were created by vortex-induced erosion during repeated, violent, catastrophic mega-flooding below a regionally extensive ice sheet possibly covering the entire Tharsis region (i.e., the Tharsis ice cap), (2) the subglacial floods exploited bedrock and/or ice sheet fracture sets resulting in linear and parallel chains, (3) localized pit-linking and pit-terminating U-shaped troughs and round-topped boulder ridges represent subglacial channel bodies including glacial eskers, (4) surficial boulders represent glacial deposits, (5) local trough-bounded pit chains resemble coulees and their hosted rock basins on Earth, and (6) rampart craters with viscous-flow ejecta deposits represent surface or near surface ice generated by the inferred glaciation. We suggest that the excavated pit material was transported by subglacial megafloods along the giant (>6000 km long) circum-Tharsis outflow channels to the outwash plains in the northern-hemisphere lowlands.

Deglaciation and postglacial evolution of the Cère Valley (Cantal, French Massif Central) based on geomorphological mapping, 36Cl surface exposure dating and glacier modelling

ABSTRACTThe landform assemblage in the Cère Valley (Cantal, France) provides one of the most complete sequences for Late Pleistocene glacial fluctuations in the French Massif Central. However, the associated glacial chronology has been debated since the 1980s. This paper aims to improve the glacial chronology of the Cère Valley using 36Cl surface exposure ages. Geomorphological results define two glacier stadials with reconstructed equilibrium line altitudes of 1078 ± 43 and 1152 ± 34 m above sea level. These results are comparable to those obtained in the Alps or the Pyrenees during the Last Glacial Maximum (26–19.5 ka). However, 36Cl surface exposure ages are centred around the Younger Dryas (YD), between 13 and 11 ka (n = 4). We suggest that these 36Cl ages are not related to a standstill during the YD but rather to the effects of the postglacial evolution of the Cère Valley. We investigate two geomorphological end‐member scenarios to explain the postponed exposure of sampled boulders: the Aurillac Lake scenario and the later fluvial incision scenario. While the nature of the geomorphological events leading to the boulder exhumation is not fully resolved, we highlight a long phase of postglacial evolution in the Cère Valley.

The impact of Holocene deglaciation and glacial dynamics on the landscapes and geomorphology of Potter Peninsula, King George Island (Isla 25 Mayo), NW Antarctic Peninsula

The timing and impact of deglaciation and Holocene readvances on the terrestrial continental margins of the Antarctic Peninsula (AP) have been well-studied but are still debated. Potter Peninsula on King George Island (KGI) (Isla 25 de Mayo), South Shetland Islands (SSI), NW Antarctic Peninsula, has a detailed assemblage of glacial landforms and stratigraphic exposures for constraining deglacial landscape development and glacier readvances. We undertook new morphostratigraphic mapping of the deglaciated foreland of the Warszawa Icefield, an outlet of the Bellingshausen (Collins) Ice Cap on Potter Peninsula, using satellite imagery and new lithofacies recognition and interpretations, combined with new chronostratigraphic analysis of stratigraphic sections, lake sediments, and moraine deposits. Results show that the deglaciation on Potter Peninsula began before c. 8.2 ka. Around c. 7.0 ka, the Warszawa Icefield and the marine-facing Fourcade Glacier readvanced across Potter Peninsula and to the outer part of Potter Cove. Evidence of further readvances on Potter Peninsula was absent until the Warszawa Icefield margin was landward of its present position on three occasions: c. 1.7–1.4 ka, after c. 0.7 ka (most likely c. 0.5–0.1 ka), and by 1956 CE. The timing of Holocene deglaciation and glacier fluctuations on Potter Peninsula are broadly coeval with other glacier- and ice-free areas on the SSI and the northern AP and likely driven by interactions between millennial–centennial-scale changes in solar insolation and irradiance, the southern westerlies, and the Southern Annular Mode.

Geomorphologic evidence of jökulhlaups along the Hvítá River, southwestern Iceland

Glacial outburst floods (jökulhlaups) have been a significant driver of landscape evolution, environmental change, and geohazards throughout the Quaternary. Iceland experiences more frequent jökulhlaups than nearly anywhere else on Earth, though most research focuses on subglacial volcanogenic floods that drain across outwash plains. Abundant geomorphologic evidence exists for largescale jökulhlaups that drained along the modern-day course of the Hvítá River in southwestern Iceland during early Holocene deglaciation, originating from ice-dammed Glacial Lake Kjölur; yet only one previous publication has investigated these events. This study uses a combination of field mapping and remote sensing to identify new jökulhlaup geomorphologic evidence along the Hvítá River, including erosional landforms such as scoured bedrock, anastomosing channel networks, cataracts, and canyons, and depositional features such as boulder bars and channel infill. We synthesize new findings with previously reported work to: 1) present an updated geomorphologic map of Hvítá jökulhlaup evidence; 2) reconstruct flood drainage routes, landscape impact, hydrology, and relative chronology; and 3) hypothesize scenarios of ice margin position and glacial lake evolution. Interpreting flood landform assemblages reveals a more extensive geomorphologic record than previously reported, with a complex drainage pattern along four separate routes from two potentially different sources. Reconstructed peak flow discharges span four orders of magnitude from 10² to 10$^5$ m³/s. Geomorphologic and paleohydraulic results introduce four hypothesized drainage scenarios, though absolute geochronology is necessary to determine whether multiple floods drained along each route. The Hvítá jökulhlaups yield insight into the timing and dynamics of the final phase of Icelandic Ice Sheet decay, advancing understanding of Iceland’s Pleistocene–Holocene transition, demonstrating the importance of high magnitude, low frequency floods in landscape evolution, and serving as an analogue to ice and meltwater response to past, present, and future climate warming in glaciated regions worldwide.

The largest rock avalanche in China at Iymek, Eastern Pamir, and its spectacular emplacement landscape

Catastrophic rock avalanches are widely distributed on Earth and share a series of common diagnostic features that play a vital role in revealing their emplacement mechanisms. Combined with satellite imagery, field investigation, and statistical analysis, a comprehensive investigation is conducted on the gigantic Iymek rock avalanche (IRA) in eastern Pamir, China. The IRA with a volume of ~0.98 km3 detached mass advanced 16.3 km on an unconfined terrain, covered an area of 48.5 km2 with a depth of 10–90 m, and deposited an estimated volume of 1.37 km3 deposits, making it the largest rock avalanche known in China. Its spectacular emplacement landscape provides an excellent laboratory for studying rock avalanches. Morphologically, the IRA deposit exhibits characteristic undulating features, including trimlines, longitudinal ridges, hummocks, transverse ridges, raised distal edge, and raised lateral levees. On the profile, numerous representative landslide-tectonic structures, principally composed of the preserved stratigraphic sequence, pervasive shear bands, spectacular clastic dikes, diapiric intrusion, folds, and normal/thrust faults, are revealed. The sequential assemblage of these morphological landforms and internal structures demonstrates that the propagation of the IRA should behave like a laminar flow with distributed shearing and obey three major stress processes, i.e. extension-dominated process in the proximal area, compression-dominated process in the distal area, and slightly lateral spreading in the central area and the areas adjacent to the margin of the deposit sheet. During its propagation, the strong substrate, mainly composed of gravel-dominated coarse material, should play a decisive role in casting most of the depositional landscapes. Restricted by the strong substrate, prominent lateral levees are well-developed in the accumulation zone with a series of rolling flame structures. This powerfully indicates that the formation of the lateral levees should be attributed to a continuously sideward movement of the frontal mass due to the push from the rear part instead of a particle self-segregation mechanism. Furthermore, the cutting relationship between the clastic dikes and subhorizontal shear bands in local positions indicates that the localized liquefaction of the substrate is not a contributor for the high mobility of the IRA and is only a product of the strong interaction between the sliding mass and the substrate at the final stage. This comprehensive study not only provides important information that contributes to an interpretation of similar features on Earth, but also yields insight into the underlying mechanisms responsible for the emplacement of rock avalanches.

The sedimentological death mask of a dying glacier

AbstractThe Pasterze is Austria's largest glacier, and it is experiencing rapid downwasting and retreat. A mosaic of complex sedimentary deposits has been produced in recent years which have not hitherto been studied, yet provide excellent lessons into the facies distribution expected from a dying valley glacier. In this paper, a new glaciological–geomorphological–geological map is presented for the glacier in July 2021. Freshly exposed (since 2018) tills and flutes constitute a subglacial sediment–landform assemblage. An ice‐marginal sediment–landform assemblage comprises meltwater streams, a delta system and proglacial lake terrace deposits. The supraglacial assemblage, meanwhile, includes fossil englacial channel deposits revealed by ablation, together with debris bands, rockfall deposits and supraglacial channel deposits. Collectively, these sediment–landform assemblages constitute the building blocks of a dying glacier landsystem.

Karst Heritage as a Tourist Attraction: a Case Study in the White Desert National Park, Western Desert, Egypt

Geotourism is a form of maintainable tourism that emphasizes the geoheritage characteristics of a district. Karst landforms are one of the most imperative appealing aspects of the theme of nature-based tourism. The geomorphological regionalization of the karst landforms contributes to a better understanding of Earthʼs evolution and provides the necessary provincial knowledge for resource utilization, ecological protection, and general economic improvement. To achieve this goal, an integrated geomorphological approach for inventorying, appraising, and evaluating sites of karst geoheritage within the framework of geomorphosite assessment method convoyed by SWOT analysis has been performed in the White Desert National Park (WDNP), Western Desert, Egypt. The paper aims to highlight the geotourism potential of the WDNP and offer strategic plans for identifying geotourist resources to a larger community through geoeducation and geoconservation. The WDNP is covered by Upper Cretaceous-Late Tertiary karstified carbonate successions and fluvioclastic rocks that host an interesting assemblage of diverse karst landforms (geodiversity) and amazing flora (bioturbation mangrove roots) together with fauna (biodiversity), revealing a geological open-air museum. The karst sites, which offer several phenomena with significant lithological, morphological, and paleogeographic features, embrace aesthetic, educational, scientific/scenic, and touristic values that will endure spectators of the geological evolution of this province. The brilliant conspicuousness, scientific excellence, innovative appeal, and distinctiveness of karst geomorphosites involving poljes/uvalas, karst lakes, natural sculptures, mushrooms, inselbergs, towers/bridges, dolines/sinkholes, cones/domes, and speleothems deliberate resources for the progress of geotourism. These landscapes can be considered tools for science and education because they give knowledge about rock/soil types and rock permeability, and paleoenvironmental and paleoclimatic circumstances. Most of their landforms can be used as habitats for endangered bird species, which attract several sightseers, an indicative of ecological significance. This excellent karst geodiversity provides an appreciated tool for geotourism and geopark development that is preferred to raise the local economy for populations and reinforce rural growth in neighboring towns and cities. The paper’s findings reveal a comprehensive base for the improvement, planning, and management of the WDNP in order for it to become a geotourism endpoint. Furthermore, they improve the position of the WDNP in the tourist market and contribute to the local maintainable progress via giving socio-economic assistance to the local community for the advancement of geotourism through geoconservation and sustainability.

Subglacial meltwater routes of the Fennoscandian Ice Sheet

ABSTRACT Subglacial drainage systems are crucial elements of glaciers and ice sheets because they modulate ice flow velocity. However, logistical challenges of measuring subglacial processes beneath contemporary ice and natural limitations in long-term monitoring hinder our understanding about their spatio-temporal evolution. Subglacial meltwater landforms created by palaeo-ice sheets are records of past subglacial drainage systems and offer the potential to study their large-scale development throughout deglaciation. Although collectively recording subglacial drainage, individual meltwater landforms such as eskers, meltwater channels and meltwater corridors, which comprise tunnel valleys and meltwater tracks (assemblages of landforms in broad, elongated paths with irregular surface texture), have mostly been investigated as separate entities. Using high-resolution (1–2 m) digital elevation models, we map integrated networks of subglacial meltwater landforms, herein called subglacial meltwater routes, on an ice-sheet scale in Fennoscandia. Our map provides a basis for future research on the long-term evolution of subglacial drainage networks and its effect on ice dynamics of the Fennoscandian Ice Sheet.

Periglacial landforms of Dartmoor: an automated mapping approach to characterizing cold climate geomorphology

ABSTRACT A systematic mapping approach characterizes Dartmoor periglacial landform signatures using the geomorphology of nine summit areas displaying well developed tor and blockfield landforms. This combines manual vectorisation with automatic classification and surface boulder identification, using spectral signatures to reveal patterns and distribution. Tors were classified using a three-fold scheme: T0 - summits with no tors; T1 - summits with castellated and high relief tors; T2 - summits with subdued or low relief tors. Clitter (blockfield and blockstream) features identified by automated mapping include boulder lobes and stripes and boulder-fronted lobes and terraces, arranged according to distance downslope from parent tors. This zonation of periglacial landforms is proposed as a landsystem signature for areas exposed to periglacial and permafrost processes for significant time during the Quaternary. It represents a process-form regime in which cold climate processes, acting on partially deeply weathered and pneumatolysised granite, produce castellated tors, cryoplanation benches and autochthonous blockfield (clitter), and permafrost creep develops boulder lobes that elongate and evolve downslope as allochthonous blockslopes with boulder stripes and boulder-fronted lobes and terraces. This demonstrates that automated mapping can be applied to areas of upland periglacial landforms to rapidly and systematically compile quantifiable patterns of landform assemblages.

Modelling geoarchaeological resources in temperate alluvial environments: The capability of higher resolution satellite remote sensing techniques

Temperate river systems cover large regions of the earth's surface and provide challenging environments for the detection of archaeological remains. The deposition of alluvium above, and interbedded with, archaeological deposits means conventional forms of archaeological prospection such as geophysical survey or aerial photography are often ineffective. Consequently, archaeologists have turned to the construction of deposit models to evaluate the archaeological potential of various landforms. However, despite the high capacity of satellite multispectral data to identify alluvial landforms and archaeological deposits, the contribution that it can make towards deposit models has only received limited attention. This research assesses the capability of higher resolution satellite multispectral imagery to identify alluvial landform assemblages and subsequently facilitate the modelling of geoarchaeological resources. As image enhancements are often required to improve interpretation or classification, it includes a quantitative evaluation of 45 different processes, comprising two spectral separability measures on paired regions of interest (ROIs) from the Lower Lugg Valley, Herefordshire, UK. The results define optimal image processing techniques for the detailed geoarchaeological interpretation of alluvial environments and demonstrate that relatively simple visualisation methods (e.g. composite images) and summative techniques (Principal Components Analysis) offer some of the most effective approaches.

Glacitectonic evidence of ice sheet interaction and retreat across the western part of Dogger Bank (North Sea) during the Last Glaciation

High-resolution 2D seismic data from the western side of Dogger Bank (North Sea) has revealed that the glacigenic sediments of the Dogger Bank Formation record a complex history of sedimentation and penecontemporaneous, large-scale, ice-marginal to proglacial glacitectonism. The resulting complex assemblage of glacial landforms and sediments record the interplay between two separate ice masses revealing that Late Devensian ice sheet dynamics across Dogger Bank were far more complex than previously thought, involving the North Sea lobe of the British and Irish Ice Sheet, advancing from the west, interacting with the Dogger Bank lobe which expanded from the north. The active northward retreat of the Dogger Bank lobe resulted in the development of a complex assemblage of arcuate thrust-block moraines (≤15 km wide, >30 km long) composed of highly folded and thrust sediments, separated by sedimentary basins and meltwater channels filled by outwash. The impact of the North Sea lobe was restricted to the western margin of Dogger Bank and led to deep-seated (100–150 m thick) glacitectonism in response to ice-push from the west. During the earlier expansion of the North Sea lobe, this thrust and fold complex initially occupied a frontal marginal position changing to a more lateral ice-marginal position as the ice sheet continued to expand to the south. The complex structural relationships between the two glacitectonic complexes indicates that these ice masses interacted along the western side of Dogger Bank, with the inundation of this area by ice probably occurring during the last glaciation when the ice sheets attained their maximum extents.

Glacial processes and landforms

AbstractFrom 1965 to 2000 glacial geomorphology became increasingly specialized and developed significantly due to technological improvements, particularly in remote sensing, surveying and field-based glaciological process studies. The better understanding of basal thermal regimes in ice sheets and glaciers led to the development of concepts such as spatial and temporal migration of ice divides in dynamic ice sheets that could overprint subglacial landform assemblages, debris entrainment processes related to polythermal glacier systems, and glacier and ice sheet beds composed of cold and warm based mosaics. Process observations at the ice–bed interface led to the discovery of the third glacier flow mechanism, substrate deformation, which provided the impetus to reconstruct the genesis of subglacial bedforms such as drumlins and to evaluate the origins and potential flow law for till. Numerical evaluations of glacial erosion led to a better understanding of abrasion and quarrying as well as the erection of genetic models and erosion rates for larger-scale features such as U-shaped valleys and cirques. Linkages were made between debris transport pathways and moraine construction in supraglacial environments, with the role of glacier structure being linked to specific landforms, such as medial, lateral, hummocky and ice-cored moraines as well as rock glaciers. Our appreciation of the erosional and depositional impacts of glacifluvial systems was enhanced significantly with the advent of process observations on the hydrology of modern glaciers as well as the final vindication of J.H. Bretz and his proposed jökulhlaup origins of the Channelled Scablands and the Missoula Floods. In addition to the increasing numbers of studies at modern glacier snouts, the embracing of sedimentology by glacial geomorphologists was to result in significant developments in understanding the process-form regimes of subglacial, marginal and proglacial landforms, particularly the recognition of landform continua and hybrids. Advances resulting from this included the recognition of different modes of moraine and glacitectonic thrust mass development, lithofacies models of the varied glacifluvial depositional environments, and the initial expansion of work on the sediments and depocentres of glacimarine settings, the latter being the result of glacial research taking to submersibles and ice-strengthened ships for the first time. A similarly new frontier was the expansion of research on the increasingly higher resolution images returning from Mars, where extraterrestrial glaciations were recognized based on comparisons with Earth analogues. Holistic appreciations of glaciation signatures using landform assemblages were developed, initially as process-form models and later as glacial landsystems, providing an ever-expanding set of templates for reconstructing palaeoglaciology in the wide variety of topographic and environmental settings, which also acknowledge spatial and temporal change in glacier and ice sheet systems.

Using bed-roughness signatures to characterise glacial landform assemblages beneath palaeo-ice sheets

AbstractPalaeo-glacial landforms can give insights into bed roughness that currently cannot be captured underneath contemporary-ice streams. A few studies have measured bed roughness of palaeo-ice streams but the bed roughness of specific landform assemblages has not been assessed. If glacial landform assemblages have a characteristic bed-roughness signature, this could potentially be used to constrain where certain landform assemblages exist underneath contemporary-ice sheets. To test this, bed roughness was calculated along 5 m × 5 m resolution transects (NEXTMap DTM, 5 m resolution), which were placed over glacial landform assemblages (e.g. drumlins) in the UK. We find that a combination of total roughness and anisotropy of roughness can be used to define characteristic roughness signatures of glacial landform assemblages. The results show that different window sizes are required to determine the characteristic roughness for a wide range of landform types and to produce bed-roughness signatures of these. Mega scale glacial lineations on average have the lowest bed-roughness values and are the most anisotropic landform assemblage.