Sven Lukas

Formation, Meltout Processes and Landscape Alteration of High-Arctic Ice-Cored Moraines—Examples From Nordenskiold Land, Central Spitsbergen

The debris-covered ice-margins of three largely cold-based glaciers in central Spitsbergen were investigated to reconstruct their formation and degradation. Clast shapes indicate dominant englacial and supraglacial transport with a smaller subglacial component. Emplacement of material is inferred to have been through meltout along flowlines due to the relatively uniform and continuous debris cover along the glacier margins; no evidence of thrusting has been found. Degradation of all three belts is rapid and involves debris flows at unstable places—e.g., the margins of meltwater channels. Resultant exposure of underlying ice initiates or accelerates melting, thereby leading to further debris flows. Hence, once degradation starts, a self-reinforcing cycle that removes material from the glacier commences. Landform preservation potential on millennial time scales in a high-arctic, continuous permafrost environment is thus limited. This work has implications for the interpretation of Pleistocene landform associations that use modern analogues from Svalbard.

Morphostratigraphic principles in glacier reconstruction ¿ a perspective from the British Younger Dryas

Glacier reconstruction enables the calculation of palaeoglaciological and palaeoclimatic variables such as the equilibrium-line altitude and palaeo-precipitation values. Such data are important for our understanding of past atmosphere-cryosphere interactions and as input variables to constrain numerical models effectively. Numerical dating is crucial to constrain the age of glacial events, but, due to absence of dateable material and/or contamination problems, ice masses can frequently be constrained satisfactorily only in a few locations. Thus, extrapolation and interpolation of geomorphological evidence is required to establish the extent of glaciers at a given time for the whole ice mass. Using examples from areas in Britain that were last covered by glaciers during the Younger Dryas, geomorphological approaches are reviewed and potential pitfalls highlighted. A multiproxy morphostratigraphic approach that utilizes clear landsystem contrasts inside and outside dated glacial limits is developed and tested in an area where numerical dates are sparse. Landform assemblages suitable in this respect are the type and frequency of moraines, river terrace sequences, glaciofluvial landforms, raised beaches, the upslope terminations of sediment cover (‘drift limits’), periglacial trimlines and periglacial features such as blockfields, solifluction lobes and thick talus accumulations. It is concluded that, if multiple lines of geomorphological evidence converge, these can be used to confine the extent of past glaciers in a given area and to guide dating programmes.

A GIS tool for automatic calculation of glacier equilibrium-line altitudes

A toolbox for the automated calculation of glacier equilibrium-line altitudes (ELAs) using the Accumulation Area Ratio, Area-Altitude Balance Ratio, Area-Altitude and Kurowski methods is presented. These are the most commonly-used methods of ELA calculation in palaeo-glacier reconstructions. The toolbox has been coded in Python and runs in ArcGIS requiring only the reconstructed surface of the palaeo-glacier (a DEM) as input. Through fast and automatic calculation this toolbox simplifies the process of ELA determination and can successfully work both for a single glacier and for large datasets of multiple glaciers. We describe Equilibrium Line Altitude calculation methods for palaeoglaciers.We examine suitability of each method for different glacier types.We present a toolbox for automatic ELA calculation on AAR and AABR methods.Toolbox is coded in Python and runs in ArcGIS.Toolbox use and operation are described.

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.

GlaRe, a GIS tool to reconstruct the 3D surface of palaeoglaciers

Glacier reconstructions are widely used in palaeoclimatic studies and this paper presents a new semi-automated method for generating glacier reconstructions: GlaRe, is a toolbox coded in Python and operating in ArcGIS. This toolbox provides tools to generate the ice thickness from the bed topography along a palaeoglacier flowline applying the standard flow law for ice, and generates the 3D surface of the palaeoglacier using multiple interpolation methods. The toolbox performance has been evaluated using two extant glaciers, an icefield and a cirque/valley glacier from which the subglacial topography is known, using the basic reconstruction routine in GlaRe. Results in terms of ice surface, ice extent and equilibrium line altitude show excellent agreement that confirms the robustness of this procedure in the reconstruction of palaeoglaciers from glacial landforms such as frontal moraines. GlaRe is a tool for palaeoglacier 3D surface reconstruction from bed topography.GlaRe is coded in Python and runs in ArcGIS as a toolbox.The theory of perfect plasticity equilibrium glacier profile is considered.Interpolation methods for glacier 3D surface creation are described and discussed.GlaRe is tested with two extant glaciers, showing a small, acceptable error.

Debris entrainment and landform genesis during tidewater glacier surges

The englacial entrainment of basal debris during surges presents an opportunity to investigate processes acting at the glacier bed. The subsequent melt-out of debris-rich englacial structures during the quiescent phase produces geometrical ridge networks on glacier forelands that are diagnostic of surge activity. We investigate the link between debris entrainment and proglacial geomorphology by analyzing basal ice, englacial structures, and ridge networks exposed at the margins of Tunabreen, a tidewater surge-type glacier in Svalbard. The basal ice facies display clear evidence for brittle and ductile tectonic deformation, resulting in overall thickening of the basal ice sequence. The formation of debris-poor dispersed facies ice is the result of strain-induced metamorphism of meteoric ice near the bed. Debris-rich englacial structures display a variety of characteristics and morphologies and are interpreted to represent the incorporation and elevation of subglacial till via the squeezing of till into basal crevasses and hydrofracture exploitation of thrust faults, reoriented crevasse squeezes, and preexisting fractures. These structures are observed to melt-out and form embryonic geometrical ridge networks at the base of a terrestrially grounded ice cliff. Ridge networks are also located at the terrestrial margins of Tunabreen, neighboring Von Postbreen, and in a submarine position within Tempelfjorden. Analysis of network characteristics allows these ridges to be linked to different formational mechanisms of their parent debris-rich englacial structures. This in turn provides an insight into variations in the dominant tectonic stress regimes acting across the glacier during surges.

A glacial geological and geomorphological map of the far NW Highlands, Scotland. Part 1

Abstract Please click here to download the map associated with this article. The “Glacial geological and geomorphological map of the NW Highlands, Scotland” is the result of detailed aerial photograph interpretation and field mapping at a scale of 1: 25,000 and presents the distribution of glacial deposits and landforms in an area of ca. 1000 km2 in the far NW Scottish Highlands (58°5″N 4°58″W to 58°29″N 4°34″W; British National Grid: NC 250140 to NC 500 540). This area has never been mapped in detail before, and previous glacier reconstructions have solely been carried out from aerial photographs without much ground-truthing. The present mapping reveals that glacial landforms, most notably recessional “hummocky” moraines attributed to the Younger Dryas (ca. 12.7-11.5 ka BP), are more widely distributed throughout the study area than recognised on earlier overview maps. Detailed mapping enables the detailed reconstruction of part of a large mountain icefield of ca. 211 km2 which is significantly larger than the 36 km2 previously envisaged for the NW Highlands. These findings demonstrate that “traditional” mapping from aerial photographs and in the field can result in a high-resolution reconstruction of palaeo-glaciers from which palaeoclimatic variables can then be calculated. Such variables are crucial to validate and further constrain numerical models used to predict future climate change.

The formation of Alpine lateral moraines inferred from sedimentology and radar reflection patterns: a case study from Gornergletscher, Switzerland

Abstract Studies on the formation of alpine lateral moraines are rare; consequently, their internal structure and their modes of formation are relatively poorly understood. We present here sedimentological and ground-penetrating radar (GPR) data from a lateral moraine complex where an exposure allows radar facies to be compared to the field evidence. The moraine, which is slightly asymmetric with a slightly steeper distal slope, consists of alternating clast- and matrix-supported stratified diamicts and intercalated sorted sediment units which are all subparallel to the moraine surface. They are interpreted as subaerial debris flows and fluvial sediments, respectively. The GPR, using frequencies of 50, 100 and 200 MHz, allows tracing of very similar subparallel reflectors to c. 10 m into the subsurface. These are interpreted to represent the diamict units while the thickness of the sorted sediment units is below GPR resolution. Our data suggests that a two or three frequency approach supplemented by common-midpoint (CMP) measurements works well in glaciated high-mountain environments. Based on our sedimentological and GPR data we develop a conceptual framework for the formation of successive lateral moraines which involves ice-contact fan sedimentation, followed by collapse and incremental reworking of the proximal side during glacier retreat.

Chapter 2 The Quaternary

Abstract The Quaternary is the youngest geological period, beginning 2.58 Ma ago and including the present day; it is therefore the only geological period that is continuously growing. During the first epoch of the Quaternary, the Pleistocene, extremely cold and warm conditions alternated, frequently over short periods of time. This resulted in processes currently only operating in cold (polar and high-mountain) environments extending to and affecting the mid-latitudes, including the currently densely populated areas of North America and Europe. In Britain every region has been affected by cold-region processes, which have produced unique sedimentary and geomorphological signatures. Hence, an intimate knowledge of these processes is of direct relevance to engineering geologists and anyone working with natural materials. This chapter reviews the state of the art of (a) the stratigraphic (nomenclatorial) framework of the Quaternary, (b) prominent concepts that are of direct relevance to understanding the detailed overviews in Chapters 3–5; and (c) key findings on the dynamics of these processes and their implications for engineering-geological questions and problems.

Editorial: quaternary of the British Isles and adjoining seas

This volume of the Journal of Maps is one of four volumes published froman Annual Discussion Meeting (ADM) of the Quaternary ResearchAssociation (QRA), in January 2008, to examine the Quaternary of theBritish Isles and the adjoining seas. This volume deals with evidence forQuaternary environmental change in map-form, and the other volumes,which will be published in the journals Quaternary Science Reviews,Journal of Quaternary Science and Proceedings of the Geologists’Association will be concerned, respectively with Quaternary climates andclimate change, Quaternary landscapes, and Quaternary Geology.The QRA ADM on the topic of the Quaternary of the British Islesand the adjoining seas was organised to review the subject upon which avast amount of work has been done since the last meeting on the topic in1977. The meeting also marked the 40