/pdf/glacial-geomorphological-mapping-a-review-of-approaches-and-3juhdcq1lp.pdf

Glacial geomorphological mapping: A review of approaches and frameworks for best practice

During the last glaciation, most of the British Isles and the surrounding continental shelf were covered by the British–Irish Ice Sheet (BIIS). An earlier compilation from the existing literature (BRITICE version 1) assembled the relevant glacial geomorphological evidence into a freely available GIS geodatabase and map (Clark et al. 2004: Boreas 33, 359). New high-resolution digital elevation models, of the land and seabed, have become available casting the glacial landform record of the British Isles in a new light and highlighting the shortcomings of the V.1 BRITICE compilation. Here we present a wholesale revision of the evidence, onshore and offshore, to produce BRITICE version 2, which now also includes Ireland. All published geomorphological evidence pertinent to the behaviour of the ice sheet is included, up to the census date of December 2015. The revised GIS database contains over 170 000 geospatially referenced and attributed elements – an eightfold increase in information from the previous version. The compiled data include: drumlins, ribbed moraine, crag-and-tails, mega-scale glacial lineations, glacially streamlined bedrock (grooves, roches moutonnees, whalebacks), glacial erratics, eskers, meltwater channels (subglacial, lateral, proglacial and tunnel valleys), moraines, trimlines, cirques, trough-mouth fans and evidence defining ice-dammed lakes. The increased volume of features necessitates different map/database products with varying levels of data generalization, namely: (i) an unfiltered GIS database containing all mapping; (ii) a filtered GIS database, resolving data conflicts and with edits to improve geo-locational accuracy (available as GIS data and PDF maps); and (iii) a cartographically generalized map to provide an overview of the distribution and types of features at the ice-sheet scale that can be printed at A0 paper size at a 1:1 250 000 scale. All GIS data, the maps (as PDFs) and a bibliography of all published sources are available for download from: https://www.sheffield.ac.uk/geography/staff/clark_chris/britice.

/pdf/britice-glacial-map-version-2-a-map-and-gis-database-of-4gw87ei7c3.pdf

BRITICE Glacial Map, version 2: a map and GIS database of glacial landforms of the last British-Irish Ice Sheet

/pdf/theoretical-contemporary-observational-and-palaeo-526abcvkw2.pdf

Theoretical, contemporary observational and palaeo-perspectives on ice sheet hydrology: Processes and products

The last Scottish Ice Sheet (SIS) expanded from a pre-existing ice cap after ∼35 ka. Highland ice dominated, with subsequent build-up of a Southern Uplands ice mass. The Outer Hebrides, Skye, Mull, the Cairngorms and Shetland supported persistent independent ice centres. Expansion was accompanied by ice-divide migration and switching flow directions. Ice nourished in Scotland reached the Atlantic Shelf break in some sectors but only mid-shelf in others, was confluent with the Fennoscandian Ice Sheet (FIS) in the North Sea Basin, extended into northern England, and fed the Irish Sea Ice Stream and a lobe that reached East Anglia. The timing of maximum extent was diachronous, from ∼30–27 ka on the Atlantic Shelf to ∼22–21 ka in Yorkshire. The SIS buried all mountains, but experienced periods of thickening alternating with drawdown driven by ice streams such as the Minch, the Hebrides and the Moray Firth Ice Streams. Submarine moraine banks indicate oscillating retreat and progressive decoupling of Highland ice from Orkney–Shetland ice. The pattern and timing of separation of the SIS and FIS in the North Sea Basin remain uncertain. Available evidence suggests that by ∼17 ka, much of the Sea of the Hebrides, the Outer Hebrides, Caithness and the coasts of E Scotland were deglaciated. By ∼16 ka, the Solway lowlands, Orkney and Shetland were deglaciated, the SIS and Irish Ice Sheet had separated, the ice margin lay along the western seaboard, nunataks had emerged in Wester Ross, the ice margin lay N of the Cairngorms and the sea had invaded the Tay and Forth estuaries. By ∼15 ka, most of the Southern Uplands, the Firth of Clyde, the Midland Valley and the upper Spey valley were deglaciated, and in NW Scotland ice was retreating from fjords and valleys. By the onset of rapid warming at ∼14.7 ka, much of the remnant SIS was confined within the limits of Younger Dryas glaciation. The SIS, therefore, lost most of its mass during the Dimlington Stade. It is uncertain whether fragments of the SIS persisted on high ground throughout the Lateglacial Interstade.

/pdf/the-last-scottish-ice-sheet-2w5z3idk8b.pdf

The last Scottish Ice Sheet

In the UK, a combination of outcrop mapping, satellite Digital Elevation Models, high-resolution marine geophysical data, and a range of dating techniques have constrained the maximum limit and overall retreat behaviour of the British and Irish Ice Sheet (BIIS). The changing styles of deglaciation have been most extensively studied in the west and north-western sectors of the BIIS, primarily using offshore geophysical surveys. The surviving record in the southern, terrestrial sector is fragmentary, permitting only large-scale (tens of kilometres) and longer timescale (c. 1 ka) reconstructions of ice-margin movement, with limited information on deglacial processes. Here we present a high-resolution study of the retreat behaviour for a section of the southern ice-margin from Windermere in the the Lake District, using high-resolution 2D multi-channel seismic (MCS) data, processed using prestack depth migration. By combining the seismic stratigraphy with landform morphologies, extant cores, and seismic velocity measurements, we are able to distinguish between: over-consolidated till; recessional moraines; De Geer moraines; flowed till/ice-front fan; supra-/en-glacial melt-out till; and subsequent glaciolacustrine/lacustrine sedimentation. The results reveal a complex and active valley glacier withdrawal from Windermere that changed character between basins and produced two small, localised areas of ice-stagnation and downwasting. This study indicates that similar active ice-margin retreats probably took place in other valleys of the Lake District during the Late Devensian deglaciation rather than the previously held view of rapid ice-stagnation and downwasting. When combined with the regional terrestrial record, this supports a model of early ice loss in terrestrial England compared to other parts of the United Kingdom.

Deglacial history of glacial lake Windermere, UK: implications for the central British and Irish Ice Sheet

We present results from three geophysical campaigns using high-resolution sub-bottom profiling to image sediments deposited in Loch Ness, Scotland. Sonar profiles show distinct packages of sediment, providing insight into the loch’s deglacial history. A recessional moraine complex in the north of the loch indicates initial punctuated retreat. Subsequent retreat was rapid before stabilisation at Foyers Rise formed a large stillstand moraine. Here, the calving margin produced significant volumes of laminated sediments in a proglacial fjord-like environment. Subsequent to this, ice retreated rapidly to the southern end of the loch, where it again deposited a sequence of proglacial laminated sediments. Sediment sequences were then disturbed by the deposition of a thick gravel layer and a large turbidite deposit as a result of a jo¨kulhlaup from the Spean/Roy ice dammed lake. These sediments are overlain by a Holocene sheet drape. Data indicate: (i) a former tributary of the Moray Firth Ice Stream migrated back into Loch Ness as a major outlet glacier with a calving margin in a fjord-like setting; (ii) there was significant sediment supply to the terminus of this outlet glacier in Loch Ness; and (iii) that jo¨kulhlaups are important for sediment supply into proglacial fjord/lake environments and may compose >20% of proglacial sedimentary sequences.

Geophysical surveys of the sediments of Loch Ness, Scotland: implications for the deglaciation of the Moray Firth Ice Stream, British-Irish Ice Sheet

This paper presents a detailed glacial Main Map of the Great Glen region of Scotland, UK, covering an area of over 6800 km2 extending from 56°34′7″ to 57°41′1″ N and from 3°44′2″ to 5°33′24″ W. This represents the first extensive mapping of the glacial geomorphology of the Great Glen and builds upon previous studies that conducted localised field mapping or ice-sheet wide mapping using remote sensing. Particular emphasis is placed on deriving medium-scale glacial retreat patterns from these data, and examining differences in landsystem assemblages across the region. Features were typically mapped at a scale of 1:8000 to 1:10,000 and will be used to investigate the pattern and dynamics of the British-Irish Ice Sheet during deglaciation. Mapping was conducted using the NEXTMap digital terrain model. In total, 17,637 glacial landforms were mapped, with 58% identified as moraines, 23% as meltwater channels, 10% as bedrock controlled glacial lineations, 3% as eskers, 2% as cirques or aretes, 2% as kame topography or kame terraces, and 1% as drumlins. Additionally, 10 palaeo-lake shorelines were identified. Complex landform assemblages in the form of streamlined subglacial bedforms, moraines and glaciofluvial features exist across the region. Extensive subglacial meltwater networks are found over the Monadhliath Mountain Range. Transverse and longitudinal moraine ridges generally arc across valley floors or are located on valley slopes respectively. Hummocky moraines are found almost exclusively across Rannoch Moor. Finally, eskers, meltwater channels and kame landforms form spatial relationships along the axis of Strathspey. These glacial landsystems reveal the dynamics and patterns of retreat of the British-Irish Ice Sheet during the last deglaciation.

https://www.tandfonline.com/doi/pdf/10.1080/17445647.2013.866369

Andrew J. Turner

Papers

Geophysical surveys of the sediments of Loch Ness, Scotland: implications for the deglaciation of the Moray Firth Ice Stream, British-Irish Ice Sheet

Glacial geomorphology of the Great Glen Region of Scotland