After the ice: Lateglacial and Holocene landforms and landscape evolution in Scotland

Abstract

During Lateglacial cold periods, permafrost developed throughout Scotland, sediment-mantled slopes were extensively modified by solifluction and other forms of periglacial mass movement, large-scale sorted patterned ground formed on plateaux, and enhanced rockfall resulted in talus accumulation below cliffs. Most rock-slope failures occurred within five millennia following ice-sheet deglaciation, with many probably triggered by uplift-induced earthquakes; numerous debris-free scarps represent sites where Lateglacial rockslide debris was excavated by glaciers during the Younger Dryas Stade (∼12.9–11.7 ka). Sandar and outwash fans deposited by glacial rivers during ice-sheet retreat were incised to form high-level terraces. Under the cool temperate but relatively stable climate of the Holocene, solifluction and patterned ground formation continued to operate on high ground, though accumulation of high-level aeolian deposits on most mountains was terminated by erosion during the Little Ice Age. Drift-mantled slopes and talus slopes have been extensively eroded by translational failures and debris flows, the latter depositing debris cones on upland valley floors. The incidence of Holocene rockslides has been much lower than during the Lateglacial period. Dating of alluvial deposits and low Holocene terraces suggests no consistent pattern of Holocene floodplain evolution: incision has apparently dominated in the Highlands, aggradation in the lowlands, and floodplains in the Southern Uplands have asynchronous histories of incision and aggradation. Studies of floodplain behaviour over the past 200–300 years suggest that though major floods rework the floodplains of braided and piedmont rivers, there is no tendency towards net floodplain aggradation or incision. Most valley-side alluvial fans accumulated episodically in the last 4000 years, many in response to lowering of hillslope stability by woodland clearance. For many postglacial landsystems, disentangling the effects of declining paraglacial sediment supply, climate change and local influences (extreme rainstorm events or anthropogenic impacts) remains challenging.

Late Pleistocene sediments, landforms and events in Scotland: a review of the terrestrial stratigraphic record

“…Several geographically distinct members have been recognised associated with late-stage glacier oscillations, namely the Allt na h-Airbhe Member (predominantly offshore), and the Allt an t-Srathain, Rhiroy and Glen Douchary members. The last of these occurs within the ice limits correlated with the Loch Lomond Stadial in the region (Ballantyne 2018). The Ullapool Gravel Formation includes glaciofluvial fan, deltaic and outwash deposits that formed during high relative sea levels around Ullapool, along margins of Loch Broom and adjoining sea lochs, and locally along the coast of the NW Highlands Bradwell 2010b).…”

“…The use of satellite imagery and digital surface models derived from remote sensing, and particularly NEXTMap Britain topographic dataset, has progressed geomorphological mapping and morphostratigraphy (Chandler et al 2018). It has enabled the recognition of multiple sequential ice-flow patterns during the life of the last BIIS indicated by superimposed glacial lineations (e.g., Salt & Evans 2004;Golledge & Stoker 2006;Hughes et al 2014) and has considerably improved knowledge of glaciation during the Younger Dryas (Ballantyne 2018;Bickerdike et al 2018). 4.…”

“…It has enabled the recognition of multiple sequential ice-flow patterns during the life of the last BIIS indicated by superimposed glacial lineations (e.g., Salt & Evans 2004;Golledge & Stoker 2006;Hughes et al 2014) and has considerably improved knowledge of glaciation during the Younger Dryas (Ballantyne 2018;Bickerdike et al 2018).…”

“…The focus of the paper on Late Pleistocene terrestrial stratigraphy complements the accompanying review of the terrestrial record of Early and Middle Pleistocene environments, landforms and sediments in Scotland (Hall et al 2018), offshore stratigraphy (Stewart et al 2019) and the geomorphological evidence for the last Scottish Ice Sheet and its deglaciation . Lateglacial landforms and landscape evolution, including evidence relating to the glaciation of Scotland during the Loch Lomond Stadial (Younger Dryas), are reviewed by Ballantyne (2018), whereas evidence for sea level change is reviewed by Smith et al (2018).…”

Early and Middle Pleistocene environments, landforms and sediments in Scotland

“…In Buchan, the record of permafrost, frost weathering and mass wasting extends back into the Middle Pleistocene (Connell & Hall 1987). Largely through the work of Colin Ballantyne and his collaborators, the periglacial landforms and materials of the Late Pleistocene and Holocene have been mapped, analysed and dated in Scotland to a level of detail that is unmatched in any other similar-sized terrain in the world (Ballantyne 2018). This dataset provides the starting point for assessment of the impacts of periglacial processes in earlier periods.…”