Contribution to the field guide to acomapany the Glacial Landsystems Working Group (GLWG) meeting to review the evidence for Younger Dryas glaciation of the Tweedsmuir Hills
Synopsis We present new interpretations of Digital Elevation Model (DEM) data and marine fossils collected from three sites on the Rhins of Galloway which, contrary to recent proposals, suggest that the landforms and deposits of the region do not represent evidence for a readvance during the Lateglacial Period. Rather we suggest that the high-arctic fauna found in the region are representative of an earlier, colder part of a Middle Devensian ice-free interval. The predominantly streamlined topography, and distinct lack of identifiable discrete moraine limits argues for only minor, local glacial advances, in combination with widespread rapid retreat across the peninsula at the end of the Lateglacial.
New data is presented regarding the character and timing of glaciation in Orkney and Shetland and adjoining continental shelf, and a chronology of deglaciation is reconstructed for this critical area of the North Atlantic sector of the British and Fennoscandian Ice Sheets (BIS & FIS). Specifically seabed morphology is interpreted using the Olex echosounder dataset to determine ice stream tracks and glacial limits. Onshore landscape morphology is interpreted using the NEXTMap high resolution DEM and tested using ground survey, and a landsystems approach is applied in the reconstruction of styles of glaciation across the Northern Isles of Scotland. Crucially using Olex, terminal positions of the confluent BIS-FIS offshore at maximum glacial extent and during retreat are determined, and evidence of ice sheet separation is shown. The seabed and landscape evidence for ice streaming, in both erosive and depositional terrains is highlighted. There is evidence for several phases of ice sheet dynamics during Late Devensian deglaciation: confluent streaming ice from FIS/BIS; separation of the ice sheets and the establishment of a remnant ice cap over Shetland; and finally a readvance phase where ice flowing from the Moray Firth overwhelmed much of Orkney. New cosmogenic surface exposure age data is presented giving the first dated constraints on the timing of ice sheet separation, which combined with evidence from the UK continental shelf and North Sea Basin begin to give a chronology for the decline of the ice sheet systems on the western European margin. Finally, it is argued that the timing of these phase changes in the dynamics of the FIS and BIS are coincident with major changes in wider Earth systems, in particular eustatic sea level rise in response to global warming during the waning phase of the Lateglacial.
In glacial systems, hydrological forcing of ice velocity may lead to instability and accelerated mass loss. However, recent studies have demonstrated that the relationship between ice melt and ice dynamics is non-linear because subglacial drainage configuration strongly modulates meltwater inputs and results in asynchroneity between surface melt production and ice movement. Furthermore, subglacial drainage undergoes temporal evolution and can vary spatially between and within individual glaciers. As such, the degree of connectivity between ice melt and ice dynamics exhibits spatio-temporal variability. To address this, time-lapse images from Falljokull, SE Iceland, were analysed using Pointcatcher, a feature tracking software. Surface velocities and thinning rates were quantified for the period 2011-2013 and compared to results from energy balance modelling (EBM) to determine the climatic, hydrological and structural controls on glacier dynamics. The results show that melt production at Falljokull is closely linked to energy inputs to the glacier surface, although consistent thinning underestimation by the EBM, equivalent to ~1-3 m, reflects the poor optimisation of the model for thin debris cover. In addition, melt production is strongly modulated by individual events e.g. Grimsvotn eruption, which modify surface conditions and enhance/supress melt. A clear relationship between ice melt and ice dynamics is also evident in these data although subglacial drainage structure i.e. discrete/distributed, and surface conditions e.g. debris or snow cover, account for periods of de-coupling. Hydrologically induced speed-up events are identified and occur more readily when inefficient distributed systems are present. In contrast, flow variability is markedly reduced when meltwater inputs are suppressed and when efficient discrete drainage is present. Enhanced flow is strongly linked to sliding at the ice-bed interface although this varies spatially and temporally as a function of subglacial drainage configuration. Finally, these data conflict markedly with previous research which inferred that Falljokull was stagnant and wasting away in-situ. Instead, Falljokull is ‘active’ with movement through ice deformation, basal sliding and subglacial deformation although forward motion is insufficient to offset retreat.
The primary objective of International Ocean Discovery Program Expedition 381 was to retrieve a record of early continental rifting and basin evolution from the Corinth rift, central Greece.Continental rifting is fundamental for the formation of ocean basins, and active rift zones are dynamic regions of high geohazard
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