20 results on '"Glasser, N.F."'
Search Results
2. The 2015 Chileno Valley glacial lake outburst flood, Patagonia
- Author
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Wilson, R., Harrison, S., Reynolds, J., Hubbard, A., Glasser, N.F., Wündrich, O., Iribarren Anacona, P., Mao, L., and Shannon, S.
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- 2019
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3. Luminescence dating of glacial advances at Lago Buenos Aires (∼46 °S), Patagonia
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Smedley, R.K., Glasser, N.F., and Duller, G.A.T.
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- 2016
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4. Modelling outburst floods from moraine-dammed glacial lakes
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Westoby, M.J., Glasser, N.F., Brasington, J., Hambrey, M.J., Quincey, D.J., and Reynolds, J.M.
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- 2014
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5. Ice-stream initiation, duration and thinning on James Ross Island, northern Antarctic Peninsula
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Glasser, N.F., Davies, B.J., Carrivick, J.L., Rodés, A., Hambrey, M.J., Smellie, J.L., and Domack, E.
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- 2014
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6. Morphological and ice-dynamical changes on the Tasman Glacier, New Zealand, 1990–2007
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Quincey, D.J. and Glasser, N.F.
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- 2009
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7. Early recognition of glacial lake hazards in the Himalaya using remote sensing datasets
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Quincey, D.J., Richardson, S.D., Luckman, A., Lucas, R.M., Reynolds, J.M., Hambrey, M.J., and Glasser, N.F.
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- 2007
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8. Cenozoic landscape evolution of an East Antarctic oasis (Radok Lake area, northern Prince Charles Mountains), and its implications for the glacial and climatic history of Antarctica
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Hambrey, M.J., Glasser, N.F., McKelvey, B.C., Sugden, D.E., and Fink, D.
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- 2007
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9. Debris-covered glacier systems and associated glacial lake outburst flood hazards: challenges and prospects.
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Racoviteanu, A.E., Nicholson, L., Glasser, N.F., Miles, Evan, Harrison, S., and Reynolds, J.M.
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GLACIERS ,GLACIAL lakes ,ABSOLUTE sea level change ,FLOOD warning systems ,WATER supply ,HAZARDS ,CLIMATE change - Abstract
Glaciers respond sensitively to climate variability and change, with associated impacts on meltwater production, sea-level rise and geomorphological hazards. There is a strong societal interest in understanding the current response of all types of glacier systems to climate change and how they will continue to evolve in the context of the whole glacierized landscape. In particular, understanding the current and future behaviour of debris-covered glaciers is a 'hot topic' in glaciological research because of concerns for water resources and glacier-related hazards. The state of these glaciers is closely related to various hazardous geomorphological processes which are relatively poorly understood. Understanding the implications of debris-covered glacier evolution requires a systems approach. This includes the interplay of various factors such as local geomorphology, ice ablation patterns, debris characteristics and glacier lake growth and development. Such a broader, contextualized understanding is prerequisite to identifying and monitoring the geohazards and hydrologic implications associated with changes in the debris-covered glacier system under future climate scenarios. This paper presents a comprehensive review of current knowledge of the debris-covered glacier landsystem. Specifically, we review state-of-the-art field-based and the remote sensing-based methods for monitoring debris-covered glacier characteristics and lakes and their evolution under future climate change. We advocate a holistic process-based framework for assessing hazards associated with moraine-dammed glacio-terminal lakes that are a projected end-member state for many debris-covered glaciers under a warming climate. [ABSTRACT FROM AUTHOR]
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- 2022
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10. Variations in near‐surface debris temperature through the summer monsoon on Khumbu Glacier, Nepal Himalaya
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Gibson, M.J., Irvine-Fynn, T., Wagnon, P., Rowan, A.V., Quincey, D.J., Homer, R., and Glasser, N.F.
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Himalaya ,debris cover ,surface temperature ,Khumbu Glacier ,ablation - Abstract
Debris surface temperature is a function of debris characteristics and energy fluxes at the debris surface. However, spatial and temporal variability in debris surface temperature, and the debris properties that control it, are poorly constrained. Here, near-surface debris temperature (T-s) is reported for 16 sites across the lower elevations of Khumbu Glacier, Nepal Himalaya, for the 2014 monsoon season. The debris layer at all sites was 1m thick. We confirm the occurrence of temporal and spatial variability in T-s over a 67-day period and investigate its controls. T-s was found to exhibit marked temporal fluctuations on diurnal, short-term (1-8days) and seasonal timescales. Over the study period, two distinct diurnal patterns in T-s were identified that varied in timing, daily amplitude and maximum temperature; days in the latter half of the study period (after Day of Year 176) exhibited a lower diurnal amplitude (mean = 23 degrees C) and reduced maximum temperatures. Days with lower amplitude and minimum T-s were concurrent with periods of increased seasonal variability in on-glacier air temperature and incoming shortwave radiation, with the increased frequency of these periods attributed to increasing cloud cover as the monsoon progressed. Spatial variability in T-s was manifested in variability of diurnal amplitude and maximum T-s of 7 degrees C to 47 degrees C between sites. Local slope, debris clast size and lithology were identified as the most important drivers of spatial variability in T-s, with inclusion of these three variables in the stepwise general linear models resulting in R-2 0.89 for six out of the seven sites. The complexity of surface energy fluxes and their influence on T-s highlight that assuming a simplified relationship between air temperature and debris surface temperature in glacier melt models, and a direct relationship between debris surface temperature and debris thickness for calculating supraglacial debris thickness, should be undertaken with caution.
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- 2018
11. Late Devensian deglaciation of south-west Wales from luminescence and cosmogenic isotope dating
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Glasser, N.F., Davies, J.R., Hambrey, M.J., Davies, B.J., Gheorghiu, D.M., Balfour, J., Smedley, R.K., and Duller, G.A.T.
- Abstract
The Welsh Ice Cap was a dynamic component of the last British–Irish Ice Sheet at the Last Glacial Maximum, but there are few chronological constraints on the pace and timing of deglaciation. This paper presents new geomorphological and geochronological evidence that constrains the timing of the separation of the Welsh Ice Cap from the Irish Sea Ice Stream and the subsequent deglaciation of south-west Wales; and allow these to be assessed in the context of late Pleistocene climatic events. Luminescence ages from glacial outwash sediments south of Cardigan demonstrate that the Irish Sea Ice Stream was receding by �26.7 ka. The subsequent recession of the Welsh Ice Cap is documented by cosmogenic ages from landforms and sediments in the Aeron and Teifi valleys and upland areas. Deglaciation of the Cambrian Mountains was underway by �19.6 ka. Cross-valley moraines and associated deglaciation deposits show that minor re-advances interrupted the recession of the Aeron Glacier twice, and the Teifi Glacier on at least 12 occasions. By �14.9 ka, the Aeron valley was probably ice-free, but the northwards withdrawal of the Teifi glacier had halted in the Tregaron area. The final rapid recession of this glacier into the uplands of central Wales was completed during the Windermere Interstadial (13.5 cal ka BP) when, in common with much of the UK, the whole of Wales is believed to have become ice-free. There is no evidence that the Cambrian Mountains contained ice-free enclaves at the Last Glacial Maximum, as has been previously suggested. The new ages presented here support suggestions that there was rapid change in the configuration of the Welsh Ice Cap between 20 and 17 ka as upland areas became exposed and there was increasing topographic control on patterns of ice discharge.
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- 2018
12. Supraglacial Ponds Regulate Runoff From Himalayan Debris-Covered Glaciers
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Irvine-Fynn, T., Porter, P.R., Rowan, A.V., Quincey, D.J., Gibson, M.J., Bridge, J.W., Watson, C.S., Hubbard, A., and Glasser, N.F.
- Abstract
Meltwater and runoff from glaciers in High Mountain Asia is a vital freshwater resource for one fifth of the Earth's population. Between 13% and 36% of the region's glacierized areas exhibit surface debris cover and associated supraglacial ponds whose hydrological buffering roles remain unconstrained. We present a high-resolution meltwater hydrograph from the extensively debris-covered Khumbu Glacier, Nepal, spanning a seven-month period in 2014. Supraglacial ponds and accompanying debris cover modulate proglacial discharge by acting as transient and evolving reservoirs. Diurnally, the supraglacial pond system may store >23% of observed mean daily discharge, with mean recession constants ranging from 31 to 108 hours. Given projections of increased debris-cover and supraglacial pond extent across High Mountain Asia, we conclude that runoff regimes may become progressively buffered by the presence of supraglacial reservoirs. Incorporation of these processes is critical to improve predictions of the region's freshwater resource availability and cascading environmental effects downstream.
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- 2017
13. Reconstruction of ice-sheet changes in the Antarctic Peninsula since the Last Glacial Maximum
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Ó Cofaigh, C., Davies, B.J., Livingstone, S.J., Smith, J.A., Johnson, J.S., Hocking, E.P., Hodgson, D.A., Anderson, J.B., Bentley, M.J., Canals, M., Domack, E., Dowdeswell, J.A., Evans, J., Glasser, N.F., Hillenbrand, C.D., Larter, R.D., Roberts, S.J., and Simms, A.R.
- Subjects
Deglaciation ,Last Glacial Maximum ,Antarctic Peninsula Ice Sheet ,Antarctica ,Glacial geology - Abstract
This paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the Antarctic Peninsula Ice Sheet (APIS) from the Last Glacial Maximum (LGM) through deglaciation to the present day. These data are used to reconstruct grounding-line retreat in 5 ka time-steps from 25 ka BP to present. Glacial landforms and subglacial tills on the eastern and western Antarctic Peninsula (AP) shelf indicate that the APIS was grounded to the outer shelf/shelf edge at the LGM and contained a series of fast-flowing ice streams that drained along cross-shelf bathymetric troughs. The ice sheet was grounded at the shelf edge until ∼20 cal ka BP. Chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains, as well as cosmogenic nuclide dates on erratics and ice moulded bedrock. Retreat in the east was underway by about 18 cal ka BP. The earliest dates on recession in the west are from Bransfield Basin where recession was underway by 17.5 cal ka BP. Ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid-shelf. The timing of initial retreat decreased progressively southwards along the western AP shelf; the large ice stream in Marguerite Trough may have remained grounded at the shelf edge until about 14 cal ka BP, although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18 ka BP. Between 15 and 10 cal ka BP the APIS underwent significant recession along the western AP margin, although retreat between individual troughs was asynchronous. Ice in Marguerite Trough may have still been grounded on the mid-shelf at 10 cal ka BP. In the Larsen-A region the transition from grounded to floating ice was established by 10.7–10.6 cal ka BP. The APIS had retreated towards its present configuration in the western AP by the mid-Holocene but on the eastern peninsula may have approached its present configuration several thousand years earlier, by the start of the Holocene. Mid to late-Holocene retreat was diachronous with stillstands, re-advances and changes in ice-shelf configuration being recorded in most places. Subglacial topography exerted a major control on grounding-line retreat with grounding-zone wedges, and thus by inference slow-downs or stillstands in the retreat of the grounding line, occurring in some cases on reverse bed slopes.
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- 2014
14. Late Quaternary glacier sensitivity to temperature and precipitation distribution in the Southern Alps of New Zealand
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Rowan, A.V., Brocklehurst, S.H., Schultz, D.M., Plummer, M.A., Anderson, L.S., and Glasser, N.F.
- Abstract
Glaciers respond to climate variations and leave geomorphic evidence that represents an important terrestrial paleoclimate record. However, the accuracy of paleoclimate reconstructions from glacial geology is limited by the challenge of representing mountain meteorology in numerical models. Precipitation is usually treated in a simple manner and yet represents difficult-to-characterize variables such as amount, distribution, and phase. Furthermore, precipitation distributions during a glacial probably differed from present-day interglacial patterns. We applied two models to investigate glacier sensitivity to temperature and precipitation in the eastern Southern Alps of New Zealand. A 2-D model was used to quantify variations in the length of the reconstructed glaciers resulting from plausible precipitation distributions compared to variations in length resulting from change in mean annual air temperature and precipitation amount. A 1-D model was used to quantify variations in length resulting from interannual climate variability. Assuming that present-day interglacial values represent precipitation distributions during the last glacial, a range of plausible present-day precipitation distributions resulted in uncertainty in the Last Glacial Maximum length of the Pukaki Glacier of 17.1 km (24%) and the Rakaia Glacier of 9.3 km (25%), corresponding to a 0.5°C difference in temperature. Smaller changes in glacier length resulted from a 50% decrease in precipitation amount from present-day values (−14% and −18%) and from a 50% increase in precipitation amount (5% and 9%). Our results demonstrate that precipitation distribution can produce considerable variation in simulated glacier extents and that reconstructions of paleoglaciers should include this uncertainty.
- Published
- 2014
15. 8.6 Water in Glaciers and Ice Sheets
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Glasser, N.F.
- Published
- 2013
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16. The structural and dynamic responses of Stange Ice Shelf to recent environmental change.
- Author
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Holt, T.O., Glasser, N.F., Fricker, H.A., Padman, L., Luckman, A., King, O., Quincey, D.J., and Siegfried, M.R.
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GLOBAL environmental change ,REMOTE sensing ,APERTURE antennas ,RADAR ,REMOTE-sensing images - Abstract
Stange Ice Shelf is the most south-westerly ice shelf on the Antarctic Peninsula, a region where positive trends in atmospheric and oceanic temperatures have been recently documented. In this paper, we use a range of remotely sensed datasets to evaluate the structural and dynamic responses of Stange Ice Shelf to these environmental changes. Ice shelf extent and surface structures were examined at regular intervals from optical and radar satellite imagery between 1973 and 2011. Surface speeds were estimated in 1989, 2004 and 2010 by tracking surface features in successive satellite images. Surface elevation change was estimated using radar altimetry data acquired between 1992 and 2008 by the European Remote Sensing Satellite (ERS) -1, -2 and Envisat. The mean number of surface melt days was estimated using the intensity of backscatter from Envisat’s Advanced Synthetic Aperture Radar instrument between 2006 and 2012. These results show significant shear fracturing in the southern portion of the ice shelf linked to enhanced flow speed as a consequence of measured thinning. However, we conclude that, despite the observed changes, Stange Ice Shelf is currently stable. [ABSTRACT FROM AUTHOR]
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- 2014
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17. Luminescence dating of glacial advances at Lago Buenos Aires (∼46 °S), Patagonia
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Smedley, R.K., Glasser, N.F., and Duller, G.A.T.
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Global and Planetary Change ,GB ,Luminescence ,Feldspar ,Patagonia ,Geology ,Glacial ,Geomorphology ,Single grains ,Ecology, Evolution, Behavior and Systematics - Abstract
Understanding the timing of past glacial advances in Patagonia is of global climatic importance because of the insight this can provide into the influence on glacier behaviour of changes in temperature and precipitation related to the Southern Westerlies. In this paper we present new luminescence ages determined using single grains of K-feldspar from proglacial outwash sediments that were deposited by the Patagonian Ice Sheet around Lago Buenos Aires (∼46 °S), east of the contemporary Northern Patagonian Icefield. The new luminescence ages indicate that major outwash accumulations formed around ∼110 ± 20 ka to 140 ± 20 ka and that these correspond to the Moreno I and II moraine ridges, which were previously dated using cosmogenic isotope dating to 150 ± 30 ka. Luminescence dating at Lago Buenos Aires has also identified outwash sediments that were deposited during glacial advances ∼30.8 ± 5.7 ka and ∼34.0 ± 6.1 ka (MIS 3) that are not recorded in the moraine record. Younger outwash accumulations were then deposited between ∼14.7 ± 2.1 and 26.2 ± 1.6 ka which correspond to the Fenix I – V moraine ridges. The combined chronology suggests that glacial advances occurred ∼110 ± 20 ka to 150 ± 30 ka (MIS 6), ∼30.8 ± 5.7 ka to ∼34.0 ± 6.1 ka (MIS 3), and ∼14.7 ± 2.1 to 26.2 ± 1.6 ka (MIS 2) at Lago Buenos Aires. Overall luminescence dating using single grains of K-feldspar has excellent potential to contribute towards the ever-increasing geochronological dataset constraining the timings of glacial advances in Patagonia.
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18. Comment on ‘The production of glacial-like erosional features by children in playground areas’ by D. Flinn (2002)
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Glasser, N.F. and Hambrey, M.J.
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- 2002
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19. ‘Structure-from-Motion’ photogrammetry: A low-cost, effective tool for geoscience applications
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Westoby, M.J., Brasington, J., Glasser, N.F., Hambrey, M.J., and Reynolds, J.M.
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PHOTOGRAMMETRY , *EARTH sciences , *DIGITAL elevation models , *DIGITAL cameras , *TOPOGRAPHIC maps , *CAPITAL , *COST effectiveness , *ACQUISITION of data - Abstract
Abstract: High-resolution topographic surveying is traditionally associated with high capital and logistical costs, so that data acquisition is often passed on to specialist third party organisations. The high costs of data collection are, for many applications in the earth sciences, exacerbated by the remoteness and inaccessibility of many field sites, rendering cheaper, more portable surveying platforms (i.e. terrestrial laser scanning or GPS) impractical. This paper outlines a revolutionary, low-cost, user-friendly photogrammetric technique for obtaining high-resolution datasets at a range of scales, termed ‘Structure-from-Motion’ (SfM). Traditional softcopy photogrammetric methods require the 3-D location and pose of the camera(s), or the 3-D location of ground control points to be known to facilitate scene triangulation and reconstruction. In contrast, the SfM method solves the camera pose and scene geometry simultaneously and automatically, using a highly redundant bundle adjustment based on matching features in multiple overlapping, offset images. A comprehensive introduction to the technique is presented, followed by an outline of the methods used to create high-resolution digital elevation models (DEMs) from extensive photosets obtained using a consumer-grade digital camera. As an initial appraisal of the technique, an SfM-derived DEM is compared directly with a similar model obtained using terrestrial laser scanning. This intercomparison reveals that decimetre-scale vertical accuracy can be achieved using SfM even for sites with complex topography and a range of land-covers. Example applications of SfM are presented for three contrasting landforms across a range of scales including; an exposed rocky coastal cliff; a breached moraine-dam complex; and a glacially-sculpted bedrock ridge. The SfM technique represents a major advancement in the field of photogrammetry for geoscience applications. Our results and experiences indicate SfM is an inexpensive, effective, and flexible approach to capturing complex topography. [Copyright &y& Elsevier]
- Published
- 2012
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20. A new approach for luminescence dating glaciofluvial deposits - High precision optical dating of cobbles.
- Author
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Jenkins, G.T.H., Duller, G.A.T., Roberts, H.M., Chiverrell, R.C., and Glasser, N.F.
- Subjects
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GLACIATION , *FELDSPAR , *THERMOLUMINESCENCE dating , *LUMINESCENCE - Abstract
In recent years luminescence dating has increasingly been applied to date glaciofluvial sediments, but uncertainties about the degree of bleaching of the luminescence signal at deposition make dating of such sediments challenging. Here we test a new approach for luminescence dating of glaciofluvial sediments, based on the analysis of rock cores drilled from granite cobbles, and compare the luminescence ages generated against independent age control. Luminescence measurements from rock slices in cobble-sized clasts can be used to reconstruct the extent of bleaching, thereby giving greater confidence in the ages produced. This study illustrates that another important advantage of using cobbles is that at depths of 2 mm or more below the cobble surface >90% of the total dose rate arises from the cobble itself, making the dose rate insensitive to the water content of the sediment matrix. Ordinarily, uncertainties in estimating water content during burial are one of the largest sources of uncertainty in luminescence dating methods, and hence reducing the reliance upon the dose rate could be particularly advantageous for glacial deposits, where water contents can potentially be large and highly variable. Measurements of cobbles from Orrisdale Head, Isle of Man, demonstrate that the luminescence signal was completely bleached to depths of up to 12 mm into the cobble. Sampling of orientated cobbles from lithofacies diagnostic of bar-top environments was used to maximise the chances of exposure to sunlight. The upper-faces of these orientated cobble surfaces appear to be bleached to a greater depth than the lowermost faces. Data from 45 rock slices from these cobbles were tightly clustered, yielding a mean age of 20.7 ± 0.3 ka that is in agreement with independent age control. One of the well-bleached cobbles shows evidence of two discrete exposure events, potentially recording both the advance at 26.2 ± 0.8 ka, and retreat at 20.7 ± 0.3 ka, of the Irish Sea Ice Stream. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
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