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Understanding the evolution of debris-covered glaciers in High Mountain Asia, the physical processes governing the effect of debris cover on mass balance, and the response of debris-covered glaciers to climatic change are key for assessing water resources, the contribution of glaciers to sea level rise and the potential for glacier related hazards such as glacier lake outburst floods (GLOFs) related to moraine-dammed lakes. Here we illustrate the effects of recent glacier recession on the development of landforms and sediments at Ponkar Glacier, a debris-covered glacier in the Manaslu area of the Nepal Himalaya using a combi-nation of 2019 RapidEye satellite image (5 m spatial resolution), drone imagery (50 cm) and field observations. We describe the key features of the glacier and its ice-surface morphology, including size and extent of flow units and tributary glaciers, supraglacial features of the debris cover and vegetation. Geomorphological mapping is used to describe the moraines, proglacial geomorphology, outwash plains and proglacial streams, the development of new ice-marginal ponds and changes in vegetation. Moraines generally have steep and rapidly degrading inner faces and mature vegetation, including trees, on their outer flanks. They are typically com-posed of diamicton and silty or sandy boulder gravel. Large outer moraines are separated from the surrounding val-ley sides by 'ablation valleys'. We conclude by putting the landforms and sediments developed at Ponkar Glacier into a discussion of the likely future evolution of high-eleva-tion debris-covered glaciers

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.

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.

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.