Abstract
ABSTRACTThe presence of supraglacial debris on glaciers in the Himalaya-Karakoram affects the ablation rate of these glaciers and their response to climatic change. To understand how supraglacial debris distribution and associated surface features vary spatially and temporally, geomorphological mapping was undertaken on Baltoro Glacier, Karakoram, for three time-separated images between 2001–2012. Debris is supplied to the glacier system through frequent but small landslides at the glacier margin that form lateral and medial moraines and less frequent but higher volume rockfall events which are more lobate and often discontinuous in form. Debris on the glacier surface is identified as a series of distinct lithological units which merge downglacier of the convergence area between the Godwin-Austen and Baltoro South tributary glaciers. Debris distribution varies as a result of complex interaction between tributary glaciers and the main glacier tongue, complicated further by surge events on some tributary glaciers. Glacier flow dynamics mainly controls the evolution of a supraglacial debris layer. Identifying such spatial variability in debris rock type and temporal variability in debris distribution has implications for glacier ablation rate, affecting glacier surface energy balance. Accordingly, spatial and temporal variation in supraglacial debris should be considered when determining mass balance for these glaciers through time.
Highlights
Debris-covered glaciers, where the majority of the ablation area is covered in rock debris, are ubiquitous in mountainous regions globally (Benn & Lehmkuhl, 2000), including the Southern Alps of New Zealand, European Alps, the Andes and in High Asia
Supraglacial debris units were segregated into four lithologies, with each debris type, metasediments, being composed of different minerals that would cause them to have different thermal capacities and albedo
Temporal variations in supraglacial pond number and area are attributed to climatic conditions in this study, but should be monitored on Baltoro Glacier in the future to determine whether this trend continues and if it is linked to other aspects of glacier dynamics
Summary
Debris-covered glaciers, where the majority of the ablation area is covered in rock debris, are ubiquitous in mountainous regions globally (Benn & Lehmkuhl, 2000), including the Southern Alps of New Zealand, European Alps, the Andes and in High Asia. Debris distribution is controlled by the delivery of rock debris and debristransport by ice flow, which slows as the glacier loses mass, resulting in a constantly changing distribution of supraglacial debris (Bolch, Buchroithner, Pieczonka, & Kunert, 2008; Rowan, Egholm, Quincey, & Glasser, 2015; Thakuri et al, 2014). Supraglacial debris distribution is important when calculating glacier mass balance, as such debris layers attenuate the ablation of the underlying ice depending on the debris thickness (Evatt et al, 2015; Østrem, 1959). The critical thickness, which differs between glaciers, the ablation rate of underlying ice decreases exponentially with increasing debris thickness (Kayastha, Takeuchi, Nakawo, & Ageta, 2000; Nicholson & Benn, 2006; Østrem, 1959). Baltoro Glacier is highly appropriate for supraglacial debris mapping due to its location in a region of high erosion rates and concurrently extensive debris cover, and the large number of tributary glaciers which form the glacier system and lead to a complex flow regime and spatially varied debris distribution
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