Abstract
Seasonal evolution of the subglacial drainage system in the lower ablation area of the Hailuogou glacier ice tongue were revealed by repeated dye tracer (Rhodamine WT) experiments during the 2009 ablation season. Between April and October, 18 dye tracer experiments were conducted by injecting the tracer at one location of the lower ablation area of the Hailuogou Glacier to diagnose the seasonal variation of the subglacial drainage system of this section of glacier ice tongue. Using a simple advection-dispersion model (ADM), the flow velocity, hydrodynamic dispersion coefficient, and degree of tracer spreading were deduced. Tracer transit velocity through the tested subglacial channel varied from 0.148 to 0.555 m s−1 during the 2009 ablation season. Dispersivity showed a relatively high value than that found at other glaciers, which varied between 27.05 and 287.49 m2 s−1. Seasonal changes of these indexes indicated that the subglacial drainage system of the lower ablation area of the Hailougou Glacier is a relatively stable existing system in the case of its longitudinal shape, whereas its hydraulic efficiency is low in the early and late ablation seasons and high during the middle of summer due to subglacial channel expansion.
Highlights
Recent observations and modeling studies on either mountain valley glaciers or ice sheets have highlighted the role of subglacial water in ice flow processes (e.g., [1,2,3,4,5])
The highly one-peaked shape of the Tracer return curves (TRC) indicated that the drainage system examined by our tracing experiments was a stable and simple subglacial channel with limited tributary/branches, which could usually lead to a multi-peak of TRC [26]
Since the ice flow of the lower ablation area of the Hailuogou Glacier is constrained by the lateral terrains and the ice tongue extends longitudinally along the valley trough with a width less than 400 m, the subglacial drainage network is limited longitudinally and without much development of lateral dendritic tributaries as those reported for glaciers with a wider ablation area [20,26,41,42]
Summary
Recent observations and modeling studies on either mountain valley glaciers or ice sheets have highlighted the role of subglacial water in ice flow processes (e.g., [1,2,3,4,5]). Subglacial drainage system evolution of some mountain glaciers is conceptualized as a morphological transition from a slow or distributed drainage network to a fast or channelized drainage system over the course of the melt season [19,20]. Tracer return curves (TRC) were modelled using a transport model and, for each individual test, the flow velocity, dispersion coefficient, and other indexes were used to indicate the subglacial drainage system changes
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