An investigation of the thermomechanical features of Laohugou Glacier No. 12 on Qilian Shan, western China, using a two-dimensional first-order flow-band ice flow model

Abstract

Abstract. By combining in situ measurements and a twodimensional thermomechanically coupled ice flow model, we investigate the thermomechanical features of the largest valley glacier (Laohugou Glacier No. 12; LHG12) on Qilian Shan located in the arid region of western China. Our model results suggest that LHG12, previously considered as fully cold, is probably polythermal, with a lower temperate ice layer overlain by an upper layer of cold ice over a large region of the ablation area. Modelled ice surface velocities match well with the in situ observations in the east branch (main branch) but clearly underestimate those near the glacier terminus, possibly because the convergent flow is ignored and the basal sliding beneath the confluence area is underestimated. The modelled ice temperatures are in very good agreement with the in situ measurements from a deep borehole (110 m deep) in the upper ablation area. The model results are sensitive to surface thermal boundary conditions, for example surface air temperature and near-surface ice temperature. In this study, we use a Dirichlet surface thermal condition constrained by 20 m borehole temperatures and annual surface air temperatures. Like many other alpine glaciers, strain heating is important in controlling the englacial thermal structure of LHG12. Our transient simulations indicate that the accumulation zone becomes colder during the last two decades as a response to the elevated equilibrium line altitude and the rising summer air temperatures. We suggest that the extent of accumulation basin (the amount of refreezing latent heat from meltwater) of LHG12 has a considerable impact on the englacial thermal status.

The influence of water percolation through crevasses on the thermal regime of a Himalayan mountain glacier

“…Wilson et al (2013) showed that the interface between cold and temperate ice matching with the location of temperatures reaching the pressure melt point in the boreholes could be identified with a 10 MHz GPR on two sub-Arctic polythermal glaciers. In the Himalayas, such GPR data are rare, although Sugiyama et al (2013) showed with GPR data that the Yala Glacier in Nepal is polythermal, which was in agreement with two previous borehole measurements in the ablation and accumulation areas of the glacier (Watanabe et al, 1984).…”

“…Very little is known about the thermal regime of the Himalayan glaciers due to the harsh conditions and logistical difficulties which make direct observations challenging in remote, high-altitude areas. Borehole temperature measurements, such as carried out on Khumbu, Yala and Gyabrag glaciers in the Himalayas (Miles et al, 2018;Mae, 1976;Watanabe et al, 1984;Liu et al, 2009), provide direct observations of the glaciers' thermal condition. However, the small number of boreholes gives only very limited information about the spatial distribution of the ice temperatures within the glacier.…”

Diurnal fluctuations of glacier surface velocity observed with terrestrial radar interferometry at Laohugou No. 12 Glacier, western Qilian mountains, China

“…In-situ observations of glacier mass balance, glacier surface motion and terminus location have been conducted since 2005 (Sun and others, 2011). Wang and others (2018) modeled basal ice velocities of <4.0 m a −1 at LHG12 Glacier, which contributed little to surface velocities. However, a large discrepancy of glacier surface velocity between summer months (∼40.0 mm d −1 ) and winter months (∼10.0 mm d −1 ) was detected with the GPS technique at several stakes located over the glacier tongue in 2008-09 (Liu and others, 2010).…”

“…However, two-dimensional flow modeling results (Wang and others, 2018) suggest that the contribution of basal slip to surface flow velocity is low over the terminus. The possible reason for this difference is that basal slip over the glacier terminus area is not captured by the ice flow model (Wang and others, 2018). Observations presented in this study could therefore be used to improve and test ice flow models.…”

The influence of water percolation through crevasses on the thermal regime of Himalayan mountain glaciers

“…Borehole temperature measurements, such as carried out on Khumbu, Yala and Gyabrag Glaciers in the Himalayas (Miles et al, 2018;Mae, 1976;Watanabe et al, 1984;40 Liu et al, 2009), provide direct observations of the glaciers thermal condition. However, a restricted number of boreholes give only very limited information about the spatial distribution of the ice temperatures within the glacier and need in that case to be extrapolate from numerical modeling to estimate the thermal structure of the glacier (Wang et al, 2018, Zhang et al, 2013.…”