In the high mountains of Asia valley glaciers are pertinent features and an important water resource, both locally and downstream. In the vicinity of the mountains and in arid regions, their melt water can provide a sizeable contribution to stream flow and is of importance for cropland irrigation, drinking water and hydropower. Under future climate change, glacier melt water supply may change as glaciers will continue to lose mass because of rising temperatures. To better understand how this part of the future water balance will change, it is important to improve our knowledge of glacier dynamics from small to large scale.
Overview map of the high mountain region of Asia with its major rivers, mountain ranges and glaciers (red).
A fraction of the glaciers is covered by a layer of debris that consists of dust, rocks and boulders. These debris-covered glaciers are relatively abundant in Asia, because the young and steep mountain ranges provide a large amount of erodible material. They are therefore important for the long-term glacier melt water supply to the rivers in the region. The glaciers have dynamics different than debris-free glaciers, because the debris layer alters surface melt rates. In general, thin debris layers enhance melt while thick layers insulate the ice and reduce melt, but the complex processes involved and their interplay are poorly understood and require further research.
Example of a debris-covered glacier, Ngozumpa Glacier, Nepal (photo: Petr Melssner).
The glaciers in the region are generally difficult to study due to their inaccessibility. Debris-covered glaciers have particularly been understudied, partly due to the complications the debris layer imposes on fieldwork. Satellite remote sensing enables analyses of remote debris-covered glaciers, but spatial resolution is generally too limited for detailed analysis of the small-scale effects of the debris layer on local ice melt. Recent advances in unmanned aerial vehicle (UAV) technology offer a promising complimentary observation method, since UAVs enable on demand acquisition of imagery and elevation data at very high spatial and temporal detail. In my thesis, our understanding of debris-covered glaciers and their surface processes is improved in five separate studies by exploring the value of UAVs in the research of these glaciers.
For the first time, a debris-covered glacier in the Himalaya is monitored by a UAV before and after the melt season. Based on stereo-imaging and the Structure-from-Motion algorithm, highly detailed orthomosaics and digital elevation models (DEMs) are derived and used to determine elevation changes and surface flow in unprecedented detail. It is shown that the surface of the glacier experiences highly heterogenous mass wasting and that ice melt is considerably higher near ice cliffs and supraglacial ponds.
Continued UAV surveys enable a comparison of summer and winter surface velocities of the debris-covered glacier. The seasonal surface velocities are derived by exploring the potential of frequency cross-correlation techniques for the high-resolution UAV imagery. Large differences are shown to exist between the two seasons, with limited flow during summer and practically stagnant ice in winter.
Supraglacial debris significantly alters the surface energy balance of a glacier. Data on spatially distributed debris surface temperature can provide important information on the properties of the debris, its effects on the ice below and its influence on the near-surface boundary layer. Therefore, a methodology is presented to acquire corrected surface temperature maps of a debris-covered glacier from a UAV equipped with a thermal infrared camera.
Ice cliffs and supraglacial ponds on debris-covered glaciers were shown to cause highly heterogenous surface melt. To improve understanding of these surface features an object-based image analysis procedure is presented that enables their automated delineation, which allows for objective analysis of ice cliff characteristics and spatial distribution.
UAV data primarily provides data on the small to moderate scale. To understand the effects of climate change and debris-covered glaciers on the large scale, the UAV findings are incorporated in a large-scale model that assesses transient glacier mass loss over the 21st century. It is shown that even if climate change is limited over one third of the current glacier mass will disappear by the end of the century, and that more severe mass losses are more likely. Supraglacial debris is shown to be able to provide considerable retention of glacier mass in Asia.
View interactive web map of this study.
My thesis demonstrates that UAVs are a unique means to study small scale surface processes on remote debris-covered glaciers. Future research on debris-covered glaciers should focus on the causes of spatially variable surface melt by linking UAV data, ground-based measurements and process-based modelling. Moreover, to fully understand thinning of debris-covered glaciers and its relation with enhanced ablation at ice cliffs and supraglacial ponds more research is required of debris-covered glacier ice flow dynamics. Further improvement to our understanding of regional and local response of glaciers will be achieved by large-scale model approaches that combine UAV, ground-based and satellite data at multiple scales in innovative ways. Multidisciplinary studies that integrate findings over a broad spectrum, bringing together meteorology, glaciology and hydrology, will ultimately allow us to understand the entire mountain water cycle and current and future impacts of climate change.