High-resolution insights into the dynamics of Himalayan debris-covered glaciers

Abstract

In the high mountains of Asia glaciers are pertinent features and an important water resource, as their melt water is used for irrigation, drinking water and hydropower. To better understand how the melt water supply may change under future climate change, it is important to improve our knowledge of glacier dynamics from small to large scale. Many of the glaciers in this region are covered by a layer of rock debris that alters surface melt rates and the glacier dynamics. The changes are caused by multiple complex processes and feedbacks, which are poorly understood and difficult to monitor. Recent advances in unmanned aerial vehicles (UAVs) offer a new and promising high-resolution observation method. In this thesis, our understanding of debris-covered glaciers and their surface processes is improved by exploring the value of UAV-monitoring in the research of these glaciers. For the first time, a debris-covered glacier in the Himalaya was monitored by a UAV. Image mosaics and digital elevation models (DEMs) were derived and used to determine elevation changes and flow velocity in unprecedented detail. Continued surveys enabled determination of seasonal flow velocities by exploring the potential of frequency cross-correlation techniques. It is shown that the surface of the glacier experiences highly heterogenous mass wasting and that ice melt rates are considerably higher near ice cliffs and supraglacial ponds. Moreover, large seasonal differences exist in the flow velocity, with moderate flow during summer and practically stagnant ice in winter. Data on spatially distributed debris surface temperature provides 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. To improve the understanding of melt rates at ice cliffs and supraglacial ponds an object-based image analysis procedure is presented that enables their automated delineation, which allows for an objective analysis of ice cliff characteristics and spatial distribution. To understand the effects of climate change and debris cover at large scale, the UAV findings of this study were incorporated in a model that assesses Asia’s glacier mass loss over the 21st century. It is shown that even if climate change is limited over one third of the glacier mass will disappear by the end of the century, and that more severe losses are likely. Supraglacial debris is shown to be able to provide considerable delay in future glacier mass loss. This thesis demonstrates that UAVs provide unique and valuable means to study small scale surface processes on remote debris-covered glaciers, and provide data that can be used at the large scale. Further improvement to our understanding of regional and local glacier response will be achieved by multi-scale approaches that combine UAV data in innovative ways with ground-based and satellite data. Ultimately, multidisciplinary studies that integrate the findings will allow us to better understand the mountain water cycle and impacts of climate change.