| dc.description.abstract | The high-mountain cryosphere forms water towers that are important for ecosystem services provision, supplying large populations living in mountains and the surrounding lowlands and producing potable water resources, and water for agriculture, industry and hydropower generation. However, continued glacier recession and mass loss is projected throughout the twenty-first century, and this raises major concerns regarding the future sustainability of cryospheric water resources. While glacier meltwater represents an essential drought-resilient freshwater resource in vulnerable drought-prone regions, little research has focused on the contribution made by runoff from rock glaciers. These are located widely throughout the high-mountain cryosphere and estimates of rock glacier water volume equivalent (WVEQ) vs glaciers suggests that the former may constitute increasingly important long-term water stores. Owing to the insulating effects of thick supraglacial debris cover, rock glaciers are climatically more resilient than glaciers; therefore, their relative importance versus glaciers may increase under future climate warming. Yet, while the hydrological role of debris-free glaciers and debris-covered glaciers has been the subject of much research, that of rock glaciers has received comparatively little attention. Given the need for strong climate adaptation in many of the world’s mountain regions, it is clear that a more comprehensive understanding of all components of the hydrological cycle in the high-mountain cryosphere is required. In this thesis, I develop the scientific understanding of rock glacier significance in deglacierizing mountains across a range of spatial scales (local, national, regional and global), with a specific focus on High Mountain Asia (HMA). The review chapter critically assesses the state of current scientific knowledge regarding the hydrological role of rock glaciers in high mountain systems and serves to form the context for the empirical chapters. The thesis has three key themes to which the empirical chapters are aligned: (1) the distribution and hydrological significance of rock glaciers at global scales, (2) the distribution and hydrological significance of rock glaciers at regional and national spatial scales (Himalaya and Nepalese Himalaya), and (3) advancing rock glacier evolutionary theory. (1) the thesis created a meta-analysis of existing systematic rock glacier inventories and compiled the first near-global rock glacier database (RGDB). The RGDB presented here includes >73,000 rock glaciers (intact = ~39,500, relict = ~33,500), which contain a WVEQ of 83.7 ± 16.7 Gt [~69–102 trillion litres]. Furthermore, the estimated ratio of rock glacier: glacier WVEQ is 1:456 globally. (2) the results of the meta-analysis described in (1) show that only ~9% of studies included in the RGDB cover the Hindu Kush Himalaya (HKH); therefore, I produced the first systematic rock glacier inventory for the (i) Nepalese Himalaya (national-scale), and (ii) Himalaya (regional-scale). In the former (i) I inventoried >6,000 rock glaciers, and these are estimated to contain a WVEQ of 20.90 ± 4.18 km³ (19.16 ± 3.83 Gt). For the Nepalese Himalaya estimated rock glacier: glacier WVEQ ratio is 1:9. In the latter (ii) ~25,000 rock glaciers have been inventoried. The total WVEQ is 51.80 ± 10.36 km³ (47.48 ± 9.50 Gt) with an estimated rock glacier: glacier WVEQ ratio of 1:24. The results of Theme 1 and 2 indicate that rock glaciers form considerable long-term water stores, which may become increasingly important as climatically-driven glacier recession and mass loss continues throughout the twenty-first century and beyond. (3) in order to understand debris-free glacier transition to rock glaciers I use in situ sedimentological data and kite aerial photography (KAP) data and develop a conceptual hypothesis to explain the key drivers of this process. The thesis suggests that sediment connectivity (i.e. the strength of the link between sediment sources and downslope landforms) is one such driver of these transition processes. As a consequence, I hypothesise that the presence of well-developed lateral moraines along glacier margins serves to reduce this connectivity, and thus reduce the likelihood of glacier-to-rock glacier transition occurring. The corelationships between rock glaciers and glacial, periglacial and paraglacial processes are also evaluated in the context of rock glacier origin and the changing influence these processes have upon rock glacier evolution through their lifecycle. Collectively, this research has shaped the understanding of the current and potential future role of rock glaciers in mountain hydrology and is the first to comprehend the distribution and hydrological significance of rock glaciers globally and in the Himalaya. | en_GB |
