Assessing the mechanisms and significance of the summer 2008 glacial lake outburst floods in the upper Hunza Valley, Pakistan

During the summer of 2008, unexpected glacial lake outburst floods from Ghulkin Glacier in the upper Hunza Valley, northern Pakistan, caused widespread damage to Ghut Ghush settlement. Early reports indicate that houses, cattle sheds, irrigation channels, cultivated land, electricity supplies, and roads (including the Karakoram Highway, the only main access route through the Karakoram region) were damaged or destroyed by the floods. We aim to assess the cause(s), characteristics and consequences of these floods and establish whether they are likely to occur more frequently in the future in the Karakoram region. Climatic warming in recent decades has been associated with widespread retreat and disintegration of high-mountain glaciers. An important consequence is the increased storage of meltwater in transient lakes on glacier surfaces or impounded by moraine dams, which can burst with catastrophic consequences for society. Such large-scale lake development on stagnating and downwasting glaciers is widely reported in the central Himalaya (Nepal, Bhutan, China) but not in the Karakoram region where, historically, floods have occurred predominantly from ice-dammed lakes formed when tributary glaciers advance across the main valleys. The 2008 Chut Ghush floods are therefore unusual for the Karakoram region, but may reflect newly evolving glacial conditions that would favour the development of more hazardous lakes in the future. The occurrence of the floods provides a rare opportunity to characterise the processes and consequences of a (currently) unusual type of glacial hazard for the Karakoram. Building on research from the central Himalaya, we propose to identify the sources and mechanisms of the glacial floods from remote sensing and field investigations. In order to determine the controlling glaciological conditions under which the lakes formed, the key glacier characteristics will be mapped and glacier velocities calculated for the last decade from satellite images. To address the importance of the floods as agents of change that modify river channels and supply large amounts of sediment to river systems, their geomorphological impacts will assessed in the field by surveying flood landforms and characterising the flood sediments. Relationships between glacier dynamics and lake development will be explored and conceptual models of hazard formation developed that can be applied to environments with comparable glaciological and geomorphological characteristics. Outputs from the research will increase our understanding of current glacier responses to climatic warming and impacts upon society in the Karakoram, and will also be disseminated to stakeholders to assist with flood response and risk management efforts.