Abstract

Glacial lake outburst floods affect ice dynamics, produce distinctive and widespread onshore and offshore geomorphological impacts and are a hazard to populations and infrastructure. This presentation will firstly review the status of research into the occurrence of glacier outburst floods; those in alpine mountain ranges, those from ice sheet margins and those from subglacial volcanic eruptions. It will then detail quantification of the evolution of a single outburst flood from flume, field and numerical model analyses. It will be shown that glacier outburst floods are initially controlled by a short acceleration due to the depth of impounded water. Channel flow quickly converges to an inertial regime and thence to a viscous regime dominated by channel bed friction. Outburst floods that enter intermediary lakes are dramatically attenuated in terms of propagation whilst basin filling proceeds to the outlet level, dissipated of energy due to considerable flow recirculation during the rising stage of the flood, and after overtopping of the outlet are moderated in terms of peak discharge. Outburst floods can have kinematic waves that are introduced to a flood via hydraulic ponding. A partitioning of flow regimes occurs due to time-transgressive changes in channel cross-section; specifically between inner channel and overbank regions. Furthermore, net erosion along a reach can be related to hydraulic persistence above a marker value and net deposition can be related to a ‘time to peak’ value. These findings shed light on the diversity and complexity of the Quaternary record of outburst floods, provoke consideration of the requirements for modern hazard management strategies and quantify the controls on rapid landscape change due to outburst floods.