Outburst floods from moraine dammed lakes in the Himalayas : detection frequency and hazard The Himalayas are a region that is most dependent but also frequently prone to hazards from changing meltwater resources. This mountain belt hosts the highest mountain peaks on earth has the largest reserve of ice outside the polar regions and is home to a rapidly growing population in recent decades. One source of hazard has attracted scientific research in particular in the past two decades: glacial lake outburst floods (GLOFs) occurred rarely but mostly with fatal and catastrophic consequences for downstream communities and infrastructure. Such GLOFs can suddenly release several million cubic meters of water from naturally impounded meltwater lakes. Glacial lakes have grown in number and size by ongoing glacial mass losses in the Himalayas. Theory holds that enhanced meltwater production may increase GLOF frequency but has never been tested so far. The key challenge to test this notion are the high altitudes of >4000 m at which lakes occur making field work impractical. Moreover flood waves can attenuate rapidly in mountain channels downstream so that many GLOFs have likely gone unnoticed in past decades. Our knowledge on GLOFs is hence likely biased towards larger destructive cases which challenges a detailed quantification of their frequency and their response to atmospheric warming. Robustly quantifying the magnitude and frequency of GLOFs is essential for risk assessment and management along mountain rivers not least to implement their return periods in building design codes. [...]