Understanding the preconditioning and driving factors of the 2017 glacial lake outburst flood in the Sulzenau valley, Tyrol, Austria

This study focuses on Lake Sulzenau, where a Glacial Lake Outburst Flood (GLOF), involving a partial moraine-dam breach, hit the valley in August 2017 and damaged the water supply infrastructure of a nearby mountain hut. Located in the Stubai Alps (Tyrol, Austria), the Sulzenau Lake is continuously evolving due to the rapid retreat of the Sulzenauferner Glacier. The objective of this study was to use multi-source remote sensing data (optical and radar imagery, close-range and ground-based data) to obtain a detailed overview of the whole valley, to monitor the dynamics of lake evolution since its first appearance in the early 2000s, and to characterize the conditions that led to the sudden failure of the dam and its impacts. First, we used optical images (e.g.: Sentinel-2, Google Earth) to produce two detailed geomorphological maps (pre- and post-event) of Lake Sulzenau and its surroundings to identify, describe and quantify the impacts of the 2017 event on the local geomorphology. Secondly, based on multi-temporal Digital Elevation Models (DEMs), we analyzed the changes in the topography for several periods before and after the 2017 event. This step was supported by the construction of a recent DEM from Unmanned Aerial Vehicle (UAV) data collected during a field campaign completed in August 2021. The DEM differencing revealed vertical changes (erosion and deposition) in GLOF-affected areas. The Sulzenau Valley is a perfect example of the current dynamics of glacial environments under global warming. The GLOF of 2017, associated with the rapid retreat of the glacier and the recent growth of its lake, represents an excellent case study to better understand these natural hazards.