GERALDINE (Google earth Engine supRaglAciaL Debris INputdEtector) – A new Tool for Identifying and Monitoring SupraglacialLandslide Inputs

Abstract. Rock avalanches, a high-magnitude, long runout form of bedrock landslide, are thought to increase in frequency as a paraglacial response to ice-retreat/thinning, and arguably, due to warming temperatures/degrading permafrost above current glaciers. However, our ability to test these assumptions by quantifying the temporal sequencing of debris inputs over large spatial and temporal extents is limited in areas with glacier ice. Discrete landslide debris inputs, particularly in accumulation areas are rapidly ‘lost’, being reworked by motion and icefalls, and/or covered by snowfall. Although large landslides can be detected and located using their seismic signature, small to medium-sized landslides, particularly supraglacially deposited landslides which feature a quiet runout over snow, frequently go undetected because their seismic signature is less than the noise floor. Here, we present GERALDINE (Google earth Engine supRaglAciaL Debris INput dEtector): a new open-source tool leveraging Landsat 4–8 satellite imagery and Google Earth Engine. GERALDINE outputs maps of new supraglacial debris additions within user-defined areas and time ranges, providing a user with a reference map, from which large debris inputs such as supraglacial rock avalanches can be rapidly identified. We validate the effectiveness of GERALDINE outputs using published rock-avalanche inventories, then demonstrate its potential by identifying two previously unknown, large (> 2 km2) supraglacial debris inputs onto glaciers in the Hayes Range, Alaska, one of which was not detected seismically. GERALDINE is a first step towards a revised global magnitude-frequency of rock avalanche inputs onto glaciers over the 37 years of Landsat Thematic Mapper imagery.