Characterization and reconstruction of the Agassiz landslide using geospatial data. Southern Patagonia, Argentina

Abstract

Glaciation and deglaciation modify the stress of the slopes affected by these processes and can trigger their instability and landslides. This study describes, characterizes and reconstructs a large rotational landslide of soil and moraine material, which occurred on February 10, 2013 on the western slope of Upsala Channel, North Branch of Argentino Lake, in Southern Patagonia. With this aim a qualitative analysis of the slope condition before and after the date of the landslide occurrence, the possible conditioning and triggering factors, and the destructive consequences of the related tsunami that affected the margins of the lake was carried out. To reconstruct the state of the slope before and after the event, techniques of photo-interpretation of optical satellite imagery, digital elevation models, historical photographs, in situ observations, bathymetric data and stories of the park rangers of Los Glaciares National Park were used. The retreat of the Upsala Glacier has caused the relaxation of the slopes of the channel conditioning its stability. Among the conditioning and triggering factors that favored the process of activation and generation of the landslide event, are the presence of unconsolidated moraine material covering the channel slopes, steep slopes exposed to the east, which increases its exposure to the sun and melting of snow accumulated during the winter, and the existence of soil creep processes. Although the specific triggering factor is unknown, sediment saturation by surface runoff and water infiltration, eventually a severe rain event, foot slope erosion by glacial activity, and local and regional seismic activity can be mentioned as potential triggering factors. The slope showed evidences of instability for more than 20 years prior to the generation of the landslide, and there is currently evidence that the slope may undergo.