Hydrothermally altered deposits of 2014 Askja landslide, Iceland, identified by remote sensing imaging

Abstract

Volcanic flanks subject to hydrothermal alteration become mechanically weak and gravitationally unstable, which may collapse and develop far-reaching landslides. The dynamics and trajectories of volcanic landslides are hardly preserved and challenging to determine, which is due to the steep slopes and the inherent instability. Here we analyze the proximal deposits of the 21 July 2014, landslide at Askja (Iceland), by combining high-resolution imagery from satellites and Unoccupied Aircraft Systems. We performed a Principal Component Analysis in combination with supervised classification to identify different material classes and altered rocks. We trained a maximum-likelihood classifier and were able to distinguish 7 different material classes and compare these to ground-based hyperspectral measurements that we conducted on different rock types found in the field. Results underline that the Northern part of the landslide source region is a hydrothermally altered material class, which bifurcates halfway downslope and then extends to the lake. We find that a large portion of this material is originating from a lava body at the landslide headwall, which is the persistent site of intense hydrothermal activity. By comparing the classification result to in-situ hyperspectral measurements, we were able to further identify the involved types of rocks and the degree of hydrothermal alteration. We further discuss associated effects of mechanical weakening and the relevance of the heterogeneous materials for the dynamics and processes of the landslide. As the study demonstrates the success of our approach for identification of altered and less altered materials, important implications for hazard assessment in the Askja caldera and elsewhere can be drawn.

Infrared spectroscopy of volcanoes: from laboratory to orbital scale

“…The presence of these alteration minerals is important in mapping as they indicate active (or past) geothermal systems and also play an important role in slope failure hazards at volcanoes (Lopez and Williams, 1993;John et al, 2008;Heap et al, 2021). This approach of alternation mineral detection has been used to look for evidence of past sector collapse and debris avalanche events from volcanoes (e.g., Askja, Iceland; Marzban et al, 2023). The search for possible ancient hydrothermal systems on Mars is also important for the search for evidence of life.…”