Abstract
Landslides triggered by shrinking glaciers are an expected outcome of global climate change and they pose a significant threat to inhabitants and infrastructure in mountain valleys. In this study we document the rock slope movement that has affected the Pilatte hut (2572 m a.s.l.) in the Ecrins range (French alps) since the 1980s. We reconstructed the geometry of the unstable rock mass using Terrestrial Laser Scanning and quantified the unstable volume (~ 400,000 m3). Field observations and annual crack surveys have been used to identify the dynamics of past movements. These movements initiated in the late 1980s and have accelerated since 2000. The current trend seems to be towards a relative stabilization. Reconstruction of the glacier surface using past images taken since 1960 and ‘Structure from Motion’ photogrammetry showed that the glacier probably applied stresses to the rock slope during its short-lived advance during the 1980s, followed by debuttressing caused by rapid surface lowering until the present day. The relationship between observed crack propagation and glacier surface change suggests that the rock slope instability is a paraglacial response to glacier surface changes, and highlights that such responses can occur within a decade of glacier change.
Highlights
Temperatures in the French Alps have risen by 1.5–1.8◦C since 1950 (Einhorn et al, 2015)
This study focuses on the Pilatte hut (2,572 m a.s.l., in the Écrins mountain range, French Alps)
Three different methods were used over different time periods following an initial structural and geological survey of the rock outcrop: (i) annual crack measurements were done from 2003 to 2017, and the results analyzed to detect and study the rock dynamics in progress directly beneath the Pilatte hut, (ii) Terrestrial Laser Scanning (TLS) surveys were carried out in 2014 and 2016 to assess the volume of unstable rock and to monitor any substantial geomorphological activity over that 2 year period, and (iii) Structure for Motion (SfM) photogrammetry from historical aerial photographs was carried out to measure elevation changes of the glacier surface from 1960 to 2016
Summary
Temperatures in the French Alps have risen by 1.5–1.8◦C since 1950 (Einhorn et al, 2015). 4,000 m a.s.l., the mean annual air temperature increased by 0.14◦C per decade between 1900 and 2004 (Gilbert and Vincent, 2013). High alpine environments are strongly affected by this warming (Beniston et al, 2018), especially with regards to glacial shrinkage (Vincent, 2002) and permafrost degradation (Harris et al, 2009). In the Alps, the glacierized areas shrank by half between 1860 and 2012, with a strong acceleration in recession since the 1980s (Huss, 2012; Gardent et al, 2014). Mountain permafrost, defined as ground that remains below 0◦C for 2 years or more, has experienced an almost continuous warming (PERMOS, 2016) since the beginning of the 2000s.
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