1 Introduction

Often large-scale postglacial rock slope failures like rock-falls, rock-slides or deep-seated gravitational slope deformations (DSGSD, (Crosta et al. 2013)) can be found in formerly-glaciated alpine areas. It is supposed that failure in these alpine landscapes is directly conditioned by former glaciation and deglaciation (Ballantyne and Stone 2013; Clayton et al. 2017; Evans and Clague 1994; Holm et al. 2004; McColl 2012). Glacial steepening and deglaciation processes have been subject to many studies in the last decades (Grämiger et al. 2017). In contrast preparatory factors like daily, annual and interstadial climatic variations have rarely been studied as well as the historical evolution of failure processes in a paraglacial context since the little ice age (LIA, 1880). The interaction between the retreating glacier and the large DSGSD at Moosfluh is studied in this research. Based on historical data and recent landslide-monitoring and–mapping we present the progressively upslope development of a DSGSD into an active toppling-mode landslide.

2 Study site

Being located in the Swiss Alps, the Great Aletsch Glacier region with its long glacial history, its climate and geology, forms a scientifically unique study area. We are monitoring a rockslide with an estimated volume of about 0.2 km3 occupying the southern valley slope at the tongue of the glacier consisting of a steeply into the slope dipping Pre-Variscan Gneiss (Ambühl 1930).

The rockslide toe is buttressed by the Great Aletsch Glacier, which has thinned since LIA more than 300 m at the study location and lost more than three kilometers of length (Glaciological Reports, 1881–2013). The glacier tongue at the Moosfluh instability lies at 1700 m a.s.l., whereas the ridgetop with the Moosfluh cable car station, which is the only direct infrastructure on the active landslide, is located at 2330 m a.s.l. To be noticed is the damned lake Gibidum 3.5 km downstream the Massa which proceeds the Aletsch Glacier with a water volume of 9.2?10−6 km3.

From the current point of knowledge (May 2017) according to morphological features and movement patterns the slope can be divided into three different sectors. These sectors are always characterized by a steep slope (around 35°) followed by a flat sector of 5–15°.

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