The Chironico Landslide (Valle Leventina, Southern Swiss Alps): Age and Evolution
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Research Collection Journal Article The Chironico landslide (Valle Leventina, southern Swiss Alps): age and evolution Author(s): Claude, Anne; Ivy-Ochs, Susan; Kober, Florian; Antognini, Marco; Salcher, Bernhard; Kubik, Peter W. Publication Date: 2014 Permanent Link: https://doi.org/10.3929/ethz-b-000096009 Originally published in: Swiss Journal of Geosciences 107(2-3), http://doi.org/10.1007/s00015-014-0170-z Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Swiss J Geosci (2014) 107:273–291 DOI 10.1007/s00015-014-0170-z The Chironico landslide (Valle Leventina, southern Swiss Alps): age and evolution Anne Claude • Susan Ivy-Ochs • Florian Kober • Marco Antognini • Bernhard Salcher • Peter W. Kubik Received: 22 November 2013 / Accepted: 24 September 2014 / Published online: 22 October 2014 Ó Swiss Geological Society 2014 Abstract In this study, we focus on the postglacial Chi- boulders were dated using the cosmogenic nuclides 10Be ronico landslide in Valle Leventina, the valley of the and 36Cl. Mean exposure ages indicate that the landslide Ticino river immediately south of the Gotthard pass occurred at 13.38 ± 1.03 ka BP, during the Bølling- (southern Swiss Alps). At Chironico, 530 million m3 of Allerød interstadial. This implies that the Chironico land- granite gneiss detached from the eastern wall of Valle slide, one of the few pre-Holocene slides known in Alps, is Leventina and slid along valley-ward dipping foliation also the oldest in crystalline rock. With runout modelling joints and fractures. The slide mass was deposited into the using DAN3D we could reproduce the hypothesized single- valley bottom and blocked the Ticino river, as well as a event failure scenario, as well as the character and extent of tributary, the Ticinetto stream, on the opposite side of the motion of the landslide mass. Both the ages and the valley. Wood fragments found in lacustrine sediments in modelling suggest that the landslide was released in one the slide-dammed upstream lake were previously dated, event around 3,000 years following deglaciation. yielding a minimum age for the landslide of approximately 13,500 cal years BP. Based on the deposit morphology, the Keywords Switzerland Á Canton ticino Á landslide was in the past interpreted as being composed of Surface exposure dating Á Cosmogenic nuclides two events. In order to directly date the landslide, ten (10Be, 36Cl) Á Landslide modelling 1 Introduction Editorial handling: S. Lo¨w and A. G. Milnes. The interaction of rock uplift with surface processes results Electronic supplementary material The online version of this article (doi:10.1007/s00015-014-0170-z) contains supplementary in the development of mountain topography. As a major material, which is available to authorized users. mechanism for bedrock erosion, landslides control the A. Claude Á F. Kober Á B. Salcher A. Claude (&) Geological Institute, ETH Zurich, Sonneggstrasse 5, Institute of Geological Sciences, University of Bern, 8092 Zurich, Switzerland Baltzerstrasse 1-3, 3012 Bern, Switzerland e-mail: [email protected] S. Ivy-Ochs Á P. W. Kubik Laboratory of Ion Beam Physics (LIP), ETH Zurich, Present Address: Otto-Stern-Weg 5, 8093 Zurich, Switzerland F. Kober Nagra, Hardstrasse 73, Postfach 280, 5430 Wettingen, S. Ivy-Ochs Switzerland Department of Geography, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland Present Address: B. Salcher M. Antognini Department of Geography and Geology, Salzburg University, Museo Cantonale di storia naturale, Viale Cattaneo 4, Hellbrunner Strasse 34, 5020 Salzburg, Austria 6900 Lugano, Switzerland 274 A. Claude et al. variability of sediment flux from tectonically active accumulation area of the landslide is subdivided into two mountain ranges (Hovius et al. 1997; Shroder and Bishop different lobes (Fig. 2), which are separated by the Tici- 1998) and have therefore a long term impact on landscape netto river, a tributary of the Ticino river. Earlier work by evolution in mountain chains (Hovius and Stark 2007). Naegeli (1920) and Dal Vesco (1979) suggested that the Mass wasting sets geomorphic control on fluvial processes Chironico landslide consisted of two events because of the (Hovius and Stark 2007; Korup et al. 2010) since hillslopes apparent dual-lobe morphology of the deposit and the have to adjust to changes in fluvial incision rates in mapping of two separate detachment scarps. Dal Vesco response to rock uplift. It is suggested that mass wasting (1979) moreover argued that the boulders of the southern processes (landslides, debris flows) in valleys with critical deposit have a morphology distinguishable from those of slopes or relief (Korup et al. 2010) are influenced by cli- the northern deposit, having somewhat smaller size. mate and that they thus may be regarded as a Antognini and Volpers (2002) investigated the Chiro- geomorphological proxy for climate change (Borgatti and nico landslide by looking at cores taken for geotechnical Soldati 2010 and references therein). Preparatory factors purposes. They radiocarbon dated pieces of wood found in for landslides in contrast to triggering factors need to lacustrine sediments of the landslide-dammed lake, located accumulate over a long time period in order to induce north of the deposit (location S5 in Fig. 2). The wood failure (Gunzburger et al. 2005). Some of these preparatory fragments yielded a minimum age of approximately conditions include gradual rock weathering, frost action, 13,500 cal years BP (Antognini and Volpers 2002). Since changes in pore water pressure and stress redistribution they originate from a secondary deposit and were not found during or after glacial unloading (e.g. Gunzburger et al. at the base of the core, and furthermore because wood can 2005; Prager et al. 2008; Korup et al. 2010). Important easily be washed in by flood events, questions remained triggering factors are heavy rainfall or earthquakes, which about the absolute age of the Chironico landslide event have as a consequence a direct collapse of the slope, as itself. In addition, no information was gained on the shown by more recent events in Alpine realm (Fritsche and question of whether the event consisted of one or two Fa¨h 2009). slides. In this work, we date the Chironico landslide deposit The retreat of the late Pleistocene glaciers has played an directly using surface exposure dating with the cosmogenic important part in preconditioning numerous landslides in nuclides 10Be and 36Cl. The goals of this study are to mountain valleys (Ballantyne et al. 2014a). By applying reconstruct not only the event chronology and subsequent various dating techniques it has been demonstrated for the landscape evolution of the Chironico area (Fig. 2), but also Central Alps that the majority of dated landslides were not to explore the dynamics of the landslide. Furthermore, we released immediately after the end of the last glaciation but aim to evaluate the long-standing debate about this land- a few thousand years later, during the Lateglacial and slide, namely if it resulted from one single event or even Holocene (Heuberger 1994; Ivy-Ochs et al. 1998, 2009; several successive slides (Naegeli 1920; Dal Vesco 1979; Poschinger 2002; Gruner 2006; Prager et al. 2007, 2008). Antognini and Volpers 2002), and to further constrain the In the Alps, some of the largest landslides cluster in the release area, as the detachment scarp on the eastern valley early Holocene around 10,500–9,400 cal years BP (Soldati wall is difficult to locate. et al. 2004; Prager et al. 2008). A marked period of increased landslide activity was also assigned to the Sub- boreal in the middle Holocene, from 4,200 to 2 Geologic and geomorphologic setting 3,000 cal years BP (Dapples et al. 2003; Prager et al. 2007), accompanying climatic deterioration with a shift The Chironico area is dominated by bedrock of the Lower towards colder and more humid conditions. Raetzo- Penninic Simano- and Leventina nappes (Antognini and Bru¨hlhart (1997), Dapples et al. (2003), Soldati et al. Volpers 2002). The Simano nappe is composed of several (2004), Gruner (2006) and Prager et al. (2008) discuss orthogneiss bodies intruded into paragneisses and schists several intervals of enhanced slope instability during the (Ruetti et al. 2005), whereas the Leventina nappe consists late Holocene in the Swiss Alps (6,250–4,800; of mainly orthogneisses (Fig. 3), including the so-called 3,500–2,100; 1,700–1,150; 750–300 cal years BP), Aus- ‘‘Leventina Granitic Gneiss’’ (Casasopra 1939), that often trian Alps (4,200–3,000 cal years BP), and also in the shows an augen-gneiss texture (Timar-Geng et al. 2004). In Italian Alps (5,800–2,000 cal years BP). a few locations, Triassic quartzites separate the Simano The Chironico landslide in the Valle Leventina of the nappe from the underlying Leventina nappe (Niggli et al. southern Swiss Alps (canton Ticino) (Fig. 1), with an 1936). In all rock types, a well-developed foliation occurs estimated volume of 530 million m3, is among one of the which dips towards SSW at angles ranging from 25° to 30°, largest landslides in the Alps in crystalline rock, after the generating a dip-slope on the eastern valley flank (Antog- Ko¨fels landslide in the Austrian O¨ tztal (Abele 1974). The nini and Volpers 2002). The Chironico landslide age and evolution 275 Fig. 1 Topographic overview map of the study area (Ó Federal Office of Topography, swisstopo, CH-3084 Wabern). Valle Leventina is situated between Airolo and Biasca. The black square locates the digital elevation model (DEM) of the Chironico landslide as can be seen in Fig. 2 During the Last Glacial Maximum (LGM), the Valle stadials reaching into the Valle Leventina. Hantke (1983) Leventina was almost entirely filled with ice except for mapped different ice margins in the Leventina near Biasca nunataks, represented by the mountain peaks to the east and Bellinzona (Fig.