In this study, we focus on the postglacial Chironico landslide in Valle Leventina, the valley of the Ticino river immediately south of the Gotthard pass (southern Swiss Alps). At Chironico, 530 million m 3 of granite gneiss detached from the eastern wall of Valle Leventina and slid along valley-ward dipping foliation joints and fractures. The slide mass was deposited into the valley bottom and blocked the Ticino river, as well as a tributary, the Ticinetto stream, on the opposite side of the valley. Wood fragments found in lacustrine sediments in the slide-dammed upstream lake were previously dated, yielding a minimum age for the landslide of approximately 13,500 cal years BP. Based on the deposit morphology, the landslide was in the past interpreted as being composed of two events. In order to directly date the landslide, ten boulders were dated using the cosmogenic nuclides 10 Be and 36 Cl. Mean exposure ages indicate that the landslide occurred at 13.38 ± 1.03 ka BP, during the Bølling-Allerød interstadial. This implies that the Chironico landslide, one of the few pre-Holocene slides known in Alps, is also the oldest in crystalline rock. With runout modelling using DAN3D we could reproduce the hypothesized singleevent failure scenario, as well as the character and extent of motion of the landslide mass. Both the ages and the modelling suggest that the landslide was released in one event around 3,000 years following deglaciation.

In this study, we use isochron‐burial dating to date the Swiss Deckenschotter, the oldest Quaternary deposits of the northern Alpine Foreland. Concentrations of cosmogenic 10Be and 26Al in individual clasts from a single stratigraphic horizon can be used to calculate an isochron‐burial age based on an assumed initial ratio and the measured 26Al/10Be ratio. We suggest that, owing to deep and repeated glacial erosion, the initial isochron ratio of glacial landscapes at the time of burial varies between 6.75 and 8.4. Analysis of 22 clasts of different lithology, shape, and size from one 0.5 m thick gravel bed at Siglistorf (Canton Aargau) indicates low nuclide concentrations: <20 000 10Be atoms/g and <150 000 26Al atoms/g. Using an 26Al/10Be ratio of 7.6 (arithmetical mean of 6.75 and 8.4), we calculate a mean isochron‐burial age of 1.5 ± 0.2 Ma. This age points to an average bedrock incision rate between 0.13 and 0.17 mm/a. Age data from the Irchel, Stadlerberg, and Siglistorf sites show that the Higher Swiss Deckenschotter was deposited between 2.5 and 1.3 Ma. Our results indicate that isochron‐burial dating can be successfully applied to glaciofluvial sediments despite very low cosmogenic nuclide concentrations. Copyright © 2017 John Wiley & Sons, Ltd.

The northern Swiss Alpine Foreland exemplifies a highly transient landscape characterized by multiple knickzones along the trunk valleys and distinct bedrock straths at their junction with tributary valleys. This landscape has evolved as a result of fast base level changes in response to repeated glaciations during the Quaternary. As the archives related to the evolution of this transient landscape are scarce, available quantitative information is limited, especially for the early and middle Pleistocene. In order to track the pace of the landscape evolution in the northern Swiss Alpine Foreland during the Pleistocene, in this study, we focus on the Deckenschotter sequences, the oldest Quaternary terrestrial sedimentary archives on the northern margin of the Central European Alps. These deposits have been morphostratigraphically divided into two: Höhere (Higher; HDS) and Tiefere (Lower; TDS) Deckenschotter. We analyzed seven different sites extending from Basel in the west to Schaffhausen in the east of Switzerland for the provenance signal, and we dated these archives by depth-profile and isochron-burial dating techniques with 10Be, 26Al, and 36Cl. Investigations on the petrographic compositions of the deposits revealed distinct provenances for the HDS and TDS deposits. During HDS time, the Alpine Rhine drained through Lake Constance and into the Danube River. Rerouting of the river toward the west and into the Upper Rhine Valley occurred between the end of HDS and the beginning of TDS accumulation. The results of the depth-profile and isochron-burial dating suggest that the HDS deposits accumulated at around 2 Ma as a result of a first widespread Alpine glaciation, whereas the TDS was deposited at around 1 Ma. Based on the provenance and the chronological information, we propose a scenario where the Rhine River captured the Alpine sources of the Danube and thus increased its runoff and enhanced its baseline lowering. Consequently, the landscape evolution has been accelerated possibly in response not only to the larger runoff but also to the climate change associated with the mid-Pleistocene revolution.

The Swiss Deckenschotter (''cover gravels'') is the oldest Quaternary units in the northern Swiss Alpine Foreland. They are a succession of glaciofluvial gravel layers intercalated with glacial and/or overbank deposits. This lithostratigraphic sequence is called Deckenschotter because it ''covers'' Molasse or Mesozoic bedrock and forms mesa-type hill-tops. Deckenschotter occurs both within and beyond the extent of the Last Glacial Maximum glaciers. The Swiss Deckenschotter consist of two subunits: Höhere (Higher) and Tiefere (Lower) Deckenschotter. Although the Höhere Deckenschotter sub-unit (HDS) is topographically higher than the Tiefere Deckenschotter, it is older. The only available age for the Swiss Deckenschotter is 2.5-1.8 Ma based on mammal remains found in HDS at the Irchel site. In this study, we present an exposure age for the topographically lowest HDS, calculated from a cosmogenic 10 Be depth-profile. Our results show that the first phase of the Deckenschotter glaciations in the Swiss Alps terminated at least 1,020 þ80 À120 ka ago, which is indicated by a significant fluvial incision. This line of evidence seems to be close to synchronous with the beginning of the Mid-Pleistocene Revolution, when the frequency of the glacial-interglacial cyclicity changed from 41 to 100 ka and the amplitude from low to high, between marine isotope stages 23 and 22.