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The Lavini di Marco, Marocche di Dro and Molveno rock avalanches in Trentino, and the Termeno landslide in South Tyrol are here presented as case studies for the western Dolomites(Adige and Sarca Valleys, NE Italy). Their structural predisposition, run-out and timing are discussed, also in consideration of other evidence for the Alpine region. The detailed geomorphologi-cal mapping of deposits and their release area, combined with regional and local structural analysis, isotopic dating, and numerical modelling, have led to updated interpretations of their mechanisms, timing, and triggering/driving forces. In particular, the major role of structural controls is investigated. Intense rock damage and rock fatigue, which are related to tectonic activity along the Southern Giudicarie and Schio-Vicenza fault systems, together with high topographic relief energy and local dip slope, all combine to promote detachment of huge rock volumes. Besides structural predisposition, other factors like glacial erosion/unloading and climate can exert a primary control. Three large rock avalanches occurred between 5-3 ka ago: Lavini di Marco(200 Mm, 3.0±0.4 ka), Marocca Principale(1000 Mm, 5.3 ±0.9 ka)belonging to the Marocche di Dro complex, and Molveno(600 Mm, 4.8±0.5 ka). This period has been recognized as one of enhanced slope failure activity in the Alps, perhaps related to the climatic transition to cooler and wetter conditions at the beginning of the late Holocene. This is particularly valid for the close contemporaneity of the Marocca Principale and Molveno rock avalanches. Conversely, younger ages at the Kas rock avalanche(Marocche di Dro complex; 300 Mm, 1.1±0.2 ka)likely imply a close relation with seismic forcing.

Landslides are a critical process in landscape evolution and may pose a serious threat to people and infrastructure. In the last decades, a growing interest in such phenomena has developed in the Alps, where narrow valleys are increasingly inhabited, and landslides have caused several casualties. Understanding the driving factors, triggers, evolution, and impact of past and future failures is of the utmost importance when dealing with land use and risk reduction. In this paper, four distinct case studies are presented, showing how different approaches can interact and produce a comprehensive understanding of a landslide event. All examples lie in the middle sector of the Piave Valley (NE Italy) and deal with failures that occurred in the distant past (i.e., the historic Masiere di Vedana rock avalanche), in the near past (i.e., the 1963 Vajont event), in the present (i.e., the 60-years -lasting Tessina landslide) and in the future (i.e., possible Mt. Peron instabilities). The final goal of the paper is to show how the understanding of past landslides is fundamental to obtain reliable predictions on future failures, and how modelling designed to predict the evolution of potential detachments can be applied to understand the dynamics of ancient events.

There is growing interest in geochronological applications of terrestrial in situ-produced cosmogenic nuclides, with the most commonly measured being ¹⁰Be and ²⁶Al in quartz. To extract and then separate these radionuclides from quartz and prepare them in the oxide form suitable for accelerator mass spectrometry (AMS) requires extensive and careful laboratory processing. Here we discuss the suitability of a crushed, sieved and etched, sub-aerially exposed vein quartz specimen (CoQtz-N) to act as a reference material for chemical laboratory preparation and AMS measurements. Splits of CoQtz-N were distributed to eleven target preparation laboratories. The CoQtz-N ¹⁰Be targets were then measured at seven different AMS facilities and five of the preparation laboratories had their ²⁶Al targets measured at four different AMS facilities. We show that CoQtz-N splits are sufficiently homogeneous with regard to nuclide concentrations, that it has been cleaned of any atmospheric derived (i.e. meteoric) ¹⁰Be and that it has low concentrations of the major elements that can interfere with Be and Al extraction chemistry and AMS measurements. We derive preliminary concentrations for ¹⁰Be and ²⁶Al in CoQtz-N as 2.53 ± 0.09 × 106 at/g and 15.6 ± 1.6 × 106 at/g, respectively, at the 95% confidence limit.

Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as intercomparison material (ICM) for in situ-produced cosmogenic ³⁶Cl and natural chlorine (Clnat) analysis. The sample CoCal-N is derived from calcite crystals in a Namibian lag deposit, while the sample CoFsp-N is derived from a single crystal of alkali-feldspar from a Namibian pegmatite. The sample preparation took place at the University of Cologne and a rotating splitter was used to obtain homogeneous splits of both ICMs. Forty-five measurements of CoCal-N (between 1 and 16 per facility) and forty-four measurements of CoFsp-N (between 2 and 20 per facility) have been undertaken by ten target preparation laboratories measured by seven different AMS facilities. The internal laboratory scatter of the ³⁶Cl concentrations indicates no overdispersion for half of the laboratories and 3.9 to 7.3% (1σ) overdispersion for the others. We show that the CoCal-N and CoFsp-N splits are homogeneous regarding their ³⁶Cl and Clnat concentrations. The grand average (average calculated from the average of each laboratory) yields initial consensus ³⁶Cl concentrations of (3.74 ± 0.10) × 10⁶ at ³⁶Cl/g (CoCal-N) and (2.93 ± 0.07) × 10⁶ at ³⁶Cl/g (CoFsp-N) at 95% confidence intervals. The coefficient of variation is 5.1% and 4.2% for CoCal-N and CoFsp-N, respectively. The Clnat concentration corresponds to the lower and intermediate range of typical rock samples with (0.73 ± 0.18) µg/g in CoCal-N and (73.9 ± 6.8) µg/g in CoFsp-N. We discuss the most relevant points of the sample preparation and measurement and the chlorine concentration calculation to further approach inter-laboratory comparability. We propose to use continuous measurements of the ICMs to provide a valuable quality control for future determination of ³⁶Cl and Clnat concentrations.

Geophysical Research Abstracts, 21, ISSN:1029-7006, ISSN:1607-7962

Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as intercomparison material (ICM) for in situ-produced cosmogenic 36Cl and natural chlorine (Clnat) analysis. The sample CoCal-N is derived from calcite crystals in a Namibian lag deposit, while the sample CoFsp-N is derived from a single crystal of alkali-feldspar from a Namibian pegmatite. The sample preparation took place at the University of Cologne and a rotating splitter was used to obtain homogeneous splits of both ICMs. Forty-five measurements of CoCal-N (between 1 and 16 per facility) and forty-four measurements of CoFsp-N (between 2 and 20 per facility) have been undertaken by ten target preparation laboratories measured by seven different AMS facilities. The internal laboratory scatter of the 36Cl concentrations indicate no overdispersion for half of the laboratories and 3.9 to 7.3% (1σ) overdispersion for the others. We show that the CoCal-N and CoFsp-N splits are homogeneous regarding their 36Cl and Clnat concentrations. The grand average (average calculated from the average of each laboratory) yields initial consensus 36Cl concentrations of (3.74 ± 0.10) x 106 at 36Cl/g (CoCal-N) and (2.93 ± 0.07) x 106 at 36Cl/g (CoFsp-N) at 95% confidence intervals. The coefficient of variation is 5.1% and 4.2% for CoCal-N and CoFsp-N, respectively. The Clnat concentration corresponds to the lower and intermediate range of typical rock samples with 0.73 ± 0.18 μg/g in CoCal-N and 73.9 ± 6.8 μg/g in CoFsp-N. We discuss the most relevant points of the sample preparation and measurement and the chlorine concentration calculation to further approach intra-laboratory comparability. We propose to use continuous measurements of the ICMs to provide a valuable quality control for future determination of 36Cl and Clnat concentrations.