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The junction of the Dinaric and Hellenic mountain belts hosts a trans-orogenic normal fault system (Shkoder-Peja Normal Fault, SPNF) that has accommodated oroclinal bending, as well as focused basin formation and drainage of the Drin River catchment. Analysis of fluvial morphology of this catchment reveals higher values of river slope indices (ksn) and χ (Chi) between the normal faults of the SPNF and the Drin drainage divide. The drainage divide is predicted to be migrating away from the SPNF, except at the NE end of the SPNF system. Two basins analysed in the hangingwall of the SPNF, the Western Kosovo Basin (WKB) and Tropoja Basin (TB), contain late Pliocene-to-Holocene sedimentary rocks deposited well after the main fault activity and immediately after the Last Glacial Maximum (LGM). These layers document an early Pleistocene transition from lacustrine to fluvial conditions that reflects a sudden change from internal to external drainage of paleo-lakes. In the TB, these layers were incised to form three generations of river terraces, interpreted to reflect episodic downstream incision during re-organisation of the paleo-Drin River drainage system. 36Cl-cosmogenic-nuclide depth-profile ages of the two youngest terraces (∼12, ∼8 ka) correlate with periods of wetter climate and increased sediment transport in post-LGM time. The incision rate (∼12 mm/yr) is significantly greater than reported in central and southern Albania. Thus, glacial/interglacial climatic variability, hinterland erosion and base-level changes appear to have regulated basin filling and excavation cycles when the rivers draining the WKB and TB became part of the river network emptying into the Adriatic Sea. These dramatic morphological changes occurred long after normal faulting and clockwise rotation on the SPNF initiated in late Oligocene-Miocene time. Faulting provided a structural and erosional template upon which climate-induced erosion in Holocene time effected reorganisation of the regional drainage pattern, including the formation and partial demise of lakes and basins. The arc of the main drainage divide around the SPNF deviates from the general coincidence of this divide with the NW-SE trend of the Dinaric-Hellenic mountain chain. This arc encompasses the morphological imprint left by roll-back subduction of the Adriatic slab beneath the northwestern Hellenides.

Large rock-slope failures are among the primary geohazards in high mountain areas. These rock avalanches and rockslides constitute most of the world’s largest landslide deposits. This study focuses on the formation and geomorphological activity of the Akdag landslide complex located on the southern slope of Mount Akdag, SW Turkey. We employed detailed mapping in the field, spatial and morphometric analysis using GIS and remote sensing technologies, and surface exposure dating with cosmogenic 36Cl to reconstruct the chronology of the landslide complex. For the analysis of cosmogenic 36Cl, we collected 18 surface samples from calcareous boulders within the landslide deposit. Our field mapping shows that the Akdag rock avalanche is a large and active slope failure developed between carbonates and flysch. The rock-avalanche deposits cover an area of 9.8 km2 and together with the primary and secondary slope failures which form the landslide complex, cover an area of 15 km2. The Akdag rock avalanche is one of the largest (3 × 108 m3) known bedrock landslides in Turkey. Cosmogenic 36Cl exposure ages indicate that the main collapse occurred at 8.3 ± 1.4 ka (2σ), followed by secondary failures. We dated one of the latter to 1.1 ± 0.2 ka (2σ). Based on field evidence, we surmise that increased water discharge in the springs along the carbonate-flysch contact zone played a key role in the Early Holocene failure.

Rock avalanches are low frequency natural hazards that can alter landscape morphology, and constraining the timing, volume and emplacement dynamics of pre-historic rock avalanches is crucial for understanding the hazards posed by these events. Here we perform cosmogenic nuclide dating, topographic reconstruction and runout modeling of the Molveno rock avalanche, located north of Lake Garda in the Province of Trento, Italy. The unique morphology of the deposits, which features numerous large scarps and prominent lineaments, have previously led researchers to interpret the Molveno rock avalanche as being the result of multiple events. Our results show that the Molveno rock avalanche had a volume of approximately 600 Mm3, and failed from a prominent niche located on Monte Soran. 36Cl cosmogenic nuclide dating results shows that the deposits were emplaced as a single event approximately 4.8 ± 0.5 ka, and suggests that the unique deposit morphology is due to the emplacement processes acting during and soon after failure. Numerical runout modeling shows that this morphology could have resulted from a combination of runup and extensional spreading of the debris along the complex valley floor topography. The ages we determined for this event are coincident with the nearby Marocca Principale rock avalanche (5.3 ± 0.9 ka), which may suggest a common trigger. Our results have important implications for interpreting the morphology of rock avalanche deposits, and contribute to the evolving understanding of rock avalanche processes in the Alps.

In this study, we focus on the Kandersteg rock avalanche in the central Bernese Alps in Switzerland. We achieved an improved understanding of the release and emplacement of the rock avalanche through a combination of detailed field mapping, remote image analysis, reconstruction of deposit and source area volumes, and runout modelling with DAN3D. Based on cosmogenic 36Cl dating of siliceous limestone boulders all across the landslide deposit, we determined an age of 3210 ± 220 years for the event. This age is markedly younger than the previously suggested age of 9600 years. An estimated 750–900 Mm3 of Cretaceous limestones, siliceous limestones (Oehrlikalk, Kieselkalk and Bänderkalk formations) and Tertiary sandstones of the Doldenhorn nappe detached along pre-existing discontinuities from the northwest face of the Fisistock peak. The sliding body fragmented upon encountering the valley floor and the steep opposite valley wall. Next, the dry fragmented rock avalanche propagated northward over a substrate of fluvial sediments. As it moved, the debris became more fluid through entrainment of water and water-rich sediments, until it finally came to a halt 10 km downstream. The final volume of the deposit is estimated at 1.1 km3. Our multi-method approach allowed us to establish that the deposit stems from one colossal event at 3.2 ka and to reconstruct the processes that dominated each phase of the rock avalanche. Our research contributes significantly to understanding not only the Kandersteg event but also complex emplacement processes and mechanics of large rock slope failures. [ABSTRACT FROM AUTHOR]

The Namaras rock avalanche (NRA) deposit originated from the northern flank of the glaciokarstic Geyikdağ Mountain in the Central Taurus Range, SW Turkey. The deposit has an area of ~0.430 km2 and an estimated average thickness of 10 m, corresponding to 4.3 million m3 volume. The fan-shaped deposit area consists of house-sized Jurassic-Cretaceous neritic limestone boulders that overlie lateral and hummocky moraines down into the valley. We used geomorphological mapping and 36Cl surface exposure dating to obtain six boulder ages which unravelled the NRA age, the number of events and their geometric features. Our results indicate that the NRA consists of two successive mid-to-late Holocene events; the first high magnitude main event with a weighted average age of 4.59 ± 0.25 ka followed by a second low magnitude event with a weighted average age of 3.77 ± 0.20 ka. 36Cl exposure dating of the lateral moraine covered by the rock avalanche deposit yielded approximately an age of ~12.30 ± 1.20 ka. The older event with a maximum runout distance of 1550 m and 600 m elevation loss yielded in a travel angle of 21°. Similarly, the younger event with 1720 m maximum runout length and 640 m vertical elevation loss resulted in a travel angle of 20°. The bedded limestone with cross-joints in the glacial cirque preconditioned the NRA slope failure. The significant lag time between deglaciation and the rock avalanche indicates that the glacial erosion and debuttressing acted as preparatory factors. Based on the low seismic activity in the Central Taurus Range and the synchronicity of the rock avalanche with mid-to-late Holocene climatic transitions, we propose that climatic factors may have triggered the NRA failure. The age of the older main event coincides with the warm drought period of the mid-Holocene associated with torrential rainfalls in the Taurus Mountains, while the age of the younger event correlates with the long wet period in the late Holocene. Thus, the main NRA event may have been triggered by the influence of warm temperatures and intense rainfall, while the second event may have been triggered by prolonged period of high precipitation. The two events of the NRA are coeval with the enhanced rock slope failures dating back to 5–3 ka in the Alps. • A rock avalanche with two successive events in the SW Turkey was mapped and dated. • First event: high magnitude, with 0.415 km2 area and 4.59 ± 0.25 ka age • Second event: low magnitude, with 0.127 km2 area and 3.77 ± 0.20 ka age • The glacial erosion appears as the preparatory factor of the rock avalanche. • The mid-Holocene climatic variabilities possibly triggered the rock avalanche. [ABSTRACT FROM AUTHOR]