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To improve current understanding of ongoing deglaciation dynamics in relation to climatic forcing, it is critical to build long-term series of climate and glacier changes. This task is typically hampered by availability and resolution of Quaternary glacier paleo-reconstructions. To explore opportunities and challenges, we present a case study from Val Viola, which integrates area, volume and ELA changes across a 13k-year time window, including four Younger Dryas–Early Holocene glacier stadials and eight post-LIA periods. Results suggest that relevant shifts in climatic forcing associated with the Pleistocene–Holocene transition and post-LIA deglaciation phases are of comparable magnitude, with an atmospheric temperature increase of about 1.5–2°C. Post-LIA decline in glacierized areas (68.9 ± 6%) is comparable with retreat rates recorded in other Italian glaciers, but is greater than elsewhere in the Alps, where glaciers are comparably larger. Glacier stability in the particularly warm 2007–2015 period testifies to the decoupling attained by small glaciers from synoptic atmospheric conditions. We argue that this is caused by enhanced wind drift and avalanche accumulation, occurred in response to morphological changes on ice surfaces following progressive glacier shrinking. This positive feedback not only could delay glacier extinction in certain physiographic settings but also could introduce bias in paleo-glaciological reconstructions of climatic conditions.

High-resolution active-source seismic surveys target the stratigraphic and structural configuration of the mid-Venosta Valley, which hosts two mega fans located at the confluence between the Adige River and its tributaries: the Gadria-Strimm fan and the Lasa fan. We aimed at imaging with high detail: 1) the postglacial sediment accumulation within the fans, 2) the characteristics of Adige river deposits, and 3) the stratigraphic/structural relationships among fans, alluvial deposits and top of the bedrock (i.e. Otztal- Ortles-Campo Nappe units). Alluvial and debris-flow fan environments often pose significant challenges to high-resolution seismic exploration , due to the high heterogeneity and the rugged topography of the near surface. We processed our data by integrating first-arrivals refraction tomography with Common Midpoint, and Common Reflection Surface seismic reflection techniques. All methods produced complementary results which allowed us reaching a well-constrained imaging of the internal architecture of the Quaternary sedimentary cover, as well as of the geometry of the hosting bedrock surface. Our result show that the sedimentary record investigated by our profiles is nested in a strongly asymmetrical valley geometry, suggesting that the tectonic forcing associated with the contact between Otztal- Ortles-Campo Nappe units has interacted closely with fluvial and/or glacial valley incision over the past millennia. We provide also a quantitative estimation of the overall thickness of sediment accumulation in the valley and allow to evaluate the complex postglacial sediment dynamics between the Adige River and the Gadria and Lasa fans, with the Gadria system playing a dominant role in terms of sediment supply.

We reconstruct the post-Last Glacial Maximum (LGM) evolution of the upper Adige River floodplain, Eastern Italian Alps. In particular, we are interested in constraining the time scales associated with fan building and understanding how the relevant sediment supply at tributary confluences has interacted with the Adige River to form the present landscape configuration. By combining high-resolution seismic imaging with drillhole data and radiocarbon dating, we show (i) that ~80% of the valley fill was deposited in post-LGM times, (ii) that sediment evacuation from tributaries began with local deglaciation at the end of the Younger Dryas; and (iii) that tributary basin aspect and size, by controlling the local pattern of deglaciation, may have delayed fan building by up to two millennia. Debris-flow sediment supply from the Gadria-Strimm system drove the evolution of this valley segment between 12 and 6.25 k.y. B.P., first deflecting, then damming the course of the Adige River, forming a lake, and affecting the shape and size of the neighboring fans. Our data show an anisotropic development of the Gadria fan, with growth focused on the central and eastern portion of the fan between 10 and 8.5 k.y. B.P., followed by gradual lateral shifting toward west for about the next two millennia. The estimated sediment yield associated with the fan formation describes a debris flow-driven paraglacial sedimentary wave that conforms to the conceptual model originally proposed by Church and Ryder (1972), but never tested before in upland basins with empirical data. The wave lasted for ~4 k.y. and around 9 k.y. B.P. peaked at ~390,000 m3yr-1. At the valley profile scale, results suggest that similar fans functioned as effective sediment traps, which prevented, and still limit, fluvial reworking and valley floor incision. We argue that these geomorphic barriers, which have enhanced fragmentation of the valley long profile, with knickpoints located at major tributary fans, have delayed postglacial landscape recovery until today. © 2018 Geological Society of America.

Across the northern European Alps, a long tradition of Quaternary studies has constrained post-LGM (Last Glacial Maximum) landscape history. The same picture remains largely unknown for the southern portion of the orogen. In this work, starting from existing 10Be exposure dating of three boulders in Val Viola, Central Italian Alps, we present the first detailed, post-LGM reconstruction of landscape (i.e., glacial, periglacial and paraglacial) response south of the Alpine divide. We pursue this task through Schmidt-hammer exposure-age dating (SHD) at 34 sites including moraines, rock glaciers, protalus ramparts, rock avalanche deposits and talus cones. In addition, based on the mapping of preserved moraines and on the numerical SHD ages, we reconstruct the glacier extent of four different stadials, including Egesen I (13.1 ± 1.1 ka), Egesen II (12.3 ± 0.6 ka), Kartell (11.0 ± 1.4 ka) and Kromer (9.7 ± 1.4 ka), whose chronologies agree with available counterparts from north of the Alpine divide. Results show that Equilibrium Line Altitude depressions (ΔELAs) associated to Younger Dryas and Early Holocene stadials are smaller than documented at most available sites in the northern Alps. These findings not only support the hypothesis of a dominant north westerly atmospheric circulation during the Younger Dryas, but also suggest that this pattern could have lasted until the Early Holocene. SHD ages on rock glaciers and protalus ramparts indicate that favourable conditions to periglacial landform development occurred during the Younger Dryas (12.7 ± 1.1 ka), on the valley slopes above the glacier, as well as in newly de-glaciated areas, during the Early Holocene (10.7 ± 1.3 and 8.8 ± 1.8 ka). The currently active rock glacier started to develop before 3.7 ± 0.8 ka and can be associated to the Lobben oscillation. Four of the five rock avalanches dated in Val Viola cluster within the Early Holocene, in correspondence of an atmospheric warming phase. By contrast, the timing of the main Val Viola rock avalanche, 7.7 ± 0.3 ka during the Holocene Thermal Optimum, suggests a possible causal linkage to permafrost degradation. Overall, Schmidt-hammer proved to be an effective, inexpensive and versatile tool for improving the spatial resolution of Val Viola post-LGM landscape history, starting from existing numerical age constrains.

Rock avalanches are large flow-like movements of fragmented rock that can cause extensive and rapid topographic changes, for which very few quantitative data are available. This paper analyses the geomorphological and hydrological impact of the 3 million m 3 Thurwieser rock avalanche (2004, Italian Central Alps) by using Terrestrial Laser Scanner, airborne Lidar and GNSS data collected from 2005 to 2014. Sediment yield with respect to the normal valley regime, the dynamic and mass balance of affected glaciers, and the reorganization of superficial and groundwater flow networks are quantified. In the middle portion of the avalanche deposit, a natural sediment trap collected sediments from a new stream channel developed along the upper portion of the deposit and from a lateral drainage basin. This made possible to assess the 10-year impact of the rock avalanche on the sediment yield, which increased from about 120 to about 400 t km − 2 ·a − 1 . The rock avalanche partially covered a glacier with a shallow debris layer that acted as a thermal insulator, limiting ice ablation and producing a 10-m high scarp between the free surface of the glacier and the debris-covered portion. A reduction of 75% of ice ablation was observed due to thermal insulation. The rock avalanche filled a tributary valley, splitting the original drainage basin in two. Under ordinary flows, seepage occurs within the avalanche deposit along the old valley axis. During high flow conditions, a new stream channel is activated along the middle and lower margin of the deposit, which has produced a new alluvial fan on the main valley floor. The fan evolution is described up to the present volume of about 2000 m 3 .

We examine preliminary data from a landslide inventory that combines the mapping of landslides and deep-seated gravitational slope deformations (DSGSDs) in Val di Sole, eastern Central Alps, Italy. Landslide identification and classification was conducted via interpretation of sequential airphotos (API), LiDAR shaded-relief rasters. Landslide geometries were measured in the field for a sample of events. Seeking to evaluate landslide-driven sediment flux, we consider landslides as sediment sources and we classify them into rapid, full-mobility failures and slow, partial-mobility ones. The corresponding sediment flux, solely associated with rapid failures, exhibits clear lithologic controls, with metamorphic rocks displaying markedly higher landslide activity. DSGSDs occur exclusively in metamorphic terrain and landslides tend to cluster around them. Accordingly, these large-scale slope deformations could play a prominent role in modulating the contemporary landslide sediment flux. In the compilation of the inventory, the use of LiDAR and airphotos did not prove to be mutually exclusive. We recommend the two methodologies be employed in an integrated framework. © Springer-Verlag Berlin Heidelberg 2013.