To describe the sedimentary signal delivered at catchment outlets, many authors now refer to the concept of connectivity. In this framework, the sedimentary signal is seen as an emergent organization of local links and interactions. The challenge is thus to open the black boxes that remain within a sediment cascade, which requires both accurate geomorphic investigations in the field (reconstruction of sequences of geomorphic evolution, description of sediment pathways) and the development of tools dedicated to sediment cascade modeling. More precisely, the development of tools devoted to the study of connectivity in geomorphology is still in progress, although graph theory offers promising perspectives (Heckmann and Schwanghart, 2013). In this paper, graph theory is applied to abstract the network structure of sediment cascades, keeping only the nodes (sediment sources, sediment stores, outlet) and links (linkage by a transportation agent), represented as vertices and edges. From the description of the assemblages of sedimentary flows, we provide three main indices to explore how small-scale processes may result in significant broad-scale geomorphic patterns. The main hypothesis guiding this work is that the network structure dictates how sediment inputs from various sources interact at tributary junctions and finally at the outlet of a cascading system. First, we use the flow index to assess the potential contribution of each node to the sediment delivery at the outlet. Second, we measure the influence of each node regarding how it is accessible from both sediment sources and the outlet (using the Shimbel index). Third, we propose a new connectivity index named Network Structural Connectivity index (NSC) revealing whether the potential contribution of a node is lower or higher than expected from its location within the network. These indices are first computed for a conceptual sediment cascade network and then applied to a catchment located in the southern French Alps. We demonstrate that this index may be used to simulate sediment transfer and help in identifying the hotspots of geomorphic change. In the present case, we try to predict how a sediment cascade may be impacted by an edge disruption or a reconnection.

Three decades after the early definition of the "paraglacial" concept, a general model of paraglaciation was established, integrating the typical sediment paraglacial cascading system and the responses of associated sediment storages. The residuals of this model should now be examined and explained through controlling factors that may act at both regional (e.g. tectonics) and local (topography, lithology, etc.) scales. We compare here the patterns identified in a few mountain ranges of the northern hemisphere, located in various seismotectonic settings (especially western Alps, northwestern Scotland, central Norway, Svalbard and Iceland). By combining our field observations with a literature review, the effectiveness of the paraglacial response on mountain-slope erosion and the contribution of paraglaciation to the sedimentary cascading system are discussed. In most cases, paraglaciation generates sediment storage and aggradation in headwaters and glacial trough, as the evacuation rate into sinks remains low. Finally, paraglaciation appears to be a period of hillslope denudation, preparing reservoirs of sediments, which can only be effectively evacuated during further glaciation periods.

Studies on large and rapid mass movements have become a challenging issue in relation to paraglacial and morpho-tectonic evolution of mountain slopes. Rockfalls, rockslides and rock avalanches will be considered here on the basis of selected sites in the French and Swiss Alps and in the Himalayas. The main topics developed relate firstly to the modes of emplacement of, and the internal structures observed in, the body of the runout deposits and the influence of the surface (bedrock, superficial deposits, glacier, lake) over which the propagation takes place. The impacts of these rockslope failures on geomorphic systems (damming effects, storage, control on sediment fluxes) are then considered. Finally, the possible influence of climate change on high-alpine rockwalls, and potential threat to adjacent inhabited areas, are presented.

While the resilience of French vineyards is currently threatened, this paper focuses on the Beaujolais terroir, where the disappearance of vineyards has been qualitatively observed by local stakeholders. A targeted survey was led at three complementary scales. First, we provide an overview of the evolution of agricultural landscapes and practices for the whole Beaujolais area since 1990 from national statistical databases. It shows that the vineyard extent reached a maximum during the 1990s and that significant bifurcation occurred in 2000. Second, we document land use evolution in relation to vineyard abandonment at a more local scale. Three case studies (lower Ardières, Marverand, Merloux) exemplify the main local settings, and the land uses are described over time from an analysis that employed multitemporal photo interpretation. The results quantified the decrease in the vineyard surface extent since 1999: approximately 30% was lost in regular terroirs and 5% was lost in high added-value terroirs. Third, at a fine scale, we explained the precise location of the abandoned parcels regarding the site characteristics (e.g., incoming solar radiation, slope gradient, terroir quality). The results showed differences in evolution patterns between southern and northern Beaujolais. In northern Beaujolais, winegrowers tended to abandon vine parcels that were considered of lower quality; while, in southern Beaujolais, the winegrowers tended to abandon vine parcels in relation to the difficulty of maintenance (remote and steep parcels were preferentially abandoned) or in relation to suburbanization (parcels close to built-up areas were preferentially abandoned).

La formalisation des cascades sédimentaires à l’intérieur d’un bassin-versant constitue l’un des champs de recherche actuels de la géomorphologie. Depuis les études pionnières sur ces systèmes ouverts, leur inefficacité à exporter les sédiments produits dans les bassins-versants a été observée, de même que la complexité avec laquelle s’organisent les flux sédimentaires dans le temps. Résumés dans des concepts tels que le sediment delivery problem ou la sedimentological anarchy, ces deux constats ne restent que très partiellement compris. Après avoir effectué une synthèse des questions relatives au fonctionnement des cascades sédimentaires, nous proposons dans cet article de considérer ces objets comme un réseau, pour lequel des outils d’analyse issus de la théorie des graphes ou de la simulation par compartiments peuvent être appliqués. Les méthodes mobilisées aident à l’exploration des cascades sédimentaires, et notamment à la mise en évidence d’effets réseaux, c’est-à-dire la mesure d’une contribution nette du réseau au volume de flux « toute chose égale par ailleurs ». Appliquées à un bassin-versant alpin, ces méthodes illustrent que les propriétés de connexité et de connectivité des cascades sédimentaires peuvent expliquer leur inaptitude structurelle à exporter des sédiments.