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During the last decade, sediment connectivity has been widely used and studied in many topics related to physical geography and geomorphology. It is defined as the degree of linkage of sediment fluxes between different compartments of a system, and it can be considered as a useful approach to detect changes in sediment routing also after large disturbances as, for instance, wildfires. In this study, the adaption and application of the Index of Connectivity (IC) was carried out in the Chilean catchment of Rio Toro (11 km2). The Rio Toro catchment was affected by two subsequent wildfires in 2002 and 2015, respectively. Wildfires can be considered as large disturbances that lead significant geomorphological and hydrological changes mostly due to: i) the alteration of the vegetation cover, structure and typology; ii) the changes in soil structure and moisture and iii) the increase of water repellence. In order to assess how the IC responds to these disturbances, two types of analysis have been developed in the present study: i) a multitemporal analysis from 2001 to 2018; ii) a short term analysis considering only the 2015 wildfire. The former was carried out taking advantage from freely available Landsat Multispectral Bands Image and Alos Palsar DEMs (resolution of 12.5 m), while the latter was based on Google Earth's Images and UAV dataset collected in January 2019. Thus, in the first analysis, in order to detect the general dynamics of forest cover and to compute a basic land use classification (i.e. bare soil, shrub/regrowth vegetation, native forest), the calculation of Normalized Difference Vegetation Index (NDVI) was performed. In the second analysis instead, a supervised classification on high-resolution data allowed to obtain more detailed land use classification. Furthermore, in order to determine the weighting factor in the IC model, different Manning's coefficients were derived as a parameter of resistance to sediment flux, according to the land use characteristics. Preliminary results demonstrated the applicability of this approach, permitting to better comprehend not only the changes in qualitative terms (IC), as well as the predominant changes in forest cover defining the preferential source areas that are also contributing in large wood recruitment from hillslopes to the channel network.

The balance of energy, water, and sediment fluxes exerts control over forms and processes of the landscape, and it can be continuously affected by natural and/or anthropic disturbances. Large disturbances, such as volcanic eruptions, are able to disrupt the links among different compartments of the system in which the fluxes take place. Recently, sediment connectivity indices represent powerful tools to assess the potential sediment behavior in post-disturbance scenarios, according to the structural properties of the geomorphic system itself. The objective of the present research is to adapt and apply the Index of Connectivity in a catchment affected by an explosive volcanic eruption, using a combination of field surveys and image classification techniques. Moreover, a multi-temporal analysis, which relies upon open source data, was carried out. The area of interest is located in southern Chile, where the Blanco River catchment suffered from the eruption of the nearby Chaitén volcano (2008-2009). The river network was completely filled by a huge amount of sediments, causing the entire floodplain's burial of several meters and the sudden widening of the active channel. Along the river corridor, as well as on the slopes, the old-native vegetation was removed or largely damaged. Due to the multitude of factors involved, the analysis of connectivity index was outlined through a workflow aimed at deriving a land cover-based weighting factor, representing the impedance to the sediment fluxes. A compound of field observations and satellite image classification techniques was used to implement the weighting factor derived from the Manning's n coefficient for the overland flow. The base Digital Elevation Model (DEM) with a resolution of 12.5 m is freely available on the web, as well as the Landsat images used (period 1999-2017) to derive the weighting factor. The results showed a general increase of IC values throughout the catchment after the eruption mainly related to the removal of vegetation, which facilitates the transfer of sediment fluxes. In addition, due to the widening of the active channel, the sediment source areas became more connected to the channel network. Finally, the combination of the land cover changes and active channel expansion promoted the increase of IC values all over the Blanco River catchment. The use of satellite image classification along with field observations helped the spatial characterization of structural connectivity in the densely vegetated study area. Nonetheless, further improvements to involve also the functional connectivity can not be neglected, especially in such complex environment.

This work aims at analysing variations in sediment connectivity induced by geomorphological changes in a Chilean volcanicimpacted environment. To this end a multitemporal analysis has been carried out.

The Chaitén volcanic eruption (Chile) severely modified the geomorphological settings of the Blanco River catchment. These abrupt changes can enhance or reduce the sediment connectivity between hillslope and main channel with important consequences for the downstream village.