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Slow moving landslides are widespread geomorphological features in the Northern Apennines of Italy where they represent one of the main landscape forming processes. The lithology of the Northern Apennines fold and thrust belt is characterized by alternations of sandstone, siltstone and clayshales, also known as flysch, and clay shales with a chaotic block in matrix fabric, which are often interpreted as tectonic or sedimentary melanges. While flysch rocks with a high pelitic fraction host earthslides that occasionally evolve into flow like movements, earthflows are the dominant landslide type in chaotic clay shales. In the present work, we document the kinematic response to rainfall of landslides in these different lithologies using radar interferometry. The study area includes three river catchments in the Northern Apennines. Here, the Mediterranean climate is characterized by two wet seasons during autumn and spring respectively, separated by dry summers and winters with moderate precipitation. We use SAR imagery from the X-band satellite COSMO SkyMed and from the C-band satellite Sentinel 1 to retrieve spatial displacement measurements between 2009 and 2016 for 25 landslides in our area of interest. We also document detailed temporal and spatial deformation signals for eight representative landslides, although the InSAR derived deformation signal is only well constrained by our dataset during the years 2013 and 2015. In spring 2013, long enduring rainfalls struck the study area and numerous landslide reactivations were documented by the regional authorities. During 2013, we measured higher displacement rates on the landslides in pelitic flysch formations compared to the earthflows in the clay shales. Slower mean velocities were measured on most landslides during 2015. We analyse the temporal deformation signal of our eight representative landslides and compare the temporal response to precipitation. We show that earthslides in pelitic flysch formations accelerate faster than earthflows in chaotic clay shales and reach higher velocities, while the kinematic behaviour of the earthflows can be described as rather steady with only minor accelerations. Although we have no detailed pore pressure measurements for the period of interest, the observed behaviour can be explained in our view by the morphological and hydrological characteristics of the different landslide types. On the one hand landslide material and bedrock in the pelitic flysch rocks are more resistant, which is why slope angles are higher in this lithology. On the other hand, landslides in the pelitic flysch formations have often deeper slip surfaces and landslide material is more permeable. This is why long persistent rainfall is necessary to saturate the landslide material and induce pore pressures that are high enough to trigger displacement.

In the Dolomitic region, abundant coarse hillslope sediment is commonly found at the toe of rocky cliffs. Ephemeral channels originate where lower permeability bedrock surfaces concentrate surface runoff. Debris flows initiate along such channels following intense rainfall and determine the progressive erosion and deepening of the channels. Sediment recharge mechanisms include rock fall, dry ravel processes and channel-bank failures. Here we document debris flow activity that took place in an active debris flow basin during the year 2015. The Cancia basin is located on the southwestern slope of Mount Antelao (3264 m a.s.l.) in the dolomitic region of the eastern Italian Alps. The 2.5 km2 basin is incised in dolomitic limestone rocks. The data consist of repeated topographic surveys, distributed rainfall measurements, time-lapse (2 s) videos of two events and pore pressure measurements in the channel bed. During July and August 2015, two debris flow events occurred, following similarly intense rainstorms. We compared rainfall data to existing rainfall triggering thresholds and simulated the hydrological response of the headwater catchment with a distributed model in order to estimate the total and peak water discharge. Our data clearly illustrate how debris entrainment along the channel is the main contributor to the overall mobilized volume and that erosion is dominant when the channel slope exceeds 16°. Further downstream, sediment accumulation and depletion occurred alternately for the two successive events, indicating that sediment availability along the channel also influences the flow behaviour along the prevailing-transport reach. The comparison between monitoring data, topographical analysis and hydrological simulation allows the estimation of the average solid concentration of the two events and suggests that debris availability has a significant influence on the debris flow volume. © 2020 John Wiley & Sons, Ltd.

Landscape evolution in active mountain chains can be dominated by gravitational slope movements. This is observed in a large portion of the Reno river catchment, Apennines, Italy, where weak rocks, such as clayshales, are subject to earthflows that control hillslope morphology and supply sediments to the channel network. In this paper, we evaluate the sediment flux generated by earthflows and compare it with Holocene-averaged deposition rates to assess the contribution of mass movements to landscape evolution. Present-day hillslope sediment flux is estimated by combining measured displacement rates (72 inclinometers) and spatial attributes of earthflows and historical frequency of reactivations. Averaged sediment yield (~ 1.6 x 10 3 t/km 2 /yr) compares well with similar studies on earthflow-dominated landscapes, despite notable differences in methodology. In the study area, the connectivity between hillslopes and the stream network is well developed and no significant sediment sinks influence the sediment transport processes. We document best estimates of regional sediment fluxes and related uncertainties, based on available data. Coarse limestone fragments, present in the clayshales, are used as a natural sediment tracer to allow a comparison with sedimentation rates taking place at the mouth of the intramontane catchment. Here, available borehole logs, 14 C datings and stratigraphic correlations of the alluvial fan are used to obtain an estimate of the deposition that took place during Holocene times. Taking also into account the role of solute transport, sedimentation rates are compared to earthflow sediment production rates. Results show a good agreement and demonstrate that earthflows are the primary mass wasting process in these weak rock lithologies. We document best estimates of regional sediment fluxes and related uncertainties. Present earthflow sediment production outpaces Holocene-averaged sedimentation rates by a factor of two. The gap between sediment production and deposition can be partly justified by uncertainties associated with our estimates and by time-scale differences. With this respect, the dynamic equilibrium between erosion and deposition, is likely affected by intra-Holocene oscillations at a short time scale (10 to 1 ky) attributable to climate variability. Terraced deposits documenting sedimentary episodes would also support such interpretation.

A method proposed for delineating lahar-hazard zones in volcanic valleys is adapted to debris flows. The original method is based on two predictive equations that relate the lahar volume to the cross-sectional inundated area and to the planimetric inundated area. These predictive equations were derived by combining a scaling analysis of lahar kinematics with the statistical analysis of data for 27 historical lahars. This paper tests the applicability of this approach to debris flow fans. Forty debris flow basins in the Italian Alps were surveyed, and data on 27 historical debris flow events were collected in the field or by means of aerial-photo analysis. Collected data reveal that the flow area ( A ) and the planimetric area ( B ) of a debris flow are linearly correlated to the debris flow volume ( V ) on a logarithmic scale, with high statistical significance. Moreover, the computed regression equations are very similar to those obtained from other published datasets on debris flows, leading to the global fitting equations A = 0.08 V 2 / 3 and B = 17 V 2 / 3 . These predictive equations are then implemented in an automated code (DFLOWZ) that delineates the inundated area on a debris flow fan on the basis of a user-specified debris flow volume, taking the statistical uncertainty in the prediction into account. DFLOWZ is simple reproducible, and it can handle both confined and unconfined flow. The model is tested against 10 historical debris flow events, providing a satisfactory agreement between observed and computed inundated areas. In spite of the limitations due to DEM accuracy and statistical uncertainty of the regression parameters, test results show that the method can be useful for practical applications.

The topographic evolution of mountain chains is fundamentally dictated by the balance of erosional and tectonic processes. In the Northern Apennines, several questions about the late Holocene to present deformation style and uplift rates are still open. We consider a typical NE facing drainage basin, focusing on all the geomorphic markers capable of supplying direct or indirect information regarding tectonic forcing on the landscape. Characteristics of altitude and relief, drainage pattern, river profile and fluvial response expressions were found to be in good agreement, indicating that the most recent tectonic activity consists of a general persistent uplift of the chain, associated with an extensional regime, where different sectors are distinguished through differential uplift. Such differences have been found to act both along and transverse to the chain, causing similar coherent patterns of response in erosional processes. The geomorphology of the catchment displays several features, which together with the long sustained tectonic forcing indicate the near-attainment of a dynamic equilibrium between the rates of tectonic forcing and erosional processes, creating steady-state topography.

In this work we describe the deployment of a probabilistic model for landslide occurrence to support the decisional process within the Civil Protection Agency of the Emilia-Romagna Region (Italy). The model is based on the Bayes’ theorem and computes the conditional probability to have a landslide in response to a rainfall event of given duration and intensity. Unlike most the methods used to date to define rainfall thresholds, our probabilistic approach takes into account of the uncertainty in the data and provides a quantitative assessment of the threshold reliability. The model was recently applied to evaluate the landslide probability in the Emilia-Romagna region, taking advantage of the landslide historical archive that includes about 3,000 landslides whose date of occurrence is known with daily accuracy. For the operational use, we fitted the isolines of landslide probability on the rainfall duration-intensity plane and created two easy-to-read probability charts useful at two different scales: the rain gauge reference area (about 65 km2) and the regional alert zone (about 2,600 km2). The user combines the rainfall data recorded by the automated rain gauge network and the rainfall forecasts to characterize the rainfall event, and plot the rainfall path on the probability charts to evaluate the probability of failure. A sample application of the model is described.

The importance of preserving Italian hilltop towns through a general geotechnical strategy is discussed and is followed by a specificreview of the hydrogeologicalconditions responsible for regional mass movements at ancient hilltop towns in Basilicata. A historical survey of reactivations in colluvial deposits at selected sitesin the region suggested that increased activity was taking place in response to extreme rainfall events, possibly related to long-term climatic changes. The importance of natural and anthropogenic processes along critical hydrogeological boundary conditions in relation to this activity is then reviewed and one example of urban landsliding from Grassano in the Basento valley is described. Local structure, such as faulting, was shown to be especially important in the location of both groundwater discharge (springs) and the landsliding. The landslide activity in the town was also shown to be related to a period of population expansion and possible domestic water leakages following the provision of a pumped supply. It is suggested that these anthropogenic processes reduce the usefulness of empirical links between landslide frequency, rainfall extremes or other explanations involving climatic change. Finally, a strategy for landslide management based on the use of hydrogeological conceptual models and GIS technology is proposed.

Diverse sources of information, which describes landslide movement, hillslope-channel connectivity and sedimentation rates, are analyzed to detect trends that took place during the last 12,000 years. We estimate the landslide-related sediment production rates by combining measured landslide velocities and geometries and historical landslide frequency. Coarse sediment deposition rates are measured throughout the Holocene by means of dating and stratigraphy of the alluvial fan and terraced deposits. The comparison between present-day hillslope sediment production and Holocene averaged sediment deposition rates confirms that landsliding is the main agent conveying sediments to higher order trunk streams. The connectivity between hillslopes and the stream network is well developed and no significant sediment sinks influence the sediment transport process. However fluctuations of sediment delivery rates at the outlet of the catchment took place during Holocene and are likely associated to periods of increased hillslope sediment production and channel discharge caused by climatic forcing.

Clay-shales largely outcrop in the Northern Apennines of Italy, where they are associated with frequent and widespread landslide activity. The paper presents the results of monitoring activities carried out in two field-sites and focused on the hydrology of clay-shales prone to landsliding. In the monitored slopes, the water table is close to the ground surface throughout the year, with seasonal fluctuations of tens of centimetres to a couple of metres. Shallow weathered soils, or clay cover, and unaltered material exhibit a much different behaviour. Although responses to single rainfalls are clearly identifiable as pressure pulses in the clay cover, they are never observed in the underlying parental clay-shales where downward gradients indicate recharge and only long-term seasonal fluctuations are recorded. Short-term variations of pressure head in the clay cover are ruled by downward propagation of a pressure wave in saturated conditions. More than 400 pore-pressure responses collected in the two sites are analysed in terms of lag time, rate and amount of pressure increase and timing of pressure peaking. It emerges that the linear diffusion theory can satisfactorily explain the observed behaviour. In deeper unaltered material, the barometric effect influences the measures similarly to what is observed in confined aquifers. After its removal, the corrected data exhibit regular seasonal fluctuations which are used to estimate the diffusivity of the material based on phase-lag and attenuation of the downward propagating long-term periodic pulse. Copyright © 2011 John Wiley & Sons, Ltd.

Debris flow initiation by channel bed mobilization is a common process in high mountainous areas. Initiation is more likely to occur at the outlet of small, steeply sloping basins where concentrated overland flow feeds an ephemeral channel incised in slope deposits. Such geological conditions are typical of the Dolomite region (Italian Alps), which is characterized by widespread debris flow activity triggered by severe summer thunderstorms. Real-time data and field observations for one of these catchments (Acquabona catchment, Belluno, Italian Alps) were used to characterize the hydrological response of the initiation area to rainfalls of varying intensity and duration. The observed behaviour was then reproduced by means of a simple hydrological model, based on the kinematic wave assumption, to simulate the generation of channel runoff. The model is capable of predicting the observed hydrological response for a wide range of rainfall impulses, thus providing a physical basis for the understanding of the debris flow triggering threshold.

In 1997 a field monitoring system was installed in Acquabona Creek in the Dolomites (Eastern Italian Alps) to observe the hydrologic conditions for debris flow occurrence and some dynamic properties of debris flow. The monitoring system consists of three remote stations: an upper one located at the head of a deeply-incised channel and two others located downstream. The system is equipped with sensors for measuring rainfall, pore pressures in the mobile channel bottom, ground vibrations, debris flow depth, total normal stress and fluid pore-pressure at the base of the flow. Two video cameras record events at the upper channel station and one video is installed at the lowermost station. During summer 1998, three debris flows (volumes from less than 1000 m3 up to 9000 m3) occurred at Acquabona. The following results were obtained from a preliminary analysis of the data: 1) All of the flows were triggered by rainfalls of less than 1 hour duration, with peak rainfall intensities ranging from 4.8 to 14.7 mm / 10 minute. 2) Debris flows initiated in several reaches of the channel, including the head of the talus slope. 3) The initial surges of the mature flows had a higher solid concentration and a lower velocity (up to 4 m/s) than succeeding, more dilute surges (more than 7 m/s). 4) Total normal stress and pore fluid pressures measured at the base of the flow. (mean depth about 1.1 m) were similar (about 15 kPa), indicating a completely liquefied flow. 5) Peak flows entrained debris at a rate of about 6 m 3/m of channel length and channel bed scouring was proportional to the local slope gradient and was still evident in the lower channel where the slope was 7°.