Short-term geomorphological evolution of the Poggio Baldi landslide upper scarp via 3D change detection

On 19 March 2010, a 4 million m³ landslide occurred at Poggio Baldi, a small village in the Santa Sofia municipality, central Apennines (Forlì-Cesena, Italy). The landslide caused severe damages to some homes and obstructed both the SS310 national road and the Bidente river. The Poggio Baldi landslide arose in the “Marnoso-Arenacea Romagnola” formation composed of a pelitic-arenaceous turbiditic sequence. The landslide was classified as a rotational landslide, evolving into a partially confined flow-like landslide and causing the reactivation of the deposit of a previous landslide that took place in 1914. This paper reports a study of the phenomena currently occurring on the 100-m high main scarp of this landslide complex. The aim of the study was to assess ground changes that occurred on the upper scarp from 2015 to 2018 and to infer a preliminary evolutionary model capable of supporting short-term landslide scenarios. For this purpose, multi-station terrestrial laser scanner surveys were performed in 2015, 2016, 2017, and 2018. Additionally, an unmanned aerial vehicle three-dimensional photogrammetric survey was carried out in 2016. Analyses of the three-dimensional digital models of the main scarp made it possible to carry out several exhaustive multi-temporal investigations and to derive a detailed three-dimensional change detection scheme for it. The results showed an active geomorphological evolution of the rock scarp area due to frequent rockfalls and topples (of the order of a few m³), with significant local volume changes (a few thousand m³/year) and with potential implications for the long-term evolution of the entire slope.

     

Assessing soil erosion hazard in a key badland area of Central Italy

In this work, an integrated methodology was applied to assess the water erosion hazard in Upper Orcia Valley, an area of Southern Tuscany (Italy), greatly affected by severe denudation processes, that caused the development of widespread badlands. Prediction of areas prone to calanchi badland development was carried out by applying a susceptibility assessment method based on conditional statistical analysis, preceded by a bivariate statistical analysis aimed at selecting the most influential causal factors of erosion. Water erosion rates at badland sites were estimated by means of an empirical statistical method, implemented to evaluate the erosion intensity (Tu denudation index) and based on some geomorphic parameters as independent variables. This methodology allows associating the denudation intensity to the spatial prediction. The validation procedure, based on a random partition of calanchi badland areas, confirmed the efficiency of the spatial zonation of the erosion hazard values. Moreover, the comparison of the estimated erosion rates with the results of decadal investigations on denudation processes affecting the study area, performed by different monitoring methods, showed the effectiveness of the estimation model. These results allowed concluding that the proposed procedure represents a useful tool to be applicable for soil protection strategy planning in land management of Mediterranean areas characterized by similar morphoclimatic features, even when direct erosion rate measures are not available.     

Antarctic shallow water benthos in an area of recent rapid glacier retreat

The West Antarctic Peninsula is one of the fastest warming regions on Earth. Faster glacier retreat and related calving events lead to more frequent iceberg scouring, fresh water input and higher sediment loads, which in turn affect shallow water benthic marine assemblages in coastal regions. In addition, ice retreat creates new benthic substrates for colonization. We investigated three size classes of benthic biota (microbenthos, meiofauna and macrofauna) at three sites in Potter Cove (King George Island, West Antarctic Peninsula) situated at similar water depths but experiencing different disturbance regimes related to glacier retreat. Our results revealed the presence of a patchy distribution of highly divergent benthic assemblages within a relatively small area (about 1 km²). In areas with frequent ice scouring and higher sediment accumulation rates, an assemblage mainly dominated by macrobenthic scavengers (such as the polychaete Barrukia cristata), vagile organisms and younger individuals of sessile species (such as the bivalve Yoldia eightsi) was found. Macrofauna were low in abundance and very patchily distributed in recently ice‐free areas close to the glacier, whereas the pioneer nematode genus Microlaimus reached a higher relative abundance in these newly exposed sites. The most diverse and abundant macrofaunal assemblage was found in areas most remote from recent glacier influence. By contrast, the meiofauna showed relatively low densities in these areas. The three benthic size classes appeared to respond in different ways to disturbances likely related to ice retreat, suggesting that the capacity to adapt and colonize habitats is dependent on both body size and specific life traits. We predict that, under continued deglaciation, more diverse, but less patchy, benthic assemblages will become established in areas out of reach of glacier‐related disturbance.     

Analysis of Ground Deformation Detected Using the SBAS-DInSAR Technique in Umbria, Central Italy

Ground deformation affecting the Umbria region (central Italy) in the 9-year period from 1992 to 2000 was investigated through multi-temporal Differential Synthetic Aperture Radar Interferometry (DInSAR). For the purpose, the Small BAseline Subset (SBAS) technique was adopted, which allows studying the temporal evolution of the detected deformation at two spatial scales: a low-resolution (regional) scale, and a full-resolution (local) scale. For the analysis, SAR data acquired by the European Remote Sensing (ERS-1/2) satellites along ascending and descending orbits were used. The detected deformation was analysed to investigate its relevance to geophysical, geomorphologic, and human-induced processes that may result in hazardous conditions to the population of Umbria. Low-resolution deformation data were used to: (i) determine the amount of displacement caused by the Umbria-Marche earthquake sequence from September 1997 to April 1998 in the Foligno area, (ii) determine the number and percentage of the known landslides that can be monitored by the DInSAR technology in the investigated area, and (iii) identify and measure subsidence induced by exploitation of a confined aquifer in the Valle Umbra. Results indicate that earthquakes moved through the Foligno area westwards up to 3.9 cm and with an uplift reaching 1.7 cm. Intersection in a GIS of the low-resolution deformation maps with a detailed landslide inventory map allowed the determination that the portion of landslides that can be monitored by the SBAS-DInSAR technique in Umbria ranges from 2.7% to 3.4%, and the percentage of the total landslide area ranges from 10.4% to 12.8%. In the Valle Umbra, a dependency was found between the time and the amount of detected ground deformation, and the record of water withdrawal. The full-resolution deformation data were used to investigate the movement of the Ivancich landslide, in the Assisi Municipality. Joint analysis of the spatial and the temporal characteristics of the ground displacement allowed the formulation of a hypothesis on the landslide geometry and deformation pattern.     

Seismic response of bridge piers on pile groups for different soil damping models and lumped parameter representations of the foundation

This paper presents a wide parametric study aimed at elucidating the influence, on the computed seismic response of bridge piers, of two related aspects of the model: (1) the adoption of the classical hysteretic or the causal Biot's damping models for the soil and (2) the use of two different lumped parameter models of different complexity and accuracy to approximate the impedances of the pile foundation. A total of 2072 cases, including different superstructures, pile foundations, soil deposits, and seismic input signals, are studied. The results are presented so that the influence of the different parameters involved in the analysis can be assessed. From an engineering point of view, both lumped parameter models provide, in general, sufficiently low errors. The choice of the most adequate model for each case will depend not only on the configuration of the structure and the soil-foundation system but also on the assumed soil damping model, whose influence on the computed seismic responses is relevant in many cases. The nonphysical behaviour provided by the classical hysteretic damping model for the soil at zero frequency generates issues in the process of fitting the impedance functions. It is also found that larger deck displacements are predicted by Biot's model due to the higher damping at low frequencies provided by the classical hysteretic damping model.     

Evolutionary convergence of the highly adapted desert rodent Tympanoctomys barrerae (Octodontidae)

Octodontid rodents have a long evolutionary history in arid landscapes of South America. The red vizcacha rat, Tympanoctomys barrerae , is a monotypic, micro-endemic species that inhabits salt pan-sand dune habitats in west-central Argentina. Its natural history is almost unknown. We present an analysis of the ecology, morphology, behavior, and physiology of the red vizcacha rat and assess the overall degree of convergence of this species with rodents that inhabit similar habitats in different deserts. Our results show that Tympanoctomys barrerae is highly adapted to salt flat basin habitats. Its diet of halophytic vegetation with a high salt content, and physiological and anatomical traits related to salt consumption, are similar to those found in some members of the families Heteromyidae (Dipodomys microps) of North America, and Muridae (Psammomys obesus and Rhombomys opimus) of Africa and Asia. Similarities include feeding behavior, diet composition, kidney morphology, and urine concentration, among other traits. Tympanoctomys barrerae is more similar to these desert rodents than it is to confamilials that do not feed on halophytes.     

Silicic magmas from the continental Cameroon Volcanic Line (Oku, Bambouto and Ngaoundere): 40Ar-39Ar dates, petrology, Sr-Nd-O isotopes and their petrogenetic significance

The intraplate Cameroon Volcanic Line (CVL) straddles the African-South Atlantic continent-ocean boundary and is composed mainly of alkaline basic volcanic rocks. Voluminous silicic volcanics characterize the continental sector of the CVL. We present here new geochemical, isotopic (Sr-Nd-O) and ⁴⁰Ar/³⁹Ar geochronological data on the main silicic volcanic centres of the Western (Mt. Oku, Sabga and Mt. Bambouto) and Eastern (Ngaoundere plateau) Cameroon Highlands. The silicic volcanism of Mt. Oku, Sabga and Mt. Bambouto occurred between 25 and 15 Ma and is represented by voluminous quartz-normative trachytes and minor rhyolitic ignimbrites. At Mt. Bambouto central volcano about 700 m of silicic volcanics erupted in less than 2.7 million years. These silicic volcanics are associated with slightly to moderately alkaline basalts and minor basanites. In general, onset of the silicic volcanism migrated from NE (Oku: 25 Ma) to SW (Sabga: 23 Ma; Bambouto: 18 Ma; and Mt. Manengouba: 12 Ma). The silicic volcanism of the Ngaoundere plateau (eastern branch of the CVL) is instead dominated by nepheline-normative trachytes which are associated with strongly alkaline basalts and basanitic rocks. These Ne-trachytes are younger (11-9 Ma) than the Q-trachytes of the Western Highlands. The least differentiated silicic volcanics are isotopically similar (⁸⁷Sr/⁸⁶Sr < 0.70380; ¹⁴³Nd/¹⁴⁴Nd > 0.51278) to the associated alkaline basalts suggesting differentiation processes without appreciable interaction with crustal materials. Such interactions may, however, have played some role in the genesis of the most evolved silicic volcanics which have ⁸⁷Sr/⁸⁶Sr as high as 0.705–0.714. Fractional crystallization is the preferred mechanism for genesis of the silicic melts of both Western and Eastern Highlands, as shown by modeling major and trace element variations. The genesis of the least evolved Q-trachytes from the Western Highlands, starting from slightly to moderately alkaline basalts, is compatible with fractionation of dominantly plagioclase, clinopyroxene and magnetite. Crystal fractionation may have occurred at low pressure and at QFM buffer f _O2conditions. Parental magmas of the Ngaoundere Ne-trachytes are likely instead to have been strongly alkaline basalts which evolved through crystal fractionation at higher P (6-2 kbar) and f _O2 (QFM + 2). The migration (25 to 12 Ma) of the silicic volcanism from NE to SW in the continental sector of the CVL is reminiscent of that (31-5 Ma) of the onset of the basic volcanism in the oceanic sector (Principe to Pagalu islands) of the CVL. These ages, and that (11-9 Ma) of the silicic volcanism of the Ngaoundere plateau, indicate that the Cameroon Volcanic Line as a whole may not be easily interpreted as the surface expression of hot-spot magmatism. Received: 24 February 1998 / Accepted: 22 September 1998     

Spatial and temporal patterns in the movement of Procambarus clarkii, an invasive crayfish

Introduced in Italy in the 1980s for aquaculture enterprises, the red swamp crayfish, Procambarus clarkii, has invaded many water bodies, giving rise to breeding populations that now threaten freshwater ecosystems. An understanding of the spatial behaviour of this crayfish could be the baseline for future research aimed at control and management. Following the same pattern as other freshwater decapods, P. clarkii, studied in an irrigation ditch system in Florence, Tuscany, displayed stationary phases (several marked individuals were recaptured in the area) interposed with nomadic bursts of movement (many marked crayfish disappeared). With a few exceptions, nocturnal activity prevailed in almost all the seasons in two different analysed habitats (irrigation ditches and the Massaciuccoli Lake, Lucca). However, in the laboratory, locomotion occurred mostly at daytime. Although still prevailing, P. clarkii's nocturnal activity appeared puzzling, because some of its major predators are nocturnal and this species is mostly herbivorous. The intercalation between stationary and wandering phases leaves open further promising studies on social structures in the field.     

Sub-basalt seismic imaging using optical-to-acoustic model building and wave equation datuming processing

The presence of highly heterogeneous basalt layers has a detrimental effect on seismic imaging of underlying structures. Due to the prevalence of basalt, the challenge of imaging below basalts impinges on a broad spectrum of geological problems, from hydrocarbon exploration to volcano seismology. Both internal basalt characteristics and rough interfaces can degrade the sub-basalt image quality. In this paper we investigate the effects of both internal and surface heterogeneity on the wavefield. Using highly heterogeneous models of basalts derived from optical imagery and borehole sonic logs, combined with wave simulations to generate synthetic data, we explore the causes of poor sub-basalt imagery. We establish the significant role that surface roughness plays in the imagery problem and demonstrate, through a novel application of wave equation datuming, how to suppress its effect. The methodology demonstrated herein may be applicable in any environment where heterogeneous surface structures/interfaces severely degrade seismic image quality.