Physically based dynamic run-out modelling for quantitative debris flow risk assessment: a case study in Tresenda,northern Italy

Quantitative landslide risk assessment requires information about the temporal, spatial and intensity probability of hazardous processes both regarding their initiation as well as their run-out. This is followed by an estimation of the physical consequences inflicted by the hazard, preferentially quantified in monetary values. For that purpose, deterministic hazard modelling has to be coupled with information about the value of the elements at risk and their vulnerability. Dynamic run-out models for debris flows are able to determine physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk can suffer an impact. These results can then be applied for vulnerability and risk calculations. Debris flow risk has been assessed in the area of Tresenda in the Valtellina Valley (Lombardy Region, northern Italy). Three quantitative hazard scenarios for different return periods were prepared using available rainfall and geotechnical data. The numerical model FLO-2D was applied for the simulation of the debris flow propagation. The modelled hazard scenarios were consequently overlaid with the elements at risk, represented as building footprints. The expected physical damage to the buildings was estimated using vulnerability functions based on flow depth and impact pressure. A qualitative correlation between physical vulnerability and human losses was also proposed. To assess the uncertainties inherent in the analysis, six risk curves were obtained based on the maximum, average and minimum values and direct economic losses to the buildings were estimated, in the range of 0.25–7.7 million €, depending on the hazard scenario and vulnerability curve used.     

Ecosystem-based marine spatial management: Review of concepts, policies, tools, and critical issues

Conventional sectoral management and piecemeal governance are considered less and less appropriate in pursuit of sustainable development. Ecosystem based marine spatial management (EB-MSM) is an approach that recognizes the full array of interactions within an ecosystem, including human uses, rather than considering single issues, species, or ecosystem services in isolation. Marine spatial planning and ocean zoning are emerging concepts that can support EB-MSM. EB-MSM is driven by high-level goals that managers aim to achieve through the implementation of measures. High-level goals and objectives need to be translated into more operational objectives before specific targets, limits and measures can be elaborated.Monitoring, evaluation and adaptation are necessary to ensure that marine management measures are both effective and efficient. Solid monitoring frameworks are the foundation of adaptive management, as they provide the necessary information to evaluate performance and the effectiveness of management actions. Marine protected areas (MPAs) - possibly set up in networks - constitute a key component in EB-MSM policies and practises and have been applied as a cornerstone in conservation of marine biodiversity, management of fish populations, development of coastal tourism, etc. Moreover, MPA experiences have provided methods and concepts (such as zoning) to a wider EB-MSM context. The assignment of values to biophysical features of the marine environment allows the direct assessment of related management choices and may assist EB-MSM.A range of monetary valuation techniques have been proposed to reduce attributes of goods and services to a single metric. However, in the marine environment such an approach is often over simplistic, and thus less reductive techniques may be necessary. Rather than producing a single metric, the results of non-monetary assessments guide policy allowing weight to be given as necessary to potential areas of conflict and consensus.Strategies to take into account climate change effects and geohazard risks in EB-MSM have been applied or proposed worldwide. EB-MSM regimes must be alert to such risks and flexible to account for changes.     

A simple DEM assessment procedure for gully system analysis in the Lake Manyara area,northern Tanzania

Gully erosion is a major threat concerning landscape degradation in large areas along the northern Tanzanian Rift valley. It is the dominant erosion process producing large parts of the sediments that are effectively conducted into the river network. The study area is located in the Lake Manyara—Makuyuni River catchment, Arusha, northern Tanzania. During fieldwork, we measured topographic data of eight gully systems close to Makuyuni Town. The main focus of this study is to assess gully erosion dynamics using improved DEMs with original resolutions of 30 and 20 m, respectively. We assessed terrain characteristics to extract information on environmental drivers. To improve the DEM, we integrated information deduced from satellite images as well as from acquired GPS field data. Topographic indices such as Stream Power Index or Transport Capacity Index were derived from the re-interpolated DEM. To evaluate gully evolution, we assessed also the longitudinal slope profiles. Finally, the gully evolution phases of each gully were classified according to the concept proposed by Kosov et al. (Eksperimental’naya geomorfologiya, vol 3. Moscow University, Moskva, pp 113–140, 1978). The re-interpolated DEMs revealed a positive response especially for the more developed gullies. We show that the extraction of information on this spatial process scale based on “low-resolution” data is feasible with little additional fieldwork and image interpretation. In fact, areas identified as having a greater risk of gully erosion have been confirmed by observations and surveys carried out in the field.     

The Th/La and Sm/La conundrum of the Tethyan realm lamproites

The Oligocene–Pleistocene Tethyan Realm Lamproites, from the Mediterranean to Himalayas, have a clear subduction-related signature and represent one of the most exotic and rare ultrapotassic mantle-derived magmas. They share the major element and mineralogical characteristics of the lamproite clan rocks, but clearly define a distinct subgroup with respect to within-plate lamproites on the basis of a number of key trace element ratios and radiogenic isotopes. The most striking characteristic of the Tethyan Realm Lamproites is the positive correlation between Th/La (up to > 1.5) and Sm/La (up to > 0.3), which is opposite to what observed in subduction-related magmas worldwide and cannot be reconciled with typical slab recycling processes. The geochemical conundrum of the Tethyan Realm Lamproites requires a component with high Sm/La and Th/La (hence named SALATHO), in addition to a normal K₂O–rich sediment melt component (with low Th/La and Sm/La). The Pb isotope composition of the Tethyan Realm Lamproites also displays a mixing array from a normal sediment melt component to a high ²⁰⁸Pb/²⁰⁶Pb and low ²⁰⁶Pb/²⁰⁴Pb end-member that can be reconciled with the SALATHO component. This end-member requires a history of high time-integrated κ? (²³²Th/²³⁸U) and low time-integrated μ (²³⁸U/²⁰⁴Pb) and ought to be older than some hundreds of million years.We propose a multi-stage process for the formation of the mantle sources of the Tethyan Realm Lamproites related to the tectonic mélange domains (i.e. chaotic mixture of depleted peridotite, basalt, and sediment) accreted to the Eurasia plate during the collisional events of the northward drifting continental slivers from Gondwana. In a first stage, the mélange domains experienced high P and low T metamorphism with segregation and stabilisation of lawsonite and zoisite/epidote veins, which potentially match the geochemical characteristics required by the SALATHO component. Successively, the subduction of the Neotethys and Alpine Tethys oceanic plates produced normal K₂O-rich sediment melts that migrated through the mantle wedge and metasomatised the depleted lithospheric mantle blocks within the chaotic mélange, forming a clinopyroxene–phlogopite vein network. Eventually, the Tertiary orogenic belt collapses triggered the onset of low-degree melting of the low-solidus fractions within the mélange domains, producing lamproitic magmas.     

Lake levels in the southern Bolivian Altiplano (19°–21°S.) during the Late Glacial based on diatom studies

This study is focused on the endorheic Uyni-Coipasa Basin located in the southern Bolivian Altiplano. Stratigraphical and fossil diatom studies based on a detailed radiocarbon chrnology revealed six phases in water-level changes and paleosalinity variations. At 15,430±80 yr B.P., lacustrine conditions settled in the southern Bolivian Altiplano. A saline lake, characterized by benthic meso-metasaline species, reached +4 m altitude above the present bottom of the basin. After 15,430±80 yr B.P., the level rapidly rose to +27 m, as suggested by a tychoplanktonic mesosaline flora. Between 14,500 years and 13,000 years, finely lanminated sediments at +32 m contained successively a dominance of epiphytic mesosaline to hypersaline species and tychoplanktonic oligosaline diatoms, indicating weak fluctuations in water-level and salinity. At 13,000 years, strong changes in the diatom flora occurred; epiphytic oligo-hypersaline diatoms were replaced by planktonic meso-polysaline species. They indicate a deep salt lake (the lake reached +100 m). After 12,000 years, the lake level abruptly dropped, as suggested by fluviatile sediments with a benthic mesopolysaline diatom flora. The main lake was replaced by shallow saline ponds. A wet pulse occurred at 11,400 years, characterized by low water level (+7 m) and high salinity. This lacustrine phase remained until 10,400 yr B.P. These data indicate changes in Precipitation minus Evaporation (P-E). Our regional interpretations are based on a comparison with teh available data on the northern (Lake Titicaca) and southern (Lipez are) Bolivian Altiplano and on the northern Chilean Altiplano (Atacama Desert).     

Local Holocene environmental indicators in Upper Mesopotamia: Pedogenic carbonate record vs. archaeobotanical data and archaeoclimatological models

It has been suggested that pedogenic carbonate coatings on stones in archaeological sites can be used to reconstruct late Quaternary environmental changes in the area of the Fertile Crescent. This research compares a pedogenic carbonate record from southeastern Turkey with three other local or regional sources of palaeoenvironmental information in order to evaluate the correlation of this new proxy with other independent data from the area: (1) ancient plant macroremains from archaeological sites as ecological indicators, (2) stable carbon isotope composition of ancient plant macroremains available in the literature and from our own investigations in six mid-Holocene archaeological sites, and (3) modelled Holocene precipitation and temperature changes in the northern Fertile Crescent. Comparison involved selected palynological and isotopic data from lacustrine sediments as well as speleothem isotopic records in Near Eastern locations available in the literature. Although the data show a certain amount of variation of proxy records on the regional scale, for the northern Fertile Crescent (Upper Mesopotamia) they suggest three pronounced features of the Holocene environmental history: (1) a trend toward warmer temperatures may have affected the area during the early Holocene (between ca. 10,000–6000 cal BP), (2) increased moisture availability and relatively high temperatures in the mid-Holocene (ca. between 5000 and 4000 cal BP), and (3) a significant decrease in moisture availability around 4000 cal BP.Further research is needed to enhance the chronological resolution of both pedogenic carbonate and plant macrofossil records. This study stresses the complexity of the Holocene palaeogeography of the Near East and underlines the need for careful analysis of local sources of palaeonvironmental information in the region.     

A comparative analysis of three habitat suitability models for commercial yield estimation of Tapes philippinarum in a North Adriatic coastal lagoon (Sacca di Goro, Italy)

Habitat Suitability (HS) models have been extensively used by conservation planners to estimate the spatial distribution of threatened species and of species of commercial interest. In this work we compare three HS models for the estimation of commercial yield potential and the identification of suitable sites for Tapes philippinarum rearing in the Sacca di Goro lagoon (Italy) on the basis of six environmental factors. The habitat suitability index (HSI) is based on expert opinion while the habitat suitability conditional (HSC) is calibrated on observational data. The habitat suitability mixed (HSM) model is a two-part model combining expert knowledge and regression analysis: the first component of the model uses logistic regression to identify the areas in which clams are likely to be present; the second part applies the same parameter-specific suitability functions of the HSI model only in the areas previously identified as productive by the logistic component.The HS models were validated on an independent data set and estimates of potential yield of the Goro lagoon were compared. The effectiveness of the three approaches is then discussed in terms of predicted yield and identification of suitable sites for farming.     

Boron recycling in the continental crust of the central Andes from the Palaeozoic to Mesozoic, NW Argentina

Whole-rock chemical composition and ¹¹B/¹⁰B isotope ratios in tourmaline was investigated to study the geochemical recycling of boron during the evolution of the Andean basement from the Palaeozoic to Mesozoic. In the basement (Cambrian to Ordovician high-grade paragneisses, migmatites and orthogneisses, the Eocambrian Puncoviscana Formation, and Paleozoic-Mesozoic granitoid igneous rocks) whole-rock B contents are generally below 100 ppm, but B contents of ˜1 wt% are found in cogenetic aplite and pegmatite dikes and in tourmaline–quartz rocks. In the metasedimentary rocks, no systematic variation in B content because of metamorphic grade and no correlation of B with other incompatible elements are apparent. Tourmalines from the high-grade metamorphic basement yield δ¹¹B values ranging from −11.2 to −6.8‰ and isotope fractionation during migmatisation was small. Metamorphic tourmalines from the Puncoviscana Formation have δ¹¹B values between −6.3 and −5.8‰. The calculated (corrected for fractionation) δ¹¹B values of −6 to −2‰ for the sedimentary protolith of the metamorphic basement indicate a continental B source with subordinate marine input. Tourmalines from Palaeozoic and Mesozoic granitoids display an identical range of δ¹¹B values from −12 to −5.3‰ and indicate a similarly homogeneous B source throughout time. Tourmalines from pegmatites and tourmaline–quartz rocks record the average δ¹¹B values of the parental granitic magma. We assume that B in the Palaeozoic and Mesozoic granitoids is derived from the local metamorphic basement supporting the hypothesis that recycling of the lower Palaeozoic crust is the dominant process in granitic magma formation from Palaeozoic to Mesozoic. Received: 15 December 1999 / Accepted: 11 July 2000