Neogene and quaternary volcanism of the Bijar Area (Western Iran)

In the Bijar region (Western Iran) two distinct volcanic cycles have been recognized. The first, of Upper Miocene age, consists of high-K cale-alkaline volcanic rocks interpreted as final products of the cale-alkaline Tertiary phase of central Iran. The second volcanic cycle, mostly of Pleistocene age (0.5–1.3 m.v.) consists of undersaturated, mainly potassic, alkaline products. As the lavas of this last phase are slightly fractionated, the chemical differences shown by these rocks have been interpreted as primitive features related to the physical conditions governing the partial melting in the mantle and/or the mantle heterogeneity. In a volcanic center (Sarajukh volcano) contemporaneous basic and acid magmas have been found, and interpreted as derived from two different and independent sources. The alkaline basic volcanism is considered as an expression of disjunctive processes that have affected the western margin of the Iranian plate after the Pliocene.     

Isoseismals of the strongest Friuli aftershocks of September 1976

Summary Isoseismal maps of the three strongest Friuli aftershocks of September 1976 were compiled using the contributions from European countries within the shaken area. The characteristic features of the macroseismic fields are discussed.     

Seismotectonic models and CN algorithm: The case of Italy

The CN algorithm is utilized here both for the intermediate term earthquake prediction and to validate the seismotectonic model of the Italian territory. Using the results of the analysis, made through the CN algorithm and taking into account the seismotectonic model, three main areas, one for Northern Italy, one for Central Italy and one for Southern Italy, are defined. Two transition areas between the three main areas are delineated. The earthquakes which occurred in these two areas contribute to the precursor phenomena identified by the CN algorithm in each main area.     

Copula-based mixed models for bivariate rainfall data: an empirical study in regression perspective

A comprehensive parametric approach to study the probability distribution of rainfall data at scales of hydrologic interest (e.g. from few minutes up to daily) requires the use of mixed distributions with a discrete part accounting for the occurrence of rain and a continuous one for the rainfall amount. In particular, when a bivariate vector (X, Y) is considered (e.g. simultaneous observations from two rainfall stations or from two instruments such as radar and rain gauge), it is necessary to resort to a bivariate mixed model. A quite flexible mixed distribution can be defined by using a 2-copula and four marginals, obtaining a bivariate copula-based mixed model. Such a distribution is able to correctly describe the intermittent nature of rainfall and the dependence structure of the variables. Furthermore, without loss of generality and with gain of parsimony this model can be simplified by some transformations of the marginals. The main goals of this work are: (1) to empirically explore the behaviour of the parameters of marginal transformations as a function of time scale and inter-gauge distance, by analysing data from a network of rain gauges; (2) to compare the properties of the regression curves associated to the copula-based mixed model with those derived from the model simplified by transformations of the marginals. The results from the investigation of transformations’ parameters are in agreement with the expected theoretical dependence on inter-gauge distance, and show dependence on time scale. The analysis on the regression curves points out that: (1) a copula-based mixed model involves regression curves quite close to some non-parametric models; (2) the performance of the parametric regression decreases in the same cases in which non-parametric regression shows some instability; (3) the copula-based mixed model and its simplified version show similar behaviour in term of regression for mid-low values of rainfall. An erratum to this article can be found at     

When do rock glacier fronts fail? Insights from two case studies in South Tyrol (Italian Alps)

The fronts of two rock glaciers located in South Tyrol (Italian Alps) failed on 13 August 2014, initiating debris flows in their downslope channels. A multimethod approach including climate, meteorological, and ground temperature data analysis, aerial image correlation, as well as geotechnical testing and modeling, led to the reconstruction of the two events. An integrated investigation of static predisposing factors, slowly changing preparatory factors, and potential triggering events shed light on the most likely reasons for such failures. Our results suggest that the occurrence of front destabilization at the two rock glaciers can only partly be explained by the occurrence of heavy rainfall events. Indeed, antecedent hydrological and thermal ground conditions were characterized by a saturated active layer favored by a snow-rich winter and extensive precipitation in late spring and summer. Also, the rising trend of air temperature during spring and summer months since 1950s might explain the concurrent marked displacement of the two rock glaciers. Indeed, geotechnical investigations have provided strong indications that one of the investigated rock glacier fronts was at a marginally stable state prior to 2014. As rainfall events more intense than the one that occurred in August 2014 were previously recorded in the same area without resulting failures at the studied rock glaciers, we propose that both predisposing and preparatory destabilizing factors have played a key role in the 2014 rock glacier front failures.     

Sediment transport at the network scale and its link to channel morphology in the braided Vjosa River system

In this article we apply the CASCADE network-scale sediment connectivity model to the Vjosa River in Albania. The Vjosa is one of the last unimpaired braided rivers in Europe and, at the same time, a data scarce environment, which limits our ability to model how this pristine river might respond to future human disturbance. To initialize the model, we use remotely sensed data and modeled hydrology from a regional model. We perform a reach-by-reach optimization of surface grain size distribution (GSD) and bedload transport capacity to ensure equilibrium conditions throughout the network. In order to account for the various sources of uncertainty in the calculation of transport capacity, we performed a global sensitivity analysis. The modeled GSD distributions generated by the sensitivity analysis generally match the six GSDs measured at different locations within the network. The modeled bedload sediment fluxes increase systematically downstream, and annual fluxes at the outlet of the Vjosa are well within an order of magnitude of fluxes derived from previous estimates of the annual suspended sediment load. We then use the modeled sediment fluxes as input to a set of theoretically derived functions that successfully discriminate between multi-thread and single-thread channel patterns. This finding provides additional validation of the model results by showing a clear connection between modeled sediment concentrations and observed river morphology. Finally, we observe that a reduction in sediment flux of about 50% (e.g., due to dams) would likely cause existing braided reaches to shift toward single thread morphology. The proposed method is widely applicable and opens a new avenue for application of network-scale sediment models that aid in the exploration of river stability to changes in water and sediment fluxes.     

Can we tell more than we can know? The limits of bivariate drought analyses in the United States

The joint occurrence of extreme hydroclimatic events, such as simultaneous precipitation deficit and high temperature, results in the so-called compound events, and has a serious impact on risk assessment and mitigation strategies. Multivariate frequency analysis (MFA) allows a probabilistic quantitative assessment of this risk under uncertainty. Analyzing precipitation and temperature records in the contiguous United States (CONUS), and focusing on the assessment of the degree of rarity of the 2014 California drought, we highlight some critical aspects of MFA that are often overlooked and should be carefully taken into account for a correct interpretation of the results. In particular, we show that an informative exploratory data analysis (EDA) devised to check the basic hypotheses of MFA, a suitable assessment of the sampling uncertainty, and a better understanding of probabilistic concepts can help to avoid misinterpretation of univariate and multivariate return periods, and incoherent conclusions concerning the risk of compound extreme hydroclimatic events. Empirical results show that the dependence between precipitation deficit and temperature across the CONUS can be positive, negative or not significant and does not exhibit significant changes in the last three decades. Focusing on the 2014 California drought as a compound event and based on the data used, the probability of occurrence strongly depends on the selected variables and how they are combined, and is affected by large uncertainty, thus preventing definite conclusions about the actual degree of rarity of this event.     

Erodibility of soft freshwater sediments in Markermeer: the role of bioturbation by meiobenthic fauna

The Markermeer is a large and shallow man-made freshwater lake in the Netherlands, characterized by its high turbidity. As part of a study aiming to mitigate this high turbidity, we studied the water–bed exchange processes of the lake’s muddy bed. The upper centimeter’s–decimeter’s of the lake bed sediments mainly consists of soft anoxic mud. Recent measurements have proved the existence of a thin oxic layer on top of this soft anoxic mud. This oxic layer, which is much easier to be eroded than the anoxic mud, is believed to be related with Markermeer’s high-turbidity levels. Our hypothesis is that the thin oxic layer develops from the anoxic mud, enhanced by bioturbation. Actually, we will demonstrate that it is the bioturbated state of the bed that increases its erodability, and not the oxidation state of the sediments. In particular, we will refer to bioturbation caused by meiobenthic fauna. The objective of this study is therefore to determine the influence of the development of the thin oxic layer on the water–bed exchange processes, as well as to establish the role of bioturbation on those processes. This is done by quantifying the erosion rate as a function of bed shear stresses, and at different stages of the development of the oxic layer. Our experiments show that bioturbation increases the rate at which Markermeer sediments are eroded by almost an order of magnitude. The short-term fine sediment dynamics in Markermeer are found to be driven by the complex and highly dynamic interactions between physics, chemistry, and biology. Finally, the long-term fine sediment dynamics are driven by the erosion of the historical deposits in the lake’s bed, which is only possible after bioturbation, and which leads to an increase of the stock of sediments in the lake’s muddy bed.     

How natural are Alpine mountain rivers? Evidence from the Italian Alps

Historical, human‐induced channel adjustments in lowland gravel‐bed rivers have been documented in several geographical contexts worldwide. In particular, it is now widely accepted that the vast majority of European rivers are far from any natural, reference state prior to anthropic disturbances, and a ‘complete’ restoration is hardly achievable. However, few investigations have addressed changes that have occurred in mountain rivers of the Alps, and these channels are commonly reckoned quite ‘natural’ by society. This paper intends to describe how human pressure on Italian Alpine basins has been quite relevant for several centuries – in terms of land‐use variations, in‐channel structures, timber transport (splash damming) and riparian vegetation management – such that nowadays ‘reference conditions’ cannot be found even in small mountain creeks. In addition, recent natural climatic variations (e.g. the Little Ice Age) are superimposed on human disturbances, thus defying the definition of any ‘equilibrium’ morphological conditions even under ‘human‐free’ states. A summary of published as well as unpublished works on historical channel adjustments in rivers of the Italian Alps is presented in order to document the impacts deriving from human pressure at different basin scales and for different river morphologies, from steep confined streams to large unconfined rivers. General options for river management and restoration actions aiming to combine geomorphological functionality and flood hazard mitigation are discussed, in the light of the current European legislative context. Copyright © 2011 John Wiley & Sons, Ltd.