Implications of geomorphological research for recent and prehistoric avalanches and related hazards at Huascaran,Peru

Detailed research of superficial deposits below the northern peak of Huascaran (Cordillera Blanca) provides new information on the limits of a paleo-avalanche originating from this mountain. Geomorphological mapping of the sediments identified glacial deposits, deposits from historical rock-debris avalanches and huge boulders from a paleo-avalanche. Schmidt Hammer rock-hardness tests were used to distinguish between the several generations of rock-debris avalanches, but largely failed to distinguish between the much older moraine and the paleo-avalanche sediments. Thus, only the field geomorphological mapping proved to be reliable for identifying the limits of the paleo-avalanche. The limits identified as granite boulders deposited over volcanic rocks were found to extend 30 m further up the opposite valley slope than previously had been mapped. This larger extent implies a greater volume and/or greater mobility for the prehistoric event.     

Rock displacement and thermal expansion study at historic heritage sites in Slovakia

The paper discusses the results of the research devoted to the preservation of cultural heritage carried out within last two decades in Slovakia. The aim of the study depended on monitoring of selected castle rocks showing instability problems due to extremely slow displacements of creep character. Apart from traditional methods of investigation at one test site (Spis Castle), authors implemented in their work the study of thermal expansion of the rocks as a result of seasonal periodic temperature changes having potential influence on displacements and numerical modeling in order to understand better the landslide failure mechanism. The results obtained from all study sites confirmed that even slow movements have to be implemented into preservation and stabilization works in order to safeguard the sites of great historic value.     

Deep Structure and Dynamics of Passive Continental Margin from Shelf to Ocean of the Northern South China Sea

To study the deep dynamic mechanism leading to the difference in rifting pattern and basin structure from shelf to oceanic basin in passive continental margin,we constructed long geological sections across the shelf,slope and oceanic basin using new seismic data.Integrated gravity-magnetic inversion and interpretation of these sections were made with the advanced dissection method.Results show that the basement composition changes from intermediate-acid intrusive rocks in the sheff to intermediate-basic rocks in the slope.The Moho surface shoals gradually from 31 km in the sheff to 22.5 km in the uplift and then 19 km in the slope and finally to 13 km in the oceanic basin.The crust thickness also decreases gradually from 30 km in the northern fault belt to 9 km in the oceanic basin.The crustal stretching factor increases from the shelf toward the oceanic basin,with the strongest extension under the sags and the oceanic basin.The intensity of mantle upwelling controlled the style of basin structures from sheff to oceanic basin.In the Zhu 1 depression on the shelf,the crust is nearly normal,the brittle and cold upper crust mainly controlled the fault development;so the combinative grabens with single symmetric graben are characteristic.In the slope,the crust thinned with a large stretching factor,affected by the mantle upwelling.The ductile deformation controlled the faults,so there developed an asymmetric complex graben in the Baiyun (白云) sag.     

Tidal exposure or microhabitats: what determines sandy‐beach nematode zonation? a case study of a macrotidal ridge‐and‐runnel sandy beach in Belgium

Lately, across‐shore zonation has been found to be more important in structuring the nematode community of a tropical macrotidal sandy beach than microhabitat heterogeneity. To evaluate whether this zonation pattern applies to a temperate beach, a macrotidal ridge‐and‐runnels sandy beach in the North Sea was studied. We investigated whether a similar zonation occurs in sandbar and runnel microhabitats, and whether the runnels harbour a different community from the subtidal. Our results indicate that nematode communities from runnel and sandbar habitats are significantly different. In addition, horizontal zonation patterns for nematode communities differ between both habitats. Nematode assemblages from sandbars are divided to lower, middle and upper beach while upper and middle runnels cluster together. The subtidal and upper runnels showed dissimilar nematode assemblages, although runnels showed the same dominant species (Daptonema normandicum), which increases its abundance towards the upper runnels. This study illustrates the importance of microhabitat heterogeneity, which resulted in different zonation patterns across the sandy beach examined. The divergent zonation between sandbars and runnels in the macrotidal temperate sandy beach, compared with the pattern observed for a subtropical sandy beach with similar morphodynamics, indicates that generalizations about nematode distribution patterns should be made with caution.     

Carry-over effects of the membrane interface probe

The membrane interface probe (MIP) is widely used to characterize the subsurface distribution of volatile organic compounds (VOCs). One problem that arises during MIP application is that disproportionately high MIP signals are obtained after passing source zones which contain mobile or residual phases. This serious problem occurs because of a carry-over effect, in particular caused by compound-specific retention times in the conventional unheated transfer line, commonly used during such an investigation. The objective of this study was to perform a qualitative methodical field evaluation of the carry-over effect of a conventional MIP system with a conventional unheated transfer line. This was achieved by coupling a mobile mass spectrometer to the MIP device. Results obtained were then further compared with those achieved using a laser induced fluorescence (LIF) system. Because of this coupling, time- and depth-dependent signals for different substances became known. Field evaluation data obtained showed complex superpositions of compounds with MIP system results. As a result of this superposition, MIP signals from the saturated zone beneath the source zone (zone with free and/or residual phase) are blurred and are therefore not representative of particular depths. However, utilizing multidirectional probing alongside conventional MIP probing (forwards and backwards), it was possible to detect the upper and lower phase boundary of the source zone. These MIP results correlated excellently with the LIF results. An important conclusion that can be drawn from the field investigation is that coupling a mobile mass spectrometer to the MIP system enables advanced MIP signal interpretation to be successfully achieved.     

Pathways of marine debris derived from trajectories of Lagrangian drifters

Global set of trajectories of satellite-tracked Lagrangian drifters is used to study the dynamics of marine debris. A probabilistic model is developed to eliminate the bias in spatial distribution of drifter data due to heterogeneous deployments. Model experiments, simulating long-term evolution of initially homogeneous drifter array, reveal five main sites of drifter aggregation, located in the subtropics and maintained by converging Ekman currents. The paper characterizes the geography and structure of the collection regions and discusses factors that determine their dynamics. A new scale R(c)=(4k/|D|)(?) is introduced to characterize tracer distribution under competing effects of horizontal divergence D and diffusion k. Existence and locations of all five accumulation zones have been recently confirmed by direct measurements of microplastic at the sea surface.     

Review of ray-Born forward modeling for migration and diffraction analysis

The ray-Born approximation is a very useful tool for forward modeling of scattered waves. The fact that ray-Born modeling underlies most seismic migration techniques, and therefore shares their assumptions, is a justification in itself to consider it for forward modeling. The ray-Born approximation does not make an explicit distinction between specular reflections and nonspecular diffractions. It therefore allows the modeling of diffractions from structural discontinuities such as edges and tips, as well as caustic diffractions. In the simplest implementation ray-Born seismograms are multiple-free. Ray-Born modeling can be orders of magnitude faster than finite-difference modeling, both in two-and three dimensions.     

Combining long- and short-term probabilistic volcanic hazard assessment with cost-benefit analysis to support decision making in a volcanic crisis from the Auckland Volcanic Field,New Zealand

By using BET_VH, we propose a quantitative probabilistic hazard assessment for base surge impact in Auckland, New Zealand. Base surges resulting from phreatomagmatic eruptions are among the most dangerous phenomena likely to be associated with the initial phase of a future eruption in the Auckland Volcanic Field. The assessment is done both in the long-term and in a specific short-term case study, i.e. the simulated pre-eruptive unrest episode during Exercise Ruaumoko, a national civil defence exercise. The most important factors to account for are the uncertainties in the vent location (expected for a volcanic field) and in the run-out distance of base surges. Here, we propose a statistical model of base surge run-out distance based on deposits from past eruptions in Auckland and in analogous volcanoes. We then combine our hazard assessment with an analysis of the costs and benefits of evacuating people (on a 1 × 1-km cell grid). In addition to stressing the practical importance of a cost-benefit analysis in creating a bridge between volcanologists and decision makers, our study highlights some important points. First, in the Exercise Ruaumoko application, the evacuation call seems to be required as soon as the unrest phase is clear; additionally, the evacuation area is much larger than what is recommended in the current contingency plan. Secondly, the evacuation area changes in size with time, due to a reduction in the uncertainty in the vent location and increase in the probability of eruption. It is the tradeoff between these two factors that dictates which cells must be evacuated, and when, thus determining the ultimate size and shape of the area to be evacuated.     

An integrated geophysical study of Vestbakken Volcanic Province, western Barents Sea continental margin, and adjacent oceanic crust

This paper describes results from a geophysical study in the Vestbakken Volcanic Province, located on the central parts of the western Barents Sea continental margin, and adjacent oceanic crust in the Norwegian-Greenland Sea. The results are derived mainly from interpretation and modeling of multichannel seismic, ocean bottom seismometer and land station data along a regional seismic profile. The resulting model shows oceanic crust in the western parts of the profile. This crust is buried by a thick Cenozoic sedimentary package. Low velocities in the bottom of this package indicate overpressure. The igneous oceanic crust shows an average thickness of 7.2 km with the thinnest crust (5–6 km) in the southwest and the thickest crust (8–9 km) close to the continent-ocean boundary (COB). The thick oceanic crust is probably related to high mantle temperatures formed by brittle weakening and shear heating along a shear system prior to continental breakup. The COB is interpreted in the central parts of the profile where the velocity structure and Bouguer anomalies change significantly. East of the COB Moho depths increase while the vertical velocity gradient decreases. Below the assumed center for Early Eocene volcanic activity the model shows increased velocities in the crust. These increased crustal velocities are interpreted to represent Early Eocene mafic feeder dykes. East of the zone of volcanoes velocities in the crust decrease and sedimentary velocities are observed at depths of more than 10 km. The amount of crustal intrusions is much lower in this area than farther west. East of the Kn?legga Fault crystalline basement velocities are brought close to the seabed. This fault marks the eastern limit of thick Cenozoic and Mesozoic packages on central parts of the western Barents Sea continental margin.