The March 25 and 29, 2016 landslide-induced debris flow at Clapar,Banjarnegara, Central Java

The Clapar landslide induced debris flow consisted of the Clapar landslide occurred on 24 March 2017 and the Clapar debris flow occurred on 29 March 2017. The first investigation of the Clapar landslide induced debris flow was carried out two months after the disaster. It was followed by UAV mapping, extensive interviews, newspaper compilation, visual observation and field measurements, and video analysis in order to understand chronology and triggering mechanism of the landslide induced debris flow in Clapar. The 24 March 2016 landslide occurred after 5 hours of consecutive rainfall (11,2 mm) and was affected by combination of fishponds leak and infiltration of antecedent rain. After five days of the Clapar landslide, landslide partially mobilized to form debris flow where the head scarp of debris flow was located at the foot of the 24 March 2016 landslide. The Clapar debris flow occurred when there was no rainfall. It was not generated by rainstorm or the surface erosion of the river bed, but rather by water infiltration through the crack formed on the toe of the 24 March 2016 landslide. Supply of water to the marine clay deposit might have increased pore water pressure and mobilized the soil layer above. The amount of water accumulated in the temporary pond at the main body of the 24 March 2016 landslide might have also triggered the Clapar debris flow. The area of Clapar landslide still shows the possibility of further retrogression of the landslide body which may induce another debris flow. Understanding precursory factors triggering landslides and debris flows in Banjarnegara based on data from monitoring systems and laboratory experiments is essential to minimize the risk of future landslide.     

High-resolution atmospheric forcing for regional oceanic model: the Iroise Sea

This study was aimed at modeling, as realistically as possible, the dynamics and thermodynamics of the Iroise Sea by using the Model for Applications at Regional Scale (MARS), a regional ocean 3D model. The horizontal resolution of the configuration in use is 2 km with 30 vertical levels. The 3D model of the Iroise Sea is embedded in a larger model providing open boundary conditions. As regards the atmospheric forcing, the originality of this study is to force the regional ocean model with the high-resolution (6 km) regional meteorological model, Weather Research and Forecasting (WRF). In addition, as the air surface temperature is highly sensitive to the sea surface temperature (SST), this regional meteorological model is improved by taking into account a regional climatologic SST to compute meteorological parameters. By allowing a better coherence between the SST and the temperature of the atmospheric boundary layer while giving a more realistic representation of heat fluxes exchanged at the air/sea interface, this forcing constitutes a noticeable improvement of the Iroise Sea modeling. The different sensitivity tests discussed here pinpoint the importance of entering, in WRF, SST data of sufficiently high quality before the computation of meteorological forcing when the aim is a study of dynamics and thermodynamics far away from the coast. On the other hand, when the target is the reproduction of coastal small-scale features in Iroise Sea modeling, the resolution of the meteorological forcing and the quality of SST are both paramount. The simulation of reference was carried out throughout the Summer and Autumn of year 2005 to allow comparisons with a campaign of surface current measurements by high-frequency radars conducted at the same period.     

Contribution of long-term hydrothermal experiments for understanding the smectite-to-chlorite conversion in geological environments

The smectite-to-chlorite conversion is investigated through long-duration experiments (up to 9 years) conducted at 300 °C. The starting products were the Wyoming bentonite MX80 (79 % smectite), metallic iron and magnetite in contact with a Na–Ca chloride solution. The predominant minerals in the run products were an iron-rich chlorite (chamosite like) and interstratified clays interpreted to be chlorite/smectite and/or corrensite/smectite, accompanied by euhedral crystals of quartz, albite and zeolite. The formation of pure corrensite was not observed in the long-duration experiments. The conversion of smectite into chlorite over time appears to take place in several steps and through several successive mechanisms: a solid-state transformation, significant dissolution of the smectite and direct precipitation from the solution, which is over-saturated with respect to chlorite, allowing the formation of a chamosite-like mineral. The reaction mechanisms are confirmed by X-ray patterns and data obtained on the experimental solutions (pH, contents of Si, Mg, Na and Ca). Because of the availability of some nutrients in the solution, total dissolution of the starting smectite does not lead to 100 % crystallization of chlorite but to a mixture of two dominant clays: chamosite and interstratified chlorite/smectite and/or corrensite/smectite poor in smectite. The role of Fe/(Fe + Mg) in the experimental medium is highlighted by chemical data obtained on newly formed clay particles alongside previously published data. The newly formed iron-rich chlorite has the same composition as that predicted by the geothermometer for diagenetic to low-grade metamorphic conditions, and the quartz + Fe-chlorite + albite experimental assemblage in the 9-year experiment is close to that fixed by water–rock equilibrium.     

A catalog of tsunamis in New Caledonia from 28 March 1875 to 30 September 2009

In order to establish a tsunami alert system in New Caledonia in April 2008, the French Secretary of State for Overseas Affairs, with the aid of the UNESCO French Commission, mandated an investigation to build a more complete record of the most recent tsunamis. To complete this task, a call for witnesses was broadcast through various media and in public locations. These witnesses were then interviewed onsite about the phenomenon they had observed. Previous witness reports that had been obtained in the last few years were also used. For the most recent events, various archives were consulted. In total, 18 events were documented, of which 12 had not been previously mentioned in past work. These results confirm an exposure to a hazard of: (1) local origin (the southern part of the Vanuatu arc) with a very short post-seismic delay (< 30 min) before the arrival of wave trains; (2) regional origin (Solomon Islands arc, northern part of the Vanuatu arc) with a delay of several hours; and (3) an exposure to trans-oceanic tsunamis (Kamchatka 1952, South Chile 1960, Kuril Islands 2006, North Tonga 2009), unknown until today. These results highlight the necessity for New Caledonia to adopt an alert system, coupled with ocean tide gauges, that liaises with the main alert system for the Pacific (Pacific Tsunami Warning Center), and brings to light the importance of establishing a prevention campaign.     

Extreme Nd isotope homogeneity in a large rhyolitic province: the Estérel massif, southeast France

 Previous detailed studies of large rhyolite bodies propose that their elemental and isotopic characteristics were largely acquired in shallow crustal magma chambers. This model explains the common chemical and isotopic zonations of large volumes of rhyolites as well as the less common chemical and isotopic homogeneity of such bodies. We report an intermediate situation (the Estérel massif, southeast France) in which chemical variations contrast with Nd-isotope homogeneity. We thus infer that, in this case, large volumes of rhyolite resided for enough time in shallow magma chambers to develop chemical zonations through differentiation, but this process was not accompanied by crustal assimilation. The subordinate amount of mafic rocks cropping out in the Estérel probably evolved from basalt to trachyte through assimilation and fractional crystallization. The relatively radiogenic Nd-isotope signatures of the rhyolite compared with the Hercynian crust show that it cannot have been generated by partial melting of exposed basement rocks. Several geological similarities with large rhyolitic provinces could suggest that the rhyolite was purely mantle derived or, alternatively, generated by partial melting of an ad hoc crustal component. However, mineralogical, geochemical, and geodynamic connections between the Estérel rhyolite and the hypersolvus anorogenic granites of Corsica, as well as the extreme Nd-isotope homogeneity of the rhyolite, lead us to propose that the rhyolite was generated by mixing between mantle-derived magmas and a mafic lower crust. This scenario accounts for the relatively radiogenic Nd-isotope signatures of the rhyolite compared with the Hercynian crust. The good Nd-isotope homogeneity observed in the rhyolite implies that the mixing process, which occurred in the deep crust, was complete and provided a shallow magma chamber with isotopically and probably chemically homogeneous magmas. Received: 5 December 1997 / Accepted: 16 June 1998     

An interpretation of the nitrogen deficiency in comets

We propose an interpretation of the composition of volatiles observed in comets based on their trapping in the form of clathrate hydrates in the solar nebula. The formation of clathrates is calculated from the statistical thermodynamics of Lunine and Stevenson (1985, Astrophys. J. Suppl. 58, 493-531), and occurs in an evolutionary turbulent solar nebula described by the model of Hersant et al. (2001, Astrophys. J. 554, 391-407). It is assumed that clathrate hydrates were incorporated into the icy grains that formed cometesimals. The strong depletion of the N₂ molecule with respect to CO observed in some comets is explained by the fact that CO forms clathrate hydrates much more easily than does N₂. The efficiency of this depletion, as well as the amount of trapped CO, depends upon the amount of water ice available in the region where the clathration took place. This might explain the diversity of CO abundances observed in comets. The same theory, applied to the trapping of volatiles around 5 AU, explains the enrichments in Ar, Kr, Xe, C, and N with respect to the solar abundance measured in the deep troposphere of Jupiter [Gautier et al 2001a] and [Gautier et al 2001b].     

Keck AO observations of Io in and out of eclipse

We present adaptive optics (AO) observations of Io taken with the W.M. Keck II telescope on 18 December 2001 (UT) before the satellite went into eclipse, and while it was in Jupiter's shadow. Making these kind of Io-in-eclipse observations, as well as the associated data reduction and analysis are challenging; hence one focus of the paper is to explain the methods and tools used for these data sets. For the sunlit images Io itself was used as the wavefront reference source, while nearby Ganymede was used as reference ‘star’ when Io was in eclipse. Observations were obtained in K′-, L′-, and M-bands. The sunlit images have been deconvolved using MISTRAL. The Io-in-eclipse data were deconvolved with IDAC and MISTRAL. The former gives better results, both in absolute photometry and in matching the original images. We determined the flux densities of the hot spots from the original Io-in-eclipse data with StarFinder, as well as from the deconvolved images by integrating the intensity over the relevant areas. We determined the highly anisoplanatic PSF via a FFT method from the original data, and used this in StarFinder and as a starting PSF for IDAC and MISTRAL. We derived temperatures and areal coverage of all 19 spots detected in both K′- and L′-band images of Io-in-eclipse. We also determined temperatures and areal coverage of the hot spots visible on the L′- and M-band images of sunlit Io. Most volcanoes contain a compact hot ‘core’ (?10 km² at 600-800 K) within a larger area at lower temperatures (e.g., ∼10²-10⁴ km² at 300-500 K). The total heat flow contributed by these active volcanoes is 0.2 W m⁻², ∼8% of the average global heat flow measured at 5-20 μm by Veeder et al. [J. Geophys. Res. 99 (1994) 17095].     

Estimating rockfall release frequency from blocks deposited in protection barriers,growth disturbances in trees,and trajectory simulations

Landslides - The spatial and temporal quantification of rockfall frequency remains a major challenge in mountain environments, especially also in terms of rockfall management. Approaches that have...     

Formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river

Feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors. We describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized Isère River in France. The channel was laterally confined with embankments and mostly straightened. From the beginning of the 1970s to the end of the 1990s, alternate bars were progressively but heavily colonized by vegetation. This context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions. Based on a GIS analysis of aerial photographs (between 1948 and 1996), we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age, size and mobility. Field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars. A highly significant statistical association of geomorphological and vegetation variables (RV of co-inertia analysis = 0.41, p < 0.001) explained 95% of the variability in just one axis, supporting the existence of very strong feedback between geomorphological changes (i.e. the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest, and vegetation succession). Such dynamics reflect the fluvial biogeomorphological successions model, as described by the authors earlier. © 2020 John Wiley & Sons, Ltd.     

Seismic velocity models for an internally asymmetric Mars

The well-known dichotomy in topography, surface age, and crustal structure between the northern lowlands and the southern uplands of Mars has been explained by both endogenic and exogenic processes. According to the used model this asymmetry might be a result of a certain mechanism of core fommation influencing the following planetary evolution. Therefore it has been assumed that the present internal structure of Mars is characterized by different velocity-depth distributions of the mantle for the northern and southern hemisphere, respectively. For both regions significant differences in travel times of seismic waves were calculated. These results may be important for the future seismic exploration of Mars.