GIS-based assessment of landslide susceptibility on the base of the Weights-of-Evidence model

The major scope of the study is the assessment of landslide susceptibility of Flysch areas including the Penninic Klippen in the Vienna Forest (Lower Austria) by means of Geographical Information System (GIS)-based modelling. A statistical/probabilistic method, referred to as Weights-of-Evidence (WofE), is applied in a GIS environment in order to derive quantitative spatial information on the predisposition to landslides. While previous research in this area concentrated on local geomorphological, pedological and slope stability analyses, the present study is carried out at a regional level. The results of the modelling emphasise the relevance of clay shale zones within the Flysch formations for the occurrence of landslides. Moreover, the distribution of mass movements is closely connected to the fault system and nappe boundaries. An increased frequency of landslides is observed in the proximity to drainage lines, which can change to torrential conditions after heavy rainfall. Furthermore, landslide susceptibility is enhanced on N-W facing slopes, which are exposed to the prevailing direction of wind and rainfall. Both of the latter geofactors indirectly show the major importance of the hydrological conditions, in particular, of precipitation and surface runoff, for the occurrence of mass movements in the study area. Model performance was checked with an independent validation set of landslides, which are not used in the model. An area of 15% of the susceptibility map, classified as highly susceptible, “predicted” 40% of the landslides.     

The December 4, 1983 to February 18, 1984 eruption of Piton de la Fournaise (La Reunion, Indian Ocean): Description and interpretation

On December 4, 1983 an eruption started at vents located 1.5 km southwest of the summit of Piton de la Fournaise at the base of the central cone. After 31 months of quiescence this was one of the longest repose period in the last fifty years. The eruption had two phases: December 4 to January 18 and January 18 to February 18. Phase 1 produced about 8 × 10⁶ m³ of lava and Phase II about 9 × 10⁶ m³. The erupted lava is an aphyric basalt whose mineralogical and geochemical composition is close to that of other lavas emitted since 1977.The precursors of the December 4 outbreak were limited to two-week shallow (1.5–3 km) seismic crisis of fewer than 50 events. No long-term increase was noted in the local seismicity which is very quiet during repose periods and no long-term ground inflation preceded the eruption. Outbreaks of Phases I and II were preceded by short (2.5 hours and 1.5 hours) seismic swarms corresponding to the rise of magma toward the surface from a shallow reservoir. Large ground deformation explained by the emplacement of the shallow intrusions, was recorded during the seismic swarms. A summit inflation was observed in early January, before the phase II outbreak, while the phase I eruption was still continuing.Piton de la Fournaise volcanological observatory was installed in 1980. Seismic and ground deformation data now available for a period of 4 years including the 1981 and the 1983–1984 eruptions, allow us to describe the physical behavior of the volcano during this period. These observations lead us to propose that the magma transfer from deep levels to the shallow magma reservoir is not a continuous process but a periodic one and that the shallow magma reservoir was not resupplied before the 1981 and 1983–1984 eruptions. Considerations on the eruptive history and the composition of recent lavas indicate that the reservoir was refilled in 1977.     

March 1986 eruptive episodes at Piton de la Fournaise volcano (Reunion Island)

From May 1985 to April 1986 five discrete eruptions have occurred at Piton de la Fournaise volcano. On March the 17th, a sixth episode began with four distinct stages. They took place along the southeast rift zone of the volcano, from the summit to the sea coast. It was the first rift zone eruption in the south since 1800 A.D. and the first ever monitored at Piton de la Fournaise volcano.Three fissural vents opened at decreasing altitude emitting about 12 to 15 × 10⁶ m³ of olivine basalts between 19th March and 1st April. Strong seismic activity was accompanied by deformation of the summit area, and large-scale variations of the magnetic field. A summital event characterized the end of the flank activity with collapse of a new pit-crater and outflow of small amounts of degassed aphyric basalt.     

Depositional mechanics of turbulent nuées ardentes (surges) from their grain sizes

The ability of turbulent nuées ardentes (surges) to transport coarse pyroclasts has been questioned on the basis that settling velocities of coarse fragments in the deposits are much too high for them to have been supported by turbulence in a dilute gas suspension. A computer model is used to evaluate the settling velocity of pyroclasts in suspensions of varying concentration and temperature. Since suspension of grains in low-concentration surges occurs if the shear velocity exceeds the settling velocity, the shear velocities related to the 16th and 84th percentiles, and the mean of the grain-size distribution are compared in surge deposits of the Vulsini, with the shear velocity necessary to move the coarsest grain on the bed surface (the Shields criterion). The results show that the settling velocities do not vary significantly in gaseous suspensions having volume concentrations lower than 15%, and that an increase in concentration to 25% is not sufficient to decrease the settling velocity of the coarser fraction, if it represents flow shear velocity. It is shown that the settling velocity of the mean grain size (M _z ) best depicts the shear velocity of a dilute turbulent suspension. Applying the results to the May 1902 paroxysmal nuées ardentes of Mount Pelée shows that the estimated mean velocities are well within the observed velocities, and sufficient to support all the clasts in dilute, turbulent suspensions.     

H-chondrites: Trace element clues to their origin

We have analyzed 10 H-chondrites for 20 trace elements, using RNAA. The meteorites included 4 of petrologic type 4 and 2 each of types 3, 5 and 6.The data show that H-chondrites are not isochemical. H3's are depleted by some 10% not only in Fe (Dodd, 1976), but also in the siderophiles Os, Re, Ir, Ni, Pd, Au, and Ge. Moreover, the abundance pattern of siderophiles varies systematically with petrologic type. As similar fractionations of REE have been observed by Nakamura (1974), it appears that both the proportions and compositions of the main nebular condensates varied slightly during accretion of the H-chondrites. Thus the higher petrologic types are independent nebular products, not metamorphosed descendants of lower petrologic types.Abundances of highly volatile elements (Cs, Br, Bi, Tl, In, Cd, Ar³⁶) correlate with petrologic type, declining by ≤ 10^?3 from Type 3 to Type 6. The trends differ from those for artificially heated Type 3's (Ikramuddinet al., 1977b; Herzoget al., 1979), but agree passably with theoretical curves for nebular condensation. Apparently the low volatile contents of higher petrologic types are a primary feature, not the result of metamorphic loss.The mineralogy of chondrites suggests that they accreted between 405 K (absence of Fe₃O₄) and 560 K (presence of FeS), and the abundances of Tl, Bi, and In further restrict this interval to 420–500 K. Accretion at 1070 ± 100 K, as proposed by Hutchisonet al. (1979, 1980), leads to some extraordinary problems. Volatiles must be injected into the parent body after cooling, which requires permeation of the body by 10¹¹ times its volume of nebular gas. This process must also achieve a uniform distribution of the less volatile elements (Rb, Cu, Ag, Zn, Ga, Ge, Sn, Sb, Se, F), without freezeout in the colder outer layers.Factor analysis of our data shows 3 groupings: siderophiles (Os, Re, Ir, Ni, Pd, Au, and Ge), volatiles (Ag, Br, In, Cd, Bi, and Tl) and alkalis (Rb and Cs). The remaining 5 elements (U, Zn, Te, Se, and Sb) remain unassociated.     

On the accuracy of location of local shocks on the territory of Czechoslovakia and adjacent areas

Summary The calculation procedures for determining epicentre parameters of weak near shocks with foci in Poland are discussed and tested for explosions with known epicentres.

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The pre-Cretaceous deep-seated tectonics of the Abukuma massif and its place in the structural framework of Japan

The structures and microstructures of the Takanuki and Hitachi areas in the Abukuma massif, Northeast Japan are described. In the Takanuki area, the basic Gosaisho series thrusts the pelitic Takanuki ones in a HP metamorphic context. The nappe structure is afterwards refolded by a migmatitic dome: the Samegawa dome, in a HT metamorphic context. Microtectonic analysis shows that the nappe was transported from south to north along the stretching lineation. Geometric features suggest that the Samegawa dome was emplaced by diapirism. The role of the thrust surface as an instable interface promoting the doming is emphasized. The Hitachi metamorphic rocks composed of basic schist, limestone and sandstone shist thrust the pelitic rocks of the western Hitachi gneisses. As for the Takanuki area, the thrusting occurred in ductile synmetamorphic conditions with a north or northeastward displacement. Owing to lithologic, petrologic, structural similitudes, the nappe of the Hitachi metamorphic rocks and that of the Gosaisho series are unified into a unique nappe with a northward motion. The emplacement occurred between late Permian and late Cretaceous likely in late Jurassic. The allochthonous units of the Abukuma massif are correlated with the Green Schist nappe described in Southwest Japan, since they are surrounded by the same zones, namely the Tanba zone and the Kurosegawa-Kitakami one. Moreover both in Southwest and Northeast Japan, the emplacement of the Green Schist nappes is due to a shear deformation inducing rotational structures along the stretching lineation indicating the same sense of transport, that is eastward in Southwest Japan and northward in Northeast Japan, owing to the late bending of the Japanese Islands. The late Jurassic nappe structure is obliquely overprinted by a HT metamorphism, Ryoke in Southwest Japan, Abukuma in Northeast Japan, and afterwards cut by late faults as the Median Tectonic Line or the Tanakura fault, giving rise to the present complexity.