The 2007 eruptions and caldera collapse of the Piton de la Fournaise volcano (La Réunion Island) from tilt analysis at a single very broadband seismic station

International audienceSeismic records from La Réunion Island very broadband Geoscope station are investigated to constrain the link between the 2007 eruptive sequence and the related caldera collapse of the Piton de la Fournaise volcano. Tilt estimated from seismic records reveals that the three 2007 eruptions belong to a single inflation-deflation cycle. Tilt trend indicates that the small-volume summit eruption of 18 February occurred during a phase of continuous inflation that started in January 2007. Inflation decelerated 24 days before a second short-lived, small-volume eruption on 30 March, almost simultaneous with a sudden, large-scale deflation of the volcano. Deflation rate, which had stabilized at relatively low level, increased anew on 1 April while no magma was erupted, followed on 2 April by a major distal eruption and on 5 April by a summit caldera collapse. Long-term tilt variation suggests that the 2007 eruptive succession was triggered by a deep magma input

Magnetic Structure Investigations at the Nuclear Center

The magnetic structure of the compounds UOS, ß-CoSO4, YCO5, and HoCO5 is briefly described. UOS is antiferromagnetic. The Néel temperature is Tn=55°K. The magnetic cell is doubled in the c direction with a ++ - - sequence of U moments along c. The apparent spin is S∼1. The negative interaction corresponds to U-O-U links. In ß-CoSO4 (high-temperature modification, space group Pbnm), Co atoms are in 000, 00½, ½½½, ½½0. Here three different antiferromagnetic spin modes, mutually perpendicular, Ax(+ - - +), Gy(+-+-), and Cz(++ - - ), in the Wollan-Koehler notation, are coupled. Direction cosines are 0.71, 0.50, and 0.50, respectively. The Co moment is about 3,84 µB at 4.2°K. A field-induced spin flip to the configuration Fx, Cy, Gz is predicted. YCO5 is ferromagnetic at room temperature with a moment value of Co practically equal to that of metallic Co and moment direction along c, which is conserved down to 4.2°K. In HoCO5 the moment of Ho is opposite to those of the Co atoms. When cooling from room to liquid helium temperature, the direction of easy magnetization changes from near c to a direction in the basal plane and the Ho moment increases from 4 to about 9 µB. The compensation temperature is 70°K

Dynamics of the 2007 Eruptions of Piton de la Fournaise and the Related Caldera Collapse from a Single Very Broad-band Seismic Station

International audienceSeismic records from the RER very broad-band seismic station (La Réunion Island) belonging to the GEOSCOPE network are investigated to understand the eruptive succession (February to May) of Piton de la Fournaise and the caldera collapse episode of April 2007. Data first indicate that the short-lived, small volume, summit eruption of February 18 occurred during a phase of continuous inflation initiated in January 2007. Inflation decelerated around 2 weeks before a second short-lived small volume eruption on March 30-31 on the SE flank, almost simultaneous with a sudden, large deflation of the edifice. Deflation rate, which had stabilized at a relatively low level, increased anew on April 1 while no magma was emitted, followed on April 2 by a more distant and one of the most voluminous eruptions of the last two centuries at La Réunion Island. The RER station shows that very long period (VLP) and ultra long period (ULP) events developed during this period. Seven ULP events preceded the caldera collapse and 48 ones occurred during the caldera collapse over 9 days, most of which during the first 30 hours. A thorough examination of the seismic signals corrected for tide effects shows that each collapse event was coeval with VLP and ULP signals. Each individual collapse showed similar ULP and VLP signals characterized by periods of ∼ 500 s and ∼ 7 s, respectively. The back-azimuth of most ULP signals related to the caldera collapse points clearly toward the Dolomieu caldera. The strikingly constant duration of the VLP signals (around 20 s) related to the collapse events and their occurrence before the collapse initiation suggest a physical control of the volcanic edifice. Waveforms and spectrograms of the various caldera collapse events show very homogeneous patterns, suggesting a similar and repeating volcano-tectonic process for the formation of the VLP signals events. Although tilt may be responsible of part of the ULP signals observed during the collapse events, we show that it cannot explain most of the records. The ULP signals occurring during the collapse and also recorded by the OVPF GNSS (Global Navigation Satellite System) permanent network likely correspond to relaxation of the volcanic edifice. This analysis allows us to propose a scenario that may explain each successive collapse event as starting with a short-period event induced by the rock failure, followed by a VLP signal induced by dip-slip motion on the caldera ring fault, and ending with a ULP signal likely related to a relaxation process of the edifice

Developing a sense of place toolkit: Identifying destination uniqueness

It has long been recognised that the tangible and intangible characteristics that make a location distinctive and memorable, contribute significantly to destination image. How this destination feel is communicated, has largely been the domain of place branding and destination marketing, which have the potential to miss stakeholder voices. Recently though, practitioners are starting to carefully consider ‘sense of place’; that is an emotional attachment to place, which is defined more carefully in the literature review of this article, and which corresponds with long-running academic discussions. This paper attempts to identify some of these and bridge the gap between academic theory on sense of place and practice. In the UK, many rural areas are now seeking to operationalise sense of place through toolkit documents that might inform landscape interpretation and destination branding. A scenario echoed internationally, where local distinctiveness features in both rural and urban planning. However, sense of place in a tourism context, and more specifically the development of these toolkits, has received limited academic attention. Hence, this paper presents the case of Morecambe Bay, and the development of a dedicated sense of place toolkit. The subsequent case emerges from a collaboration between academics and practitioners and draws on participant observation, semi-structured interviews and document analysis. Specifically, the paper outlines a series of workshop activities developed with destination stakeholders and identifies how these inform subsequent toolkit design. It offers a critical analysis of the benefits and potential pitfalls of employing this approach. This case is of value to academics and destination stakeholders interested in identifying and communicating the uniqueness and emotional tone of the destination. Key lessons and recommendations are identified for those engaging in similar toolkit development initiatives

Effects of off great-circle propagation on the phase of long-period surface waves

Surface wave phase corrections for departures from great-circle propagation are computed using two-point ray-tracing through the aspherical earth model M84C of Woodhouse & Dziewonski (1984). For Rayleigh and Love waves with periods in the range 100–250 s, we determine whether these corrections provide significant variance reductions in source determinations compared with corrections calculated assuming great-circle propagation through the heterogeneous structure. For most source-receiver geometries, the off great-circle travel-time effects are small (< 10 s) for second and third orbits (e.g. R2 and R3), and their application in source determinations does not significantly reduce the data variance. This suggests that for the loworder heterogeneous models currently available the geometrical optics approximation is valid for long-period low orbit surface waves. Off great-circle phase anomalies increase quasi-linearly with increasing orbit number, indicating that the geometrical optics approximation degrades for higher orbits, which emphasizes the importance of developing higher order approximations for free-oscillation studies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73147/1/j.1365-246X.1987.tb05217.x.pd

The Southeast Indian Ridge between 88°E and 118°E: Variations in crustal accretion at constant spreading rate

The temperature of the mantle and the rate of melt production are parameters which play important roles in controlling the style of crustal accretion along mid-ocean ridges. To investigate the variability in crustal accretion that develops in response to variations in mantle temperature, we have conducted a geophysical investigation of the Southeast Indian Ridge (SEIR) between the Amsterdam hotspot and the Australian-Antarctic Discordance (88°E- 118°E). The spreading center deepens by 2100 m from west to east within the study area. Despite a uniform, intermediate spreading rate (69-75 mm yr- 1), the SEIR exhibits the range in axial morphology displayed by the East Pacific Rise and the Mid-Atlantic Ridge (MAR) and usually associated with variations in spreading rate. The spreading center is characterized by an axial high west of 102°45'E, whereas an axial valley is prevalent east of this longitude. Both the deepening of the ridge axis and the general evolution of axial morphology from an axial high to a rift valley are not uniform. A region of intermediate morphology separates axial highs and MAR-like rift valleys. Local transitions in axial morphology occur in three areas along the ridge axis. The increase in axial depth toward the Australian-Antarctic Discordance may be explained by the thinning of the oceanic crust by ~ 4 km and the change in axial topography. The long-wavelength changes observed along the SEIR can be attributed to a gradient in mantle temperature between regions influenced by the Amsterdam and Kerguelen hot spots and the Australian-Antarctic Discordance. However, local processes, perhaps associated with an heterogeneous mantle or along-axis asthenospheric flow, may give rise to local transitions in axial topography and depth anomalies

Étude par diffraction neutronique du spinelle FeCr2S4

Neutron diffraction study of the spinel FeCr2S4 shows the degree of inversion to be zero and the sulphur parameter to be u = 0,2608. Low temperature results agree with a simple ferrimagnetic model.L'étude par diffraction de neutrons du spinelle FeCrS4 montre que le degré d'inversion est nul et que le paramètre du soufre est de u = 0,2608. L'étude à basse température a confirmé l'existence d'un ferrimagnétisme simple

Structures magnétiques de Cr3X4 (X = S, Se, Te)

The pseudo-hexagonal monoclinic compounds Cr3X4 = □ Cr2+I (Cr3+II)2 X24-(X = S, Se, Te) belong to a deformed (space group I/2m) NiAs-type. Vacancy ordering in the cation lattice takes place in (1 01) planes. With the hypothesis of isotropic exchange, the possible magnetic configurations are derived theoretically. The observed configurations belong to the propagation vector k0 = [1/2 0 1/2], implying a doubling of the chemical cell in the a and c direction. In Cr3S 4, ferromagnetic sheets parallel to the (1 0 1) planes, alternate in the succession □ CrII (+) CrI (—) Cr II (+) □ CrII (-) CrI (+) CrII (—). Spins are parallel to [101]. TN is ≈ 280 °K ; Θp = 547 °K. Cr3Se 4 has the same configuration with spins in the (101) plane and T N ≈ 80 °K ; Θp = — 6 °K. At very low temperatures (4.2 °K) a weak component (~10 %) □ CrII (+) CrI (+) CrII (+) □ CrII (—) CrI (—) CrII (—) is observed. Cr3Te 4 has a ferromagnetic Curie temperature Tc = 329 °K. At temperatures below 80 °K, a weak antiferromagnetic component is superimposed on the strong ferromagnetism, which explains the decrease of the magnetization below 80 °K. In the three compounds, the Curie constant is near to the theoretical spin-only value.Les composés monocliniques pseudo-hexagonaux (groupe I/2m) Cr3X4 = □ Cr2+I (Cr3+II)2 X24- (X = S, Se, Te) dérivent du type NiAs. Les lacunes □ ordonnées du réseau des cations se trouvent dans des plans (101). Dans l'hypothèse d'interactions isotropes, on déduit théoriquement les configurations magnétiques possibles. Les configurations antiferromagnétiques observées appartiennent au vecteur de propagation k0 = [1/2 0 1/2], c'est-à-dire la maille magnétique est double de la maille chimique selon a et c. Dans Cr3S 4, des couches ferromagnétiques, parallèles au plan des lacunes (101) se succèdent selon [1 0 1] dans l'ordre □ CrII (+) Cr I (-) CrII (+) □ CrII (—) Cr I (+) CrII (—). Les spins sont parallèles à [101]. On a TN ≈ 280 °K ; Θp = — 547 °K. Dans Cr3Se 4, on a la même configuration, le spin étant dans le plan (101) avec TN ≈ 80 °K et Θp = — 6 °K. Aux très basses températures (4,2 °K) on observe une faible composante (~ 10 %) □ CrII (+) CrI (+) CrII (+) □ CrII (-) CrI (-) CrII (-). Cr3Te 4 a une température de Curie ferromagnétique Tc = 329 °K. Aux températures inférieures à 80 °K, une faible composante antiferromagnétique se superpose à la forte composante ferromagnétique ce qui explique la décroissance de l'aimantation au-dessous de 80 °K. Dans les trois composés, la constante de Curie est proche de la valeur théorique, calculée pour le spin seul