Integration of micro-gravity and geodetic data to constrain shallow system mass changes at Krafla Volcano, N Iceland

New and previously published micro-gravity data are combined with InSAR data, precise levelling and GPS measurements to produce a model for the processes operating at Krafla volcano, 20 years after its most recent eruption. The data have been divided into two periods: from 1990 to 1995 and from 1996 to 2003 and show that the rate of deflation at Krafla is decaying exponentially. The net micro-gravity change at the centre of the caldera is shown, using the measured Free Air Gradient, to be -85 μGal for the first and -100 μGal for the second period. After consideration of the effects of water extraction by the geothermal power station within the caldera, the net gravity decreases are -73 ± 17 μGal for the first and -65 ± 17 μGal for the second period. These decreases are interpreted in terms of magma drainage. Following a Mogi point source model we calculate the mass decrease to be ~2 x 1010 kg/yr reflecting a drainage rate of ~0.23 m3/s, similar to the ~0.13 m3/s drainage rate previously found at Askja volcano, N-Iceland. Based on the evidence for deeper magma reservoirs and the similarity between the two volcanic systems, we suggest a pressure-link between Askja and Krafla at deeper levels (at the lower crust or the crust-mantle boundary). After the Krafla fires, co-rifting pressure decrease of a deep source at Krafla stimulated the subsequent inflow of magma, eventually affecting conditions along the plate boundary in N-Iceland, as far away as Askja. We anticipate that the pressure of the deeper reservoir at Krafla will reach a critical value and eventually magma will rise from there to the shallow magma chamber, possibly initiating a new rifting episode. We have demonstrated that by examining micro-gravity and geodetic data, our knowledge of active volcanic systems can be significantly improved

Mise au point d'une méthode d'extraction et de dosage des acides gras

*INRA de Colmar, laboratoire d'oenologie Diffusion du document : INRA de Colmar, laboratoire d'oenologi

Détermination de certains éléments du coefficient non-alcool d'une eau de vie

*INRA de Colmar, laboratoire d'oenologie Diffusion du document : INRA de Colmar, laboratoire d'oenologi

Deformation at the northern end of the Icelandic rift mapped by InSAR (1992-2000), a decade after the Krafla Rifting Episode

International audienceFrom 1975 to 1984 the northern Icelandic rift underwent a rifting crisis. Large widening, rapid and local subsiding and uplifting occurred on the Krafla fracture swarm with several fissure eruptions. Since 1992 the area has been regularly covered by the two ERS radar satellites, allowing us to form 110 INSAR interferograms with 22 SAR scenes for mapping crustal deformation. At the regional scale, the signal is characterised by a series of parallel fringes oriented N15°W. The polarity of these fringes is constant throughout the mapped area. The measurement represents an increase of 1.7 cm/y in ground to satellite distance for the Western bloc. This signal is estimated to correspond to the combination of a horizontal opening movement and a vertical movement. In addition, the local signal at Krafla is marked by a series of concentric circular fringes forming a circle centred on the volcano and two U shaped structures, respectively upright to the South and upside down to the North of the volcano. The signal geometry indicates that the main component of movement affecting Krafla is vertical. The measured signal corresponds to a 2.2 cm/y increase in the ground to satellite distance, representing a maximum 2.4 cm/y ground subsidence. The large number of interferograms on which the deformation signal affecting Krafla is visible allows us to ascertain that the deformation rate remains constant since 1992

Expériences sur l'engagement d'atomes dans un faisceau magnéto-cathodique ou cathodique

Des atomes de substances diverses (W, C, Pt, Na, S) peuvent être engagés dans un faisceau magnéto-cathodique ou cathodique. Une fois engagés, ils semblent solidaires du flux d'électrons dans ses déformations par des champs électriques et magnétiques. Ils peuvent être dégagés du faisceau électronique aux points de forte courbure de celui-ci