### 3- Dynamique de chambre, intrusions et déformation

En grande majorité, les compositions de laves du Piton de la Fournaise ont pu être expliquées par trois mécanismes de différenciation magmatique distincts, à partir d'un seul et unique magma source (Famin et al., 2009; Figure 4). La première différenciation privilégie la cristallisation de clinopyroxène et de plagioclase, dans le réservoir le plus profond (> 7,5 km). La deuxième différenciation favorise la cristallisation d'olivine à 0,5 - 2,6 km, ce qui explique son abondance dans les éruptions d'océanites comme la coulée de février 2005. La troisième différenciation se produit lors de la remontée des magmas en surface ou dans des poches à très faible profondeur (0,5 km), et se traduit à nouveau par la cristallisation d'un assemblage clinopyroxène + plagioclase. Le passage d'un mode de différenciation au suivant dépend principalement de la pression.

<figure><img src="image_43.png" /></figure>

Figure 4 : Profondeur des réservoirs de magma sous le piton de la Fournaise et style de différenciations chimiques. Les couleurs correspondent aux compositions des laves, qui indiquent trois styles de différenciation magmatique en fonction de la profondeur des réservoirs (Famin et al. 2009).

Les cristaux d'olivine des éruptions récentes montrent des textures associées à des cycles rapides de refroidissement et de réchauffement (Figure 5). Ceci suggère que le réservoir situé entre 0,5 et 2,6 km de la surface entre en convection thermique juste avant les éruptions. Il est donc possible d'imaginer que ce sont les instabilités thermiques qui engendrent les éruptions (Welsch et al., 2009).

<figure><img src="image_44.png" /></figure>

<figure><img src="image_45.png" /></figure>
Figure 5 : a) Microcristal d'olivine à croissance symétrique ayant piégé une paire d'inclusions vitreuses à chaque cycle de refroidissement-réchauffement. Ce cristal a subi trois cycles. b) Modèle de convection dans le réservoir magmatique à olivine, d'après la texture des microcristaux. La convection se produit au toit de la chambre car c'est la zone où l'instabilité thermique se développe (Welsch et al., 2009).

L'étude des éruptions depuis 1981 nous a permis de montrer qu'au Piton de la Fournaise le magma s'injectait le long de deux rift zones perpendiculaires orientées N25-30 et N120 (Michon et al., 2007a). La majorité des intrusions entraine le développement de fissures éruptives qui s'organisent selon une géométrie en échelon sur le cône actif. Nous avons montré que cette distribution ne traduisait pas un cisaillement latéral associé au déplacement co-éruptif du flanc est du volcan mais résultait du champ de contraintes prévalant en sub-surface (Michon et al. 2009a).

La modélisation numérique d'intrusions récurrentes le long des rift zones N25-30 et N120 a montré que cette activité intrusive produisait une déformation asymétrique du cône actif du Piton de la Fournaise, identique à celle observée par GPS et au niveau de la topographie (Michon et al., 2009a; Figure 6).

<figure><img src="image_46.png" /></figure>

Figure 6: a) Modélisation des changements de pente dus à l'intrusion répétée de dykes dans les rift zones N25-30 et N120. La trace des dykes en surface est représentée par une ligne blanche. b) Carte de pente suggérant l'effet des dykes dans le développement des flancs est et sud-est du cône actif. c) Coupe E-W présentant l'inflation de la moitié est du cône.

Parallèlement, nos travaux menés dans le cœur du Piton des Neiges ont révélé qu'en profondeur, les intrusions magmatiques se développaient essentiellement sous forme de sills faiblement inclinés vers l'extérieur. Un niveau de forte concentration en sills, mis en place dans la partie nord, entre un massif gabbroïque et des dépôts d'avalanche de débris, a été reconnu comme un détachement ayant contrôlé la déstabilisation latérale du volcan (Famin et Michon, 2010; Figure 7). Ce type de structure et de processus, jamais observé sur les autres volcans boucliers car localisé en profondeur, constitue une alternative mécanique au modèle d'injections de dykes le long des rift zones.

Figure 7: Coupe géologique au niveau du gabbro de l'ilet à Vidot montrant la zone de déformation (vert) sur laquelle le flanc nord du Piton des Neiges a continuellement glissé (Famin et Michon, 2010).
<figure><img src="image_47.png" /></figure>

## 4- Structuration et dynamique des systèmes hydrothermaux

Les systèmes hydrothermaux correspondent à la zone d'interaction entre le système purement magmatique et les fluides météoriques descendants. Les nombreuses campagnes géophysiques (tomographie de résistivité électrique, polarisation spontanée et température du sol) et d'analyse de gaz (CO2 dans le sol) ont permis d'imager les systèmes hydrothermaux du Stromboli, de Vuclano, du Piton de la Fournaise et des volcans Santa Maria, Cerro Quemado et Zunil au Guatemala (Finizola et al., 2008, 2009, 2010; Revil et al. 2008, 2010). Sur ces différents systèmes, nous avons pu mettre en évidence le contrôle étroit des limites structurales sur la remontée de fluides et dans le confinement latéral du système hydrothermal (Figure 8). A Stromboli, la récurrence des campagnes de mesure a permis de suivre les variations du système hydrothermal lors des phases d'activité "normales" ou exceptionnelles, comme lors de la crise éruptive de 2002-2003.

<figure><img src="image_48.png" /></figure>

Figure 9: Représentation 3D de la Fossa, à Stromboli, avec en coupe un profil de tomographie de résistivité électrique et en surface une carte de température du sol. Cf. Finizola et al., (2009) pour une description détaillée.

## 5- Dynamique des calderas magmatiques

L'effondrement du cratère Dolomieu d'avril 2007 au Piton de la Fournaise constitue l'exemple le plus récent d'effondrement caldérique. La déformation péri-caldérique a été enregistrée par un dense réseau GPS. Les déplacements associés à cet événement, pluri-métriques pour certains, ont été maximum le long de la bordure sud du Dolomieu (Michon et al., 2009b; Figure 8). La décroissance rapide des déplacements depuis la bordure vers l'extérieur a entrainé la formation d'un dense réseau de fractures concentriques, fragilisant cette partie du sommet.
<figure><img src="image_49.png" /></figure>

Figure 8: Déplacements enregistrés sur la bordure du Dolomieu entre mars et mai 2007. a) Déplacements totaux (en cm). b) Vecteurs déplacement pour la composante horizontale. c) Composantes horizontale et verticale du déplacement (en cm).

La dynamique d'effondrement du Dolomieu a été comparée à celle enregistrée lors des effondrements caldériques du Fernandina en 1968 et du Miyakejima en 2000. Nous avons pu montrer que ces trois événements s'étaient produits de manière similaire, i.e. en un effondrement incrémental d'un piston dans la chambre magmatique (Michon et al., 2009b). L'intégration des données sismiques et de déformation a permis de déterminer le déplacement vertical du piston lors de chaque incrément d'effondrement, et incidemment les taux de vidange magmatique pour ces trois volcans (Michon et al., 2011). La dynamique d'effondrement observée dans le cas des calderas basaltiques est identique à celle, supposée, des calderas siliceuses.

## 6- Erosion des volcans insulaires et transfert sédimentaire

L'exploitation des données acquises lors des campagnes à la mer, FOREVER (2006) et ERODER (2008, 2010), a permis une caractérisation précise des processus mis en jeu dans la construction des pentes sous-marines de La Réunion. En particulier, la découverte de plusieurs systèmes turbiditiques en connexion avec les grandes rivières de l'île de La Réunion démontre l'efficacité du transfert sédimentaire depuis la zone émergée vers le domaine marin. Le système de Cilaos a été bien étudié (thèses de Saint-Ange - 2009 et Sisavath - en cours, Saint-Ange et al. 2011; Figure 9). Il constitue le plus bel exemple de système volcanoclastique sous-marin décrit autour d'une île. Loin de toute source continentale, il fournit des informations uniques sur l'architecture et les processus associés à la mise en place de ce type de formation, dont l'importance était jusqu'alors largement minimisée dans le volcanisme insulaire intraplaque.

<figure><img src="image_50.png" /></figure>

Figure 9: Le système turbiditique de Cilaos : Imagerie acoustique au sud-ouest de l'île de La Réunion acquise durant les campagnes FOREVER ET ERODER (in Saint-Ange et al., Geology, 2011). Abbreviations: dad—Dépôts d'avalanche de débris; dsf—deep-sea fan; vr—rides volcaniques.
Publications

* Finizola A., Ricci T., Deiana R., Barde-Cabusson S., Rossi M., Praticelli N., Giocoli A., Romano G., Delcher E., Suski B., Revil A., Menny P., Di Gangi F., Letort J., Peltier A., Villasante-Marcos V., Douillet G., Avard G., Lelli M. (2010). Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes. *J. Volcanol. Geotherm. Res.*, 196, 111-119. doi: 10.1016/j.jvolgeores.2010.07.022.

* Komorowski, J.-C., Y. Legendre, T. Christopher, M. Bernstein, R. Stewart, E. Joseph, N. Fournier, L. Chardot, A. Finizola, G. Wadge, R. Syers, C. Williams, V. Bass (2010), Insights into processes and deposits of hazardous vulcanian explosions at Soufrière Hills Volcano during 2008 and 2009 (Montserrat, West Indies), *Geophys. Res. Lett.*, 37, L00E19, doi:10.1029/2010GL042558.

* Drouin, M., Ildefonse, B., Godard, M. (2010), A microstructural imprint of melt impregnation in slow-spread lithosphere: the olivine-rich troctolites from the Atlantis Massif (Mid-Atlantic Ridge 30°N, IODP Hole U1309D). *Geochem. Geophys. Geosyst.*, 11, Q06003, doi:10.1029/2009GC002995.

* Revil, A., T.C. Johnson, A. Finizola (2010), Three-dimensional resistivity tomography of Vulcan's forge, Volcano Island, southern Italy, Geophys. Res. Lett., 37, L15308, doi:10.1029/2010GL043983.

* Merle, O., Ph. Mairine, L. Michon, P. Bachèlery, M. Smietana (2010), Calderas, Landslides and Paleocanyons at Piton de la Fournaise Volcano (La Réunion Island, Indian Ocean), *J. Volcanol. Geotherm. Res.*, 189, 131-142, doi:10.1016/j.jvolgeores.2009.11.001

* Famin V., Michon L. (2010), Volcano desabilization by magma injection in a detachment, *Geology*, 38, 219-222.

* Peltier A., Staudacher T., Bachèlery P. (2010), New behaviour of the Piton de la Fournaise volcano feeding system (La Réunion Island) deduced from GPS data: Influence of the 2007 Dolomieu caldera collapse, *J. Volcanol. Geotherm. Res.*, 192 (1-2), 48-56.

2009

* Welsch B., Faure F., Bachèlery P., Famin V. (2009), Microcrysts record transient convection at Piton de la Fournaise volcano (La Réunion hotspot). *Journal of Petrology*, 50, 2287-2305.

* Barruol, G., D. Suetsugu, H. Shiobara, H. Sugioka, S. Tanaka, G. H. R. Bokelmann, F. R. Fontaine, and D. Reymond (2009), Mapping upper mantle flow beneath French Polynesia from broadband ocean bottom seismic observations, *Geophys. Res. Lett.*, 36, L14301, doi:10.1029/2009GL038139.

* Barde-Cabusson, S., Levieux, G., Lénat, J.-F., Finizola A., Revil, A., Chaput, M., Dumont, S., Duputel, Z., Guy, A., Mathieu, L., Saumet, S., Sorbadère, F. and Vieille, M., (2009). Transient self-potential anomalies associated with recent lava flows at Piton de la Fournaise volcano (Réunion Island, Indian Ocean). *J. Volcanol. Geotherm. Res.*, vol. 187, 3-4, 158-166.

* Bani P., Join J.-L., Cronin S. J., Lardy M., Rouet I. Garaebiti E. (2009). Characteristics of the summit lakes of Ambae volcano and their potential for generating lahars. *Nat. Hazards Earth Syst. Sci.*, 9, p 1471-1478.

* Morin J., Lavigne F., Bachèlery P., Finizola A., Villeneuve N. Institutional and social responses to hazards related to Karthala volcano, Comoros. Part I - Analysis of the May 2006 eruptive crisis. *SHIMA The International Journal of Research into Island Cultures*, vol 3, n° 1, 33 - 53.

* Morin J., Lavigne F. Institutional and people's response in the face of volcanic hazards in island environment: Case of Karthala volcano, Comoros Archipelago. Part II - Deep-seated root causes of Comorian vulnerabilities. *SHIMA The International Journal of Research into Island Cultures*, vol 3, n° 1, 54-71.

* Antoine R., Baratoux D., Rabinowicz M., Fontaine F., Bachèlery P., Staudacher T., Saracco G., Finizola A., (2009). Thermal infrared image analysis of a quiescent cone on Piton de la Fournaise volcano: Evidence of convective air flow within an unconsolidated soil. *J. Volcanol. Georthern. Res.*, 183, 228-244, doi: 10.1016/j.jvolgeores.2008.12.003

* Boivin P. and P. Bachèlery (2009). Petrology of 1977 to 1998 eruptions at Piton de la Fournaise, la Réunion Island. *J. Volcanol. Georthern. Res.*, 184, p 109-125, doi: 10.1016/j.jvolgeores.2009.01.012

* Drouin, M., Godard, M., Ildefonse, B., Bruguier, O., Garrido, C. J. (2009). Geochemical and petrographic evidence for magmatic impregnation in the oceanic lithosphere at Atlantis Massif, Mid-Atlantic Ridge (IODP Hole U1309D, 300N), *Chem. Geol.*, doi: 10.1016/j.chemgeo.2009.02.013

* Famin V., B. Welsch, S. Okumura, P. Bachèlery and S. Nakashima (2009). Three differentiation stages of a single magma at Piton de la Fournaise (Reunion hotspot). *G-Cubed*. 10(1) Q01007, doi: 10.1029/2008GC002015

* Fontaine, F. R., G. Barruol, B. L. N. Kennett, G. H. R. Bokelmann, and D. Reymond (2009). Upper mantle anisotropy beneath Australia and Tahiti from P wave polarization: Implications for real-time earthquake location, *J. Geophys. Res.*, 114, B03306, doi:10.1029/2008JB005709

* Gailler L.-S., J.-F. Lénat, M. Lambert, G. Levieux, N. Villeneuve, J.-L. Froger (2009). Gravity structure of Piton de la Fournaise volcano and inferred mass transfer during the 2007 crisis. *J. Volcanol. Georthern.*
Res., 184, 199-207, doi:10.1016/j.jvolgeores.2009.01.024

* Lénat J.-F., P. Boivin, C. Deniel, P.-Y. Gillot, **P. Bachèlery** and Fournaise 2 Team (2009). Age and nature of deposits on the submarine flanks of Piton de la Fournaise (Reunion Island). *J. Volcanol. Geortherm. Res.*, 184, 199-207, doi:10.1016/j.jvolgeores.2009.01.013

* **Michon L.**, V. Cayol, L. Letourneur, A. Peltier, **N. Villeneuve**, T. Staudacher (2009). Edifice growth, deformation and rift zone development in basaltic setting: insights from Piton de la Fournaise shield volcano (La Réunion Island, Indian Ocean). *J. Volcanol. Geortherm. Res.*, 184, 14-30, doi: 10.1016/j.jvolgeores.2008.11.002.

* **Michon L.**, **N. Villeneuve**, **Th. Catry**, O.Merle (2009). How summit calderas collapse on basaltic volcanoes: new insights from the April 2007 caldera collapse of Piton de la Fournaise volcano. *J. Volcanol. Geortherm. Res.*, 184, 138-151, doi: 10.1016/j.jvolgeores.2008.11.003

* Peltier, A., T. Staudacher, **P. Bachèlery**, V. Cayol (2009). Formation of the April 2007 caldera collapse at Piton de La Fournaise volcano: insights from GPS data. *J. Volcanol. Geortherm. Res.*, 184, 152-163, doi:10.1016/j.jvolgeores.2008.09.009

* Peltier, A., **P. Bachèlery**, T. Staudacher (2009). Magma transport and storage at Piton de La Fournaise (La Réunion) between 1972 and 2007: A review of geophysical and geochemical data. *J. Volcanol. Geortherm. Res.*, 184, 93-108, doi:10.1016/j.jvolgeores.2008.12.008

* Staudacher T., V. Ferrazzini, A. Peltier, P. Kowalski, P. Boissier, P. Catherine, F. Lauret, **F. Massin** (2009). The April 2007 eruption and the Dolomieu crater collapse, two major events at Piton de la Fournaise. *J. Volcanol. Geortherm. Res.*, 184, 126-137, doi:10.1016/j.jvolgeores.2008.11.005

* Vlastélic, I., C. Deniel, C. Bosq, P. Télouk, P. Boivin, **P. Bachèlery**, **V. Famin**, T. Staudacher (2009). Pb isotope geochemistry of Piton de la Fournaise historical volcanism. *J. Volcanol. Geortherm. Res.*, 184, 63-78, doi:10.1016/j.jvolgeores.2008.08.008

* Barde-Cabusson S., **Finizola A.**, Revil A., Ricci T., Piscitelli S., Rizzo E., Engeletti B., Balasco M., Bennati L., Byrdina S., Carzaniga N., Crespy A., Di Gangi F., **Morin J.**, Perrone A., Rossi, M., Roulleau E., Suski B., **Villeneuve N.** (2009). New geological insights and structural control on fluid circulation in La Fossa cone (Vulcano, Aeolian Islands, Italy). *J. Volcanol. Geortherm. Res.*, 185, 3, 231-245.

* **Finizola A.**, Aubert M., Revil A., Schütze C., Sortino F. (2009). Importance of structural history in the summit area of Stromboli during the 2002-2003 eruptive crisis inferred from temperature, soil CO2, self-potential, and electrical resistivity tomography. *J. Volcanol. Geortherm. Res.*, 183, 3-4, p. 213-227.

## 2008

* **Michon, L.**, and F. Saint-Ange (2008), Morphology of Piton de la Fournaise basaltic shield volcano (La Réunion island): Characterization and implication in the volcano evolution. *J. Geophys. Res.*, 113, B03203, doi:101029/2005JB0044118.

* Merle, O., **L. Michon, P. Bachèlery** (2008). Caldera rim collapse: a hidden volcanic hazard, *J. Volcanol. Geotherm. Res.*, 177, 525-530. doi:10.1016/j.jvolgeores.2008.06.011

* Peltier, A., **V. Famin, P. Bachèlery**, V. Cayol, Y. Fukushima, and Th., Staudacher (2008), Cyclic magma storages and transfers at Piton de La Fournaise volcano (La Réunion Island) inferred from deformation and geochemical data. *Earth. Planet. Sci. Lett.* doi:10.1016/j.epsl.2008.02.042, 270,180-188.

* Revil, A., **A. Finizola**, S. Piscitelli, E. Rizzo, T. Ricci, A. Crespy, B. Angeletti, M. Balasco, S. B. Cabusson, L. Bennati, A. Boleve, S. Byrdina, N. Carzaniga, F. Di Gangi, **J. Morin**, A. Perrone, M. Rossi, E. Roulleau, and B. Suski (2008). The inner structure of La Fossa di Vulcano (Vulcano Island, southern Tyrrhenian Sea, Italy) revealed by high resolution electric resistivity tomography coupled with self-potential, temperature, and CO2 diffuse degassing measurements, *J. Geophys. Res.*, doi:10.1029/2007JB005394.

* Lavigne F., B. De Coster, N. Juvin, F. Flohic, JC. Gaillard, P. Texier, **J. Morin**, J. Sartohadi (2008). People's behaviour in the face of volcanic hazards: Perspectives from Javanese communities, Indonesia, *J. Volcanol. Geortherm. Res.*, 172, 273-287, doi: 10.1016/j.jvolgeores.2007.12.013.

* **Morin J.**, De Coster B., Flohic F., Lavigne F., Le Floch D., Paris R., 2008. Assessment and prevention of tsunami risk in Indonesia. *Disaster Prevention and Management*, vol.17:3, pp. 430-446.

* **Villeneuve N.**, Neuville D., Boivin P., **Bachèlery P.**, Richet P., Magma crystallization and viscosity: A study of molten basalts from the Piton de la Fournaise volcano (La Réunion island), *Chemical Geology*, 256, 242-251.

## 2007

* Aubert, M., S. Diliberto, **A. Finizola**, and Y. Chébli (2007), Double origin of hydrothermal convective flux variations in the Fossa of Vulcano (Italy), *Bull. Volcanol.*, doi: 10.10007/s00445-007-0165-y.

* Carter, A., B. van Wyk de Vries, K. Kelfoun, **P. Bachèlery**, P. Briole (2007), Pits, rifts and slumps: the summit structure of Piton de la Fournaise, *Bull. Volcanol.*, 69, 741-756, 10.1007/s00445-006-0103-4.

* **Michon, L.**, **F. Saint-Ange, P. Bachèlery, N. Villeneuve**, and Th. Staudacher (2007), Role of the structural inheritance of the oceanic lithosphere in the magmato-tectonic evolution of Piton de la Fournaise volcano (La Réunion Island). *J. Geophys. Res.* 112, B4, B04205, 10.1029/2006JB004598.
* Michon, L., Th. Staudacher, V. Ferrazzini, P. Bachèlery, J Marti, (2007), April 2007 collapse of Piton de la Fournaise: a new example of caldera formation, Geophys. Res. Lett., 34, L21301, doi:10.1029/2007GL031248.

* Peltier, A., T. Staudacher, P. Bachèlery (2007), Constraints on magma transfers and structures involved in the 2003 activity at Piton de La Fournaise from displacement data. J. Geophys. Res., 112, B3, B03207, 10.1029/2006JB004379.

* Vlastelic, I., A. Peltier, and T. Staudacher, Short-term (1998-2006) fluctuations of Pb isotopes at Piton de la Fournaise volcano (Reunion Island): origins and constrains on the size and shape of the magma reservoir. *Chemical Geology*, 244, 202-220.

* Fontaine F. R., Barruol G., Tommasi A., and Bokelmann G. H. R. (2007), Upper mantle flow beneath French Polynesia from shear-wave splitting, vol 170, 1262-1288, Geophys. J. Int, doi:10.1111/j.1365-246X.2007.03475.x.

Autres publications IPG

Cortés, A., Garduño, V.H., Navarro-Ochoa, C., Komorowski, J-C., Saucedo R., Macias J. L., and Gavilanes J. C. (2009) Geologic mapping of the Colima Volcanic Complex (Mexico), and implications for hazard assessment. Geological Society of America Book Series, "Stratigraphy and geology in volcanic areas", Edited by G. Groppelli, L. Viereck-Goette and A. Basu, in press.

Drouin, M., Godard, M., Ildefonse, B., Bruguier, O., Garrido, C. J. (2009). Geochemical and petrographic evidence for magmatic impregnation in the oceanic lithosphere at Atlantis Massif, Mid-Atlantic Ridge (IODP Hole U1309D, 300N), Chem. Geol., doi: 10.1016/j.chemgeo.2009.02.013.

Mehl, C., F. Gueydan, V Famin., L. Jolivet, Fluid-rock interaction and strain localization in the middle crust, *Earth. Planet. Sci. Lett.* (accepté

Massin F., Ferrazzini V., Bachelery P., Nercessian A., Duputel Z., Staudacher T., Seismological study of the structure and the evolution of le Piton de la Fournaise plumbing system from the April 2007 major eruption, 2009 submitted to J.G.R.

Morin J., Lavigne F. Institutional and people's response in the face of volcanic hazards in island environment: Case of Karthala volcano, Comoros Archipelago. Part II - Deep-seated root causes of Comorian vulnerabilities. *SHIMA The International Journal of Research into Island Cultures*, in press.

Pascal, M.L., A. Di Muro, M. Fonteilles, C. Principe, (2008) Zirconolite and calzirtite in skarn ejecta from Vesuvius 1631 eruption - inferences for the magma - wallrock zoneography. *The Mineralogical Magazine*, in press.

Vigouroux N., Williams-Jones A.E., Wallace P., Staudacher Th., The November 2002 eruption of Piton de la Fournaise, Reunion : Tracking the pre-eruptive thermal evolution of magma using melt inclusions., Bull. Volc., 2009.

Coppola D., James M.R., Staudacher T. and Cigolini C., A comparison of field- and satellite-derived thermal flux at Piton de la Fournaise: implications for the calculation of lava discharge rate, Bulletin of Volcanology, 2009

Wada K., Heggy E., Staudacher T., Yarai H., L-band interferometric observations of the Fournaise Volcano: Monitoring and modeling the displacements of the 2007 major eruption, GRL 2009.

Bhugwant C., Siéja B., Bessafi M., Staudacher T., Ecormier J. (2009). Atmospheric sulfur dioxide measurements during the 2005 and 2007 eruptions of the Piton de La Fournaise volcano: Implications for human health and environmental changes J. Volcanol. Geotherm. Res., special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.04.012, 184, 208-224.

Balcone-Boissard H., A. Michel, B. Villemant, (2009). Simultaneaus determination of Fluorine, Chlorine, Bromine and Iodine in six Geochemical Reference Materials Using Pyrohydrolysis, Ion Chromatography and Inductively Coupled Plasma Mass Spectrometry. *Geostandards and Geoanalytical Research*

Barde-Cabusson, S., Finizola, A., Revil, A., Ricci, T., Piscitelli, S., Rizzo, E., Angeletti, B., Balasco, M., Bennati, L., Byrdina, S., Carzaniga, N., Crespy, A., Di Gangi, F., Morin, J., Perrone, A., Rossi, M., Roulleau, E., Suski, B., Villeneuve, N., (2009). New geological insights and structural control on fluid circulation in La Fossa cone (Vulcano, Aeolian Islands, Italy). J. Volcanol. Geotherm. Res., doi: 10.1016/j.jvolgeores.2009.06.002, 185, 231-245.

Barde-Cabusson S., Levieux G., Lénat J.-F., Finizola, A., Revil A., Chaput M., Dumont S., Duputel Z., Guy A., Mathieu L., Saumet S., Sorbadère F., Vieille M. (2009). Transient self-potential anomalies associated with recent lava flows at Piton de la Fournaise volcano (Réunion Island, Indian Ocean). *Journal of Volcanology and Geothermal Research*,

Boivin P., Bachèlery P., Petrology of 1977-1998 Eruptions of Piton de la Fournaise, La Reunion Island. J. Volcanol. Geotherm. Res., special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2009.01.012, 184, 109-125.

Bhugwant, C., B. Siéja, L. Perron, E. Rivière, and Th. Staudacher, Regional transport of polluants emitted from the June-July 2001 eruption of Piton de la Fournaise volcano (Reunion Island), *Atmospheric research*, in press.

Coppola D., Piscopo D., Staudacher T., Cigolini C., (2009). Lava discharge rate and effusive pattern at Piton de la Fournaise from MODIS data, J. Volcanol. Geotherm. Res., special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.11.031, 184 174-192.
Deroussi S., Diament M., Feret J.B., Nebut T., **Staudacher T.**, (2009). Localization of cavities in a thick lava flow by microgravimetry, *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.10.002, 184, 193-198.

Duputel Z., **Ferrazzini V.**, Brenguier F., Shapiro N., Campillo M., Nercessian A. (2009). Real time monitoring of relative velocity changes using ambient seismic noise at the Piton de la Fournaise volcano (La Réunion) from January 2006 to June 2007 *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.11.02', 184, 164-173.

Famin V., B. Welsh, S. Okumura, **P. Bachèlery**, S. Nakashima (2009), Three differentiation stages of a single magma at Piton de la fournaise volcano (Reunion hotspot). G-Cubed, 10(1) Q01007, doi: 10.1029/2008GC002015.

Finizola A., Aubert M., Revil A., Schütze C., Sortino F. (2009). Importance of structural history in the summit area of Stromboli during the 2002-2003 eruptive crisis inferred from temperature, soil CO2, self-potential, and electrical resistivity tomography. *J. Volcanol. Geotherm. Res.*, doi:10.1016/j.jvolgeores.2009.04.002, 183, 213-227

Hill, B., Connor, C., Aspinall, W.P., Komorowski, J-C., Nakada, S. (2009) Chapter 25: Recommendations for Assessing Volcanic Hazards of Nuclear Installations. In: C. Connor, N. Chapman, L. Connor (Eds), Volcanism and Tectonism in siting of Nuclear Power Plants, Cambridge University Press, Cambridge, United Kingdom, pp. 566-592.

Le Friant, A., **G. Boudon**, A. Arnulf, R. Robertson (2009). Debris Avalanche Deposits Offshore St Vincent (West Indies): Impact Of Flank-Collapse Events On The Morphological Evolution Of The Island. J. Volcanol. Geotherm. Res., DOI: 10.1016/J.VOLGEORES.2008.09.022, 179, 1-10.

Le Friant A., C. Deplus, **G. Boudon**, R.S.J. Sparks, J. Trofimovs, P. Talling (2009). Submarine deposition of volcaniclastic material from the 1995-2005 eruptions of Soufrière Hill Volcano, Montserrat, *Geol. Soc. London* 166, doi: 10.1144/0016-76492008-047

Lénat J.-F., Boivin P., Deniel C., Gillot P.-Y., **Bachèlery P.** and Fournaise 2 Team (2009). *Age and nature of deposits on the submarine flanks of Piton de la Fournaise (Reunion Island) J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2009.01.013, 184, 199-207.

Michon L., V. Cayol, L. Letourneur, **A. Peltier**, **N. Villeneuve**, T. Staudacher (2009). Edifice growth, deformation and rift zone development in basaltic setting: insights from Piton de la Fournaise shield volcano (Réunion Island). *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.11.002, 184, 14-30.

Michon L., Villeneuve N., Catry Th, Merle O. (2009). How summit calderas collapse on basaltic volcanoes: New insights from the April 2007 caldera collapse of Piton de la Fournaise volcano, *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.11.003, 184, 138-151.

Morin J., Lavigne F., **Bachèlery P.**, **Finizola A.**, Villeneuve N., 2009. Institutional and social responses to hazards related to Karthala volcano, Comoros. Part I: Analysis of the May 2006 eruptive crisis. *Shima: The International Journal of Research into Island Cultures*, 3-1, 33-53.

Peltier A., **Bachèlery P.**, **Staudacher T.**, Magma transport and storage at Piton de La Fournaise (La Réunion) between 1972 and 2007: A review of geophysical and geochemical data, *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.12.008, 184 (2009) 93-108.

Peltier, A., T. Staudacher, **P. Bachèlery**, V. Cayol, (2009). Formation of the April 2007 caldera collapse at Piton de La Fournaise volcano: insights from GPS data. *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.09.009, 184, 152-163.

Peltier, A., T. Hurst, B. Scott, V. Cayol (2009), Structures involved in the vertical deformation at LakeTaup (New Zealand) between 1979 and 2007: New insights from numerical modelling *J. Volcanol. Geotherm. Res.* 181, 207-219.

Peltier, A., B. Scott, T. Hurst (2009), Ground deformation patterns at White Island volcano (New Zealand) between 1967 and 2008 deduced from levelling data, *J. Volcanol. Geotherm. 181*, 207-219.

Staudacher T., V. **Ferrazzini, A. Peltier**, P. Kowalski, P. Boissier, P. Catherine, F. Lauret, F. **Massin** (2009). The April 2007 eruption and the Dolomieu crater collapse, two major events at Piton de la Fournaise (La Réunion Island, Indian Ocean). *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.11.005, 184, 126-137.

Perrier F., **Richon P.**, Sabroux J.C. (2009), Temporal variations of radon concentration in the saturated soil of Alpine grassland: The role of groundwater flow. *Science of the Total Environment*, 407: 2361-1371.

Perrier F., **Richon P.**, Byrdina S., France-Lanord C., Rajaure S., Koirala B., Shrestha P., Gautam U., Tiwari D. R., Revil A., Bollinger L., Contraires S., Bureau S., Sapkota S. N. (2009). A direct evidence for high carbon dioxide and radon-222 discharge in Central Nepal. *Earth and Planetary Science Letters*, doi:10.1016/j.epsl.2008.12.008, 278: 198-207.

Prôno E., Battaglia J., Monteiller V., Got J.-L., **Ferrazzini V.** (2009). P-wave velocity structure of Piton de la Fournaise volcano deduced from seismic data recorded between 1996 and 1999. *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.12.009, 184, 49-62.

**Richon P.**, Perrier F., Pili E. and Sabroux J.C., (2009), Detectability and significance of 12h barometric tide in radon-222 signal, dripwater flow rate, air temperature and carbon dioxide concentration in an underground tunnel. *Geophysical J. Int.*, doi: 10.111/j.1365-246X.2008.04000.x, 176: 683-694.
Toutain J.-P., Sortino F., Baubron J.-C, **Richon P.**, Surono, Sumarti S., Nonell A. (2009). Structure and CO2 budget of Merapi volcano during inter-eruptive periods. Bull. Volcanol., doi: 10.1007/s00445-009-0266-x.

Samper A., X. Quidelleur, J.-C. **Komorowski**, P. Lahitte, G. **Boudon**, Effusive History Of The Grande Découverte Volcanic Complex, Southern Basse-Terre (Guadeloupe, French West Indies) From New K-Ar Significance of Volcaniclasticagenesis in the Early Miocene of the Guadeloupe Island, *Grenville Symposium* 200, 101-114.

Sulem, J., **V. Famin**, Thermal decomposition of carbonates in fault zones: slip-weakening and temperature limiting effects, J. Geoph. Res. 114, B03309, doi:10.1029/2008JB006004.

Viane C., Bhugwant C., Sieja B., **Staudacher T.**, Demoly P., Étude comparative des émissions de gaz volcanique du Piton de la Fournaise et des hospitalisations pour asthme de la population réunionnaise de 2005 à 2007, Revue française d'allergologie (2009), doi:10.1016/j.reval.2009.02.010.

Villemant B., **Salaün A.**, **Staudacher T.**, Evidence for a homogeneous primary magma at Piton de la Fournaise (La Réunion): A geochemical study of matrix glass, melt inclusions and Pélé's hairs of the 1998-2008 eruptive activity, *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2009.03.015, 184 (2009) 79-92.

Vlastélic I., Deniel C., Bosq C., Télouk P., Boivin P., **Bachlery P.**, **Famin V.**, **Staudacher T.**, Pb isotope geochemistry of Piton de la Fournaise historical lavas, *J. Volcanol. Geotherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.08.008, 184 (2009) 63-78.

## 2008

Antoine R., Baratoux D., Rabinowicz M., Fontaine F., **Bachlery P.**, **Staudacher Th.**, Saracco G., **Finizola A.**, Thermal infrared analysis of a quiescent cone on Piton de la Fournaise volcano: evidence of convective air flow within an unconsolidated soil, doi:10.1016/j.chemgeo.2008.08.018

Baker D.R., **H. Balcone-Boissard**, (2008), Halogen diffusion in magmatic systems. Special Issue, "Halogens in Volcanic Systems and Their Environmental Impacts" *Chemical Geology*, doi:10.1016/j.chemgeo.2008.10.010.

Balcone-Boissard, H., D.R. Baker, B. Villemant, G. Boudon, (2008), F and Cl diffusion inphonolitic melts : Influence of the Na/K ratio. Special Issue, "Halogens in Volcanic Systems and Their Environmental Impacts" *Chemical Geology*, doi:10.1016/j.chemgeo.2008.08.018

Balcone-Boissard, H., B. Villemant, G. Boudon, and A. Michel, (2008), Non-volatile vs volatile behaviours of halogens during the 79 AD plinian eruption of Vesuvius, Italy. *Earth. Planet. Sci. Lett.*, doi:10.1016/j.epsl.2008.02.003, 269 (1-2), 66-79

Boichu, M., B. Villemant, G. Boudon, (2008). A Model For Episodic Degassing Of An Andesitic Magma Intrusion. *J. Geophys. RES.* DOI:10.1029/2007JB005130.

Boudon, G., J.-C. Komorowski, B. Villemant, M.P. Semet, (2008). A new scenario for the last magmatic eruption of La Soufrière de Guadeloupe (Lesser Antilles) in 1530 A.D.: evidence from stratigraphy, radiocarbon dating and magmatic evolution of erupted products. *J. Volcanol. Geortherm. Res.*, doi: 10.1016/j.jvolgeores.2008.03.006, 178:474-490.

Brenguier F., Shapiro N.M., Campillo M., **Ferrazzini V.**, Duputel Z., Coutant O., Nerceessian A. (2008), Toward forecasting volcanic eruptions using seismic noise, *Nature*, doi:1001038/ngeo104

Coppola D., Piscopo D., **Staudacher Th.**, Cigolini, C., Lava discharge rate and effusive pattern at Piton de la Fournaise from MODIS data, *J. Volcanol. Geortherm. Res.*, special issue: Piton de La Fournaise doi : 10.1016/j.jvolgeores.2008.11.031

Davies, A.G., Castaño, R., Chien, S., Tran, D.Q., Mandrake, L., Wright, R., Kyle, P., **Komorowski, J.-C.**, Mandl, D., Frye, S. Rapid Response to Volcanic Eruptions with an Autonomous Volcano Sensor Web: the Nyamulagira Eruption of 2006, *Aerospace Conference, 2008, IEEE*, 1-8 March 2008, paper 1180, pp 1-11, DOI: 10.1109/AERO.2008.4526456

Deroussi S., Diament M., Ferret M., Nebut J.B. **Staudacher Th.**, Localisation of cavities in a thick lava flow by microgravity, *J. Volcanol. Geortherm. Res.*, special issue: Piton de La Fournaise. doi : 10.1016/j.jvolgeores.2008.10.002

Di Muro, A., J. Palister, B. Villemant, C. Newhall, M. Semet, M., Martinez, C. Mariet, (2008), Pre-1991 sulfur transfer between mafic injections and dacite magma in the Mt. Pinatubo reservoir. *J. Volcanol. Geortherm. Res.*, doi: 10.1016/j.jvolgeores.2008.02.025.

Di Muro, A., M. Rosi, E. Aguilera, R. Barbieri, G. Massa, F. Mundula, F. Pieri, (2008) Transport and sedimentation dynamics of transitional explosive eruption columns: the exemple of the 800 BP Quilotoa plinian eruption (Ecuador). *J. Volcanol. Geotherm. Res.*, 174, 307-324.

Duputel Z., V **Ferrazzini**, F. Brenguier, N. Shapiro, M. Campillo, A. Nerceessian, Real Time Monitoring of Relative Velocity Changes Using Ambient Seismic Noise on the Piton de la Fournaise Volcano (La Réunion) from January 2006 to June 2007. *J. Volcanol. Geortherm. Res.*, special volume, doi : 10.1016/j.jvolgeores.2008.11.024

Famin, V., S. Nakashima, A. M. Boullier, K. Fujimoto and T. Hirono (2008). Earthquakes produce carbon dioxide in crustal faults *Earth. Planet. Sci. Lett.* doi:10.1016/j.epsl.2007.10.041, 270 (1-2), 487-497.

Hirono, T., T. Yokoyama, Y. Hamada, W. Tanikawa, T. Mishima, M. Ikehara, **V. Famin**, M. Tanimizu, W. Lin, W. Soh, and S. Song (2008). Correction to “A chemical kinetic approach to estimate dynamic shear stress during the 1999 Taiwan Chi-Chi earthquake” *Geophys. Res. Lett.*, 35, L02301, doi:10.1029/2007GL032512.

Komorowski, J.-C., Y. Legendre, B. Caron, And G. Boudon (2008), Reconstruction And Analysis Of Sub-Plinian Tephra Dispersal During The 1530 A.D. Soufrière (Guadeloupe) Eruption: Implications For Scenario
Definition And Hazards Assessment J. VOLCANOL. GEORTHERM. RES. DOI: 10.1016/J.JVOLGEORES.2007.11.022, 178: 491-515.

Lavigne F., B. De Coster, N. Juvin, F. Flohic, JC. Gaillard, P. Texier, J. Morin, J. Sartohadi, People's behaviour in the face of volcanic hazards: Perspectives from Javanese communities, Indonesia, *J. Volcanol. Geortherm. Res.*, 172, 273-287, doi: 10.1016/j.jvolgeores.2007.12.013.

Le Friant, A., E.J. Lock, M.B. Hart, G. Boudon, R.S.J. Sparks, M.J. Leng, C.W. Smart, J.C. Komorowski, C. Deplus, and J.K. Fisher (2008), Late Pleistoicene tephrochronology of marine sediments adjacent to Montserrat, Lesser Antilles volcanic arc. *J. Geol. Soc. London*, 165, 279-289.

Le Friant, A., P. Heinrich, G. Boudon (2008). Field survey and numerical simulation of the 21 November 2004 tsunami at Les Saintes (Lesser Antilles), *Geophys. Res. Lett.* doi:10.1029/2008GL034051

Letourneur, L., A. Peltier, Th. Staudacher, and A. Gudmundsson (2008). The effects of rock heterogeneities on dyke paths and asymmetric ground deformation; the example of Piton de la Fournaise (Réunion Island), *J. Volcanol. Geotherm. Res.*, doi:10.1016/j.jvolgeores.2008.01.018, 173, 289-302

Merle, O., L. Michon, P. Bachèlery (2008). Caldera rim collapse: a hidden volcanic hazard, *J. Volcanol. Geotherm. Res.*, doi: 10.1016/j.jvolgeores.2008.06.011, 177, 525-530.

Michon L., L. V. Cayol, Letourneur, A. Peltier, N. Villeneuve, T. Staudacher (2008), Edifice growth, deformation and rift zone development in basaltic setting: insights from Piton de la Fournaise shield volcano (La Réunion Island). *J. Volcanol. Geortherm. Res.*, special issue: Piton de La Fournaise doi: 10.1016/j.jvolgeores.2008.11.02

Michon, L., And F. Saint-Ange (2008), Morphology Of Piton De La Fournaise Basaltic Shield Volcano (La Réunion Island): Characterization And Implication In The Volcano Evolution. *J. Geophys. Res.*, 113, B03203, DOI:101029/2005JB0044118.

Michon L., Villeneuve N., Catry Th, Merle O. (2008), How summit calderas collapse on basaltic volcanoes: new insights from the April 2007 caldera collapse of Piton de la Fournaise volcano, *J. Volcanol. Geortherm. Res.*, special issue: Piton de La Fournaise doi: 10.1016/j.jvolgeores.2008.11.003.

Morin J., De Coster B., Flohic F., Lavigne F., Le Floch D., Paris R., (2008), Assessment and prevention of tsunami risk in Indonesia. Disaster Prevention and Management, vol.17:3, pp. 430-446.

Peltier, A., V. Famin, P. Bachèlery, V. Cayol, Y. Fukushima, and Th., Staudacher (2008), Cyclic magma storages and transfers at Piton de La Fournaise volcano (La Réunion Island) inferred from deformation and geochemical data. *Earth. Planet. Sci. Lett.* doi:10.1016/j.epsl.2008.02.042, 270,180-188.

Pili E., S. Bureau, F. Perrier, D. Patriarche, L. Charlet, P. M. Adler, P. Richon (2008). Reactive transport and residence times in unsaturated fractured rocks from field-scale experiments, American Chemical Society Developments in Earth & Environmental Sciences, M. Barnett and D. Kent (Editors), 7, 445-473, 2008. DOI 10.1016/S1571-9197(07)07016-4.

Prono E., J. Batttaglia, V. Monteiller, J.L. Got, V. Ferrazzini (2008). P-wawe veLOCITY structure of piton de la Fournaise volcano deduced from seismic data recorded between 1996 and 1999. *J. Volcanol. Geotherm. Res.* special issue: Piton de la Fournaise, doi: 10.1016/j.jvolgeores.2008.12.009.

Revil A., Finizola A., Piscitelli S., Rizzo E., Ricci T., Crespy A., Angeletti B., Balasco M., Barde Cabusson S., Bennati L., A. Bolève., Byrdina S., Carzaniga N., Di Gangi F., Morin J., Perrone A., Rossi M., Roulleau E., Suski B. Inner structure of La Fossa di Vulcano (Vulcano Island, southern Tyrrhenian Sea, Italy) revealed by high resolution electric resistivity tomography coupled with self-potential, temperature, and CO2 diffuse degassing measurements. Journal of Geophysical Research, Vol. 113, B07207, doi:10.1029/2007JB005394.

Samper, A., X. Quidelleur, G. Boudon, A. Le Friant, and J.C. Komorowski (2008). Radiometric dating of three large volume flank-collapses in the Lesser Antilles Arc, *J. Volcanol. Geortherm. Res.* doi: 10.1016/j.jvolgeores.2008.02.028.

Spence, R., J-C. Komorowski, K. Saito, A. Brown, A. Pomonis, G. Toyos, and P. Baxter (2008), Modelling the impact of a hypothetical sub-Plinian eruption at la Soufrière of Guadeloupe (West Indies). *J. Volcanol. Geotherm. Res.*, doi: 10.1016/j.jvolgeores.2008.03.016, 178:516-528

Staudacher T., V. Ferrazzini, A. Peltier, P. Kowalski, P. Boissier, P. Catherine, F. Lauret, F. Massin, The April 2007 eruption and the Dolomieu crater collapse, two major events at Piton de la Fournaise. *J. Volcanol. Geortherm. Res.*, special issue: Piton de La Fournaise doi: 10.1016/j.jvolgeores.2008.11.005

Villemant, B., J. Mouatt, and A. Michel (2008), Andesitic Magma Degassing Investigated Through H2O Vapour-Melt Partitioning of Halogens at Soufrière Hills Volcano, Montserrat (Lesser Antilles) *Earth. Planet. Sci. Lett.*, doi:10.1016/j.epsl.2008.02.014, 269 (1-2), 212-229.

Vlastelic I., Deniel C. Bosq C., Télouk P., Boivin P., Bachèlery P., Famin V., Staudacher Th. (2008), Pb isotopic geochemistry of Piton de la Fournaise historical lavas, change *J. Volcanol. Geortherm. Res.*, special issue: Piton de La Fournaise, doi: 10.1016/j.jvolgeores.2008.08.008.

Villeneuve N., Neuville D., Boivin P., Bachèlery P., Richet P., Magma crystallization and viscosity: A study of molten basalts from the Piton de la Fournaise volcano (La Réunion island), *Chemical Geology*, 256, 242-251.

• 2007

Aubert, M., S. Diliberto, A. Finizola, and Y. Chébli (2007), Double origin of hydrothermal convective flux variations in the Fossa of Vulcano (Italy), *Bull. Volcanol.*, doi: 10.1007/s00445-007-0165-y.
Bernard, M.L., M. Zamora, Y. Géraud, and **G. Boudon** (2007), Transport properties of pyroclastic rocks from Montagne Pelée volcano (Martinique, Lesser Antilles). *J. Geophys. Res.*, **112**(B5), B05205, 10.1029/2006JB004385.

Boudon, G., A. Le Friant, J.-C. Komorowski, C. Deplus, and M.P. Semet (2007), Volcano flank instability in the Lesser Antilles Arc: diversity of scale, processes, and temporal recurrence. *J. Geophys. Res.* **112**, B08205, doi:10.1029/2006JB004674

Bouhifd, M.A., **P. Besson**, P. Courtial, C. Gérardin, A. Navrotsky and P. Richet (2007), Thermochemistry and melting properties of basalt. *Contrib. Mineral. Petrol.* **153**, 689-698.

Brenguier, F., N.M. Shapiro, M. Campillo, A. Nercessian, and **V. Ferrazzini** (2007), 3-D surface wave tomography of the Piton de la Fournaise volcano using seismic noise correlations. *Geophys. Res. Lett.*, **34**, L02305, doi:10.1029/2006GL028586.

Carter, A., B. van Wyk de Vries, K. Kelfoun, **P. Bachèlery**, and P. Briole (2007). Pits, rifts and slumps: the summit structure of Piton de la Fournaise. *Bull. Volcanol*. doi 10.007/s00445-006-0103-4

Chopart JL., **N. Payet**, H. Saint Maccary, M. Vauclin, Is maize root growth affected by pig slurry application on a tropical acid soil?, *Plant Root*, **1**: 75-84, doi: 10.3117/plantroot.1.75

Coppola D, **Th. Staudacher**, and C. Cigolini (2007), Field thermal monitoring during the August 2003 eruption at Piton de la Fournaise (La Réunion). *J. Geophys. Res.*, **112**, B5, B05215, 10.1029/2006JB004659.

Halama, R., J.L. Joron, **B. Villemant**, G. Markl, and M.Treuil (2007), Trace element constraints on mantle sources during mid-Proterozoic magmatism: Evidence for a link between the Gardar (South Greenland) and Abitibi (Canadian Shield) mafic rocks. *Can. Jour. Sci.*, **44**, 459-478.

Hirono, T., T. Yokoyama, Y. Hamada, W. Tanikawa, T. Mishima, M. Ikehara, **V. Famin**, M. Tanimizu, W. Lin, W. Soh, and S. Song (2007). A chemical kinetic approach to estimate dynamic shear stress during the 1999 Taiwan Chi-Chi earthquake, *Geophys. Res. Lett.*, 34, L19308, doi:10.1029/2007GL030743.

Longpré, M.-A., **Th. Staudacher** and J. Stix (2007), The November 2002 eruption at Piton de la Fournaise volcano, La Réunion Island: ground deformation, seismicity, and pit crater collapse, *Bull. Volcanol*. doi: 10.1007/s00445-006-0087-0.

Michon, L., F. Saint-Ange, **P. Bachèlery**, N. Villeneuve, and **Th. Staudacher** (2007), Role of the structural inheritance of the oceanic lithosphere in the magmato-tectonic evolution of Piton de la Fournaise volcano (La Réunion Island). *J. Geophys. Res.* **112**, B4, B04205, 10.1029/2006JB004598.

Michon, L., **Th. Staudacher**, **V. Ferrazzini**, **P. Bachèlery**, J Marti, (2007), April 2007 collapse of Piton de la Fournaise: a new example of caldera formation, *Geophys. Res. Lett.*, 34, L21301, doi:10.1029/2007GL031248.

Nicollin, F., D.Gibert, **F. Beauducel**, **G. Boudon**, and **J.-C. Komorowski** (2007), Reply to comment on "Electrical Tomography of La Soufrière of Guadeloupe Volcano: Field Experiments, 1D Inversion and Qualitative Interpretation by N. Linde and A. Revil. *Earth Planet. Sci. Lett.* 258, 623-626.

Peltier, A., **T. Staudacher**, **P. Bachèlery** (2007), Constraints on magma transfers and structures involved in the 2003 activity at Piton de La Fournaise from displacement data. *J. Geophys. Res.*, **112**, B3, B03207, 10.1029/2006JB004379.

Perrier F., **P. Richon**, U. Gautam, D.R. Tiwari, P. Shrestha, and S.N. Sapkota (2007), Seasonal variations of natural ventilation and radon-222 exhalation in a slightly rising dead-end tunnel. *J. Environmental Radioactivity*, **97**, 220-235.

Remusat, L., F. Robert, and S. Derenne (2007), The Insoluble Organic Matter in carbonaceous chondrites: chemical structure, isotopic composition and origin. *C.R. Geosciences*, doi:10.1016/j.crte.2007.10.001, 339, 895-906.

Richon P., P. Bernard, V. Labed, J.-C. Sabroux, A. Beneïto, D. Lucius, S. Abbad, and M.C. Robe (2007), Results of monitoring 222Rn in soil gas of the Gulf of Corinth region, Greece. *Radiation Measurements* **42**, 87-93.

Touboul, M., B. Bourdon, **B. Villemant**, **G. Boudon**, J.L. Joron (2007) ²³⁸U·²³⁰Th·²²⁶Ra disequilibria in andesitic to dacitic lavas of the 1440 Soufrière eruption (Guadeloupe): processes and timescales of magma differentiation. *Chemical Geology*, **246**, 181-206.

Urai, M., N. Geshi, and **T. Staudacher** (2007), Size and volume evaluation of the caldera collapse on Piton de la Fournaise volcano during the April 2007 eruption using ASTER stereo imagery, *Geophys. Res. Lett.*, 34, L22318, doi: 10.1029/2007GL031551

Vlastelic, I., **A. Peltier**, and **T. Staudacher**, Short-term (1998-2006) fluctuations of Pb isotopes at Piton de la Fournaise volcano (Reunion Island): origins and constrains on the size and shape of the magma reservoir.
*Chemical Geology*, **244**, 202-220.

**Equipe Géochronologie - Dynamique des Systèmes Volcaniques**

UMR IDES 8148, Université Paris-Sud 11, Orsay.

Les recherches de l'équipe géochronologie-dynamique des systèmes volcaniques (GDSV) portent principalement sur la reconstruction de l'histoire des systèmes éruptifs en tous types de contextes géodynamiques et l'analyse des différents facteurs de risque liés à leur évolution (aléas éruptifs et gravitaires). Ces recherches mettent en œuvre des compétences et des approches variées, à l'interface entre les différentes disciplines des Sciences de la Terre et des Planètes (cartographie des systèmes volcaniques,
géochronologie, géomorphologie quantitative, géochimie des magmas et des fluides crustaux, modélisations numériques). Une part importante des travaux est également consacrée à la calibration des échelles des temps géologiques et des inversions magnétiques et à la datation des grandes crises de l'histoire de la Terre. L'originalité du groupe GDSV est en effet fondée sur des techniques de mesure d'âge exploitant le K-Ar et le $^{40}$Ar/$^{39}$Ar. Les techniques de datation sont mises au point et les appareils conçus et réalisés par les chercheurs afin d'atteindre la meilleure performance analytique adaptée aux besoins des études. Les recherches du groupe sont réalisées en partenariat avec des collègues français et étrangers dans le cadre de programmes nationaux (ANR, DYETI, INSU-relief, CNES) et internationaux (UFI, TEAMINT, GTS-Next, MEGA-HAZARDS). Ces financements servent actuellement de support à la réalisation de cinq thèses en cours, dont 1 en cotutelle, et quatre thèses soutenues ces quatre dernières années. Les travaux de l'équipe ont donné lieu à la publication de plus de 30 articles de rang A dans des revues internationales entre 2007 et 2010.

## English summary

Research topics of the team geochronology-dynamics of volcanic systems in Orsay are mostly focussed on the reconstruction of the history of volcanic systems in all types of geodynamic settings and on the analysis of natural hazards linked to their evolution (eruptive and mass-wasting processes). This research involves Earth scientists with complementary skills and expertise (geological mapping of volcanic systems, geochronology, quantitative geomorphology, geochemistry of magma and crustal fluids, numeric modelling). An important part of our work is also devoted to the calibration of the geological and paleomagnetic timescales, and to dating of the major crises in the history of the Earth. The originality of our group relies on the development of high-precision accurate geochronology including conventional unspiked K/Ar and $^{40}$Ar/$^{39}$Ar. The techniques and instruments are designed and developed in-house to reach the best performance adapted to the requirements of our different studies. Our research is conducted in collaboration with partners from France and abroad in the framework of national and international programs (e.g., UFI, TEAMINT, GTS-Next, MEGA-HAZARDS). Such funding is presently supporting 5 ongoing PhDs, including one in co-supervision with academics from foreign universities, and 4 thesis defended during the last four years. The research from our team for the 2007-2010 period has been published as more than 30 articles in peer-reviewed international journals.

## List of IDES publications

Germa A., Quidelleur X., Lahitte P., Labanieh S, and Chauvel C, 2011. The K-Ar Cassignol-Gillot technique applied to western Martinique lavas: A record of the evolution of the recent Lesser Antilles island arc activity from 2 Ma to Mount Pelée volcanism, Quaternary Geochronology, accepté.

Lahitte, P., Samper, A. and Quidelleur X., 2011. DEM-based reconstruction of Southern Basse Terre volcanoes (Guadeloupe archipelago, FWI): a contribution to the Lesser Antilles Arc volumetric extrusion and erosion rates. Geomorphology, accepté.

Germa A., Quidelleur X., Labanieh S., Lahitte P. and Chauvel C, 2010. The eruptive history of Morne Jacob volcano (Martinique Island, French West Indies): geochronology, geomorphology and geochemistry of the earliest volcanism in the recent Lesser Antilles arc. J. Volcanol. Geotherm. Res., 198, 297-310.

Quidelleur, X., Holt, J.W., Salvany, T. and Bouquerel H., 2010. New K-Ar ages from La Montagne massif, Réunion Island (Indian Ocean) supporting two geomagnetic events in the time period 2.2 – 2.0 Ma. Geophys. J. Int., 182 : 699-710.

Germa, A., Quidelleur, X., Gillot, P.Y., Tchilingurian, P., 2010. Volcanic evolution of the back-arc Pleistocene Payun Matru volcanic field (Argentina). J. South Am. Earth Sci., 29 : 717-730.

Samper, A., Quidelleur X., Komorowski, J.C., Lahitte, P., Boudon, G., 2009. Effusive history of the Grande Découverte Volcanic Complex, southern Basse-Terre (Guadeloupe, French West Indies) from new K-Ar Cassignol-Gillot ages. J. Volcanol. Geotherm. Res., 187: 117-130.

Hildenbrand, A., Madureira, P., Ornelas Marques, F., Cruz, I., Henry, B., and P. Silva, 2008. Multi-stage evolution of a sub-aerial volcanic ridge over the last 1.3 Myr: S. Jorge Island, Azores Triple Junction. Earth Planet. Sci. Lett., 273: 289-298.

Samper, A., Quidelleur X., Boudon, G., Le Friant, A., Komorowski, J.C., 2008. Radiometric dating of three large volume flank collapses in the Lesser Antilles arc. J. Volcanol. Geotherm. Res., 176: 485-492.

Rouchon, V., Gillot, P.Y., Quidelleur, X., Chiesa, S., Floris, B., 2008. Temporal Evolution of the Roccamonfina volcanic complex (Plesitocene), Central Italy. J. Volcanol. Geotherm. Res., 177 : 500-514.

Quidelleur, X., Hildenbrand, A., Samper, A., 2008 ; Link between paleoclimatic changes and oceanic islands evolution. Geophys. Res. Lett., 35: L02303.

Hildenbrand, A., Gillot, P.Y. and Marlin, C., 2008. Geomorphological study of long-term erosion on a tropical volcanic ocean island: Tahiti-Nui (French Polynesia), Geomorphology, 93 (3-4) : 460-481.

Samper, A., Quidelleur X., Lahitte, P., Mollex, D., 2007. Timing of effusive volcanism within the whole Basse Terre Island (Guadeloupe, F.W.I.) from new K-Ar Cassignol-Gillot Ages. Earth Planet. Sci. Lett., 258: 175-191.

Guérin, G and Gillot, P-Y, 2007. Nouveaux éléments de chronologie du volcanisme Pléistocène du Bas-Vivarais (Ardèche, France) par thermoluminescence. C.R. Geosciences, 339, 40-49.
# DATATIONS DES ACTIVITES VOLCANIQUES HISTORIQUES

M. Condomines (Montpellier), J-C. Tanguy (St Maur)

L'essentiel de nos résultats concerne la succession des éruptions des derniers millénaires pour les volcans italiens par la méthode archéomagnétique de haute précision particulière au laboratoire de St Maur (Tanguy et al., 2007, 2009, Figure 1). Dans de nombreux cas cependant il a été nécessaire de recourir à la méthode $^{226}$Ra-$^{230}$Th (Condomines et al., 2005, Fig. 2) pour discriminer entre des directions géomagnétiques semblables à des époques différentes.

<figure><img src="image_51.png" /><figcaption>Figure 1</figcaption></figure>

La Figure 1 montre la variation de la direction du champ géomagnétique en Sicile (ligne orange) au cours des derniers 2000 ans, en bon accord avec la courbe archéomagnétique en France (tireté noir). Les cercles de confiance à 95% de probabilité des directions magnétiques figées dans les laves (Etna en bleu, Vésuve en rouge, Ischia en jaune), permettent des datations très précises (±40 ans en moyenne). On voit cependant qu'il est impossible de discriminer les périodes 600-800 et 1600-1650 où le champ montrait des orientations très voisines.

La Figure 2 montre la corrélation ($^{226}$Ra)$_0$ - Th obtenue à partir de coulées historiques d'âges connus, et qui sert de référence pour la datation des coulées d'âge indéterminé. ($^{226}$Ra)$_0$ est l'activité du $^{226}$Ra en désintégrations par minute et par gramme, recalculée au moment de l'éruption.

<figure><img src="image_52.png" /></figure>

L'identification des produits volcaniques (par exemple) méthodes montre que beaucoup de laves « historiquement datées » (80% de celles antérieures à 1700, dates entre guillemets sur la fig. 1) sont dues en réalité à d'autres éruptions (dates entre parenthèses), souvent non enregistrées par les documents écrits, les écarts atteignant plusieurs siècles et parfois plus d'un millénaire. Cette révision de l'histoire des volcans italiens a des implications importantes sur la cartographie, les statistiques, les mécanismes éruptifs, la protection civile.

Un autre aspect des travaux basés sur les déséquilibres $^{226}$Ra-$^{230}$Th récents concerne un modèle d'accumulation du $^{222}$Rn (Radon) dans les magmas, qui peut expliquer les excès de $^{210}$Pb observés dans beaucoup de roches volcaniques actuelles (Condomines et al., 2010). Ce modèle vient compléter celui établi par Gauthier et Condomines (1999) pour le dégazage du $^{222}$Rn. Il a été appliqué au cas de Santorin et de Surtsey, et les
résultats suggèrent que l'accumulation de Rn peut en effet expliquer les forts excès de $^{210}$Pb, aussi bien dans une chambre zonée (Santorin) que dans les vésicules de ségrégation d'une coulée de lave (Surtsey).

## Publications

CONDOMINES M., GAUTHIER P. J., TANGUY J. C., GERTISSER R., THOURET J.C., BERTHOMMIER P., CAMUS G. (2005) $^{226}$Ra or $^{226}$Ra/Ba dating of Holocene volcanic rocks: Application to Mt Etna and Merapi volcanoes. Earth and Planet. Sci. Lett. 230, 289-300.

CONDOMINES M., SIGMARSSON O., GAUTHIER P. J. (2010). A simple model of $^{222}$Rn accumulation leading to $^{210}$Pb excesses in volcanic rocks. Earth and Planet. Sci. Lett. 293, 331-338.

LIOTARD J. M., DAUTRIA J. M., BOSCH D., CONDOMINES M., MEHDIZADEH H., RITZ J. F. (2008). Origin of the absarokite-banakite association of the Damavand volcano (Iran). Trace element and Sr, Nd, Pb isotope constraints. Int. J. of Earth Sciences, 97/1, 89-102.

TANGUY J.C., CONDOMINES M., LE GOFF M., CHILLEMI V., LA DELFA S., PATANÈ G. (2007) *Mount Etna eruptions of the last 2750 years: revised chronology and location through archeomagnetic and $^{226}$Ra-$^{230}$Th dating*. Bull. of Volcanology 70: 55-83.

TANGUY J.C., LE GOFF M., ARRIGHI S., PRINCIPE C., LA DELFA S., PATANÈ G. (2009) *The History of Italian Volcanoes revised by Archeomagnetism*. EOS, vol. 90, n. 40, 349-350.

VEZZOLI L., PRINCIPE C., MALFATTI J., ARRIGHI S., TANGUY J.C., LE GOFF M. (2009) *Modes and times of caldera resurgence: The <10 ka evolution of Ischia Caldera, Italy, from high-precision archeomagnetic dating*. J. Volcanol. Geotherm. Res. 186, 305-319.

TANGUY J.C., BACHÈLERY P., LE GOFF M. (in press). *Archeomagnetism of Piton de la Fournaise: bearing on volcanic activity at La Réunion Island and geomagnetic secular variation in Southern Indian Ocean*. Earth Planet. Sci. Letters, accepted for publication.
# COOPERATION FRANCO-INDONESIENNE EN VOLCANOLOGIE

Avec le partenaire
DVGHM Center of Volcanology and Geologic Hazards Mitigation
Bandung, Java, Indonesia

## 1 RAPPORT D'ACTIVITE 2010

Coordonnateur : Jean-Claude THOURET

PRES Clermont, Université Blaise Pascal, Laboratoire Magmas et Volcans UMR 6524
CNRS et IRD, OPGC
5 rue Kessler, 63038 Clermont-Ferrand cedex
(J.C.Thouret@opgc.univ-bpclermont.fr)

<figure><img src="image_53.png" /></figure>

### INTRODUCTION

Avec plus de 120 volcans actifs répartis sur les 4000 km de l'archipel et une densité de population de l'ordre de 120 habitants/km² (830 à Java), l'Indonésie est le pays au monde où le risque volcanique est le plus élevé. L'Indonésie est par ailleurs un terrain d'activité exceptionnel pour la communauté volcanologique française. La coopération franco-indonésienne en volcanologie, initiée en 1986 sous l'égide de Haroun Tazieff, alors secrétaire d'Etat à la Prévention des Risques Majeurs, s'est développée sous
l'impulsion du MAEE (Ministère des Affaires Etrangères et Européennes). Outre les activités de formation et de transfert de technologies vers le partenaire indonésien, les équipes françaises ont obtenu des résultats scientifiques remarquables qui se traduisent par une bibliographie fournie et une reconnaissance internationale incontestable. Le partenaire privilégié en Indonésie est le Center of Volcanology and Geological Hazards Mitigation (CVGHM, ex-VSI : Volcanological Survey of Indonesia). Il est chargé de la gestion des risques naturels et est l'autorité de tutelle des observatoires répartis dans l'archipel. Il contribue à la mise en place et soutient les missions et la maintenance des équipements.

L'Ambassade de France, dans le cadre de son programme de coopération culturelle et scientifique, co-finance pour partie les activités de recherche appliquée et d'échanges (équipements et fonctionnement, missions). Elle finance également des bourses d'étude pour les étudiants indonésiens pour la réalisation de mémoires de M2 et de thèses dans les laboratoires français.

**Cette coopération poursuit trois objectifs :**

1) la formation à la recherche à l'intention des Indonésiens (thèses, stages, collaborations sur site), l'aide à la surveillance opérationnelle (mise en place de réseaux de surveillance) et le transfert de technologie ;

2) Une contribution essentielle à l'évaluation de l'aléa et du risque volcanique grâce à la surveillance des volcans dangereux, la prévision de certains phénomènes précurseurs et l'aide à la prévention, qui incombe à notre partenaire DVGHM en Indonésie ;

3) un retour d'expérience fondamental pour la France : compréhension des processus, mise au point d'instrumentation et de protocoles expérimentaux, formation de scientifiques français (chercheurs, doctorants), apprentissage de la confrontation aux situations de crise sur les volcans explosifs.

4)

## ACTEURS DE LA COOPERATION

**Responsables de thématiques intervenus en 2010 :**

Franck LAVIGNE (LGP, aspect sociétal du risque) : [francklavigne@yahoo.fr](mailto:francklavigne@yahoo.fr)

Philippe LESAGE (OSUG-LGIT, sismologie) : [lesage@univ-savoie.fr](mailto:lesage@univ-savoie.fr)

Jean-Philippe METAXIAN (OSUG-LGIT, sismologie) : [Jean-Philippe.Metaxian@univ-savoie.fr](mailto:Jean-Philippe.Metaxian@univ-savoie.fr)

Patrick RICHON (CEA-DASE, géochimie gaz) : [patrick.richon@cea.fr](mailto:patrick.richon@cea.fr)

Coordonnateur : Jean-Claude THOURET (LMV-OPGC, dynamique coulées pyroclastiques et lahars) : [J.C.Thouret@opgc.univ-bpclermont.fr](mailto:J.C.Thouret@opgc.univ-bpclermont.fr)

Jean-Paul TOUTAIN (OMP-LMTG et IRD, géochimie) : [toutain@lmtg.obs-mip.fr](mailto:toutain@lmtgobs-mip.fr)

**Impliqués également dans la coopération, n'étant pas intervenus en 2010, mais susceptibles d'intervenir dans les années prochaines :**

François BEAUDUCEL (IPGP, déformations, GPS) : [beauducel@ipgp.jussieu.fr](mailto:beauducel@ipgp.jussieu.fr)

Anastasia BORISSOVA (LMTG, pétrologie) : [borisova@lmtg.obs-mip.fr](mailto:borisova@lmtgobs-mip.fr)

Hélène Celle-JEANTON (LMV-OPGC, hydrogéologie) : [h.celle-jeanton@opgc.univ-bpclermont.fr](mailto:h.celle-jeanton@opgc.univ-bpclermont.fr)

Catherine DENIEL (LMV-OPGC, géochimie) : [deniel@opgc.univ-bpclermont.fr](mailto:deniel@opgc.univ-bpclermont.fr)

Alain GOURGAUD (LMV-OPGC, dynamique des dômes) : [A.Gourgaud@opgc.univ-bpclermont.fr](mailto:A.Gourgaud@opgc.univ-bpclermont.fr)

Philippe JOUSSET (BRGM), [p.jousset@brgm.fr](mailto:p.jousset@brgm.fr)
Karim KELFOUN (LMV-OPGC, dynamique des dômes) : [K.Kelfoun@opgc.univ-bpclermont.fr](mailto:K.Kelfoun@opgc.univ-bpclermont.fr)

Jean-Luc LE PENNEC (LMV-IRD, volcanologie physique) : J.L.Lepennec@opgc.univ-bpclermont.fr

Séverine MOUNE (LMV-OPGC, géochimie gaz, flux de SO₂) : [S.Moune@opgc.univ-bpclermont.fr](mailto:S.Moune@opgc.univ-bpclermont.fr)

Dominique REMY (LMTG-OMP, télédétection, INSAR) : [remy@lmtgobs-mip.fr](mailto:remy@lmtgobs-mip.fr)

Jacques ZLOTNICKI (LMV-OPGC, électromagnétisme) : [jacques.zlotnicki@wanadoo.fr](mailto:jacques.zlotnicki@wanadoo.fr)

## Affiliations :

**LMV-OPGC** : Observatoire de Physique du Globe de Clermont-Ferrand, Laboratoire Magmas et Volcans CNRS et IRD, Université Blaise Pascal (Clermont-Ferrand)

**LMTG-OMP** : Observatoire Midi-Pyrénées, Laboratoire d'Etude des Mécanismes de Transfert en Géologie (Toulouse)

**OSUG-LGIT** : Observatoire des Sciences de l'Univers de Grenoble, Laboratoire de Géophysique Interne et de Tectonophysique (Grenoble) et Université de Savoie à Chambéry

**IPGP** : Institut de Physique du Globe de Paris (Paris)

**CEA-DASE** : Département Analyse Surveillance Environnement, Commissariat à l'Energie Atomique

**LGP** : Laboratoire de Géographie Physique, CNRS UMR 8591, Meudon et Université Panthéon-Sorbonne.

## ACTIVITES EN 2010 : OBJECTIFS

Nos activités en 2010 se sont plus particulièrement concentrées sur les volcans Merapi et Semeru. Elles ont inclus trois thèmes de recherche appliquée et une action de valorisation et de diffusion du savoir.

### 1. Surveillance des appareils actifs

- Etude des gaz des sols au volcan Merapi, actuellement en état d'alerte (éruption le 26 octobre 2010),

- Sismologie et exploration pour un projet ANR

### 2. Mesures des lahars au Semeru et télédétection haute résolution :

- suivi de l'évolution de l'appareil sommital par télédétection,

- étude des écoulements pyroclastiques de l'éruption du Merapi en 2006 par télédétection.

### 3. Evaluation des aléas et des risques, utilisation des matériaux volcaniques

### 4. Valorisation et diffusion du savoir et des savoir faires.

## MISSIONS effectuées en 2010

P. Richon et J.-P. Toutain (septembre 2010), F. Lavigne (septembre 2010), J.-Ph. Metaxian (octobre 2010) ; J.-C. Thouret et A. Solikhin (février 2010).

## ACTIVITE 1 :
### SURVEILLANCE DES APPAREILS ACTIFS

#### 1.1. MESURE DES GAZ DES SOLS SUR LE MERAPI, ²²²Rn, TEMPERATURE ET CO₂, DEVELOPPEMENT D'UN NOUVEL OUTIL DE SURVEILLANCE.

P. Richon (CEA), J.P. Toutain (IRD) - CEA-DASE & BPPTK, VSI, BMKG
Le Mérapi est l'un des volcans les plus actifs et plus explosifs (VEI = 2-4) d'Indonésie. Il menace directement l'une des zones les plus densément peuplées de Java (Yogyakarta et sa région). Ses éruptions paroxysmales dans le passé, associées à des écroulements de flancs, ont recouvert toute la région d'épais dépôts pyroclastiques (ensevelissement du temple de Borobudur). En dépit d'une longue surveillance, ses éruptions font toujours des victimes, un millier en 1930 et une vingtaine en 1994. Depuis 1872, l'activité continue du volcan consiste en des phases de croissance puis démantèlement (effondrement ou/et explosion) de dômes andésitiques, avec émission de coulées pyroclastiques et de lahars. Le Merapi est considéré comme le volcan de référence pour l'émission de coulées pyroclastiques engendrées par écroulement gravitaire de dôme. Il présente également un intense dégazage magmatique, matérialisé par un panache permanent issu du dôme de lave (>900 °C) et d'évents fumerolliens latéraux (> 600 °C). C'est un des volcans de référence pour la géochimie des gaz volcaniques et l'étude des processus de dégazage. Son éruption très spectaculaire en 2006, qui a fortement affecté le tissu socio-économique javanais, fut atypique, avec un dôme de volume inhabituel, d'étroites interactions avec la sismicité régionale et une phénoménologie inhabituelle des coulées pyroclastiques. Il est surveillé par l'Observatoire du Merapi (BPPTK) qui relève de l'autorité du DVGHM.

L'intérêt pour le Mérapi est dicté d'abord par la nécessité d'apporter un soutien aux autorités scientifiques indonésiennes, et ensuite par la forte ressemblance de cet appareil avec les volcans français antillais à dômes explosifs (Soufrière, Montagne Pelée). L'objectif est donc d'obtenir également un retour d'expérience directement utilisable en cas de crise volcanique en Guadeloupe ou Martinique.

Dans le cadre de la collaboration Franco-Indonésienne, le CEA-DASE participe depuis 2002 à des campagnes de mesure des gaz des sols sur le Merapi. Notre collaboration sur place s'effectue essentiellement avec les scientifiques de l'Observatoire Volcanologique du Merapi (BPPTK) et son directeur, mais aussi, historiquement, avec le BMKG, Badan Meteorologi Klimatologi dan Geofisika, Institut national de Météorologie et de Géophysique où un VIE du CEA-DASE y est en poste permanent.

Notre domaine d'intervention réside essentiellement dans la prospection et le suivi des émanations gaz des sols (T°, ²²Rn, CO₂), cf. Fig. 1, ainsi que dans l'étude de leurs relations avec les structures volcano-tectoniques et les fluctuations d'activité volcanique.
<figure><img src="image_54.png" /><figcaption>**Figure 1.** Totalité des données enregistrées à la station MK1 (Kawha Mati crater) de 2002 à 2006, juste avant l'éruption de Juin 2006 et le séisme de Yogyakarta (Mw 6.4).</figcaption></figure>

L'objectif, à terme, est d'obtenir un outil de surveillance des phases de pressurisation du dôme de lave qui nous permettrait d'anticiper les épisodes d'écroulements catastrophiques qui se produisent de façon récurrente et qui menacent la sécurité des populations environnantes. Les objectifs principaux de cette collaboration sont :

1) La mise en place de réseaux de surveillance novateurs (mesures T°, ²²²Rn et météorologie).

2) L'expérimentation et la validation de nouvelles stratégies de prospection des zones de gaz summitales (mesure de flux par chambre d'accumulation et par imagerie thermique basse température, Testo™).

3) La surveillance par la mesure ponctuelle du radon-222 et du thoron (radon-220) dans les gaz fumerolliens de Woro et Gendol.

4) La formation des chercheurs du MVO, sur la thématique du radon-222 des gaz des sols, formation devant déboucher à terme à la maitrise de la métrologie par les chercheurs de l'observatoire.

5) Une cartographie thermique des zone de dégazage, et choisir ainsi plus judicieusement les point intéressants pour le déploiement des 4 sondes radon et des dix capteurs de températures.

6) Les données météorologiques sont nécessaires pour interpréter les signaux des réseaux électromagnétiques et géochimie. La station actuelle hors service depuis
l'éruption de 2006 sera redéfinie, se limitant à un pluviomètre équipé d'un capteur de température de l'air + pression atmosphérique (T°air, Patm, pluviométrie).

Un des objectifs à terme, une fois que la dynamique de chaque station sera bien comprise, est de transmettre en temps réel, les données collectées directement à l'observatoire, afin que les chercheurs du MVO prennent possession du réseau.

Le planning prévisionnel débutera en Septembre 2011 pour les opérations de prospection et de remise en place du réseau et ce jusqu'à la prochaine éruption.

**Intervenants :**

Patrick Richon, Ingénieur-Chercheur au CEA-DASE ; Jean-Paul Toutain (IRD, Jakarta) ; VIE DASE (BMKG Jakarta).

**References**

Richon P., J.-C. Sabroux, M. Halbwachs, J. Vandemeulebrouck, N. Poussielgue, J. Tabbagh, R. Punongbayan, Radon anomaly in the soil of Taal volcano, the Philippines: A likely precursor of the M 7.1 Mindoro earthquake (1994), Geophys. Res. Lett., 30 (9), 1481, doi:10.1029/2003GL016902, 2003.

Toutain J. P., Sortino F., Baubron J. C., Richon P., Surono, Sumarti S., Nonell A., 2009. Structure and CO₂ budget of Merapi volcano during inter-eruptive periods. B. Volcanol. 71(7), 815-826.

Richon P., Toutain J.-P., Baubron J.-C., Labat D., Radtmatopurbo A., 2010. Radon-222 and thermal transient related to the 2006 seismo-volcanic event at Merapi volcano, Indonesia. Geophys. Res. Lett., Submitted.

**1.2. Mission en sismologie et exploration pour un projet ANR en Indonésie**

(Octobre 2010) -Jean-Philippe Métaxian, IRD et LGIT

**Objectifs**

Cette mission avait pour objectifs 1) l'évaluation des besoins en sismologie volcanique ; 2) la préparation d'un projet ANR sur le thème de la modélisation de la dynamique des dômes volcaniques appliquée au Merapi. Ce projet se place dans le cadre du développement des activités scientifiques de VELI. 3) l'analyse de données en collaboration avec des collègues du CVGHM.

**Calendrier**

4 octobre 2010 : arrivée à Bandung.

5-8 Octobre : Séjour à Bandung, discussions avec le Dr Surono et le Dr Hendra Gunawan, travaux sur un logiciel de transformation de format de données sismiques.

8-14 Octobre : Séjour à l'Observatoire de Yogyakarta, discussion avec le directeur et les responsables de la surveillance. Analyse de données sismiques du volcan Merapi.

15 octobre : Visite au Service de Coopération et d'Action Culturelle à Jakarta.

**Préparation d'un projet ANR Modélisation de la croissance de dômes :**

**Application au Merapi**

Le Merapi est un volcan emblématique et un laboratoire international. Les conséquences de l'éruption actuelle montre, s'il était nécessaire, que cet appareil est le plus dangereux de l'Indonésie. Il s'agit aussi d'un volcan dont le dôme est actif, c'est-à-dire que l'extrusion de lave, lente, y est permanente. L'édification et la destruction de ce dôme, dont les pentes sont très raides au-dessus des flancs densément peuplés,
entraîne des écoulements pyroclastiques qui sont les processus volcaniques les plus meurtriers, avec les lahars.

Ce projet consiste à contraindre les modèles de dégazage, d'évolution rhéologique et de comportement mécanique d'extrusion et d'évolution de dômes magmatiques par des observations géochimiques, qui apportent par ailleurs des informations sur les processus magmatiques, des mesures géophysiques (déformations, activité sismique) et topographiques ainsi que par des données pétrologiques. Ce projet est en cours d'élaboration. Le produit devrait être un ou des modèles numériques d'écoulement du magma dans le conduit et de formation des dômes magmatiques. Le projet comporte également un volet surveillance. Il regroupe plusieurs laboratoires, le Laboratoire Magmas et Volcans ; (LMV), le laboratoire des mécanismes et transferts en Géologie (LMTG), L'institut de Sciences de la Terre d'Orléans (ISTO), l'Institut de Physique du Globe de Paris (IPGP) et le Laboratoire de Géophysique Interne et Tectonophysique (LGIT). Le partenaire indonésien est le CVGHM.

Les grandes lignes du projet ont été présentées au Dr Surono, directeur du CVGHM, et au directeur de l'Observatoire du Merapi à Yogyakarta. Ils ont donnés leur accord de principe pour l'accès à des données anciennes, l'installation de nouveaux équipements, une participation du personnel du CVGHM à la maintenance des équipements sur le terrain pendant la durée du projet. J'ai recueilli des informations concernant les données géophysiques et géochimiques existantes : type d'instrument, mode d'enregistrement des données, périodes de fonctionnement. La plupart de ces données sont inexploitées. C'est le cas notamment des données sismologiques. Le catalogue de données débute en 1990, ce qui englobe 6 éruptions du Merapi. L'analyse de ces données pour une meilleure définition des précurseurs éruptifs, la recherche de corrélations entre les différents cycles pré-éruptifs et éruptifs constituera une partie du projet. Les diverses informations recueillies nous permettent d'alimenter la réflexion concernant la structuration du projet et seront exploitées pour sa rédaction.

## Analyse de données sismiques du Merapi, propositions d'amélioration du système de surveillance

Mon séjour à l'observatoire de Yogya a coïncidé avec le début d'une crise du Merapi. Le niveau 2 a été déclaré fin septembre 2010. Cela a été l'occasion d'observer le fonctionnement du service de surveillance et noter des améliorations qui pourraient être apportées.

Le système de surveillance se compose d'un réseau sismique dont les données sont transmises par radio en temps réel. Il existe un réseau de mesures de déformations (EDM). Plusieurs réflecteurs sont installés autour du cône. Les mesures sont faites depuis les observatoires lorsque la visibilité le permet. Il y a aussi des capteurs de température proches du sommet au nord (coulée 1956) et au sud (WORO). Ces données sont aussi transmises par radio. Les autres mesures (GPS, gaz) sont faîtes ponctuellement sur le terrain. Le réseau sismique se compose de 4 stations équipées de capteurs courte période et d'une transmission analogique (réseau le plus ancien), de 3 stations large bande Guralp CMG-3ESP (60 sec) du projet MIA VITA équipés d'une transmission numérique (4 ou 5 stations sont prévues) et d'une station équipée d'un capteur large bande STS2 (120 sec) et d'une télémétrie numérique. Or ces 3 systèmes ont des temps différents. C'est un problème technique majeur qui doit être résolu dès que possible car les séismes ne peuvent être localisés à l'heure actuelle qu'avec les 4 stations du réseau analogique.
Par ailleurs, le personnel de l'Observatoire n'est pas formé à la localisation des séismes. J'ai travaillé avec Agus Budi Santoso sur ce thème en installant un programme de pointé des phases sismiques (pickev) et un programme de localisation (Hypoellipse). Les figures 1 et 2 représentent les résultats des localisations effectuées pendant mon séjour avec 4 stations.

<figure><img src="image_55.png" /><figcaption>Figure 1 : Localisation de séismes volcano-tectoniques pendant la période fin Septembre-début Octobre. Coupe Ouest-Est</figcaption></figure>

<figure><img src="image_56.png" /><figcaption>Figure 2 : Localisation de séismes volcano-tectoniques pendant la période fin Septembre-début Octobre. Coupe horizontale.</figcaption></figure>
Les résultats mettent en évidence 2 zones distinctes, une au sommet correspondant à la zone du dôme et l'autre plus profonde. On observe un manque de sources sismiques entre le niveau de la mer et 2 km d'altitude. La distribution horizontale de la sismicité correspond aux résultats obtenus lors de l'éruption de 2006. Ce résultat est très préliminaire, il reste à confirmer ou à infirmer en utilisant plus de stations.

Le comptage des séismes par type est effectué manuellement sur les enregistrements papier. Les signaux précurseurs caractéristiques d'une intrusion sont principalement des signaux de fracturation type VA (profonds) et type VB (superficiels), et des signaux associés au mouvements du magma de type MP (Multi-phase). Ce travail effectué manuellement est long et fastidieux. Il peut y avoir plusieurs centaines à plusieurs milliers de signaux en une journée pendant une éruption. La figure 3 représente la sismicité depuis début 2009. Ce système de comptage pourrait être amélioré en utilisant un programme qui intègre la visualisation de signaux numériques, le pointé de phases pour identifier l'heure de début, la durée, de l'analyse spectrale permettant de différencier les différents types de sources et enfin des calculs d'énergie. La demande d'un outil de ce type a été formulée par Agu Budi Santoso. Des programmes existant au LGIT seront adaptés au cas du Merapi pour améliorer le processus de comptage et la classification des séismes. Cet outil permettra de créer un catalogue de données qui pourra être utilisé ultérieurement comme entrée d'un système de classification automatique.

<figure><img src="image_57.png" /><figcaption>Figure 3 : Nombre de séismes par jour entre le 1er janvier 2009 et le 14 octobre 2010.
Vulkanik : séismes volcano-tectoniques types A (profonds) et B (superficiels) ; MP : séismes Multi-Phase ; LF : séismes basse fréquence ; Guguran : éboulements ; Tek : séismes tectoniques.</figcaption></figure>
## Conclusions

Cette mission a permis de préparer le projet ANR modélisation de la dynamique de dômes volcaniques appliqué au Merapi en collaboration avec le CVGHM. Elle a aussi permis de mettre en évidence des améliorations à apporter au système de surveillance du Merapi.

# ACTIVITE 2

## LAHARS ET TELEDETECTION, VOLCANS SEMERU ET MERAPI

### 2.1. Mesures et surveillance des lahars au Semeru

#### J.-C. Thouret et A. Solikhin (CVGHM, futur doctorant au LMV en 2011)

Les lahars ou coulées de débris et de boue sont les phénomènes volcaniques les plus dangereux, avec les écoulements pyroclastiques qui les engendrent souvent durant la saison des pluies. Les lahars sont d'autant plus dangereux qu'ils se déclenchent en dehors des éruptions (fortes pluies) ou par la rupture d'un lac, etc. En outre, ils se propagent dans les vallées à plus grande distance que les écoulements pyroclastiques ; leur volume et parfois leur vitesse augmentent lors de leur propagation par entraînement des matériaux issus du lit et des berges de la vallée qu'ils empruntent. Comprendre les modalités de leur initiation, de leur propagation est fondamental dans le but d'alerter les populations très nombreuses sur les flancs et le long des vallées qui drainent les volcans indonésiens. Cartographier et mesurer la part des matériaux qui sont remobilisés par ces lahars dans les vallées lors des saisons des pluies après chaque éruption permettront d'évaluer plus précisément les zones affectées par les prochains lahars sur les volcans actifs (Semeru et Merapi).

Depuis quelques années, nous avons installé temporairement un équipement de mesures et surveillance des lahars dans la vallée de Lengkong sur le volcan actif Semeru à Java. L'un des posters joints (PDF) montre le thème de l'étude des lahars en Indonésie, le site choisi sur le Semeru, les outils et méthodes utilisés et enfin les résultats des mesures effectuées.

Nous installons une batterie de capteurs afin de mesurer les caractéristiques des écoulements et leur propagation entre deux stations distantes de 500 m : les capteurs de pression interstitielle (espace entre grains solides occupés par l'eau) et les géophones permettent d'estimer le débit, les capteurs de charge mesurent la force aplliquée sur le lit du chenal, un sismomètre à large bande permet d'analyser les fréquences induites par les vibrations dans le sol dues aux lahars, les cameras aident à mesurer la vitesse de l'écoulement et à enregistrer les phénomènes d'instabilité à la surface des écoulements, l'échantillonnage dans l'écoulement à intervalles réguliers fournit des valeurs de la concentration en solides, etc. (Doyle et al., 2010a,b ; Dumainsil et al., 2010)

**Notre étude expérimentale “grandeur nature” poursuit quatre objectifs :**
1. Acquérir des mesures in situ pendant ces écoulements particuliers ; 2. Comprendre les caractéristiques hydrauliques des flux, physiques des dépôts et matériaux, et leur comportement comparable à celui des "laves torrentielles" des Alpes ; 3. Suivre l'évolution d'une vallée qui convoie des lahars fréquents et estimer le bilan de l'érosion ; 4. Prévoir l'extension et l'impact des lahars sur les piémonts du Semeru où vit un million d'habitants.
Les données analysées sont le débit, la concentration en solides, la vitesse d'arrivée du front du lahar, la propagation et la vitesse des pulsations ou "bouffées" qui se succèdent pendant 1 à 2 heures. Ces données permettront de comprendre les processus d'entraînement ou de charge des matériaux dans le lahar, de sédimentation et d'érosion le long du chenal pendant l'écoulement. Les processus d'érosion et d'accumulation sont suivis annuellement depuis 2006 grâce aux levés topographiques effectués avec des GPS et au moyen de MNT (voir la dernière carte à droite). Toutes ces données serviront à calibrer des modèles d'écoulement de lahar. Les résultats sont rassemblés dans 3 publications en 2010.

<figure><img src="image_58.png" /></figure>

Fig 1. Quatre enregistrements acquis durant le lahar du 5 mars 2008 : la première et la dernière courbes représentent quatre parties de l'écoulement lors de leur passage aux stations amont et aval et les variations de leur concentration en sédiments (ellipses et trait fin interrompu). Le spectre noir indique la vitesse du mouvement du sol et la troisième ligne est l'énergie induite par les vibrations des écoulements dans le lit, deux données mesurées par un sismomètre situé à la station amont.
<figure><img src="image_59.png" /></figure>

Fig. 2. L'évolution du volume du lahar du 5 mars 2008 entre les 2 stations amont « lava » et aval « sabo ». « Packet » = segment ou pulsation. Les variations de volume et de concentration en sédiments (en %) sont liées. Ces variations sont dues aux processus d'entraînement (incorporation de matériaux) et de sédimentation (dilution). La courbe et la zone grise du bas montre qu'au passage du lahar à la station amont le volume croît peu entre les paquets (= bouffées ou pulsations du lahar). Au contraire, la courbe et la zone grise du haut montre qu'au passage du lahar à la station aval, le volume des paquets 3 et 4 a cru 4 fois. Ceci reflète l'entraînement de matériaux des berges et peut-être du lit.
<figure><img src="image_60.png" /><figcaption>Fig ; 3. Acquisition de données topographiques avec GPS différentiel, comparaison inter-annuelle de Modèles Numériques de Terrain de 2006 à 2008 : les zones d'érosion (en rouge) et d'accumulation (en bleu) de matériaux sont montrées dans le chenal de la vallée de Lengkong sur 2 km de distance.</figcaption></figure>

En 2011, nous voudrions effectuer trois tâches sur ce site expérimental grandeur nature :

1. Mesurer les lahars en février-mars pendant la saison des pluies avec l'équipement décrit plus haut durant au mois 3 semaines. Le but est d'acquérir des caractéristiques hydrauliques des écoulements et des matériaux afin de les utiliser dans les modèles d'écoulement à tester (à Grenoble, au Cemagref)

2. Acquérir une nouvelle topographie du chenal de la rivière Lengkong (avec GPS différentiel et avec des photos prises à basse altitude avec un ULM). Le but est de suivre l'évolution du chenal et surtout de mesurer les processus d'érosion et de dépôt en détail. Ce paramètre (érosion ou incorporation de matériau et dépôt ou dilution de l'écoulement) est fondamental pour comprendre le phénomène et pour prévoir la propagation vers les zones peuplées à l'aval et autour du site expérimental.

3. Collaborer avec des économistes de Montpellier qui étudient les attitudes et les réponses (assurance, etc.) face aux risques d'inondation et de coulées de boue, et qui analysent le type de gestion de ces risques par les autorités
** locales.** Ceci se fera par l'intermédiaire d'enquêtes sur place avec l'aide d'un doctorant ou post-doctorant Indonésien.

2.2. TELEDETECTION HAUTE RESOLUTION AU MERAPI ET AU SEMERU

L'imagerie satellitaire est largement utilisée pour surveiller les volcans actifs et analyser l'évolution des édifices. Les progrès des techniques instrumentales et la résolution des images actuellement disponibles (1 m pour Ikonos, 50 cm pour GeoEye) nous permettent, selon les conditions météorologiques, d'appliquer cet outil aux deux volcans dangereux choisis pour cible. Sur le Merapi, volcan laboratoire, l'interprétation des images de haute résolution nous aide à suivre l'évolution du dôme et les effets des écoulements pyroclastiques induits par les effondrements (par ex. juin 2006, octobre 2010) en direction des flancs S et SW densément peuplés. Sur le Semeru, l'activité permanente, quotidienne et les conditions d'accès difficiles nous interdisent une approche répétée de la zone sommitale et du cratère. Nous exploitons donc les images des satellites Ikonos et SPOT5 afin de détecter des modifications au sommet et afin de délimiter sur des cartes détaillées les effets actuels et futurs des écoulements pyroclastiques et des lahars sur les piémonts densément peuplés.

En 2009 et 2010, nous avons utilisé l'imagerie satellitaire de haute résolution Ikonos (1m) et Spot (5 2,5 m) disponible à CRISP (National University of Singapore) avec trois objectifs :

- Détecter les différents types d'écoulements pyroclastiques issus de l'éruption de 2006 au Merapi (effondrement de dôme, coulées de blocs et cendres, déferlantes). Nous avons détecté leurs effets sur les versants et la forêt de la vallée de Gendol et déduit les causes de débordement des écoulements hors de la vallée principale en direction du village de Kaliadem (Thouret et al., 2010). Ces débordements sont dus aux facteurs morphologiques de la vallée (sinuosité, obstacles), au changement de la capacité du chenal vis-à-vis des écoulements répétés, et aux obstacles d'origine anthropique (Sabo dam récemment construit à l'amont du village), à l'origine de débordements meurtriers vers Kaliadem en 2006 et 2010°. Ce constat remet en cause l'utilité des ouvrages de défense de type Sabo dam (Lube et al., 2010). Ceci débouche sur une évaluation des effets et des dommages lors des éruptions, qui surviennent tous les 4 ans en moyenne depuis 1904 au Merapi.

- Suivre l'évolution du sommet du Semeru et des bassins versants fréquemment empruntés par les écoulements pyroclastiques et surtout les lahars. Ceci se fera avec A. Solikhin (CVGHM, procahin doctorant au LMV).

- Reconnaître les formations géologiques du volcan, surtout les plus récentes, inventorier les produits principaux et le contexte structural de l'édifice, notamment les flancs instables comme celui exposé à l'est (A. Solikhin, Master2, 2009 à Clermont).
<figure><img src="image_61.png" /></figure>

Fig. 4. Image Ikonos drapée sur un MNT du flanc sud du Merapi (vallée de Gendol). Les types, les effets et les processus liés aux écoulements pyroclastiques mis en place lors de l'éruption de 2006 sont indiqués. NB. Un écoulement de blocs et cendres se propage à l'amont de la vallée de Gendol au moment même où le satellite IKONOS acquérait cette image le 16 juin 2006.

Références

Thouret J.-C., Gupta A., Lube G., Cronin S.J., Surono, 2010. Analysis of the 2006 eruption deposits of Merapi Volcano, Java, Indonesia, using high-resolution IKONOS images and complementary ground based observations. *Remote Sensing of Environment*, 114, 1949-1967 DOI:10.1016/j.rse.2010.03.016.

Dumaisnil C., Thouret J.-C., Chambon G., Doyle E.E., Cronin S.J., 2010. Hydraulic, physical and rheological characteristics of rain-triggered lahars at Semeru volcano, Indonesia. *Earth Surface Processes and Landforms*, online2 June, DOI: 10.1002/esp.2003.

Doyle E.E., Cronin S.J., Cole S.E., Thouret J.-C., 2010a. The coalescence and organization of lahars at Semeru, Indonesia. *Bulletin of Volcanology*, 72, 8, 961-970. DOI: 10.1007/s00445-010-0381-8.

Doyle E., Cronin S.J., Thouret J.-C., 2010b. Cycles of bulking and debulking in lahars at Semeru, Indonesia. *Geol Soc Amer Bull*, *Accepted August 2010, in the press*.

Lube G., Cronin J.S., Thouret J.-C., Surono, 2010. Kinematic characteristics of pyroclastic density currents at Merapi and controls on their avulsion from natural and engineered channels. *Geological Society America Bulletin*, accepted September 2010.

ACTIVITE 3 :
MISSION D'EVALUATION DES RISQUES, UITILSATION DES MATERIAUX VOLCANIQUES ET VALORISATION DE LA RECHERCHE
Franck Lavigne, LGP et Université Paris 1

Activités de coordination de la recherche

1. Rencontres avec Dr Surono, directeur DVGHM, Bandung
- Mercredi 7 et jeudi 8 juillet 2010, Jeudi 26 août 2010, Bandung, Lundi 20 septembre 2010, Paris, Mercredi 29 septembre 2010, Bandung.

2. Rencontres avec Dr Subandryio, directeur BPPTK, Yogyakarta en juillet - août 2010

## Activité de valorisation de la recherche

1. Conférence « Le risque volcanique en Indonésie »

- Lundi 27 septembre 2010, Lycée International Français (LIF) de Jakarta
Classes de 4e (Ecole Internationale Française de Bali) et de 1ère (LIF)

- Jeudi 30 septembre 2010, Résidence de l'ambassadeur de France à Jakarta
Une soixantaine de personnes de la communauté française et francophone de Jakarta. Conférence avec J.P. Toutain et Dr Surono.

- Vendredi 12 novembre 2010, Section française de l'Indonesian Heritage Society (IHS). Communauté française et francophone de Jakarta.

2. Visite du Musée de la Géologie et projection de film à Bandung

- Mardi 28 septembre 2010 : accompagnement de la classe de 4e de l'Ecole Internationale Française de Bali.

Projection du film de F. Lecuyer « Volcans d'Indonésie, Java sur l'échine du dragon ».

## Activités de recherche

### 1. Photographie haute résolution par ULM (Ultra-Light Motorized)

Une série de 116 photographies à haute résolution a été acquise par ULM fin août 2010 (Fig. 5).

Objectifs :

- Disposer de vues 2D et 3D des vallées Gendol et Woro en anticipant les prochains écoulements pyroclastiques du Merapi. Un second survol est prévu au lendemain de la prochaine éruption (2011 ?).

- Cartographier les impacts géomorphologiques liés aux extractions au fond des vallées.

- Compter les camions au moment du survol afin d'estimer les volumes de matériaux extraits en un temps donné.

Méthodes :

- Photointerprétation et cartographie 2D des vallées.

- Construction d'un Modèle Numérique de Terrain (MNT) à partir de couples d'images par stéréophotogrammétrie (réalisée à l'Ecole Nationale des Sciences Géographiques – ENSG).
<figure><img src="image_62.png" /><figcaption>Fig. 5. Photographie haute résolution par ULM dans la vallée Gendol.</figcaption></figure>
## 2. Relevés topographiques d'un tronçon de la vallée Gendol (Fig. 6)

Des relevés topographiques par station totale TRIMBLE ont été effectués en août 2010 (Fig. 6) afin de construire un Modèle Numérique de Terrain (Fig. 7) dans deux tronçons de la vallée : Kaliadem dam et un second site à 2 km plus en aval. Les objectifs étaient identiques que ceux présentés stéréophotogrammétrie ne s'étant concrétisés que récemment.

<figure><img src="image_63.png" /><figcaption>Fig. 2. Extraction de sable dans la vallée Gendol, août 2010</figcaption></figure>

<figure><img src="image_64.png" /><figcaption>Fig. 6. Relevés topographiques par Station Totale. Dans la vallée Gendol, août 2010.</figcaption></figure>

<figure><img src="image_65.png" /><figcaption>Fig. 7. Modèle Numérique de Terrain issu d'une campagne de relevés topographiques par Station Totale.</figcaption></figure>

## 3. Cartographie des facteurs de vulnérabilité sur les flancs du Merapi

Travaux entrepris dans le cadre du programme européen MIA VITA.

## ACTIVITE 4

### VALORISATION ET DIFFUSION DU SAVOIR ET DES SAVOIR FAIRE
Plusieurs posters destinés à la diffusion des savoir faires et des résultats acquis en Indonésie depuis quelques années ont été remis à l'Ambassade de France en juillet 2010. Les titres de ces 8 posters sont les suivants :

1) Coopération franco-indonésienne : historique, objectifs et moyens (J.-P. Toutain)

2) Emanations gazeuses à hautes et basses températures sur un volcan actif, moyen de surveillance (J.-C. Baubron, J.-P. Toutain, P. Richon, F. Sortino)

3) Mesure du radon et de la température du gaz des sols ; au sommet du Merapi (P. Richon)

4) Coopération franco-indonésienne en sismologie volcanique (Ph. Lesage et J.-Ph. Metaxian)

5) Utiliser l'imagerie satellitaire de haute résolution afin de suivre l'activité et l'évolution des deux appareils les plus actifs et dangereux en Indonésie (J.-C. Thouret et A. Solikhin)

6) Coopération franco-indonésienne en volcanologie : les lahars (J.-C. Thouret, A. Solikhin et collaborateurs)

7) Dômes du Merapi et écoulements pyroclastiques associés (K. Kelfoun)

8) Volcans et sociétés en Indonésie : vivre avec les risques (F. Lavigne, D. Grancher, E. De Bélizal, E. Mei et A. Picquout)

D'autres activités de valorisation des acquis de la recherche ont été mentionnées dans le rapport de F. Lavigne ci-dessus.

Jean-Claude Thouret, Clermont le 28 octobre 2010.
2009-2010 GRANT PROGRAMME

Project title:

# Monitoring Taal volcano unrest in Philippines with joint Electromagnetic and multi-disciplinary educational EMSEV-PHIVOLCS program

FINAL REPORT

December 2010

EMSEV Inter-Association (ElectroMagnetic Studies of Earthquakes and Volcanoes)

http://www.emsev-iugg.org/emsev/

Jacques Zlotnicki, Chairperson

CNRS-France
(UMR6524-Clermont-Ferrand Observatory, France)

Email: Jacques.zlotnicki@wanadoo.fr

Yoichi Sasai, IAVCEI Liaison member

Tokyo Metropolitan Government
The Disaster Prevention Division

Email: yosasai@zag.att.ne.jp

Toshiyasu Nagao, EMSEV Secretary

Tokai University, Shimizu
Earthquake Prediction Research Center

Email: nagao@scc.u-tokai.ac.jp

Renato Solidium, PHIVOLCS Director

Philippines Institute of Volcanology and Seismology
PHIVOLCS

Email: renato_solidium@yahoo.com

Malcolm Johnston, EMSEV vice-Chair, IASPEI Liaison

U.S. Geological Survey, Menlo Park, USA
Earthquake and Volcano Hazards

Email: mal@usgs.gov

Introduction

Following an international workshop held in Manila in January 2003 for ‘Initiating seismic and volcanic electromagnetic monitoring in Asian countries’ the Inter-Association Working Group EMSEV has developed a scientific cooperation in the electromagnetic field and other geophysical methods with the Philippines Institute of Volcanology and Seismology (http://www.phivolcs.dost.gov.ph/). Priority was given to Taal volcano which may involve large eruptions with pyroclastic flows, base surges and violent phreatic explosions. The volcano has always shown signs of sporadic activity since the last period of activity (1965-1977) during which about 200 people were killed. In 1991, 1992, 2000-2004, 2006, and 2010 major seismic crises were recorded inducing occasionally felt earthquakes, opening of fissures, cyclic ground surface uplifts, increase in ground and water temperatures, bubbling in the acidic inner crater lake, and surface activity. Based on local authorities and PHIVOLCS researches, about 10,000 inhabitants should be concerned by a mild activity within a radius of only 7 km while more than 650,000 people should be affected in case of a violent eruption as that in 1749.

To respond and mitigate to this high level volcanic risk, EMSEV and PHIVOLCS have joined their best efforts for (1) understanding the interactions between the magma feeding system and the hydrothermal system buffered by both the hot acidic inner Crater Lake (MCL) and the cold outer Taal Lake(TL), the geological discontinuities along which heat and soil degassing prevail, (2) evaluating scenarios of activities, (3) monitoring the volcanic activity, and (4) constituting an electromagnetic scientific community at PHIVOLCS.
<figure><img src="image_66.png" /></figure>

Figure 1: Topographic map of Taal volcano. White rectangle is the main area where EM and other geophysical field studies have been performed.

## Time line of the cooperation

### ♦ 2003

International EMSEV-PHIVOLCS workshop in Manila held in January 2003 on 'Initiating seismic and volcanic electromagnetic monitoring in Asian countries'

Formation an international electromagnetic (EM) EMSEV team based on Japanese and French counterparts.

### ♦ 2004

Memorandum of agreement signed by PHIVOLCS and EMSEV on 'The understanding of the geotectonics, seismicity and volcanism of the southern Luzon region'

### ♦ 2005

PHIVOLCS designs an initial EM team. First joint field campaign on Taal. Magnetic (TMF), self-potential (SP), ground temperature (GT) and soil degassing surveys (CO₂) are performed.

A first continuous multi-parametric station located across the active fissures opened during the 1991-92 seismic activities is set. Data are recorded locally.

### ♦ 2006

Two joint field campaigns are led. During the first January campaign, felt earthquakes incite people living on the volcanic Island to spontaneously evacuate for a few days.

A network of magnetic benchmarks is achieved on which the total magnetic field is regularly measured.

### ♦ 2007

Two tasks were simultaneously performed during the two multiparty field works. One is to extend the electromagnetic, soil degassing and temperature surveys on the ground through the two identified geothermal fields. The second task is to build a new continuous multi-parametric station located inside the crater above the second geothermal field.

A real telemetry system was implemented between the two multi-parametric stations and the local Taal observatory. Data can be visualized and analyzed by PHIVOLCS.
Two continuous stations recording the total magnetic field were installed in the immediate vicinity of the two multi-parametric stations. Data which are recorded locally are collected every month by PHIVOLCS members.

One cross section of 13 audio-magnetotelluric soundings along a North-South direction highlights the rooting and the interconnection of the two geothermal fields.

During field work, particular attention is made to educate EM-PHIVOLCS team to the methods which are applied. EM-PHIVOLCS team is advised on best techniques to make measurements. Reports were written, and meetings were held at PHIVOLCS headquarter.

## ♦ 2008

Two years IUGG grant is obtained. It greatly allows the cooperation to speed up research.

A memorandum of agreement was made on the use of geomagnetic data from Muntinlupa magnetic observatory in the Philippines. It was signed by the National Mapping and Resources Information Authority (Philippines), the Ocean Hemisphere Research Center, the Earthquake Research Institute (University of Tokyo) the Japan Agency for Marine-Earth Science and Technology, PHIVOLCS, and EMSEV. This memorandum allows EMSEV and PHIVOLCS to use Muntinlupa magnetic data as remote reference.

Magnetic and bathymetry surveys of the inner Crater Lake were performed during the two joint 2008 campaigns.

Water level and temperature of the Crater Lake are now recorded thanks to a combined sensor located in the middle of the Crater Lake.

Reports were, and meetings at PHIVOLCS were held.

## ♦ 2009

Meetings at PHIVOLCS, and two common field work efforts were organized.

Detail and large scale magnetic, self-potential, soil degassing and ground temperature surveys are done.

Because of the relative quietness of the surface activity of the Crater Lake, water temperatures (WTE) at the bottom of the Lake were measured. Detail bathymetry was updated.

An outstanding effort was made by both parties to install a more reliable internet connection between the computer recording multi-parametric data at the local observatory and PHIVOLCS headquarter, and the French server. Automatic transfers were set, and data can now be visualized and processed routinely on the Virtual ElectroMagnetic Laboratory (VEML; http://virtual-electromagnetic-laboratory.com/).

<figure><img src="image_67.png" /><figcaption>**Figure 2:** At MCL station, self-potential, ground temperature and gradient, seismic noise, components of the magnetic field, seismicity, and Rn emission are recorded. At DAK station, in addition to the same parameters, two components of the tilt are also recorded (2010). 2 seconds</figcaption></figure>
## ♦ 2010

Thanks to IUGG grant, PHIVOLCS and French Embassy supports, a second international workshop was held at PHIVOLCS. Title is 'Monitoring active volcanoes by electromagnetic and other geophysical methods; Application to Asian volcanoes'. About 60 participants attended the meeting (http://www.emsev-iugg.org/emsev/).

A new memorandum of agreement was signed between PHIVOLCS and EMSEV for the period 2010-2014.

Following the meeting, a large field campaign was organized:

- Resistivity, Very Low Frequency soundings are performed along the tracks followed by SP, ground temperature and soil degassing surveys (Greek participation).

- A borehole tiltmeter is installed at the northern multi-parametric station (DAK, USGS participation).

- Magnetic surveys were measured along the magnetic network of benchmarks, and new SP profiles allow building a complete map describing the extent of the hydrothermal field including the two geothermal fields.

In October and November 2010, a new step in the cooperation was achieved:

- Three magnetotelluric stations are installed under the framework of a JICA support (Japan).

- A new EMSEV multi-parametric station was build on the northwestern edge of the crater rim, at the limit of the northern geothermal field. Data recorded on site will be telemetered in real time in 2011.

From mid-April to the end of July, Taal volcano exhibited an abrupt and strong seismic crisis. PHIVOLCS raised the alert level from 1 to 2 temporarily and included a possible plan to partially evacuate the volcanic Island. Thanks to the real-time multi-parametric network, EMSEV was able to regularly process data and to inform PHIVOLCS about the observed signals and the interpretation. Two reports were sent to PHIVOLCS during this period. This several months of activity were useful for all the participants who rapidly communicate data, evaluation of the activity and so forth.

## ♦ 2011 prospective

Two main field campaigns should be done during the year.

- Magnetotelluric soundings should be performed on the volcanic Island in order to study the deep structure,

- A fourth EMSEV multi-parametric station should be installed on the volcano. The objectives of this new station are multiple. First, parameters similar to those at the other stations (SP, temperature, gradient of temperature, seismic noise ...) will be recorded, and, second, a current system which will allow dipole-dipole resistivity soundings on the basis of the multi-parametric network will be implemented.

- Depending on the budgets that each foreign EM team will get, theoretical and applied studies and stages will be proposed to PHIVOLCS EM team members.

## Main results and achievements

Combined SP, GT, WTE, soil degassing and TMF surveys indicate that the northern part of the volcano is undergoing strong thermal transfers and degassing. The activity takes place along E-W fissures that could be linked to the root of the northern border of the Crater (MC) at a depth of some hundreds of metres, and also connected to a thermal source near the MCL shore line. This thermal source location could be the initial spot of the next eruptive activity. In such a case, strong activity could induce a collapse of a part of the northern MC rim into the MCL, due to mechanical weakening by the active 1992-1994 fissures. To the south, this system appears to be bounded by a NW-SE fault suspected from the NW-SE alignment of negative SP and WT anomalies in the MC. Seismic activity and dike injection may be taking place along this alignment. Changes in SP, TMF
and GT are measured by means of repeat profiles, suggesting that potentially hazardous phreatic/and gas eruptions may be associated with future seismic unrest in these geothermal areas.
The two geothermal fields are linked at several hundreds meters depth and the hydrothermal/volcanic fluids are prevailing in the northern part of the crater. Bathymetry and bottom water temperature of MCL clearly show that a bulge of 5 to 10 m high is present and is cut by active hot springs located along a N.NW-S.SE direction.

Resistivity soundings outline that hydrothermal fluids have mineralized and altered the northern rim of the crater which make it unconsolidated.

When one considers the background seismicity on the volcano, it is clear that seismic crises appear abruptly and are accompanied by rapid ground deformation as observed on many similar volcanoes. High levels of activity can be quickly reached. Therefore, real time monitoring and data analysis systems are a necessity for anticipating the level of hazard expected.

Earthquakes during the April-July 2010 crisis have again re-activated the 1991-94 fissures, which might unconsolidate the northern outer rim of the crater. Many data indicate that the region beneath the northern Crater Lake is still active. During this crisis, the near-surface activity in MCL is apparent, and one may consider that the general hydrothermal activity will again be similar to that observed in 2007 or before. Taking into consideration all the available data, it seems that is new crisis is serious although the details of the deep activity and its potential are not clear. Magmatic intrusion, together with hydrostatic overpressure, could be reactivating the region below the northern part of the volcano. Under this hypothesis, any depressurization, resulting from faulting triggered by teleseismic or local earthquakes, landsliding, etc, could destabilize the system and lead to a phreatic explosion on the volcano.

Four real time multi-parametric EMSEV stations will be operating in 2011. They allow continuous monitoring of the volcanic activity and greatly contribute to improved understanding of the on-going activity. The program adds further value to the seismic networks, geophysical and geochemical surveys operated by PHIVOLCS. PHIVOLCS already integrate some of our results in the information planning to Local authorities and inhabitants.

Several PHIVOLCS members are now aware of EM methods and they would go further in the next years in the study of the EM field. Some of the methodologies developed during the cooperation may already be integrated in the monitoring of other volcanoes in the Philippines.

## PHIVOLCS and International EMSEV consortium and evolution

### ♦ PHIVOLCS team

From the beginning of the cooperation PHIVOLCS (Director R. Solidum) made a huge effort to mobilize active researchers, engineers and technicians in the EMSEV-PHIVOLCS cooperation. The Institute has always largely contributed to providing adequate numbers of personnel in the field in order to complete joint field campaigns. PHIVOLCS has also financially supported the contribution of PHIVOLCS members on the field.

About 8 to 10 PHIVOLCS members may be regularly involved in the cooperation. Most of them are coming from the Volcanological section (directed by J. Sincioco). Two groups were constituted and each of them has focused his interest in the ‘Magnetic field monitoring’ (J.M. Gordon, Jr, P. Alanis, Freddy)or in the ‘Electric field monitoring’ (E. Villarcorte, L. Bong, P. Reniva). During each field visit, a representative (J.P. Sabit) of the volcanological section accompanies PHIVOLCS members on the field. The local support is given by Taal observatory (A. Loza Loic, L.A. C. Banes).

### ♦ EMSEV team and other contributions

EMSEV team has largely increased during the past years.

- Initially the cooperation was supported by two teams mainly belonging to the Earthquake Prediction Research Centre (T. Nagao, M. Harada located at Tokai University, Shimizu) and Tokyo Metropolitan City (Y. Sasai) in Japan, and to the French National Research Centre in France (J. Zlotnicki, F. Fauquet, and P. Yvetot positioned at the Observatory of Physics of
Globe, Clermont-Fd). About 6 researchers and engineers, experts in the EM field, were involved.

From these countries other research teams joint the cooperation, bringing their own expertise: For instance the Aso observatory for total field magnetometers, and J.P. Toutain from the Laboratoire de Mécanismes de Transfert en Géologie for geochemical studies and soil degassing.

- Later on, F. Sortino from the Istituto Nazionale per la Vulcanologia of Palermo (INGV, Italy) contributed to heat fluxes and CO₂ degassing measurements, while A. Bernard from the Laboratoire de Géochimie et Minéralogie (Université Libre de Bruxelles, Belgium) focuses on Thermal Aster imagery of Taal Crater Lake.

- In 2010, G. Vargemezis from the Aristotle University of Thessaloniki entered the scientific consortium and manages the resistivity soundings on the volcano with J.R. Puertollano, R.C. Pigtain from PHIVOLCS. US Geological Survey greatly enlarges the monitoring of the volcano by setting a borehole tiltmeter at a first multi-parametric station (DAK). Now, M.J.S. Johnston is deeply involved in the monitoring of the volcano as the French and Japanese teams.

- Satellite observations progressively enlarge the multi-disciplinarity of the EMSEV consortium. EM observations by DEMETER are active til the end of the experiment. MOPITT observations are done by R.P. Singh working at Chapman University (USA). V. Tramutoli and N. Pergola from Department of Engineering and Physics of The Environment (DIFA, University of Basilicata) are presently setting a time domain analysis of robust satellite techniques (RST) for near real-time monitoring of active volcanoes and thermal precursor identification.

# Dissemination of results

## ♦ Articles

M. Harada, Julio P. Sabit, Y. Sasai, Paul K. B. Alanis, Jr. Juan M. Cordon, Ernesto G. Corpuz, J. Zlotnicki, T. Nagao and Jane T. Punongbayan, 2005. Magnetic and Electric Field Monitoring of Taal Volcano, Philippines. Part I: Magnetic Measurements, Japan Acad. Sci., 81, B, 261-266.

J. Zlotnicki, Y. Sasai, J.P. Toutain, E.U. Villacorte, A. Bernard, Julio P. Sabit, Juan M. Gordon Jr, Ernesto G. Corpuz, M. Harada, J.T. Punongbayan, H. Hase and T. Nagao, 2008. Combined Electromagnetic, geochemical and thermal surveys of Taal volcano (Philippines) during the period 2005-2006. Bull Volcanol., doi: 10.1007/s00445-008-0205-2.

Y. Sasai, M. Harada, J.P. Sabit, J. Zlotnicki, Y. Tanaka, J.M. Cordon Jr., S. Uyeda, T. Nagao, J.S. Sincioco, 2008, Geomagnetic and topographic survey of the Main Crater Lake in Taal Volcano (Philippines): preliminary report, J. Geography, 117, 894-900 (in Japanese with English abstract).

M. Harada, Y. Sasai, J. Zlotnicki, Y. Tanaka, H. Hase, J.P. Sabit, J.T. Punongbayan, J.M. Cordon Jr, E.U. Villacorte, E.G. Corpuz, and T. Nagao, 2008. Monitoring of volcanic activity of Taal volcano (Philippines) by electromagnetic methods, Bull. Inst. of Oceanic Res. and Dev., Tokai University, 29, 9-28, 2008 (in Japanese with English abstract).

J. Zlotnicki, Y. Sasai, J.P. Toutain, E. Villacorte, PHIVOLCS team, P. Yvetot, F. Fauquet, A. Bernard, 2009. Electromagnetic and Geochemical methods applied to investigations of Hydrothermal/magmatic unrests: Examples of Taal (Philippines) and Miyake-jima (Japan) volcanoes, Physics and Chemistry of the Earth, 34, 394-408. doi:10.1016/j.pce.2008.09.012.

I. Fikos, G. Vargemezis, J. Zlotnicki, J.R. Puertollano, R.C. Pigtain, P.B. Alanis and Y. Sasai, 2011. Shallow structure of the hydrothermal system at Taal volcano (Philippines) inferred by detailed electrical resistivity tomography, in preparation to Bull. Volcanol.

M. Harada, J. Zlotnicki, Y. Sasai, 2011. Magnetic mapping and bathymetry of Taal Crater Lake (the Philippines). In preparation.

## ♦ Conferences

J. Zlotnicki, 2003. Invited conference. Electromagnetic investigations on Volcanoes: What to observe? Workshop for initiating seismic and volcanic electromagnetic monitoring in Asian countries, organisé par IUGG et EMSEV, Manille (Philippines), 14-16 jan., 2003.

M. Harada, Y. Sasai, J. Zlotnicki, J.P. Sabit, J.T. Punongbayan, J.M. Cordon, E.U. Villacorte, P.K.B. Alanis, Ishmael C. Narag[4]; Raymond Patrick R. Maximo[4]; Teodorico, A. Sandoval, E.G. Corpuz, B.C. Bautista, R.U. Solidum, T. Nagao, S. Uyeda, 2005.
Magnetic and SP measurements in Taal Volcano, Philippines. Joint meeting for Earth and Planetary Science, May 22-26, 2005, Tokyo, Japan.

E.U. Villacorte, J. Zlotnicki, Y. Sasai, J.P. Toutain, A. Bernard, M. Harada, B.J.T. Punongbayan, I.C. Narag, R.P.R. Maximo, E.G. Corpuz and EM PHIVOLCS team, 2005. Taal volcano (Philippines): Gearing toward a new eruption? Combined land based self-potential, ground temperature and CO2 soil degassing surveys with the crater lake temperature monitored by satellite imagery. IAGA meeting, Toulouse July 18-29, France.

J. Zlotnicki, Y. Sasai, J.P. Toutain, E.U. Villacorte, A. Bernard, J.T. Punongbayan, H. Hase, M. Harada, Ernesto G. Corpuz, Julio P. Sabit, T. Nagao, 2006. Taal volcano (Philippines): Gearing toward a new eruption? Combined land based self-potential, magnetic, ground temperature and CO2 soil degassing surveys with the Crater Lake temperature monitored by satellite imagery. International Workshop on Demeter. Toulouse, June 14-16.

J. Zlotnicki, Y. Sasai, J.P. Toutain, E.U. Villacorte, A. Bernard, J.T. Punongbayan, H. Hase, M. Harada, Ernesto G. Corpuz, Julio P. Sabit, T. Nagao, 2006. Taal volcano (Philippines): Gearing toward a new eruption? Combined land based self-potential, magnetic, ground temperature and CO2 soil degassing surveys with the Crater Lake temperature monitored by satellite imagery, 2006. IWMEEMSV Workshop, India, Nov. 20-22.

J. Zlotnicki, Y. Sasai, J.P. Toutain, E.U. Villacorte, J.M Cordon Jr., A. Bernard, J. P. Sabit, M. Harada, H. Hase, J. Sincioco, J.T. Punongbayan, and T. Nagao, 2007. Electromagnetic and Geochemical monitoring of the slow unrest of Taal volcano (Philippines). IUGG, Perugia, Italy, July 2-13.

SenthilKumar, R.P. Singh J. Zlotnicki, Y. Sasai, and J. Sincioco, 2007. Monitoring slow unrest of Taal volcano (Philippines) Using Carbon Monoxide from MOPITT satellite. IUGG, Perugia, Italy, July 2-13.

J. Zlotnicki, J.P. Toutain, Y. Sasai, E.U. Villacorte, A. Bernard, J. Sincioco, J.M Cordon Jr., Senthilkumar, J. P. Sabit, M. Harada, H. Hase, J.T. Punongbayan, and T. Nagao. Electromagnetic and Geochemical monitoring of the slow unrest of Taal volcano (Philippines). IGOS, GeoHazards 2007. Frascati, Italy Nov. 6-9

Sasai, Y., J. P. Sabit, J. M. Cordon Jr., E. U. Villacorte, J. Zlotnicki, J-P. Toutain, M. Harada, H. Hase, J. Sincioco, T. Nagao: Electromagnetic and geochemical monitoring of Taal volcano, the Philippines: 2005-2007. The 5th International Congress of Cities on Volcanoes; COV-07), Shimabara, Nov. 2007.

J. Zlotnicki, J.P. Toutain, Y. Sasai, E.U. Villacorte, A. Bernard, J.M Cordon Jr., F. Sortino, J. P. Sabit, M. Harada, PHIVOLCS EM team, J. Sincioco, H. Hase, T. Nagao, 2008. Invited conference "Volcanic lakes". Integrated Electromagnetic and Geochemical methods applied to volcanic hydrothermal systems: Application to Taal volcano (Philippines). IAVCEI GA Assembly, Reykjavik, Iceland, Aug. 18-25, 2008.

J. Zlotnicki, Y. Sasai, J.P. Toutain, E. Villacorte, PHIVOLCS team, P. Yvetot, F. Fauquet, A. Bernard. Electromagnetic and Geochemical methods applied to investigations of Hydrothermal/magmatic unrests: Example of Miyake-jima (Japan) volcano, 2008. IAVCEI meeting, Reykjavik, Iceland, Aug. 18-25, 2008.

M. Harada, J.P. Sabit, Y. Sasai, J.M. Cordon Jr., J. Zlotnicki, Y. Tanaka, E.U. Villacorte, H. Hase, J.S. Sincioco and T. Nagao, 2008. Monitoring of volcanic activity in Taal volcano (Philippines) by electromagnetic methods: geomagnetic observations. EMSEV-DEMETER joint workshop, Sinaia, Romania, Sept. 7-12, 2008.

J. Zlotnicki, J.P. Toutain, Y. Sasai, E.U. Villacorte, M. Harada, A. Bernard, Paul Yvetot, F. Fauquet, J.M. Cordon Jr., F. Sortino, J. P. Sabit, J. Sincioco, PHIVOLCS EM team, H. Hase, T. Nagao, 2008. Integrated Electromagnetic and Geochemical methods applied to the volcanic hydrothermal system of Taal volcano (Philippines). EMSEV-DEMETER joint workshop, Sinaia, Romania, Sept. 7-12, 2008.

P.K.B. Alanis, J. Zlotnicki, J.P. Sabit, Y. Sasai, J.M. cordon Jr., M. Harada, J.P. Toutain, E.U. Villacorte, A. Bernard, H. Hase, J.T. Punongbayan, T. Nagao, R.U. Solidum Jr., 2009, Electromagnetic, geochemical and thermal studies on Taal Volcano (Philippines) from 2005 to present, AOGS conference, Singapore, August 11-15, 2009.

J. Zlotnicki, J.P. Toutain, Y. Sasai, E.U. Villacorte, M. Harada, A. Bernard, P. Yvetot, F. Fauquet, 4, F. Sortino, PHIVOLCS EM team, T. Nagao, and R. Solidium, 2009. Electromagnetic, Geochemical and thermal anomalies related to the hydrothermal activity of Taal volcano (Philippines). IAGA meeting, Sopron (Hungary), August 22-29, 2009.

M. Harada, Y. Sasai, J.P. Sabit, J.M. Cordon Jr., J. Zlotnicki, J.Sincioco, Y. Tanaka, T. Nagao, 2009. Magnetic and topographic studies on the main crater lake of Taal volcano (Philippines). IAGA meeting, Sopron (Hungary), August 22-29, 2009.

J. Zlotnicki, **Organisation du workshop EMSEV-PHIVOLCS International Meeting** on Monitoring active volcanoes by Electromagnetic and other geophysical methods, Mainla (Philippines), Feb. 25-27, 2010.

J. Zlotnicki, Y. Sasai, J.P. Toutain, E. Villacorte, M. Harada, PHIVOLCS team, P. Yvetot, F. Fauquet, A. Bernard, T Nagao, 2010. Electromagnetic, geochemical and thermal investigations of Taal volcano, 2010. EMSEV-PHIVOLCS Intern. Meeting on Monitoring active volcanoes by Electromagnetic and other geophysical methods, Mainla (Philippines), Feb. 25-27, 2010.

J. Zlotnicki, and EMSEV bureau, 2010. EMSEV project and its activities. EMSEV-PHIVOLCS Intern. Meeting on Monitoring active volcanoes by Electromagnetic and other geophysical methods, Mainla (Philippines), Feb. 25-27, 2010

P.K.B. Alanis, J.P. Sabit, Y. Sasai, J.M. Cordon, Jr., **J. Zlotnicki**, M. Harada, E.U. Villacorte, H. Hase, J.T. Punongbayan, T. Nagao, J.S. Sincioco and R.U. Solidum Jr, 2010. Magnetic observations on Taal Volcano (Philippines) in combination with other geophysical and geochemical methods from 2005 to present. Meeting on Monitoring active volcanoes by Electromagnetic and other geophysical methods, Mainla (Philippines), Feb. 25-27, 2010.

J.P. Toutain, F. Sortino, **J. Zlotnicki**, Phivolcs team, 2010. soil gas and heat flow assessment at Taal hydrothermal system. Meeting on Monitoring active volcanoes by Electromagnetic and other geophysical methods, Mainla (Philippines), Feb. 25-27, 2010.

J. Zlotnicki, 2010. Electromagnetic and Geochemical methods applied to the investigation of Taal hydrothermal system (Philippines). 6th International meeting Cities on Volcanoes, Tenerife, May 31- June 4, 2010.

J. Zlotnicki, 2010. Taal volcano (Philippines): gearing towards a new eruption? European Open Forum, EOSF-2010, Turino, July 3-7, 2010.

J. Zlotnicki, Y. Sasai, EM PHIVOLCS team, M.J.S. Johnston, J.P. Toutain, and G. Vargemezis, 2010. Five years of cooperation between EMSEV and PHIVOLCS for understanding and monitoring Taal volcano. EMSEV International 2010 workshop, Santa Ana, USA, 3-6 October, 2010.
# RAPPORT QUADRIENNAL DU CNFGG A L'UGGI

## QUADRENNIAL REPORT OF CNFGG TO IUGG

### SECTION 4 – GÉOMAGNÉTISME ET AÉRONOMIE

### SECTION 4 - GEOMAGNETISM AND AERONOMY
Comité National Français de Géodésie et Géophysique

Section IV - Aéronomie et Géomagnétisme

Rapport Quadriennal 2007-2011

The following pages aim describing some of the recent scientific progresses in the area of aeronomy and geomagnetism that were authored or co-authored by the French community. Rather than putting the emphasis on a very limited number of results, we chose to gather in this report very synthetic and brief notes on different topics, in the area of geomagnetic field measurements, data processing, modeling, interpretation, paleo- and archeomagnetism, bio- and rock magnetism, experimental and numerical dynamo, interactions with climate, solar wind, high atmosphere studies, troposhere, ionosphere, and planetary magnetic fields.

We are very thankful to those who unselfishly accepted to spend some time to this report. These are Hagay Amit, Pierre-Louis Blelly, Annick Chauvin, Arnaud Chulliat, Jean Pascal Cogné, Jérôme Dyment, Alexandre Fournier, Yves Gallet, Agnès Genevey, Gauthier Hulot, Aude Isambert, France Lagroix, Philippe Lanos, Guillaume Le Hir, Aurélie Marchaudon, Jean-François Pinton and Yoann Quesnel.

Erwan Thébault (Secretary)
Jean-Baptiste Renard (Vice-President)
Benoit Langlais (President)
# Earth's magnetic field measurements

Arnaud Chulliat, Jérôme Dyment, and Gauthier Hulot

Institut de Physique du Globe de Paris, INSU/CNRS, F-75005 Paris

**Abstract** The French community contributes to the international effort of monitoring the Earth's magnetic field. The "Bureau Central de Magnétisme Terrestre" (BCMT) gathers French institutions contributing to ground observations. As of Feb. 2011, 18 INTERMAGNET observatories are affiliated to BCMT, among which 8 are in collaboration with foreign institutions. During 2007-2011, BCMT developed its instrument technical abilities, installed two new observatories (Easter Island and Antarctica), and upgrade the data processing procedures to provide quasi-definitive data within one month. Regarding marine measurements, new techniques were developed and marine campaigns were conducted. The French community has also an important role in the soon-to-be-launched SWARM ESA mission, with an instrument-PIship.

## Magnetic observatories

The BCMT, founded in 1921 and attached to the Institut de Physique du Globe de Paris (IPGP), is in charge of coordinating ground observations of the Earth's magnetic field by French institutions. Three French institutions are currently operating magnetic observatories: the IPGP, the École et Observatoire des Sciences de la Terre (EOST) and the Institut de Recherche pour le Développement (IRD). A fourth institution, the Observatoire Versailles Saint Quentin (OVSQ), attached to Institut Pierre Simon Laplace (IPSL) and Université Versailles Saint Quentin (UVSQ), hosts the International Service of Geomagnetic Indices (ISGI), which provides data products derived from magnetic observatory data. The BCMT currently operates a network of 18 observatories throughout the world (including 8 observatories in cooperation with foreign institutions) and a network of 30 repeat stations in metropolitan France. All BCMT observatories belong to INTERMAGNET (www.intermagnet.org), the global network of magnetic observatories transmitting their data in near real time and fulfilling high quality standards. In addition, the BCMT develops, builds and calibrates its own lines of vector and scalar magnetometers (Figure 1), providing significant flexibility to its variations of the Earth's magnetic field having time scales from a few seconds to several decades [Matzka et al., 2010].

Over the time interval 2007-2011, the BCMT has made the following strides: New magnetometers and data acquisition systems were developed in order to acquire data every second [Chulliat et al., 2009], as opposed to every

minute which was the previous international standard. New 1 Hz systems were installed in 13 observatories (as of February 2011), thus providing new data for investigations of rapid geomagnetic variations (such as geomagnetic pulsations, tsunami generated magnetic fields, etc.) Two new INTERMAGNET-type observatories were installed in challenging locations, one in Easter Island (Chile) [Chulliat et al., 2009, Manoj et al., 2011] and the other one in Dome C (Antarctica) [Schott and Rasson, 2007, Chambodut et al., 2009, Chambodut and Schott, 2010]. Forty years of data from the Parc St Maur and Val Joyeux observatories, covering the period 1883-1922, were digitized from yearbooks, quality-controlled and distributed on the internet [Fouassier and Chulliat, 2007, 2009]. The World Monthly Means Database maintained by IPGP was upgraded [Chulliat and Telali, 2007]. Data processing procedures were upgraded [Schott and Linthe, 2007, Truong et al., 2009] and so-called quasi-definitive data are now available in one month time delay (Figure 2) [Peltier and Chulliat, 2010]. This new data product, recently endorsed by INTERMAGNET and IAGA, has been used to validate IGRF-11 candidate models [Chulliat and Thebault, 2010] and will be used during the upcoming ESA Swarm mission.

## Marine measurements

Instrumental developments have been carried out in deep-sea magnetometry, with the design and operations of a deep-tow scalar magnetometer and a vector magnetometer attached to deep-sea vehicles such as manned sub-
<figure><img src="image_68.png" /><figcaption>Figure 1: The IPGP VM391 tri-axis fluxgate magnetometer.</figcaption></figure>

<figure><img src="image_69.png" /><figcaption>Figure 2: Latencies of the BCMT data products.</figcaption></figure>

mersible, remotely operated vehicles (ROV), or autonomous underwater vehicles (AUV). A long, high-resolution magnetic profile across the whole Cretaceous Quiet Zone in the Central Atlantic Ocean off Africa has been collected by the deep-tow magnetometer and reveals variations in the geomagnetic regime during this 35 My period of constant polarity [Dyment et al., 2009]. Magnetic profiles acquired on the seafloor by deep-sea submersible Nautile have provided important constraints on the structure of slow-spreading ridge segment [Honsho et al., 2009] and on the detailed age of the seafloor, allowing a fine description of magmatic processes [Cordier et al., 2010]. Detailed magnetic and topographic surveys have been achieved by ROV Victor on several hydrothermal sites with ultra-mafic basement. Unlike the sites lying on basalt, associated to magnetic lows due to the alteration of basalt titanomagnetite to titanomaghemite and non-magnetic minerals, the sites lying on serpentinite exhibit a magnetic high due to the formation of magnetite as part of the serpentinisation process and its conservation in a reducing environment [Tivey and Dyment, 2010]. This result will help to detect and characterized potential mineral resources associated to inactive hydrothermal sites on the seafloor.

## Satellite measurements

France has also taken a very active role in the development of Low Earth Orbit (LEO) space magnetometry over the past decade, even more so over the past four years. It contributed to the two very successful Danish Oersted and German Champ missions, both of which carried OVH absolute scalar magnetometers built by CEA/LETI (and provided by CNES, in the case of Oersted). These missions provided a wealth of high quality data until very recently, well beyond the nominal lifetime of both these missions (Champ re-entered the atmosphere on September 19, 2011, after more than ten years of good and faithful service, Oersted is still in orbit). These remarkable data have allowed much progress in our ability to identify and recover the various types of magnetic signals [Hulet et al., 2007], particularly those of internal origin: the main field and its secular variation [Gillet et al., 2010], and the field of lithospheric origin [Thébault et al., 2010]. But these missions also revealed the limits of single satellite magnetometry missions and the need for more advanced concepts [Olsen et al., 2010]. Such an advanced concept, SWARM, was selected by ESA as the fifth Earth Explorer Mission in 2004, following a joint proposal by DNSC (now DTU) in Denmark, GFZ in Germany and IPGP in France [Friis-Christensen et al., 2006, 2009].

The SWARM mission is to involve two satellites orbiting side by side (Fig. 3) on a low polar orbit to measure the East-West gradient of the magnetic field, and a third satellite to be launched (with the same launcher) at a slightly higher altitude. The orbital plane of this third spacecraft will progressively shift with respect to the orbital plane of the lower spacecraft pair, to provide data at different local times [see e.g. Olsen et al., 2010, for a full justification of this constellation configuration]. It will carry similar but more advanced instruments as the Champ mission. In particular, the absolute scalar magnetometers, again built by CEA/LETI, provided by CNES as a Customer Furnished Instrument under the scientific responsibility of IPGP, is now a latest generation Helium 4 optical pumping absolute magnetometer. It will make it possible to reach an accuracy of 0.3 nT. The French scientific community has been very active in both the technical and scientific preparation of this mission, which is now due to be launched in the summer of 2012 for a nominal lifetime of five years.

SWARM will provide both so-called level 1b data
<figure><img src="image_70.png" /><figcaption>Figure 3: Two (out of three) Swarm satellites.</figcaption></figure>

(calibrated 1Hz and 50 Hz vector and scalar field values from each satellite) and level 2 products, such as core field, lithospheric field and ionospheric field models, but also local estimates of ionospheric parameters such as the Eastward Electrical Field that drives much of the ionosphere's equatorial dynamics. These level 2 products will be prepared by IPGP and several other institutions within an international consortium led by DTU in Denmark. Both level 1b data and level 2 products will be made freely available by ESA to the scientific community and are expected to considerably enhance our knowledge of the various sources of the Earth's magnetic field.

The perspective of the SWARM mission has also prompted much related scientific development in geomagnetism (for a recent review see e.g. [Hulot et al., 2010, 2011, and references therein], in particular investigations of short timescale dynamics [Finlay et al., 2010], initiation of data assimilation techniques in geomagnetism [Fournier et al., 2010], and the construction of maps of the lithospheric field by merging satellite, airborne, marine and ground-based magnetic data [Hemant et al., 2007]. All these areas of research are expected to considerably benefit from the future SWARM data.

## References

A. Chambodut and J.-J. Schott. Current status of permanent magnetic observatories in French Austral and Antarctic Territories. volume Proceedings of i-DUST (Inter-Disciplinary Underground Science and Technology Conference, pages 15–26, 2010.

A. Chambodut, D. Di Mauro, J.-J. Schott, P. Bordais, L. Agnoletto, and P. di Felice. Three years of continuous record of the Earth's magnetic field at Concordia station (Dome C, Antarctica). *Ann. Geophys.*, 52:15–26, 2009.

A. Chulliat and K. Telali. World monthly means database project. In J. Reda, editor, *Proc. of the XIIth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing*, volume C-99 of *Publs. Inst. Geophys. Pol. Acad. Sc.*, pages 268–274, 2007. 19-24 June 2006, Belsk, Poland.

A. Chulliat and E. Thebault. Testing IGRF-11 candidate models against CHAMP data and quasi-definitive observatory data. *Earth Planets Space*, 62:805–814, 2010. doi: 10.5047/eps.2010.06.004.

A. Chulliat, J. Savary, K. Telela, and X. Lalanne. Acquisition of 1-second data in ipgp magnetic observatories. volume Proceedings of the XI-th IAGA Workshop on geomagnetic observatory instruments, data acquisition and processing. U.S. Geological Survey, 2009. Open-File Report 2009-1226.

C. Cordier, M. Benoit, C. Hemond, J. Dyment, B. Le Gall, A. Briais, and M. Kitazawa. Distribution of lava compositions across a ridge axis reveals timescales of melt extraction. *Geochem., Geophys., Geosyst.*, 11, 2010. doi: 10.1029/2010GC003074.

J. Dyment, Y. Gallet, E. Hoise, and The Magongond 08 scientific party. First complete high-resolution record of the Cretaceous Normal Superchron. *AGU Fall Meeting Abstracts*, 2009.

C. C. Finlay, M. Dumberry, A. Chulliat, and M. Pais. Short timescale core dynamics: theory and observations. *Space Sci. Rev.*, 155, 2010. doi: 10.1007/s11214-010-9691-6.

D. Fouassier and A. Chulliat. The new BCMT magnetic database. In J. Reda, editor, *Proc. of the XIIth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing*, volume C-99, pages 128–134, 2007.

D. Fouassier and A. Chulliat. Extending backwards to 1883 the french magnetic hourly data series. volume Proceedings of the XIIth IAGA Workshop on geomagnetic observatory instruments, data acquisition and processing. U.S. Geological Survey, 2009. Open-File Report 2009-1226.

A. Fournier, G. Hulot, D. Jault, W. Kuang, A. Tangborn, N. Gillet, E. Canet, J. Aubert, and F. Lhuillier. An Introduction to Data Assimilation and Predictability in Geomagnetism.
*Space Sci. Rev.*, 155(1-4):247-291, 2010. doi: 10.1007/s11214-010-9669-4.

E. Friis-Christensen, H. Lühr, and G. Hulot. A constellation to study the Earth's magnetic field. *Earth Planets Space*, 58:351-358, 2006.

E. Friis-Christensen, H. Lühr, G. Hulot, R. Haagmans, and M. E. Purucker. Past as Prologue: SWARM and the Decade of Geopotential Research. *EOS, Trans. Amer. Geophys. Union*, 90, 2009. doi: 10.1029/2009EO250002.

N. Gillet, V. Lesur, and N. Olsen. Geomagnetic Core Field Secular Variation Models. *Space Sci. Rev.*, 155:129-145, 2010. doi: 10.1007/s11214-009-9586-6.

K. Hemant, E. Thébault, M. Mandea, D. Ravat, and S. Maus. Magnetic anomaly map of the world: merging satellite, airborne, marine and ground-based magnetic data sets. *Earth Planet. Sci. Lett.*, 260, 2007. doi: 10.1016/j.epsl.2007.05.040.

C. Honsho, J. Dyment, K. Tamaki, M. Ravilly, H. Horen, and P. Gente. Magnetic structure of a slow-spreading ridge segment: insights from near-bottom magnetic measurements onboard a submersible. *J. Geophys. Res.*, 114, 2009. doi: 10.1029/2008JB0059151.

G. Hulot, N. Olsen, and T. J. Sabaka. The present field. In M. Kono, editor, *Treatise on Geophysics*, volume 5, Geomagnetism, pages 33-75. Elsevier, Amsterdam, The Netherlands, 2007.

G. Hulot, A. Balogh, U. R. Christensen, C. G. Constable, M. Mandea, and N. Olsen. The Earth's Magnetic Field in the Space Age: An Introduction to Terrestrial Magnetism. *Space Sci. Rev.*, 155:1-7, 2010. doi: 10.1007/s11214-010-9703-6.

G. Hulot, A. Balogh, U. R. Christensen, C. G. Constable, M. Mandea, and N. Olsen. *Terrestrial Magnetism*, volume 36. Space Science Series of ISSI, 2011.

C. Manoj, S. Maus, and A. Chulliat. Observation of magnetic fields generated by tsunamis. *EOS, Trans. Amer. Geophys. Union*, 92:13-14, 2011.

J. Matzka, A. Chulliat, M. Mandea, C. Finlay, and E. Qamili. Geomagnetic observations for main field studies: from ground to space. *Space Sci. Rev.*, 155, 2010. doi: 10.1007/s11214-010-9693-4.

N. Olsen, G. Hulot, and T. J. Sabaka. Measuring the Earth's Magnetic Field from Space: Concepts of Past, Present and Future Missions. *Space Sci. Rev.*, 155:65-93, 2010. doi: 10.1007/s11214-010-9676-5.

A. Peltier and A. Chulliat. On the feasibility of promptly producing quasi-definitive magnetic observatory data. *Earth Planets Space*, 62, 2010. doi: 10.5047/eps.2010.02.002.

J. J. Schott and J. Linthe. The hourly mean computation problem revisited. In J. Reda, editor, *Proc. of the XIIth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing*, volume C-99, pages 135-143, 2007.

J. J. Schott and J. Rasson. Magnetic observatories in antarctica. In D. Gubbins and E. Herrero-Bervera, editors, *Enc. Geomag. Paleomag.*.. Springer, Netherlands, 2007.

E. Thébault, M. Purucker, K. A. Whaler, B. Langlais, and T. J. Sabaka. The Magnetic Field of the Earth's Lithosphere. *Space Sci. Rev.*, 155, 2010. doi: 10.1007/s11214-010-9667-6.

M. Tivey and J. Dyment. *The magnetic signature of hydrothermal systems in slow spreading environments*, pages 43-66. Diversity of hydrothermal systems on slow spreading ocean ridges, P. Rona, C. Devey, J. Dyment and B. Murton (Eds.), AGU Monograph, 2010.

F. Truong, X. Lalanne, and A. Chulliat. Magis: The information system of ipgp magnetic observatories. volume Proceedings of the XIIIth IAGA Workshop on geomagnetic observatory instruments, data acquisition and processing. U.S. Geological Survey, 2009. Open-File Report 2009-1226.
# Processing of Magnetic Field Measurements from Ground to Space

Erwan Thébault (1) and Yoann Quesnel (2)

(1) Institut de Physique du Globe de Paris, Université Paris-Cité, INSU/CNRS, F-75005 Paris

(2) Université Aix Marseille, CEREGE, CNRS, F-13545 Aix En Provence

**Abstract** Satellite and near-surface measurements are by nature different. Satellites travel at hundreds kilometers altitude and do not detect all details pertaining to the magnetic signal of the crust. However, they allow a global view, provide homogeneous vector and scalar measurements and survey almost the entire Earth, including remote and inhospitable regions. To the contrary, near-surface aeromagnetic and marine data are restricted to regions, are scalar only, but offer views at meters to kilometer resolutions. Reconciling both source of information is essential to study the Earth's magnetic crust but this requires developing very different tools.

One important resolution of the Working Group V-MOD of the International Association of Geomagnetism and Aeronomy is to encourage the production of a World Digital Magnetic Anomaly Map (WDMAP). In this framework, the French community collaborated closely with other international groups. On Earth, magnetic anomalies are defined as the vector, or scalar, differences between the measured magnetic field and an estimate of the main field originating from the core that dominates up to SH degree 13 (Figure 1). Magnetic anomalies, also known as the lithospheric field, are commonly assumed to reflect the magnetic properties of rocks lying in the Earth's crust. Therefore, a product like WDMAM should help to better identify and connect widely separated geological units. The first WDMAM was released during the IUGG meeting in Peruggia in 2007 [Thebault, 2011]. This composite map was built upon measurements from space, airplanes and ships collected during more than 60 years by researchers of all nationalities worldwide.

During the last four years, significant efforts were made to improve the first version of the WDMAM at both ends of the magnetic field spectrum and to try filling the spectral gap between large and small scales (SH degree 100 to about 200; Figure 1). The French community was involved in collecting new data. In the oceanic regions, for instance, high resolution magnetic field profiles were recorded over the whole Cretaceous Quiet Zone offshore Africa [Dyment et al., 2009]. In addition, an effort was made to retrieve old aeromagnetic maps over the French territory that are

now ready to be digitized. These new data will be included in future versions of the WDMAM map.

Many technical difficulties were faced in the first WDMAM version because of the nature of the considered data. This was further investigated. First, the available raw scalar marine measurements acquired at very different epochs are noisy. A first step consisted in screening 20 millions of GEODAS data and in removing the unrealistic spikes. Then, improved corrections for the diurnal external and the main fields were performed (see Geomagnetic Field Models) to bet-

<figure><img src="image_71.png" /></figure>

Figure 1: Synthetic view of the crustal field power spectrum at satellite altitude (400-km; dashed line) and aeromagnetic altitude (5-km; solid line). The noise at satellite altitudes does not allow seeing scales smaller than SH degree 100, or so ( 400-km), while airplanes poorly detect features larger than about 200 -km (SH degree 200, or so). After [Thebault, 2011]
<figure><img src="image_72.png" /><figcaption>Figure 2: Reprocessed oceanic compilation. After [Quesnel et al., 2009]</figcaption></figure>

ter delineate the structures of the lithospheric field. This work was compiled in a new oceanic world compilation [Quesnel et al., 2009] (Figure 2). Secondly, the CHAMP satellite data were also better processed. It appeared, thanks to the development of high-resolution modelling techniques (see Geomagnetic Field Models) that corrections for the magnetospheric field could introduce artifacts in the satellite based final anomaly maps. These artifacts may be visually distracting when they coincidentally align along oceanic ridges and could lead to wrong geophysical interpretations [Thébault et al., 2011]. It is therefore important to correct for these errors when satellite and near-surface data are merged together in a by-product such as WDMAM. Recognizing the importance of these works, a new tentative map was produced. This was performed outside the official WDMAM project because the new map intends to test prototype techniques of data analysis, such as line levelling, gridding by colocation, and an anisotropic interpolation between sparse marine track lines using a strong prior information concerning the direction of the oceanic chrons based on a model of the age of the oceanic crust [Maus et al., 2009].

## References

J. Dyment, Y. Gallet, E. Hoise, and The Magofond 08 scientific party. First complete high-

resolution record of the Cretaceous Normal Superchron. *AGU Fall Meeting Abstracts*, 2009.

S. Maus, U. Barckhausen, H. Berkenbosch, N. Bournas, J. Brozena, V. Childers, F. Dostaler, J. D. Fairhead, C. Finn, R. R. B. von Frese, C. Gaina, S. Golynsky, R. Kucks, H. Lühr, P. Milligan, S. Mogren, R. D. Müller, O. Olesen, M. Pilkington, R. Saltus, B. Schreckenberger, E. Thébault, and F. Caratori Tontini. EMAG2: A 2 arc min resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne, and marine magnetic measurements. *Geochem., Geophys., Geosyst.*, 10, 2009. doi: 10.1029/2009GC002471.

Y. Quesnel, M. Catalán, and T. Ishihara. A new global marine magnetic anomaly data set. *J. Geophys. Res.*, 114, 2009. doi: 10.1029/2008JB006144.

E. Thebault. Magnetic anomalies, interpretation. In H. Gupta, editor, *Encyclopedia of Solid Earth Geophysics*. Springer, Netherlands, 2011.

E. Thébault, F. Vervelidou, V. Lesur, and M. Hamoudi. The shortcomings of the along-track satellite filtering in planetary magnetism. *Submitted*, 2011.
# Geomagnetic Field Models

Erwan Thébault

Institut de Physique du Globe de Paris, Université Paris-Cité, INSU/CNRS, F-75005 Paris

**Abstract** Magnetic field measurements are not available everywhere on Earth. Therefore, mathematical tools must be applied and developed to estimate the field outside the dominion of data. Measurements are traditionally carried out on the Earth's surface but the availability of satellite data during the last decade allowed stupendous progresses in predicting the geomagnetic field anywhere between ground and space altitudes. Modeling the geomagnetic field is important for practical and scientific applications. It is an essential tool for aeronautic navigation, resource exploration, and fundamental research related to the dynamics of the Earth's core.

The Earth's magnetic field is traditionally represented in Spherical Harmonics when data are available worldwide. Every five years, an international team of scientists produces and releases an International Geomagnetic Reference Field model (IGRF). This activity is supervised by the working group V-MOD of the International Association of Geomagnetism and Astronomy (IAGA). The aim of this working group is to promote and coordinate international efforts to model the main geomagnetic field and its secular variation. The French community has been significantly involved in deriving the 11th generation of IGRF models [Finlay et al., 2010]. The complete process took about a year. After submission of two French candidate models [Chambodut et al., 2010; Thebault et al., 2010] (Figure 1), and models in collaborations with other teams [Olsen et al., 2010], a phase of evaluation and validation was completed [Finlay et al., 2010]. The IGRF model was released in January 2010 in a special issue published in the journal Earth Planets and Space.

During the construction of the IGRF candidate models interesting methodological and geophysical researches were conducted. For instance, comparisons between main geomagnetic field models developed during the previous decade [Gillet et al., 2010] showed how both the information contained in the data, particularly the satellite ones, and the a priori constraints introduced by their modeling could result in artificial geomagnetic spatial and time variations. Keeping in mind these limitations, independent observatory data were used to assess the occurrence of a pulse of geomagnetic field acceleration around 2006 that could be responsible of two geomagnetic jerks observed around 2003 and

2007 [Chulliat et al., 2010]. This core field acceleration pulse might be the relevant phenomenon to be investigated from the point of view of rapid core dynamics rather than the jerks (see Numerical Dynamo Modelling). Theoretical studies were also carried out in order to estimate the extent to which the secular variation could be predicted in space and forward in time. It was concluded that the minimum spatial resolution achievable for the secular variation is estimated to be about 1800 -km at the Earth's surface [Hulot et al., 2009], which confirms the need in the near future to develop alternative strategies to infer the physical properties of the Earth's core at higher resolutions using, in particular, the framework of data assimilation (see Geomagnetic Data Assimilation).

The derivation of main field models like IGRF is also of utmost importance for correcting the data for a main field in order to highlight the permanent structures of the Earth's lithospheric field that are poorly detected from space [Thébault et al., 2010] but almost invisible in near-surface data because of their poor lateral extent. After dedicated processing and the merging satellite and ground based data, it was possible to produce an integrated picture of the magnetic field contribution of the Earth's crust at 5-km altitude (see Processing the satellite and near-surface data for geomagnetic field models). The problem of reconciling surface, near-surface, and satellite measurements at high spatial resolution in Spherical Harmonics is a long standing problem because of computational burden and uneven data distribution. The French community has contributed to develop very specific tools to address these problems using local functions like wavelets, spherical caps, etc. (see Schott
<figure><img src="image_73.png" /><figcaption>Figure 1: Declination map in 2010.0 at the Earth's mean radius and mid-latitudes derived from a french candidate model to the 11th generation of IGRF Thebault et al. [2010]</figcaption></figure>

<figure><img src="image_74.png" /><figcaption>Figure 2: The declination (D in degrees) and vertical (Z in nT) components of the magnetic field in France in 2007.5 [Thébault, 2008]</figcaption></figure>

and Thebault [2011] for a review). For instance, a technique based on Spherical Cap Harmonic Analysis was specifically developed to model the Earth's magnetic field variations in France over 40 years [Thébault, 2008] (Figure 2). When the problem arises from the amount of available data, but at global scales, local expansion may be derived to speed up the computational process and to perform data compression [Minchev et al., 2009].

## References

A. Chambodut, B. Langlais, M. Menvielle, E. Thebault, A. Chulliat, and G. Hulot. Candidate models for the IGRF-11th generation making use of extrapolated observatory data. *Earth Planets Space*, 62:745–751, 2010. doi: 10.5047/eps.2010.06.006.

A. Chulliat, E. Thebault, and G. Hulot. Core field acceleration pulse as a common cause of the 2003 and 2007 geomagnetic jerks.

Geophys. Res. Lett., 37, 2010. doi: 10.1029/2009GL042019.

C. C. Finlay, S. Maus, C. D. Beggan, M. Hamoudi, F. J. Lowes, N. Olsen, and E. Thebault. Evaluation of candidate geomagnetic field models for IGRF-11. *Earth Planets Space*, 62:787–804, 2010. doi: 10.5047/eps.2010.11.005.

C. C. Finlay, S. Maus, C. D. Beggan, T. N. Bondar, A. Chambodut, T. A. Chernova, A. Chulliat, V. P. Golovkov, B. Hamilton, M. Hamoudi, R. Holme, G. Hulot, W. Kuang, B. Langlais, V. Lesur, F. J. Lowes, H. Luehr, S. Macmillan, M. Mandea, S. McLean, C. Manoj, M. Menvielle, I. Michaelis, N. Olsen, J. Rauberg, M. Rother, T. J. Sabaka, A. Tangborn, L. Toffner-Clausen, E. Thebault, A. W. P. Thomson, I. Wardinski, Z. Wei, and T. I. Zvereva. International Geomagnetic Reference Field: the eleventh generation. *Geophys. J. Int.*, 183(3):1216–1230, 2010. doi: 10.1111/j.1365-246X.2010.04804.x.

N. Gillet, V. Lesur, and N. Olsen. Geomagnetic Core Field Secular Variation Models. *Space Sci. Rev.*, 155:129–145, 2010. doi: 10.1007/s11214-009-9586-6.

G. Hulot, N. Olsen, E. Thébault, and K. Hemant. Crustal concealing of small scale core field secular variation. *Geophys. J. Int.*, 177, 2009. doi: 10.1111/j.1365-246X.2009.04119.x.

B. Minchev, A. Chambodut, M. Holschneider, I. Panet, E. Schoell, M. Mandea, and G. Ramilien. Local multi-polar expansions in potential field modeling. *Earth Planets Space*, 61:1127–1141, 2009.
N. Olsen, M. Mandea, T. Sabaka., and L. Tøffner-Clausen. The CHAOS-3 geomagnetic field model and candidates for the 11th generation IGRF. *Earth Planets Space*, 62:719-727, 2010. doi: 10.5047/eps.2010.07.003.

J. J. Schott and E. Thebault. *Geomagnetic Observations and Models*, volume 5, chapter Modelling the earth's magnetic field from global to regional scales, pages 229-264. IAGA Book Series, 2011.

E. Thébault. A proposal for regional modelling at the Earth's surface, R-SCHA2D. *Geo-phys. J. Int.*, 174, 2008. doi: 10.1111/j.1365-246X.2008.03823.x.

E. Thebault, S. Maus, A. Chulliat, G. Hulot, B. Langlais, A. Chambodut, and M. Menvielle. IGRF candidate models at times of rapid changes in core field acceleration. *Earth Planets Space*, 62:753-763, 2010. doi: 10.5047/eps.2010.05.004.

E. Thébault, M. Purucker, K. A. Whaler, B. Langlais, and T. J. Sabaka. The Magnetic Field of the Earth's Lithosphere. *Space Sci. Rev.*, 155, 2010. doi: 10.1007/s11214-010-9667-6.
# Geomagnetic Data Assimilation

## Alexandre Fournier

Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, INSU/CNRS, F-75005 Paris

**Abstract** Geomagnetic data assimilation aims at combining the information contained in present and past measurements of the Earth's magnetic field with the information contained in numerical models describing the dynamics of the Earth's core, where the main geomagnetic field is generated and sustained by means of a dynamo process. It aims at bringing new constraints on the physical processes occurring in the core responsible for the geomagnetic secular variation, in light of the available data. (Note that we are only interested in this short review with the secular variation whose origin is rooted in the core, and which occurs on interannual to millenial time scales.) In addition to the fundamental issues that such an approach could help address, it could have more practical applications, regarding for instance the design of geomagnetic field models in which the time-dependency would need not be parameterized or approximated as currently done, since it would be controlled by the numerical model. This field has recently come to the fore in geomagnetism for two main reasons: 1) the continuous increase in quality and size of the databases of geomagnetic measurements on the recent, historical, and archeomagnetic time scales and 2) our increased ability to model numerically Earth's core dynamics. It is a young field, and most studies published during the past few years are concerned with the feasibility of applying techniques routinely used in the fields of meteorology, climate dynamics or physical oceanography to the field of terrestrial magnetism. During the past year the first geophysical applications of geomagnetic data assimilation appeared. They are very encouraging and indicate that the field will continue to develop in the years to come. This development will hopefully trigger fruitful collaborations between observers and theoreticians of the geomagnetic field.

The principle of data assimilation is illustrated in Fig. 1. Starting from an unconstrained model trajectory, data assimilation aims at correcting the trajectory in order to provide an optimal fit to the available observations (the stars), given their error bars. This is an inverse problem set in a dynamical context, for which time t is a variable.

<figure><img src="image_75.png" /><figcaption>Figure 1: Assimilation starts with an unconstrained model trajectory over the time window of interest. It aims at correcting this initial model trajectory in order to provide an optimal fit to the available observations (the stars), given their error bars. Adapted from Fournier et al. [2010].</figcaption></figure>

In geomagnetism, early studies have focused on the feasibility of implementing data assimilation algorithms to the problem of the geomagnetic secular variation, by analyzing the response

and behavior of the assimilating system in a well-controlled environment, using databases of synthetic observations, starting from one-dimensional toy models [Fournier et al., 2007, Sun et al., 2007], and moving on to systems of higher complexity [Liu et al., 2007, Kuang et al., 2008, Canet et al., 2009]. Those studies are generically referred to in the literature as "observing system simulations experiments" (OSSEs), or, equivalently, "twin experiments". More recent applications have considered "level-2" observations (geomagnetic field models coefficients, also known as Gauss coefficients), thereby permitting to make some inference on the state of the core [Kuang et al., 2009]. The approaches followed nowadays, reviewed in Fournier et al. [2010], differ by the choice of the physical and numerical model employed to describe core dynamics, and the form of assimilation they resort to (sequential or variational, see Fig. 2 for an illustration). Let us stress that specific to the core problem is the remote, blurred and incomplete observation of its state. Accordingly, we lack a well-defined background state (the equivalent of a "climatological" mean), about which the dynamics of the secular variation is
<figure><img src="image_76.png" /></figure>

Figure 2: Left: The sequential approach to data assimilation. Starting from the initial time, the model trajectory follows the initial forecast. As soon as the first observation is available, the analysis is performed. The same cycle is repeated anytime an observation is available, with the assimilated trajectory deviating from the initial guess (the dashed line). Right: the variational approach to data assimilation. After adjustment of the initial condition (the green bullet on the t=t0 axis) by means of an iterative minimization algorithm, the model trajectory is corrected over the entire time window, in order to provide an optimal fit to the data (in a generalized least squares sense). The dashed line corresponds to the initial (unconstrained) guess of the model trajectory introduced in Fig. 1.

likely to take place, even though we have a fairly good idea of the large to medium length scales of the poloidal field at the top of the core over a 400 year period, and for the largest scales much longer back in time (e.g. Hulot et al. [2010]).

All the preliminary results obtained so far show that, in the assimilation framework, surface measurements of the radial component of the field at the core surface can provide some information and constraints about the structure of the field and the flow within the core. The propagation of the information (the innovation) from the core-mantle boundary to the bulk of the core is achieved either through the non-linear interactions between the dynamical actors (the various components of the state vector, which include the poloidal field), when operating with a three-dimensional (3D) model of the geodynamo, or by some a priori constraint imposed on the nature of the dynamics (under the quasi-geostrophic assumption, the invariance of the flow in the direction of rotation). This propagation can also be made more effective through the use of a background error covariance matrix coupling effectively the surface of the core with its interior.

The last year has witnessed the first geophysical applications of geomagnetic data assimilation techniques. Using geomagnetic field models spanning the past 7,000 years as observations and an iterative predictor-corrector time scheme to reduce model errors, Kuang et al. [2010] contributed to the 2010 release of the IGRF (for the secular variation); Beggan and Whaler [2010] also contributed to the same IGRF. They predict the evolution of the geomagnetic field over the next 5 years, their secular variation being based on an ensemble of steady core flows.

On a more fundamental level, Gillet et al. [2010]

<figure><img src="image_77.png" /></figure>

Figure 3: Sketch illustrating the propagation of torsional Alfvén waves in the Earth's core interior.

were able to estimate the strength of the magnetic field in the core interior (on the order of 4 mT). This represents the first application of variational data assimilation to geomagnetism. That study uses time series of core flow streamfunctions calculated with the quasi-geostrophic assumption. A recurring signal of period about 6 years was detected in the time series for the zonal flow. It can be interpreted as the result of Alfvén waves propagating in the fluid outer core. These special Alfvén waves consist in the motion of nested cylinders aligned with the rotation axis and linked by the magnetic field that threads them (see Figure 3); the stronger the field, the faster the wave. This promising study reconciles observations and theoretical estimates of the strength of the field based on scaling laws [Christensen and Aubert, 2006]. It also leaves many questions unanswered. These will likely be addressed in the years to come within the frame-
work of data assimilation.

References

C. Beggan and K. Whaler. Forecast-
ing secular variation using core flows.
*Earth Planets Space*, 62, 2010. doi:
10.5047/eps.2010.07.004.

E. Canet, A. Fournier, and D. Jault. Forward and adjoint quasi-geostrophic models of the geo-magnetic secular variation. *J. Geophys. Res.*, 114, 2009. doi: 10.1029/2008JB006189.

U. R. Christensen and J. Aubert. Scaling proper-
ties of convection-driven dynamos in rotating
spherical shells and application to planetary
magnetic fields. *Geophys. J. Int.*, 166:97–114,
2006.

A. Fournier, C. Eymin, and T. Alboussière. A case for variational geomagnetic data assimilation: Insights from a one-dimensional, nonlinear, and sparsely observed mhd system. *Nonlin. Proc. Geophy*, 14, 2007. doi: 10.5194/npg-14-163-2007.

A. Fournier, G. Hulot, D. Jault, W. Kuang, A. Tangborn, N. Gillet, E. Canet, J. Aubert, and F. Lhuillier. An Introduction to Data Assimilation and Predictability in Geomagnetism. *Space Sci. Rev.*, 155(1-4):247–291, 2010. doi: 10.1007/s11214-010-9669-4.

N. Gillet, D. Jault, E. Canet, and A. Fournier. Fast torsional waves and strong magnetic field within the Earth's core. *Nature*, 465:74–77, 2010. doi: 10.1038/nature09010.

G. Hulot, C. C. Finlay, C. G. Constable, N. Olsen, and M. Mandea. The Magnetic Field of Planet Earth. *Space Sci. Rev.*, 152:159–222, 2010. doi: 10.1007/s11214-010-9644-0.

W. Kuang, A. Tangborn, W. Jiang, D. Liu, Z. Sun, J. Bloxham, Z. Wei, Z. , R. Holme, and A. Tangborn. Mosst_das: the first generation geomagnetic data assimilation framework. *Commu. Comp. Phys.*, 3, 2008.

W. Kuang, A. Tangborn, Z. Wei, and T. Sabaka. Constraining a numerical geodynamo model with 100 years of surface observations. *Geo-phys. J. Int.*, 179, 2009. doi: 10.1111/j.1365-246X.2009.04376.x.

W. Kuang, Z. Wei, R. Holme, and A. Tangborn. Prediction of geomagnetic field with data assimilation: a candidate secular variation model for igrf-11. *Earth Planets Space*, 62, 2010. doi: 10.5047/eps.2010.07.008.

D. Liu, A. Tangborn, and W. Kuang. Observ-
ing system simulation experiments in geomag-
netic data assimilation. *J. Geophys. Res.*, 112,
2007. doi: 10.1029/2006JB004691.

Z. Sun, A. Tangborn, and W. Kuang. Data assimila-
tion in a sparsely observed one-dimensional
modeled mhd system. *Nonlin. Proc. Geophy*,
14, 2007.
# Numerical Dynamo Models

## Hagay Amit

Univrsité de Nantes and CNRS, Laboratoire de Planétologie et Géodynamique de Nantes, 44322 Nantes cedex 3

**Abstract** Studies of numerical dynamo models by researchers in France in the period 2006-2010 focused on (a) scaling laws and extrapolations of model results to the planets, (b) core-mantle thermal interactions and their impact on the dynamo, (c) dipole polarity reversals, and (d) short-term secular variation (SV) with implications to core flow inversions. Other studies include Earth-like field morphology, inner core super-rotation, dynamo predictability time, dynamos generated by shear flows and inner core size affecting stellar or planetary dynamo behavior. Here we briefly note these studies.

Numerical dynamos operate in a parameter regime very far from Earth's core (due to computational limitations), so any inference to the geodynamo is questionable. Extrapolations of scaling laws may bridge the models and the Earth. Christensen and Aubert [2006] used a large data base of dynamo models to derive scaling laws based on a buoyancy-flux Rayleigh number independent of any diffusivities. They found that inertial effects define the transition between dipole-dominated non-reversing to multipolar reversing dynamos. The magnetic field strength is controlled by the buoyancy flux. They also predicted a slow inner core growth rate and a relatively old inner core. Aubert et al. [2009] combined numerical dynamos with varying inner core sizes and different convective styles with thermal history models to expand the scaling laws to early Earth conditions. They argued that a thermally-driven dynamo acting prior to the inner core could produce a dipole moment comparable to today's field. They predicted that the early Earth field reversed less frequently due to lower convective power.

Non-axisymmetric geodynamo observations suggest that the heterogeneous mantle affects the dynamics in Earth's core. Aubert et al. [2007] used numerical dynamos with heterogeneous core-mantle boundary (CMB) heat flux to study mantle control on the dynamo. They compared long-term time-average flow below the CMB with intermediate averages corresponding to the length of available geomagnetic data. The statistically significant correlation between the intermediate and long-term flows suggests that a signature of the mantle heterogeneity on time-average core flows inverted from the historical geomagnetic SV is expected. Aubert

et al. [2008a] demonstrated that the steady part of a numerical dynamo model with tomographic CMB heat flux pattern inferred from a lower mantle seismic tomography recovers important features of geophysical observations, including the locations of high-latitude paleomagnetic flux patches, large cyclones in the time-average core flow from geomagnetic SV, and hemispheric seismic anomalies in the upper inner core. The mantle heterogeneity is coupled to the inner core via columnar convection that concentrates magnetic flux at high-latitudes of the CMB and extracts anomalous buoyancy flux from the inner-core boundary (ICB) at the same longitude on the equatorial plane. Amit and Choblet [2009] examined different interpretations of lower mantle seismic shear velocities in terms of thermal and post-Perovskite origins. Comparing their numerical dynamo time-average properties to geophysical observations, they found that accounting for post-Perovskite in the lower mantle tomography may generally improve the agreement. They also proposed that quasi-axial convective rolls may reconcile dominant rotational effects and deviations from equatorial symmetry in the CMB heat flux prescribed by the lower mantle. Amit et al. [2010] used tomographic numerical dynamos and a tracking algorithm to study the time-dependence of the robust high-latitude intense magnetic flux patches. They found that the patches oscillate about preferred locations prescribed by the mantle, with episodic drifts from one location to another. The drift events correspond to azimuthal motions of fluid downwelling structures that concentrate magnetic flux. Their models reconcile the correlation of the patches location in historical and paleomagnetic field
models together with their weaker signature in the paleomagnetic field and their mobility in archeomagnetic field models.

The mechanisms controlling geomagnetic polarity reversals are not fully understood. Aubert et al. [2008b] designed a Dynamical Magnetic Fieldlines Imaging (DMFI) algorithm to study reversals in numerical dynamos. They showed that magnetic upwellings originating in the ICB produce reversed flux patches on the CMB that subsequently trigger reversals. Olson et al. [2009] compared two dipole collapse events in a numerical dynamo model, one that reversed and one that did not reverse. They found that prior to the dipole collapse, the ratio of reversed/normal flux contributions to the axial dipole is much larger in the reversing case and may therefore serve as a possible reversal precursor. Application of their criterion to the current geomagnetic dipole decrease suggests that the present field will not reverse. Gissinger et al. [2010] found in numerical dynamos where the viscosity is smaller than the magnetic diffusivity that the reversal can be simplified to the interaction among the axial dipole, the axial quadrupole and a symmetry breaking zonal flow. In their low order system, reversals are triggered by deterministic chaos.

Numerical dynamos may assess the reliability of core flow inversions and improve their quality. Amit et al. [2007] tested their helical-geostrophic core flow inversion method against synthetic SV data generated by numerical dynamos. They found decent agreement between the true dynamo flow and their inverted flow for large-scale dynamos, but deteriorating correlations for smaller scale dynamos. They attributed the discrepancies to magnetic diffusion and data truncation effects. Amit and Christensen [2008] showed in dynamo models a correlation between radial and tangential diffusion contributions to magnetic SV. They extrapolated the ratio of the two diffusive terms to Earth-like conditions and incorporated magnetic diffusion in core flow inversions. They concluded that a thin magnetic boundary layer at the top of the core might cause strong radial diffusion and significant non frozen-flux SV.

The plethora of numerical dynamo models provide different field morphologies which one is most Earth-like? Christensen et al. [2010] defined quantitative criteria for field morphology characterization and ranked the semblance of their large data base of dynamo models to the observed geomagnetic field. They found that Earth-like dynamo models exist all the way from

accessible simulations to the geodynamo.

Some seismic observations suggest inner core super-rotation. Aubert and Dumberry [2010] used high-resolution low-viscosity numerical dynamos where the inner core is allowed to differentially rotate with respect to the mantle by viscous and magnetic torques applied by the liquid outer core and gravitational restoring torque exerted by the mantle. They found that time-dependent fluctuations dominate steady drift, and that the observed seismic signal is likely part of a fluctuation.

Assuming complete knowledge of all dynamo variables, how far in time can the field be predicted? Hulot et al. [2010] introduced small perturbations to numerical dynamo models and measured the time until the system deviates from the unperturbed models. They found that this time, i.e. the predictability time of the dynamo, depends on the magnetic Reynolds number. Applying their results to Earth's core, they found one century as the maximum predictability time, precluding the possibility to discover whether the current dipole decrease is a beginning of a reversal or not.

Spherical Couette flows may generate dynamos. Guervilly and Cardin [2010] imposed such mechanical boundary condition on a numerical dynamo. They found that non-axisymmetric flow is required to excite a dynamo. Without global rotation, the critical magnetic Reynolds number is very high. Their study has important implications for MHD laboratory experiments.

The size of the inner core may dramatically alter dynamo action. Goudard and Dormy [2008] compared numerical dynamos with different inner to outer core aspect ratios. They showed that varying the aspect ratio may cause a sharp transition from Earth-like steady dynamos to Sun-like dynamo waves.

## References

H. Amit and G. Choblet. Mantle-driven geomagnetic features-effects of post-Perovskite phase transition. *Earth Planets Space*, 61(11): 1255-1268, 2009.

H. Amit and U. R. Christensen. Accounting for magnetic diffusion in core flow inversions from geomagnetic secular variation. *Geo-phys. J. Int.*, 175(3):913-924, 2008. doi: 10.1111/j.1365-246X.2008.03948.x.
H. Amit, J. Aubert, and G. Hulot. Stationary, oscillating or drifting mantle-driven geomagnetic flux patches? *J. Geophys. Res.*, 115, JUL 27 2010. doi: 10.1029/2009JB006542.

H. Amit, P. Olson, and U. Christensen. Tests of core flow imaging methods with numerical dynamos. *Geophys. J. Int.*, 168(1):27–39, 2007. doi: 10.1111/j.1365-246X.2006.03175.x.

J. Aubert and M. Dumberry. Steady and fluctuating inner core rotation in numerical geodynamo models. *Geophys. J. Int.*, 184:162–170, 2010.

J. Aubert, H. Amit, and G. Hulot. Detecting thermal boundary control in surface flows from numerical dynamos. *Phys. Earth Planet. Int.*, 160(2):143–156, 2007. doi: 10.1016/j.pepi.2006.11.003.

J. Aubert, H. Amit, G. Hulot, and P. Olson. Thermochemical flows couple the Earth's inner core growth to mantle heterogeneity. *Nature*, 454(7205):758–U80, 2008a. doi: 10.1038/nature07109.

J. Aubert, J. Aurnou, and J. Wicht. The magnetic structure of convection-driven numerical dynamos. *Geophys. J. Int.*, 172:945–956, 2008b.

J. Aubert, S. Labrosse, and C. Poitou. Modelling the paleo-evolution of the geodynamo. *Geo-phys. J. Int.*, 179:1414–1428, 2009.

U. R. Christensen and J. Aubert. Scaling properties of convection-driven dynamos in rotating spherical shells and application to planetary magnetic fields. *Geophys. J. Int.*, 166:97–114, 2006.

U. R. Christensen, J. Aubert, and G. Hulot. Conditions for Earth-like geodynamo models. *Earth Planet. Sci. Lett.*, 296(3-4):487–496, 2010. doi: 10.1016/j.epsl.2010.06.009.

C. Gissinger, E. Dormy, and S. Fauve. Morphology of field reversals in turbulent dynamos. *Euro. Phys. Lett.*, 90(4), 2010. doi: 10.1209/0295-5075/90/49001.

L. Goudard and E. Dormy. Relations between the dynamo region geometry and the magnetic behavior of stars and planets. *Euro. Phys. Lett.*, 83(4), 2008. doi: 10.1029/2008J05075/83/59001.

C. Guervilly and P. Cardin. Numerical simulations of dynamos generated in spherical Couette flows. *Geophys. Astrophys.*

*Fluid Dyn.*, 104(2-3):221–248, 2010. doi: 10.1080/03091920903550955.

G. Hulot, F. Lhuillier, and J. Aubert. Earth's dynamo limit of predictability. *Geophys. Res. Lett.*, 37, 2010. doi: 10.1029/2009GL041869.

P. Olson, P. Driscoll, and H. Amit. Dipole collapse and reversal precursors in a numerical dynamo. *Phys. Earth Planet. Int.*, 173(1-2):121–140, 2009. doi: 10.1016/j.pepi.2008.11.010.
# Laboratory dynamo experiments

Jean-François Pinton

Laboratoire de Physique de l'École Normale Supérieure de Lyon, CNRS & Université de Lyon, F-69364 Lyon, France

**Abstract** Since the turn of the century, experiments have produced laboratory fluid dynamos which enable a study of the effect in controlled conditions. The most recent one, the VKS experiment, demonstrate the possibility of dynamo generation from turbulent motions and exhibits a rich variety of time dynamics.

Although dynamo research is essentially motivated by observations from planetary and stellar dynamos, the conditions that prevail in such natural objects cannot be reproduced in the laboratory. Experiments and numerics can only be run in quite different parameter regimes, but they both provide useful insights into the features of natural dynamos. Experiments cannot be rotated as fast as real systems do, convective motion cannot be as strong, etc, but they run with real fluids and probe quantities that cannot be accessed from remote observations of natural dynamos.

In order for a dynamo to be self-sustained, the production of induced currents by fluid motions must overcome the resistive Joule dissipation. This condition sets an instability threshold, requiring that the magnetic Reynolds number of the flow ($R_M = UL/\lambda$) exceeds a critical value $R_M^c - U$ and $L$ are characteristic velocity and length and $\lambda$ is the magnetic diffusivity. Assuming $R_M^c$ values of the order of 10 to 100 (a value often quoted for the Earth), and given the fact that all liquid metals have magnetic Prandtl numbers (ratio of kinetic to magnetic diffusivities) of the order of $P_M \sim 10^{-5}$, one realizes that dynamo flows are associated with huge kinetic Reynolds number values $R_V = R_M/P_M$, typically exceeding $10^6$. Such high $R_V$ values are associated with fully developed turbulence, an observation that raises several central issues for dynamo experiments. Turbulence is often synonymous of (a) disordered motions, and (b) strongly diffusive features. In this context, (a) means that the specific motions that favor dynamo action maybe disrupted by the randomness of the flow. In addition, the small magnetic Prandtl number values impose that the Joule resistive scale is very much larger than the hydrodynamic viscous length. It is therefore tempting to perform some kind of sub-scale average

of the action of the turbulent velocity field. Then (b) leads to an effective magnetic diffusivity that could be much larger than the molecular value. These considerations have raised doubts on the very existence of fully turbulent dynamos.

One alternative is to engineer flow configurations that will preserve flow patterns which are essential for the dynamo generation. The design of the Riga and Karlsruhe experiments have been made to ensure that the time-averaged flow field resembles laminar flows which are kinematic dynamo solutions [Moreau and Pinton, 2008]. These pioneering studies have validated the principle of a *fluid* dynamo, and have

<figure><img src="image_78.png" /></figure>

Figure 1: Sketch of the VKS flow configuration. The flow is generated by rotating two impellers 371 mm apart in a thin cylindrical copper vessel, $2R = 412$ mm in inner diameter and $524$ mm in length. The impellers are fitted with 8 curved blades of height $h = 41.2$ mm; in most experimental runs, the impellers are rotated so that the blades move in a *non-scooping* direction, defined as the positive direction by arrows. Positions 1 to 5 correspond to points where magnetic measurements have been made, using 3D Hall probes.
<figure><img src="image_79.png" /></figure>

Figure 2: Dynamical regimes observed in the von Kármán sodium experiment when the impellers driving the flow rotate at varying rates: the coordinates in the main plot are the magnetic Reynolds numbers built from the velocity of each impeller. The insets give examples of time signals of the 3 components of the magnetic field recorded in the mid-plane of the cylinder.

shown many fundamental dynamo properties. The threshold for dynamo action has been found to be in good agreement with predictions, showing the predominance of the large scales in their dynamo processes.

Another possibility, often explored in the geophysics community, is provided by strongly rotating flows. In this case, the Proudman-Taylor constrain may be able to prevent the development of strong three-dimensional turbulent fluctuations. This effect may even be strengthened by the generation of a dynamo dipole with its axis parallel to the rotation vector. Experiments in rotating Couette flows are studied in Grenoble and Maryland [Schmitt et al., 2008, Kelley et al., 2007]. Preliminary studies have not shown self-generation, but have pointed to the existence of waves in these strong rotating and magnetized flows: inertial, magneto-rotational, Alfvén, etc. Their role regarding dynamo self-generation has yet to be elucidated.

The VKS experiments have shown that it is possible to generate a dynamo from fully turbulent motions, with non-trivial dynamics [Monchaux et al., 2009]. The existence of fully turbulent motions has a major impact on the power require-

ments of the experiment. In the limit of very high $R_V$ values, the hydrodynamic power consumption (below dynamo threshold) scales as $P = \rho L^2 U^3$ ($\rho$ is the fluid's density), leading to magnetic Reynolds number $R_M = \mu\sigma(PL/\rho)^{1/3}$ ($\mu$ and $\sigma$ are the magnetic permeability and electrical conductivity of the fluid, so that $\lambda = 1/\mu\sigma$ is its magnetic diffusivity). Engineering difficulties typically scale with the size $L$ of the experiment, while operational costs are best associated with the power input $P$. Then, the above scaling shows that in order to reach high $R_M$ values, one should use a fluid with the best electrical conductivity and lowest density (hence the use of liquid sodium), with size and power consumption only contributing to the one-third power. This is a noteworthy peculiarity of the study of this hydromagnetic instability: energy and engineering constrains are such that one is not able to increase at will the control parameter of the instability; one must also choose conditions such that the thresholds is within the capacity of the selected setup. In the case of the VKS experiment this is ensured when ferromagnetic impellers are used to drive the flow. When rotating, they promote a strong omega effect in their vicinity.
pled with local sources of alpha processes (he-
lical flow structures, turbulence gradients), this
arrangement generates a dynamo at $R_M^c \sim 30$.
A stationary dynamo is produced when one im-
peller rotates while the other is kept at rest. The
main magnetic mode has the shape of an axial
dipole. When both are set into (counter) rota-
tion, a rich variety of regimes are observed from
the interactions of the dynamos generated from
the rotation of each impeller. As shown in [Mon-
chaux et al., 2008] they share many properties
with the dynamics of low dimensional systems.

Liquid metal flows reach magnetic Reynolds
numbers of the order of 100, at most. Using a
plasma as the working fluid is a possibility cur-
rently explored to generate laboratory dynamos
at significantly higher $R_M$ values [Spence et al.,
2009]. This may enable the observation in the
lab of small scale fluctuating dynamos which pre-
vail in many astrophysical situations.

References

D. H. Kelley, S. A. Z. Triana, D. S., A. Tilgner, and D. P. Lathrop. Inertial waves driven by differential rotation in a planetary geometry. *Geophys. Astrophys. Fluid Dyn.*, 101, 2007.

R. Monchaux, M. Berhanu, S. Aumaître, A. Chif-
faudel, F. Daviaud, B. Dubrulle, F. Ravelet,
M. Bourgoin, P. Odier, J.-F. Pinton, N. Plihon,
R. Volk, S. Fauve, N. Mordant, and F. Pétrélis.
Chaotic dynamos generated by a turbulent
flow of liquid sodium. *Phys. Rev. Lett.*, 101,
2008.

R. Monchaux, M. Berhanu, S. Aumaître, A. Chif-
faudel, F. Daviaud, B. Dubrulle, L. Marié,
F. Ravelet, S. Fauve, N. Mordant, F. Pétrélis,
M. Bourgoin, P. Odier, J.-F. Pinton, N. Plihon,
and R. Volk. The vks experiment: turbulent
dynamical dynamos. *Phys. Fluids*, 21, 2009.

R. Moreau and J. Pinton. (eds), dynamo ef-
fect: experimental progress and geo- and
astro-physical challenges, special issue. *C. R.
Phys.*, 9, 2008.

D. Schmitt, T. Alboussiere, D. Brito, P. Cardin,
N. Gagniere, D. Jault, and H.-C. Nataf. Rotat-
ing spherical couette flow in a dipolar magnetic
field: experimental study of magneto-inertial
waves. *J. Fluid Mech.*, 604:175–197, 2008.

E. Spence, K. Reuter, and C. Forest. A spheri-
cal plasma dynamo experiment. *Astrophys. J.*,
700, 2009.
# Paleomagnetism and Rock Magnetism

Jean Pascal Cogné and France Lagroix

Université Paris Diderot, Institut de Physique du Globe de Paris
PRES Sorbonne Paris-Cité, INSU/CNRS, F-75005 Paris

**Abstract** Paleomagnetism has proven a powerful tool providing valuable constraints on Plate Tectonics, depicting history and helping theory of continental drift. In France, Paleomagnetism and rock magnetism have grown following pioneering works of Profs. Emile Thellier and Louis NÃel in the middle of the XXth century, giving rise to the establishment of several paleomagnetic labs in the country at present. Since the time of Plate Tectonics theory and establishment of magnetic field reversal evidences, french labs have largely contributed and developed use of magnetic memory of rocks, synthetic materials and other human ancient artifacts. Here we cite some significant french contributions.

**Archeomagnetism** pioneered by St Maur lab, later joined by IPGP, is currently being developed by most paleomag labs in France. Archeomagnetism allows recovery of magnetic field direction and intensity as recorded by baked archeological artifacts (e.g. potteries, ovens...) at a given location. As a result, high resolution directional and intensity variation curves for a given region, Gallet et al. [2009] (Fig. 1) provide constraints for geomagnetic studies, and, for archeologist, a dating tool [eg Kovacheva et al., 2009, Schnepf et al., 2009].

**Magnetostratigraphy, paleointensity and geomagnetic field behaviour** polarity timescales are progressively obtained from more and more ancient eras, as far back as the Paleozoic and Proterozoic. They have noticeably revealed a long normal superchron in the Ordovician [Pavlov and Gallet, 2010], or periods of high reversal frequencies in the Proterozoic, possibly larger than 5-10 reversals per Myr [Pavlov and Gallet, 2009]. The last element defining the geomagnetic field vector, its intensity, is uneasy to evaluate. In marine sediments, relative paleointensity methods provide important contribution to the study of the geomagnetic field, particularly in its reversals and excursions history [eg Valet et al., 2008, Laj et al., 2006]. Absolute paleointensity is the last parameter which allows full definition of magnetic field vector and its changes through geological times. This parameter can be defined in effusive formations only, mainly basalts. Experimental determination of this parameter is still uneasy. Therefore, methodological developments are still being held, together

<figure><img src="image_80.png" /><figcaption>Figure 1: Directional evolution of the Earth's magnetic field in France (Paris) during the past three millennia, from [Gallet et al., 2009].</figcaption></figure>

with data acquisition [Biggin and Perrin, 2007, Valet et al., 2010, Thouveny et al., 2008].

**Plate tectonics and continental deformation**

Paleomagnetism remains a powerful tool in deciphering deformation of continents and their movements at the Earth's surface. Beyond continuing establishment of reference Apparent Polar Wandering Paths (APWP) [Moreau et al., 2007], some significant efforts, which deserve attention, have focused on tectonics of recent mountain chains such as the Andes [Arriagada et al., 2008, Fig 2.](Fig. 2) or the Asian system (Tibet, China, Mongolia... [Hankard et al., 2007, Cogne et al., 2011, Fig. 3].)

Fig. 2 and 3 illustrate tectonic analyses which
<figure><img src="image_81.png" /></figure>

Figure 2: Two-dimensional map-view restora-
tions of the central Andes using paleomagneti-
cally derived shortening and block rotation mod-
els [Moreau et al., 2007].

<figure><img src="image_82.png" /></figure>

Figure 3: Cenozoic paleolatitude anomaly over Asia, resulting from anomalously shallow paleomagnetic inclinations. The origin, geomagnetic and/or tectonic [Hankard et al., 2007] of this anomaly is still hotly debated [Cogne et al., 2011]

are now possible, due to increasing density and
coverage (but far from being sufficient and of ho-
mogeneous coverage and quality) of paleomag-
netic database, to which french labs have signif-
icantly contributed.

**True Polar Wander (TPW) and global dynam-ics** Using a geodynamic model based on plate reconstructions that estimates the location and rate of subducted slabs, and taking into account the effect of large-scale upwellings as evidenced by tomography, it is shown that temporal varia-tion of the mantle density heterogeneities is es-sentially due to changes in the subduction his-tory of plates. Since 120 Myr, both the max-imum and intermediate Principal Inertia Axes have moved in a plane perpendicular to Africa, along a circle corresponding to the low of geoid induced by subduction around the Pacific. The minimum PIA seems to be relatively stable since 120 Myr, and close to the maximum degree 2 geoid high under Africa. This can account for ob-served TPW or African APW in the last 200 Myr [Rouby et al., 2010, Fig. 4].

<figure><img src="image_83.png" /></figure>

Figure 4: Principal Inertia Axes since 120 Myr [Rouby et al., 2010] (dots every 10 Myr, stars denote present day values) for a mantle density heterogeneities model arising from circum-Pacific subductions. The corresponding present-day geoid (degrees 2-12) is also shown.

**Rock magnetism** To end this brief overview, we finally underline that a significant part of scientific activity in paleomagnetism deals with magnetic properties of natural, synthetic and/or anthropogenic materials. The aim is to further understand the remanence acquisition processes, its alteration through time and in different geological settings together with applying mineral magnetic properties to investigate a variety of questions, such as rock formation processes (weathering, deposition etc... [e.g. Lagroix and Banerjee, 2004a, Ricordel-Prognon et al., 2010], characterization of extra-terrestrial materials [Rochette et al., 2009], or environmental studies such as heavy metal pollution evaluations [Franke et al., 2009], and paleoclimate [e.g. Lagroix and Banerjee, 2004b, Blanchet et al., 2009].

References

C. Arriagada, P. Roperch, C. Mpodozis, and P. R. Cobbold. Paleogene building of the Bolivian Orocline: Tectonic restoration of the central Andes in 2-D map view. *Tectonics*, 27, 2008. doi: 10.1029/2008TC002269.

A. J. Biggin and M. Perrin. The behaviour and detection of partial thermoremanent magnetisation (PTRM) tails in Thellier palaeointensity experiments. *Earth Planets Space*, 59:717–725, 2007.

C. L. Blanchet, N. Thouveny, and L. Vidal. For-mation and preservation of greigite (Fe3S4)
in sediments from the Santa Barbara Basin: Implications for paleoenvironmental changes during the past 35 ka. *Paleooceano.*, 24, 2009. doi: 10.1029/2008PA001719.

J.-P. Cogne et al. A new Meso-Cenozoic East Asia APWP: an alternative solution to decipher the tertiary inclination anomaly issue - Implications on plate tectonics and continental deformation of Central and SE Asia, East Europe and Arctic regions of Eurasia. *Geophys. J. Int.*, Submitted:—, 2011.

C. Franke, C. Kissel, E. Robin, P. Bonte, and F. Lagroix. Magnetic particle characterization in the seine river system: Implications for the determination of natural versus anthropogenic input. *Geochem., Geophys., Geosyst.*, 10, 2009. doi: 10.1029/2009GC002544.

Y. Gallet, A. Genevey, M. Le Goff, N. Warme, J. Gran-Aymerich, and A. Lefevre. On the use of archeology in geomagnetism, and vice-versa: Recent developments in archeomagnetism. *C. R. Phys.*, 10, 2009. doi: 10.1016/j.crhy.2009.08.005.

F. Hankard, J.-P. Cogne, V. A. Kravchinsky, L. Carporzen, A. Bayasgalan, and P. Lkhagvadorj. New Tertiary paleomagnetic poles from Mongolia and Siberia at 40, 30, 20, and 13 Ma: Clues on the inclination shallowing problem in central Asia. *J. Geophys. Res.*, 112, 2007. doi: 10.1029/2006JB004488.

M. Kovacheva, A. Chauvin, N. Jordanova, P. Lanos, and V. Karloukovski. Remanence anisotropy effect on the palaeointensity results obtained from various archaeological materials, excluding pottery. *Earth Planets Space*, 61, 2009.

F. Lagroix and S. K. Banerjee. Cryptic post-depositional reworking in aeolian sediments revealed by the anisotropy of magnetic susceptibility. *Earth Planet. Sci. Lett.*, 224, 2004a. doi: 10.1016/j.espl.2004.05.029.

F. Lagroix and S. K. Banerjee. The regional and temporal significance of primary aeolian magnetic fabrics preserved in Alaskan loess. *Earth Planet. Sci. Lett.*, 225, 2004b. doi: 10.1016/j.epsl.2004.07.003.

C. Laj, C. Kissel, and A. P. Roberts. Geomagnetic field behavior during the Iceland Basin and Laschamp geomagnetic excursions: A simple transitional field geometry?

*Geochem., Geophys., Geosyst.*, 7, 2006. doi: 10.1029/2005GC001122.

M.-G. Moreau, J. Besse, F. Fluteau, and M. Greff-Lefftz. A new global Paleocene-Eocene apparent polar wandering path loop by "stacking" magneto stratigraphies: Correlations with high latitude climatic data. *Earth Planet. Sci. Lett.*, 260, 2007. doi: 10.1016/j.epsl.2007.05.025.

V. Pavlov and Y. Gallet. Variations in geomagnetic reversal frequency during the Earth's middle age. *Geochem., Geophys., Geosyst.*, 11, 2010. doi: 10.1029/2009GC002583.

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C. Ricordel-Prognon, F. Lagroix, M.-G. Moreau, and M. Thiry. Lateritic paleoweathering profiles in French Massif Central: Paleomagnetic datings. *J. Geophys. Res.*, 115, 2010. doi: 10.1029/2010JB007419.

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# Recent French activity in archeomagnetism

Annick Chauvin (1), Yves Gallet (2) Agnès Genevey (3), and Philippe Lanos (4)

(1) Géoscience Rennes, Université de Rennes 1, F-35000 Rennes

(2) Institut de Physique du Globe de Paris, INSU/CNRS, F-75005 Paris

(3) Centre de Recherche et de Restauration des Musées de France, F-75001 Paris

(1) Centre de Recherches en Physique Appliquée à l'Archéologie, Université Bordeaux 3 et Université Rennes 1

**Abstract** Archeomagnetism is a very active domain of research in France thanks to several French laboratories involved in magnetic property analyses of baked clay archeological artifacts. Here we list some recent results.

Recent archeomagnetic studies have been focused on the evolution, both in direction and in intensity, of the geomagnetic field over the past few centuries and/or millennia in several regions, in Western Europe [Gomez-Paccard et al., 2008, Genevey et al., 2009, Schneppe et al., 2009, Gallet et al., 2009a, Hervé et al., 2011], in the Middle East [Gallet et al., 2008] or in Central and Southern America [Hartmann et al., 2010]. In particular, these studies led to the acquisition of numerous high-quality archeointensity data, allowing one to gradually compensate for the lack of data of this nature, which existed until now. Hence, a 3000 year-long full (direction and intensity) geomagnetic field record is progressively emerging for Western Europe. Studies performed in Brazil further brought important new information on the geomagnetic field behavior in southern hemisphere where archeointensity results are still rare, representing as a whole less than 5% of all available intensity data [Genevey et al., 2008]. Other investigation is being conducted in Syria in order to pursue the construction of a detailed regional archeointensity variation curve encompassing a large part of the Holocene.

The main objectives of these studies are three-fold. The first target concerns geomagnetism. The new data greatly contribute to the development of more reliable and accurate regional or global archeomagnetic field models [Valet et al., 2008]. Our interest is to recover the millennial-scale evolution of the geomagnetic field with a sub-centennial temporal resolution. This ambitious objective makes necessary the acquisition of numerous archeomagnetic data from carefully selected well-dated archeological artifacts. Whatever the periods, our data sets show the important regional geomagnetic field vari-

ability. Regarding intensities, the occurrence of several peaks in intensity was detected from Western European data, with a prominent maximum during the High Middle Age (~800 AD) and two other peaks during the second half of the XIVth century and around 1600 AD (Figure 1 and Gomez-Paccard et al. [2008], Genevey et al. [2009], Schneppe et al. [2009]).

The second target of the French archeomagnetic studies is to strengthen the possibility of using the geomagnetic field secular variation as a dating tool for archeological purposes. Archeomagnetic dating relying on geomagnetic directional variations are being currently made in close collaboration with archeologists from firing *in situ* structures, such as pottery and domestic kilns. The analyses are particularly frequent for domestic kilns dated to the High Middle Age found in abundance in the Ile-de-France region and for which the archeological dating constraints are generally scarce [Warmé, 2009]. On another hand, the large number of archeointensity data recently obtained from French and Syrian objects gives rise to the possibility of further using the geomagnetic field intensity fluctuations for deriving dating constraints. The interest would be to be able to use the archeomagnetic dating technique on virtually all archeological artifacts, either found in situ or in displaced context from their original firing position (potsherds, bricks and tiles).

Our archeomagnetic studies also penetrated the domains of environmental and climatic sciences. Trends in secular variation recognized in carbonate concretions sampled in Roman water conduits were for instance used to put temporal constraints on climatic indicators obtained from the same concretions [Carlut et al., 2009]. Other studies were focused on the possible causal