Eric Gilli

Research on the February 18, 1996 earthquake in the caves of Saint-Paul-de-Fenouillet area, (eastern Pyrenees, France)

Eight caves have been investigated near Saint-Paul-de-Fenouillet after the magnitude 5.2 earthquake of February 1996 which occurred in the Eastern Pyrenees (France) and caused moderate damage at the ground surface. The earthquake has been associated with the movement of a E-W fault. The caves were not visited since the earthquake. Some damage, mainly collapses of soda straws and small rocks, could be attributed to this earthquake. The most interesting cave in the epicentral area is the Paradet cave which is situated on a recently activated fault plane. In this cave, soda straw falls could be assigned to the earthquake, but other more ancient damage were observed also. Analysis of the azimuth of fallen speleothems which are natural pendulums, may indicate the directions and an estimation of their mechanical properties gives the threshold of the seismic ground motion amplitude responsible for their collapse and thus supply information to calibrate damage due to past earthquakes. A statistical study indicates that the main direction of the collapsed soda straws is E-W. Numerical simulations confirm that soda straws are relatively strong objects that may break under certain conditions during earthquakes.

Bacterial-based additives for the production of artificial snow: what are the risks to human health?

For around two decades, artificial snow has been used by numerous winter sports resorts to ensure good snow cover at low altitude areas or more generally, to lengthen the skiing season. Biological additives derived from certain bacteria are regularly used to make artificial snow. However, the use of these additives has raised doubts concerning the potential impact on human health and the environment. In this context, the French health authorities have requested the French Agency for Environmental and Occupational Health Safety (Afsset) to assess the health risks resulting from the use of such additives. The health risk assessment was based on a review of the scientific literature, supplemented by professional consultations and expertise. Biological or chemical hazards from additives derived from the ice nucleation active bacterium Pseudomonas syringae were characterised. Potential health hazards to humans were considered in terms of infectious, toxic and allergenic capacities with respect to human populations liable to be exposed and the means of possible exposure. Taking into account these data, a qualitative risk assessment was carried out, according to four exposure scenarios, involving the different populations exposed, and the conditions and routes of exposure. It was concluded that certain health risks can exist for specific categories of professional workers (mainly snowmakers during additive mixing and dilution tank cleaning steps, with risks estimated to be negligible to low if workers comply with safety precautions). P. syringae does not present any pathogenic capacity to humans and that the level of its endotoxins found in artificial snow do not represent a danger beyond that of exposure to P. syringae endotoxins naturally present in snow. However, the risk of possible allergy in some particularly sensitive individuals cannot be excluded. Another important conclusion of this study concerns use of poor microbiological water quality to make artificial snow.

Glacial causes of damage and difficulties to use speleothems as palaeoseismic indicators

Fractures that affect cave speleothems have often been described as the result of earthquakes and their use in paleoseismic studies is more and more frequent. Nevertheless observations during and after earthquakes, modeling and laboratory experiments indicate that, except for some slender speleothems, the cave formations usually do not break during an earthquake. New observations in caves in France and Slovenia reveal other mechanisms as the creeping of ice or clay filling that easily explain most of the breaks.

Active tectonics and earthquake destructions in caves of northern and central Switzerland

INTRODUCTION The surface expressions of active tectonics and strong earthquakes are frequently obliterated due to natural surface degradation and human activities, e.g. urbanisation, agriculture, clearing of the landscape, drainage of marshes, etc. All these shortcomings for active tectonics and paleoseismological research at the Earth’s surface are insignificant, or at least significantly reduced, in most so-called inactive caves which show negligible ongoing corrosive or erosive enlargement. In such caves, sediment deformation features, faults and fractures are well protected due to almost non-existing weathering processes and can therefore be preserved for hundreds of thousands of years (Kagan et al., 2005) even in soft sediments (Lignier & Desmet, 2002).

Neotectonics and current hydrologically-induced karst deformation. Case study of the Plateau de Calern (Alpes-Maritimes, France)

The astronomical and geodetic observatory OCA, located on the karst plateau of Calern (Caussols, France), has been monitoring earth deformation for several years. Two medium baseline tiltmeters have been installed in a shaft in 2007, along with classical hydrogeological monitoring tools in order to investigate the relationship between current karst deformation and hydrology. Dye tests have shown that the plateau is drained towards the East, to the spring of Bramafam, except for its Western third. Karst tilting, as recorded by the tiltmeters, is linked to rainfall events. These instruments bring additional information to characterize different reservoirs: the deep karst aquifer of Bramafan with high amplitude oscillations of its water table, up to 100 m, the perched aquifer of Moustiques shaft whose response is attenuated, and several slope aquifers with reduced oscillations (Fontaniers, Castel Bon Pré). Tilt deformation reaches 8 μad with a definite orientation between N90°E and N100°E. The best correlation between hydrology and tilts is observed for the deep aquifers. If the first autumn rainfall is ineffective on tilt, it recharges the epikarst and refills the reserves. The winter rains cause the water to flush towards the eastern deep aquifer and provokes a quick tilting of the plateau. Finally, the long term variations in tilt and water table show a very good correlation. The relationship between current hydrological deformations and tectonics is also analyzed; broken and shifted speleothems in the shafts indicate a general shift of the plateau towards the south.

Détection de sources sous-marines et précision de l'impluvium par mesure des variations de salinité. L'exemple de la source de Cabbé-Massolins (Roquebrune-Cap-Martin, France)

Salinity measurements were used to detect and study submarine springs on the coast of southeastern France. Among them, the Cabbe-Massolins spring drains karstic formations in Arc de Nice (Alpes Maritimes, France). A salinity probe was placed in a spring. A comparison between the salinity variations and rainfall recorded at different meteorological stations, made it possible to define the location of the impluvium of the springs.

Evidence of palaeoseismicity in the caves of Arizona and New Mexico (USA)

Several caves were visited in different parts of the western USA to observe speleothems that could have been affected by ancient earthquakes. There are very few caves in California. In Arizona, it seems possible to find evidence of the 1887 Sonora earthquake in Sutherland Peak cave. In New Mexico, the caves of Guadalupe Mountain contain many broken speleothems showing evidence of, at least, one old unknown earthquake.

Rupture de spéléothèmes par fluage d'un remplissage endokarstique. L'exemple de la grotte de Ribière (Bouches-du-Rhône)

Natural caves could be good recorders for paleoearthquakes if it was possible to know precisely the underground damage caused by a seismic event. The researched effects are breakings of speleothems. Therefore, several non-coseismic mechanisms may be involved. A recent study of the Ribiere cave shows that the creeping of a karstic filling explains most of the cave breakings that are attributed to earthquakes.

Access to Coastal Karst Water Resources Through a Salinity Study During an Exceptional High-Water Event: the Case of Port-Miou (Cassis, SE France)

A conceptual model of the functioning of the complex coastal karst aquifer of Port-Miou (Cassis, SE France) is presented. The studied event consists in a high water discharge period recorded during December 2008 at Port-Miou spring. During this one week event, the discharge in the 20 m diameter saturated conduit had probably been in the range of 50 to 100 m3/s. In spite of this huge spring water discharge, the salinity remained persistently above 2 g/L, while freshwater could have been expected by a simple dilution effect. A new conceptual model has been developed to better understand the remaining salinity by taking into account the dynamic behavior of the flow and the geological heterogeneities of the reservoir. It gives new insight for water management.

Mechanism of Salt Contamination of Karstic Springs Related to the Messinian Deep Stage. The Speleological Model of Port Miou (France)

Submarine karstic springs are frequent on the Mediterranean shore but most of them are brackish which prohibits their use. The numerous attempts to catch these springs ended in failure. Recent studies on the development of karst systems and the paleogeography of the Mediterranean sea explain these failures. Studies on the shores of south-eastern France have enabled us to propose an operating model that explains the mechanism of salt contamination. The Port Miou system (Cassis, France) is a two kilometers long submarine gallery developped in the limestone series of Calanques (Marseille, France). The average discharge is between 2 to 5 m3/s but the water is brackish. In the 70s a dam was built to prevent sea intrusion in the cave but the water remained brackish upstream of the dam. The use of helium, and then rebreathers by cave divers, made it possible to explore a vertical pit down to -179 m below the sea level at the end of the cave. At that depth, the water is still brackish. Important quantity of titanium was observed at the surface of the cave sediment upstream of the dam and at the end of the cave. The titanium comes from the residual product of a factory of alumina that is discharged in the Cassidaigne submarine canyon, at a depth of 300 m b.s.l., a few kilometers south to the spring. This residual product locally called «red mud» is very rich in titanium. This supports the model of a sea water aspiration in a deep gallery connected to the canyon. The Cassidaigne canyon that cuts a limestone plateau with dolines and caves is probably a pocket valley. Its presence is related to the several stages of lowering of the Mediterranean sea at the Messinian Deep Stage that allowed the existence of cave networks up to several hundreds of meters below the present sea level. The sea water is now sucked into the system. A similar example exists in Kefalonia island (Greece) where a sea intrusion is observed in coastal sinkholes. This model explains why the different attempts to diminish the salinity of these brackish springs, by construction of dams close to the outlets, have failed.