Philippe Kowalski

A damage model for volcanic edifices: Implications for edifice strength, magma pressure, and eruptive processes

Monitoring of large basaltic volcanoes, such as Piton de la Fournaise (La Reunion Island, France), has revealed preeruptive accelerations in surface displacements and seismicity rate over a period of between 1 h and several weeks before magma reaches the surface. Such eruptions are attributed to ruptures of pressurized magma reservoirs. Elastic models used to describe surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure. This assumption requires changes in magma or pressure conditions at the base of the magma feeding system that are unrealistic over the observed timescale. Another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice. In the present study, we modeled such weakening by progressive damage to an initially elastic edifice. We used an incremental damage model, with seismicity as a damage variable with daily increments. Elastic moduli decrease linearly with each damage increment. Applied to an initially elastic edifice with constant pressure at the base of the system, this damage model reproduces surface displacement accelerations quite well when damage is sufficient. Process dynamics is controlled by the damage parameter, taken as the ratio between the incremental rupture surface and the surface to be ruptured. In this case, edifice strength and magma reservoir pressure decrease with decreasing elastic moduli, whereas surface displacement accelerates. We discuss the consequences of pressure decreases in magma reservoirs.

Toward continuous quantification of lava extrusion rate: Results from the multidisciplinary analysis of the 2 January 2010 eruption of Piton de la Fournaise volcano, La Réunion

The dynamics of the 2–12 January 2010 effusive eruption at Piton de la Fournaise volcano were examined through seismic and infrasound records, time-lapse photography, SO2 flux measurements, deformation data, and direct observations. Digital elevation models were constructed for four periods of the eruption, thus providing an assessment of the temporal evolution of the morphology, the volume and the extrusion rate of the lava flow. These data were compared to the continuous recording of the seismic and infrasonic waves, and a linear relationship was found between the seismic energy of the tremor and the lava extrusion rate. This relationship is supported by data from three other summit eruptions of Piton de la Fournaise and gives total volume and average lava extrusion rate in good agreement with previous studies. We can therefore provide an estimate of the lava extrusion rate for the January 2010 eruption with a very high temporal resolution. We found an average lava extrusion rate of 2.4 m3s−1 with a peak of 106.6 m3s−1 during the initial lava fountaining phase. We use the inferred average lava extrusion rate during the lava fountaining phase (30.23 m3s−1) to estimate the value of the initial overpressure in the magma reservoir, which we found to range from 3.7×106 Pa to 5.9×106 Pa. Finally, based on the estimated initial overpressure, the volume of magma expelled during the lava fountaining phase and geodetic data, we inferred the volume of the magma reservoir using a simple Mogi model, between 0.25 km3 and 0.54 km3, which is in good agreement with previous studies.

Fifteen Years of Intense Eruptive Activity (1998–2013) at Piton de la Fournaise Volcano: A Review

Piton de la Fournaise (La Reunion Island) is amongst the most active volcanoes in the world, having had about 130 eruptions during the last century. Over the last 50 years it has produced 970 Mm3 of magma, at a mean eruption rate of 19.4 Mm3 per year, of which 489 Mm3 had been erupted over the last 15 years (at a rate of 32.7 Mm3 per year). This indicates a relative increase in its output. In this paper we present a detailed description of the high volcanic activity spanning the 1998–2013 period (eruptive precursors, location, characteristics and volume of emitted lavas, …). This period of high volcanic activity has been the subject of numerous studies that have led to significant advances in the knowledge of the shape and dynamics of the shallow plumbing system of the volcano.

Contribution of Tiltmeters and Extensometers to Monitor Piton de la Fournaise Activity

Tiltmeters and extensometers were among the first instruments used to monitor volcano ground deformation and are used worldwide. Since their implementation in the early 80’s at Piton de la Fournaise (La Reunion Island), tiltmeters and extensometers largely contributed to the knowledge and the forecast of eruptive activity on this volcano. These instruments allowed to evidence eruptive precursors at Piton de la Fournaise on two time scales (months/weeks and hours/mins), associated with reservoir pressurization and dike propagations, respectively, but also to follow eruptive/post eruptive relaxation and collapse events.