While the prefecture has passed the Piton de la Fournaise in the safeguard phase on May 29, 2017 at 11 am, following a decrease in seismicity, and to allow the realization of the expert assessments prior to a possible reopening of certain sectors to the public, this late is busy going up this 30th of May.
Piton de La Fournaise - Histogram representing the number of superficial volcano-tectonic earthquakes recorded between 18 May and 30 May 2017. (© OVPF / IPGP)
Here is the monthly bulletin of the OVPF as of 31.05.2017:
A pressurization of the surface reservoir (located about 2 km below the Dolomieu crater) by a deep magma recharge is currently observed.
Since the recharge is rapid and already substantial, and the environment is already well damaged, any evolution and departure of magma towards the surface can be rapid as shown by the last seismic crises of 2016-2017.
Following the magma injection of 17 May 2017, seismicity gradually decreased from 40 volcanic tectonic earthquakes on 18 May to an average of 2 per day from 22 to 29 May. The day of 30 May was marked by an increase in the number of superficial volcano-tectonic earthquakes with 8 events.
In May 2017 (up to 31 May - 12 noon local time), the OVPF recorded a total of:
- 1247 superficial volcano-tectonic earthquakes (0-2 km deep) under the summit craters, 90% of which were recorded during the 17 May magma injection (1122 events);
- 46 deep earthquakes (> 2 km deep);
- 295 collapses (in the Crater Dolomieu and at the level of the ramparts of the Enclosed Fences);
- 31 local earthquakes (under the island, Piton des Neiges side);
- 2 regional earthquakes (in the Indian Ocean zone).
Piton de La Fournaise - Illustration of the deformation during the last twelve months (the eruptions of 11-18 September 2016 and 31 January-27 February 2017 are represented in yellow and the magma injection of 17 May 2017 is represented by a Black bar). Here is shown a baseline (distance between two GPS receivers) crossing the Dolomieu crater from north to south (in black the raw data, in blue the smoothed data over a week). A rise is synonymous with elongation and therefore swelling of the volcano; Conversely, a decrease is synonymous with contraction and therefore with deflation of the volcano. (© OVPF / IPGP)
The inflation (swelling) of the building resumed at a rate significantly higher than those observed before May 17, 2017 (elongation of the order of 2 mm per day between the stations of the summit zone, against 0.1-0.2 mm before May 17th.
This acceleration of the deformations is visible both at the level of the summit zone but also in the far field, testifying to the pressurization of a superficial source but also of a deep source (pressurization of the surface reservoir located 2 km Of depth under the Dolomieu crater by a deep magma recharge).
The CO2 concentrations in the soil measured at the remote stations of the Plaine des Cafres and at the level of the Gîte du volcan show an early decline. This trend will be confirmed in the next few days.
It should be noted that a decrease in CO2 concentrations in the soil is observed on remote stations several days to several weeks before a seismic crisis.
Source: OVPF 31.05.2017