The Reventador maintains an high and continuous activity. Nocturnal incandescence was visible when the summit was clear; on the morning of 31 August, falling blocks were observed on all sides, reaching 800 meters below the crater, as well as the emission of a plume of steam and ash at 400 meters above the crater, dispersing to the north-west.
The assessment of the eruption of Piton de La Fournaise from 14.07 to 28.08 has just been published by the OVPF.
I transmit it in extenso below:
"During the 45 days of the eruption, from July 14 to August 28, 2017, less than 10 million m³ of lava were released on the surface.
After high lava flows (22-30 m³ / s) recorded on the first day of the eruption, the average flows estimated by satellite thermal imaging via the MIROVA (University of Turin) and HOTVOLC (OPGC - Clermont Ferrand) platforms, decreased gradually throughout the eruption, from 5 to <1 m³ / s. This gradual decline in lava flows was accompanied by a decrease in SO2 flows into the air.
Piton de La Fournaise - Evolution of lava flows (in m3 / s, blue) and volumes (millions of m3 red) emitted. Estimates obtained from thermal imagery satellites (MIROVA platform). (© OVPF / IPGP)
Piton de La Fournaise - Evolution of lava flows (in m3 / s) emitted. Estimates obtained from satellite thermal imagery (HOTVOLC platform). (© OVPF / IPGP)
The lava field associated with the eruption changed very little during the eruption. The maximum extension was reached from the first days of the eruption, with a maximum length of 2.8 km. Subsequently, the flow was slightly broadened, but the growth was mainly due to thickening due to an activity mainly in lava tunnels and extremely low flow rates.
The deformations associated with magma migration to the eruptive site (on the night of 13-14 July) focused on the southern and eastern part of the volcano and did not exceed 30 centimeters. The satellite data (radar interferometry) associated with this 13 July injection show that the deformations are not propagated beyond the eruptive crack.
Piton de La Fournaise - (left) Surface displacements associated with magma migration to the eruptive site (July 13-14 night). The vectors represent the horizontal displacements (scale in meters given by the value VECTOR MAX) and the colored circles the vertical displacements (scale in meters given by the colored bar). The eruptive crack is indicated in red, and the supposed path of the injection of the magma at depth is indicated by the black line. (right) Interferogram covering the injection of 13 July 2017. A red-blue-yellow phase (i.e. a fringe) corresponds to a distance of the ground from the satellite position of 2.8 cm. (© OVPF / IPGP)
Piton de La Fournaise - Illustration of the deformation since July 14, 2017. Here is represented 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 on one week). An increase in the signal is synonymous with elongation and therefore swelling of the volcano; conversely, a decrease in the signal is synonymous with contraction and therefore with the volcano deflating. (© OVPF / IPGP)
Migration of magma to depth at the end of the eruption
A number of indices show that two migrations of magma occurred at the end of the eruption. Without being exceptional this is not common.
Associated with the resurgence of seismicity on the south-south sector is August 16, and at the peak of SO2 on August 18, satellite data showed in August deformation zones (in inflation) further downstream of the crack opened on 14 July. These deformation zones in inflation (swelling) correspond to two injections of magma.
During the first phase of the eruption (inflation until 15 August), the feeding system pressurized, allowing the magma to continue its propagation further downstream towards the south - south-east, in the form of two intrusions that occurred between 07 and 25 August (dates of acquisition of satellite images). The rapid change in SO2 emissions may indicate an initial shallow intrusion on 18 August.
The second phase of intrusion certainly took place on the night of 24 to 25 August when a seismic swarm was recorded on the seismological network of the OVPF and located in this sector.
Overflights conducted by the Air Force Section and the OVPF staff on August 25 indicate that no new cracks associated with these two injections surfaced.
Given the small spatial extension of the deformations associated with these two intrusions, the geodetic stations (GPS, inclinometers, extensometers) on the ground, which are outside the deformation field, have not recorded any particular signals. On the other hand, the seismicity recorded since August 16th is in the zone intruded by the magma.
In conclusion: following the stopping of the eruption, seismicity under the southeastern region of the Enclos Fouqué continues and near-field CO2 concentrations in the ground remain high. As a result, no assumption is made as to the evolution of the situation (resumption of an activity or not).