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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #volcanic activity, #Sismologia
Piton de La Fournaise - 02.09.2022 / 04:55 UT - CameraPartage / OVPF- IPG - one click to enlarge

Piton de La Fournaise - 02.09.2022 / 04:55 UT - CameraPartage / OVPF- IPG - one click to enlarge

The OVPF informs us that the period from August 1 to 27, 2022 was marked at Piton de La Fournaise by low seismicity at the level of Piton de la Fournaise with an average of 3 superficial volcano-tectonic earthquakes per day.

Since August 28, 2022, an increase in seismicity has been observed under the Piton de la Fournaise: 20 volcano-tectonic earthquakes were recorded on August 28, 24 on August 29, 41 on August 30 and 31 on August 31.

The inflation of the summit continued.

A decrease in CO2 fluxes in the soil was recorded both in the near and distal field.

 

The inflation which resumed in June, and which continued in July and August, was witness to a weak recharge and a weak pressurization of the superficial magmatic reservoir by upwellings of deep fluids.

The appearance of seismicity at the roof of the reservoir since the end of August shows that this pressurization process is intensifying.

This process of recharge from the depths to the superficial reservoir can take several days to several weeks before the reservoir roof weakens and ruptures, thus giving rise to an injection of magma towards the surface and an eruption, but can also stop without giving rise - in the short term - to an eruption.

 

Source: OVPF

Piton de La Fournaise - Histogram representing the number of superficial volcano-tectonic earthquakes recorded since August 1, 2022 (© OVPF)

Piton de La Fournaise - Histogram representing the number of superficial volcano-tectonic earthquakes recorded since August 1, 2022 (© OVPF)

Piton de La Fournaise: Illustration of the deformation over the last six months. The variations in distance between two GPS receivers crossing the Piton de la Fournaise building are shown here, at the top (reference BOMG; top), at the base of the terminal cone (reference FOAG; middle) and in the far field (reference PRAG; bottom). A rise is synonymous with elongation and therefore swelling of the volcano; conversely a decrease is synonymous with contraction and therefore deflation of the volcano (© OVPF-IPGP).

Piton de La Fournaise: Illustration of the deformation over the last six months. The variations in distance between two GPS receivers crossing the Piton de la Fournaise building are shown here, at the top (reference BOMG; top), at the base of the terminal cone (reference FOAG; middle) and in the far field (reference PRAG; bottom). A rise is synonymous with elongation and therefore swelling of the volcano; conversely a decrease is synonymous with contraction and therefore deflation of the volcano (© OVPF-IPGP).

Update on the seismovolcanic activity recorded on the island of São Jorge, in the Azores archipelago, as of 09/1/2022 10:00

The Azores Seismovolcanic Information and Monitoring Center (CIVISA) informs that the seismovolcanic activity recorded on the island of S. Jorge since 4:05 p.m. (local time = UTC-1) on March 19 continues above normal , extending, roughly, along a strip with WNW-ESE direction, from Ponta dos Rosais to the area of ​​Norte Pequeno – Silveira.

So far, about 50,146 small-scale events of tectonic origin have been recorded. Between 12:00 a.m. and 10:00 a.m. today, about 68 earthquakes were recorded. The most energetic earthquake of this crisis occurred on March 29, at 21:56 (local time = UTC), had an epicenter about 2 km SSW of Velas and a magnitude 3.8 (Richter). So far, about 318 earthquakes felt by the population have been recorded.

Overall, the seismic activity of the last few weeks shows a slight downward trend, sometimes interrupted by short periods of higher frequency and / or released energy, the hypocenters being currently located, in general, at depths greater than 5 km.

São Jorge - seismicity as of 09.01.2022 - Doc. CIVISA

São Jorge - seismicity as of 09.01.2022 - Doc. CIVISA

São Jorge - Daily frequency of recorded earthquakes - Doc. IVAR - CIVISA 01.09.2022

São Jorge - Daily frequency of recorded earthquakes - Doc. IVAR - CIVISA 01.09.2022

As part of the geodetic monitoring, the existing data since the beginning of April do not show any significant deformation in the epicentral zone.

The gas and temperature measurement campaigns in the soil that have been carried out since the beginning of this crisis in the epicentral zone have not, to date, led to the identification of anomalies resulting from the seismovolcanic activity. , now the field surveys.

Hydrogeochemical campaigns in groundwater from the two monitoring boreholes (Queimada II and Ribeira do Nabo - IROA) did not reveal any significant variations that could be associated with the ongoing seismovolcanic crisis.

The integration of the available information allows us to conclude that the tectonic structures where the historic eruptions of 1580 and 1808 took place, and the seismovolcanic crisis of 1964, in the Fissural Volcanic System of Manadas, have been reactivated, and it must be admitted that at the beginning of the phenomenon there was a deep magmatic intrusion.

The decrease in seismic activity, although slow, and the observation of such a pattern in recent weeks, as well as the absence of other anomalous signs in terms of deformation, gases and waters, have led CIVISA to determine, on June 8, the scientific alert level was raised from V4 to V3 on the island of S. Jorge. However, seismic activity continues well above baseline values ​​for the region, so the possibility of recording felt events remains and the possible occurrence of higher magnitude earthquakes cannot be ruled out.

CIVISA maintains monitoring levels on the island of S. Jorge and ensures the reinforcement of the permanent seismovolcanic observation network, in the sense that, if the pattern of activity reverses, it can detect the precursor signs of a new pre-eruption situation.

 

Source: http://www.ivar.azores.gov.pt/ - CIVISA

Revue Nature - 01.09.2022 - "Under the volcano", the mechanism behind the unexpected eruption of Nyiragongo.

Revue Nature - 01.09.2022 - "Under the volcano", the mechanism behind the unexpected eruption of Nyiragongo.

An article in the journal Nature on the eruption of Nyiragongo in May 2021 reveals the underside of the flank eruption. It is the result of a collaboration between 36 scientists from 11 different countries (26 different affiliations). Here is the summary :

" Classical mechanisms of volcanic eruptions primarily involve the buildup of pressure and the rise of magma to the surface1. Such processes produce geophysical and geochemical signals that can be detected and interpreted as eruption precursors1,2,3.

On May 22, 2021, Mount Nyiragongo (Democratic Republic of the Congo), an open-vent volcano with a persistent lava lake perched in its summit crater, challenged this interpretation by producing a roughly six-hour flank eruption with no apparent precursors. , followed - rather than preceded - by lateral movement of magma in the crust.

We show here that this reverse sequence was most likely initiated by a rupture of the edifice, producing lethal lava flows and triggering a voluminous intrusion of 25 km long dykes. The dyke propagated southward at very shallow depths (less than 500 m) below the cities of Goma (Democratic Republic of Congo) and Gisenyi (Rwanda), as well as Lake Kivu.

This volcanic crisis raises new questions about the mechanisms controlling such eruptions and the possibility of coping with much more dangerous events, such as outpourings within densely urbanized areas, phreato-magmatism or a limnic eruption from Lake Kivu. in gas. It also highlights more generally the challenges open vent volcanoes face for monitoring, early detection, and risk management when a large volume of magma is stored near the surface.”

 

Source: Smittarello, D., Smets, B., Barrière, J. et al. Precursor-free eruption triggered by edifice rupture at Nyiragongo volcano. Nature 609, 83–88 (2022). https://doi.org/10.1038/s41586-022-05047-8 – In Nature 01,09,2022

This is an open access article distributed under the terms of the Creative Commons CC BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Nyiragongo - a, COSMO-SkyMed (CSK) interferogram from May 21, 2021 at 3:37 PM UTC to May 22, 2021 at 3:37 PM UTC showing no obvious deformation less than 1 hour before the start of the eruption. . b, Comparison of PlanetScope46 images of Nyiragongo crater between March 27, 2021 and August 9, 2021. c, Daily eastward movements recorded at permanent GNSS stations KBT (blue) and RBV (orange) (see location on map a) from April 1, 2021 to June 30, 2021. d, Daily count of seismic events automatically detected and located (meeting the selection criteria defined in the Methods) from April 1, 2021 to June 30, 2021 and 12-hour moving median of the measurement real-time seismic amplitude (RSAM) filtered between 2 Hz and 10 Hz at permanent seismic stations NYI (green) and KBTI (blue). / Nature ref. abo

Nyiragongo - a, COSMO-SkyMed (CSK) interferogram from May 21, 2021 at 3:37 PM UTC to May 22, 2021 at 3:37 PM UTC showing no obvious deformation less than 1 hour before the start of the eruption. . b, Comparison of PlanetScope46 images of Nyiragongo crater between March 27, 2021 and August 9, 2021. c, Daily eastward movements recorded at permanent GNSS stations KBT (blue) and RBV (orange) (see location on map a) from April 1, 2021 to June 30, 2021. d, Daily count of seismic events automatically detected and located (meeting the selection criteria defined in the Methods) from April 1, 2021 to June 30, 2021 and 12-hour moving median of the measurement real-time seismic amplitude (RSAM) filtered between 2 Hz and 10 Hz at permanent seismic stations NYI (green) and KBTI (blue). / Nature ref. abo

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