[ACTUEEL] Vulkaanuitbarsting op komst bij San Jorge (Azoren) ??

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Intense earthquake swarm under São Jorge volcano, Azores

An intense earthquake swarm is shaking the Manadas volcanic fissure system in the NW part of the Sao Jorge Island (population 8 200), Azores, Portugal. The last eruption of this volcano took place in 1808.

According to the Center for Seismovolcanic Information and Surveillance of the Azores (CIVISA), the swarm started at 17:19 LT (16:19 UTC) on March 19. Three earthquakes were registered over the next 2 minutes, with magnitudes ranging from 2.8 to 2.9.

The first earthquakes were felt with maximum intensity IV/V (Modified Mercalli Scale) in the parish of Manadas, with intensity IV in Urzelina and Norte Grande, and with intensity III in Calheta.1

Over the next 24 hours, more than 700 earthquakes were recorded in the region. All had low magnitudes and only 48 were felt, CIVISA said.

Head of CIVISA, Rui Marques, said that Manadas volcanic fissure system, which coincides with the main volcanic cones on the island, is still active and now registers a release of energy that was not common in recent years.2

"All the earthquakes felt in São Jorge since Saturday are of tectonic origin," Marques said, adding that the largest earthquake was M3.2 at 01:43 UTC on March 20. The quake was felt by the populations of São Jorge and the island of Pico.

"We are still evaluating the behavioral pattern of this seismic crisis, which is now in a phase of lower energy release," Marques said. The seismic events are now progressing toward the village of Velas.

"The current seismic swarm makes many remember the earthquake swarms that preceded the 2021 eruption on La Palma in the neighboring Canary Islands," said Dr. Tom Pfeiffer of the VolcanoDiscovery.3

Geological summary
The linear São Jorge Island is 54 km (33 miles) long and only 6 km (3.7 miles) wide. It was formed by fissure eruptions beginning in the eastern part of the island.

The western two-thirds of dominantly basaltic São Jorge contains youthful, fissure-fed lava flows resembling those on neighboring Pico Island.

Lava effused from three locations above the south-central coast during 1580, producing flows that reached the ocean.

In 1808 a series of explosions took place from vents along the south-central crest of the island; one of the vents produced a lava flow that reached the southern coast.

Submarine eruptions were reported on several occasions from vents off the S and SW coasts. This volcano is located within the Azores, a UNESCO Global Geopark property.4

Sao Jorge, Azores Eruption Possible

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Earthquake swarm continues at Sao Jorge
Seismic activity at Manadas volcanic fissure system in the NW part of São Jorge Island, Azores, Portugal continues at a high level for the fourth day in a row. The Civil Protection of Azores is preparing preventive measures in case of a strong earthquake or an eruption. The last eruption of this volcano took place in 1808 (VEI 1).

According to the Center for Seismovolcanic Information and Surveillance of the Azores (CIVISA), the swarm started at 17:19 LT (16:19 UTC) on March 19 with three earthquakes (M2.8 - 2.9) registered over the next 2 minutes.

To date, more than 18 000 earthquakes have been detected, of which at least 94 were felt by the population.

On March 22, the Azores Regional Civil Protection and Fire Service (SRPCBA) informed that it is preparing preventive measures that can be adopted in a possible scenario of a greater magnitude earthquake or a possible eruption.1

The measures are being designed in conjunction with the municipalities, civil protection agents, and other entities responsible for this area.

A technician from the SRPCBA is already on the island of São Jorge to meet with the municipalities and provide support, SRPCBA said, adding that the dispatch of support equipment is being implemented to reinforce the island's response capacity in case of need.

CIVISA said all earthquakes detected on the island so far are of tectonic origin.

However, due to the fact that earthquakes are located in the volcanic fissure system, this is considered a seismovolcanic crisis and all scenarios must be considered, including a stronger earthquake and possible eruption.

Authorities are urging residents to keep calm, follow official information and recommendations disseminated by the authorities.

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Azores island prepares to evacuate amid major earthquake fears
Airlines increasing flights to Portuguese island after six days of tremors, say authorities

Authorities on a Portuguese island in the north Atlantic are preparing for the possible evacuation of local people, as six straight days of tremors stoked fears of a possible major earthquake or volcanic eruption.

The president of the Azores Islands’ regional government said on Thursday that airlines were increasing the number of flights into and out of São Jorge, where about 8,300 people live, for people who prefer to leave now.

Scientists say it is hard to predict the consequences of the persistent, though low-intensity, seismic activity.

“Anything could happen, nothing might happen,” the Azores president, José Manuel Bolieiro, told reporters in televised comments during a visit to the island.

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Officials in the island municipality of Velas, the epicentre of more than 2,000 minor earthquakes since 19 March, are taking elderly people who may have difficulty in quickly evacuating to another part of the island as a precautionary measure.

Emergency services have established safe corridors for traffic and temporary accommodation for evacuees on the eastern side of the island in case they are needed. Velas has about 3,000 inhabitants.

Any public alerts were to be transmitted on local radio, on social media or by ringing church bells, officials said.

São Jorge is one of the nine islands that make up the Azores, which lie roughly 1,500km (about 1,000 miles) west of the Portuguese mainland.

The island is about 58km (36 miles) long and 6km (almost four miles) across at its widest point. Fishing and farming are the island’s economic mainstays.

São Jorge is a volcanic island, which witnessed eruptions in 1580 and 1808. Both are reported to have caused casualties, but reliable information from the time is not available.

The last volcanic eruption on land in the Azores was in 1957, on Faial Island. An earthquake on the same island in 1998 killed 10 people.

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Evacuatie op de Azoren
Sao Jorge, een Portugees eiland in de Azoren, werd de voorbije dagen getroffen door duizenden kleine aardbevingen. De vrees voor een zware aardbeving of vulkaanuitbarsting neemt toe. De autoriteiten zijn begonnen met de evacuatie van inwoners die onderaan de kliffen langs de kust wonen.

Sinds zaterdag zijn op het vulkanische eiland al meer dan 2.000 aardbevingen met een kracht tussen 1,6 en 3,3 geregistreerd. Dat meldt CIVISA, het vulkaanobservatorium van de regio.

De kleine bevingen, die voorlopig geen schade hebben aangericht, werden waargenomen langs de vulkanische Manadas-kloof op het eiland, die in 1808 voor het laatst tot uitbarsting kwam. In 1980 werd het eiland getroffen door een zware aardbeving, die ernstige schade veroorzaakte.

CIVISA verhoogde het vulkaanalarm van vier naar vijf, wat aangeeft dat de kans op een uitbarsting “reëel” is. Het aantal aardbevingen is hoger dan normaal, klinkt het.

Patiënten van het ziekenhuis en bewoners van de verzorgingstehuizen in de gemeente Velas, die naar verwachting het zwaarst getroffen zou worden bij een aardbeving, werden al overgebracht naar Calheta aan de andere kant van het eiland.

De bewoners van de zogenaamde “fajas”, kleine vlakten die oorspronkelijk zijn ontstaan door lava of aardverschuivingen aan de voet van kliffen, worden preventief geëvacueerd. Er zijn ongeveer 40 “fajas” in Sao Jorge.

Luis Riviera, burgemeester van Velas, zei woensdag dat plannen om de rest van de bevolking over te brengen naar Calheta of andere eilanden enkel zullen geactiveerd worden indien nodig.

Op Sao Jorge, een van de negen eilanden van de Azorenarchipel, wonen ongeveer 8.400 mensen.

De archipel heeft haar noodplan geactiveerd. Jose Manuel Bolieiro, president van de Azoren, bezocht het eiland vanmorgen en zei dat “alles in gereedheid is gebracht om mensen te evacueren”. De regering probeert ook het aantal commerciële vluchten naar en van het eiland op te voeren.

De autoriteiten hebben de inwoners meegedeeld waar ze in geval van nood naartoe kunnen, en meldden dat de bevolking zal gewaarschuwd worden via sociale media, het lokale radiostation en het luiden van de kerkklokken op het eiland.

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The Azores government has called for the evacuation of 3,000 people from the area most sensitive to the volcanic eruption that could occur.

👉🏼 Satellite photos of the island show similar surface deformities to those that existed before the eruption in La Palma

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The likelihood of a volcanic eruption in the Azores is no longer a small one
According to latest calculations, the Volcanological Institute of the Canary Islands (INVOLCAN) estimated that as much as 20 million cubic meters of magma have intruded under the island of São Jorge since last March 19.
If the figures are correct, the likelihood of a volcanic eruption in the Azores is no longer a small one, and we therefore assign our color code "orange", as a warning of potential activity in the near future.
For comparison, the initial magma intrusion leading up to last year's eruption on La Palma Island in the Canary Islands was estimated to be only 11 million cubic meters only, while it erupted a total of approx. 300 cu m of magma in the course of the 3-month-long eruption from September-December 2021. The preceding seismic swarm lasted from 13-19 Sep 2021 and is in many ways quite similar to what is being observed now on São Jorge.

The estimates on magma intrusion volume are based on modeling the observed ground deformation, in particular its vertical inflation, from the analysis of synthetic aperture radar data acquired by the Sentinel-1 satellite of the European Space Agency. This method compares radar images of the same area but obtained on two different dates; small differences in phase variations of the reflected radio waves can be used to detect changes in the relief of the earth's surface on the scale of millimeters.
The areas with most uplift is near the northeastern coast approx. 10 km east of Velas, where ground uplift has amounted approx. 10 cm alone by now. It can be presumed that the center of the magma source is located under this area.
The seismic swarm under São Jorge itself so far contained more than 700 quakes of magnitudes above 2.0, with 26 quakes above magnitudes 3.0-3.6. In the past days, it has continued to decrease in intensity, although this does not necessarily mean that the danger is over. Earthquakes occur, when magma pressure opens new pathways, fracturing rock layers at depth. What if the rocks beneath the island are already fractured? This could be true as result of the quakes that already took place, the general setting of the island being in a tectonically active rift zone and the presence of older dikes from past eruptions. In that case, magma accumulation could take place without significant quake activity, and - as we had seen before and during La Cumbre Vieja's eruption on La Palma - an eruption could start any time with little immediate warning.

Possible scenarios for São Jorge volcano:
It is impossible to predict what will happen, whether an eruption will take place in the near future. All of the following scenarios are possible, but we do not know how likely each of them might be:
1) An eruption takes place within days or weeks from now, with little warning.
2) The seismic swarm and ground deformation end gradually or abruptly, only to be repeated in months or years from now. Eventually one of these will be leading up to an eruption then.
3) A stronger earthquake occurs and changes the configuration of the magma intrusion, either to stall or to break through to the surface in an eruption.
4) Activity dies down, and the magma intrusion at depth slowly cools over years and decades to come with no further activity directly related to it.

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Magma movement detected under Sao Jorge
The seismovolcanic crisis at Manadas volcanic fissure system on the island of São Jorge, Azores, Portugal continues since March 19, 2022. A notable change was reported on April 6, when volcano-tectonic earthquakes were detected, suggesting the movement of magma at depth. The volcanic alert remains at Level 4 of 6. The last eruption of this volcano took place in 1808 (VEI 1).

On April 6, the Azores Seismovolcanic Information and Surveillance Center (CIVISA) reported they detected volcano-tectonic earthquakes for the first time since the crisis started.

Also known as hybrid, volcano-tectonic earthquakes happen when there is a fusion of high-frequency tectonic tremors with low-frequency volcanic ones, said Fatima Viveros, from the region’s CIVISA center.1

They suggest the movement of magma at depth, Viveros said, adding that more such earthquakes are expected.

On April 4, two days before the detection of hybrid earthquakes, CIVISA warned that ‘there is a real possibility of a volcanic eruption’ in São Jorge, but ‘there is no evidence that it is imminent’.2

Since the start of the crisis, CIVISA detected more than 26 000 earthquakes, with the strongest M3.8 at 21:56 UTC on March 29.

The last eruption of this volcano took place in 1808 – Volcanic Explosivity Index 1.