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Magma movement detected under São Jorge, Azores

Seismovolcanic crisis Sao Jorge, Azores, Portugal

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. 

Volcanoseismic crisis Sao Jorge, Azores, Portugal
Image credit: CIVISA
Seismovolcanic crisis Sao Jorge, Azores, Portugal
Image credit: CIVISA

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.

References:

1 Volcano-tectonic tremors recorded for first time on quake-hit Azores island – Reuters

2 “Real possibility of volcanic eruption” – The Portugal News

Featured image credit: CIVISA

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