A strong swarm of shallow earthquakes started under Cumbre Vieja volcano1, La Palma island, the Canary Islands on September 11, 2021, leading authorities to raise the Alert Level from Green to Yellow on September 13.
There have been 10 swarms in this area of the island of La Palma, but this one is more intense and at shallow depths, suggesting magmatic intrusion is taking place under the volcano.2
Earthquakes registered in the previous two earthquake swarms under the volcano -- December 20203 and February 20214, were at depths of 20 - 30 km (12 - 18 miles) and 15 - 20 km (9 - 12 miles), respectively. This one is between 8 and 13 km (5 - 8 miles).
"Without a doubt, the current seismic swarm represents a significant change in the activity of the volcano and is related to a process of magmatic intrusion beneath La Palma Island," the Volcanology Institute of the Canaries (INVOLCAN) said.
"Our geochemical monitoring program for volcanic surveillance in La Palma has allowed us to detect in 2020 (16/09/2020), the highest emission value of helium-3 observed in La Palma over the past 30 years, and after this detection, not only the largest number of seismic swarmers in La Palma since 2017 (7 of a total 10) but also a year before recording the most important seismic swarming of the 10 occurred in La Palma."
"For these reasons described above, the management of Civil Protection and Attention to Emergencies due to Volcanic Risk (PEVOLCA) has been advised to raise the volcanic light for La Palma from GREEN to YELLOW."
The Ministry of Public Administrations, Justice and Security, the Government of the Canary Islands convened the Scientific Committee of the Special Plan for PEVOLCA to assess the situation and agreed to activate this Plan in a situation of Alert for Fuencaliente, Los Llanos de Aridane, El Paso and Mazo and the change of the traffic light from Green to Yellow for said municipalities.1
The swarm is located in the central part of the volcanic massif of Cumbre Vieja, in line with the eruptive sites of 1480,1585,1712 and 1949 and the reading of the graph above indicates that the hypocenters have moved towards the west.5
La Palma island, Canary Islands on August 21, 2021. Credit: Copernicus EU / Sentinel-2, TW
The 47-km-long (29 miles) wedge-shaped island of La Palma, the NW-most of the Canary Islands, is composed of two large volcanic centers. The older northern one is cut by the massive steep-walled Caldera Taburiente, one of several massive collapse scarps produced by edifice failure to the SW.
The younger Cumbre Vieja, the southern volcano, is one of the most active in the Canaries.
The elongated volcano dates back to about 125 000 years ago and is oriented N-S. Eruptions during the past 7 000 years have originated from the abundant cinder cones and craters along the axis of Cumbre Vieja, producing fissure-fed lava flows that descend steeply to the sea.
Historical eruptions at La Palma, recorded since the 15th century, have produced mild explosive activity and lava flows that damaged populated areas.
The southern tip of the island is mantled by a broad lava field produced during the 1677-1678 eruption. Lava flows also reached the sea in 1585, 1646, 1712, 1949, and 1971.6
1 Strong earthquake swarm under Cumbre Vieja volcano, Canary Islands - The Watchers
2 INVOLCAN - FB
3 New earthquake swarm under Cumbre Vieja volcano, La Palma, Canary Islands - The Watchers
4 Earthquake swarm under Cumbre Vieja volcano, Canary Islands - The Watchers
5 La Palma volcano: volcanic alert raised to yellow - La Culture Volcan
6 La Palma - Geological summary - GVP
Featured image: September 2021 earthquake swarm location - La Palma island, Canary Islands. Credit: Copernicus EU / Sentinel-2, TW. Acquired: August 21, 2021
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