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Major rockslide near Argaga beach in La Gomera, Canary Islands

landslide-argaga-gomera-canary-islands-november-2020

A major rockslide took place near Argaga beach in the municipality of Vallehermoso, Canary Islands on November 14, 2020. Authorities confirmed there were no people trapped under the rubble. Involcan warned there is still extreme danger in the area, so any cleanup work should be carried out with maximum caution.

Footage showed a large chunk of land collapsing into the sea, dropping debris onto the coast that covered a number of parked cars. As a result, the road between Vueltas and Argaga has been closed.

Two helicopters from the Emergency and Security Coordination Center, Civil Guard, Local Police, Civil Protection, and firefighters have been deployed to the scene to look for people who may have been trapped under the rubble.

On November 16, authorities confirmed that no-one is trapped under the debris.

The mayor of Vallehermoso said that the access to Argaga will be permanently closed, even after the work of the canine units has been successfully concluded and the security and emergency services have been deactivated.

"In view of the available information, the presence of a deep open sub-vertical fracture parallel to the slope is seen as the main cause of the landslide, together with the active erosion caused by waves that undermine the foot of the slope," Involcan (Canary Islands Volcanological Institute) said, as reported by the Canary Weekly.

"This fracture caused the detachment of part of the slope. The process is still active. The entire front of the rock face, adjacent to the collapsed part, is still at maximum risk of further landslides. Any activity at the foot of these slopes is exposed to falling rocks, so the danger is extreme.”

Dr. Dave Petley of The Landslide Blog analyzed two videos of the event– one showing the cliff about a minute before the collapse, and the other showing the aftermath.

"The first starts about a minute before the collapse. When the video starts there is some dust close to the rock slope. Over time, isolated (though not trivial) falls occur across the slope," he wrote.

"The person collecting this video is clearly concerned about the potential for a displacement wave (sensibly), and so evacuates when the collapse occurs."

First footage in the analysis

The second video captured less of the precursory activity, but it showed the aftermath of the collapse, showing the displacement wave triggered by the slide, as well as a huge cloud of dust.

Second footage in the analysis

Dr. Petley explained that in this case, failure has been controlled by near-vertical joints in the volcanic rocks. The collapse would have been controlled by the formation of new fractures that linked the existing joints together, generating the release surface.

"As this proceeded, the rock mass crept and deformed at an accelerating rate. It is this deformation that pops off the precursory rockfalls."

These precursors are crucial, said Petley, as they usually warn people nearby that failure is developing. 

Featured image credit: Ayuntamiento de Valle Gran Rey

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