Impact assessment of buildings exposed to the tephra fallout of the 2021 Cumbre Vieja eruption in La Palma, Spain

Long-lasting volcanic eruptions involving a variety of hazards have significant implications on the emergency response and on the final impact on the exposed elements. The eruption of Cumbre Vieja (La Palma, Spain), started on 19 September and ended on 13 December 2021. It was associated with earthquakes, gas emissions, lava flows, lava fountains, and tephra fallout (including large volcanic bombs) that significantly impacted the southwest of the island, caused the evacuation of more than 7,000 people and affected 1,676 buildings. In particular, the total extension of about 12 km² of lava flows, from the fissural source to the western coast, affected 3 municipalities and cut the island in two, generating a significant disruption of transportation. A comprehensive and systematic survey of about 300 buildings affected by tephra south of the lava flow was carried out during two weeks in October 2021 in order to assess the typology of affected buildings and the associated structural and non-structural damages. Structural damage was associated with partial or total roof collapse of secondary buildings (small independent constructions for warehouse, farming and garage) and annexes (small dependent constructions annexed to the main buildings). The most common non-structural damages include clamping vertical and horizontal cracks, partial or total overturning of walls (in case of clamping or thrust of the stressed roofs), and partial damage of several elements (tiles, plaster, curbs, canopies, parapets, windows, corrugate and fretted sheets and tarps). No major structural damage was observed on main buildings. The reason is due to the fact that primary residential and commercial buildings were considered necessary to meet basic needs of the local population; therefore, roofs were regularly cleaned as part of the emergency management and the daily volcanic response activity on the island. This was not the case for secondary buildings and annexes. This emphasizes the important role of clean-up operations on the resilience of buildings during long-lasting volcanic eruptions that can lapse for weeks or months. Even though structural damage has been observed only on secondary structures and annexes, the detailed impact assessment of those conducted in La Palma provides the first insights into the consequences of tephra loads on medium to weak quality buildings or constructions made with light materials (e.g., corrugated metallic tiles), which can be very common on other volcanic settings.