Ground deformation monitoring in La Palma Island (post-eruption of Cumbre Vieja), Spain (2021-12-26)

Activation date: 2021-12-26

Event type: Volcanic activity

Activation reason:

The CEMS Risk and Recovery Mapping service has been newly activated to continue monitoring the ground deformation of La Palma island (Cumbre Vieja region), Spain, after the end of the eruption phase (started on 19 September 2021 and ended on 25 December 2021). The eruption period has been the longest on the island since records began. Voluminous lava flows reached populated areas, fanning out across settlements and banana plantations, destroying thousands of buildings, and ultimately pouring over steep cliffs into the ocean.The ground deformation during the eruption phase was monitored in activation EMSN112. The results of this activation aim to support the monitoring performed by the user and complement the results obtained from Sentinel-1 data by the IGN (Spanish National Geographic Institute). In this recovery and damage assessment phase, post-event soil erosion and landslide risk assessment products were also requested.Post-event Soil erosion risk assessment (P16) and Landslide risk assessment (P17) were delivered for the area affected by the lava flow that is in the southern region of the island. To generate these products, it has been necessary to update the land cover dataset by generating the post-event LULC CLC (P03.2). The event reconfigured the island physiognomy creating more than 40 hectares of new land and also deeply changed the soil characteristics directly affecting the soil erosion risk. While before the eruption it was estimated that most of the affected area was mainly characterized by severe risk, today the lava flow has caused a massive change in the soil erosion risk, destroying urban areas and turning other soil erosion prone areas into solid bare rock. The lava flow increased the soil cohesion leading to a significant increase of the area associated to a Very Low risk (+3,259% from 35 ha to 1220 ha), occupying 100% of the affected area. In terms of post-event landslide risk, currently, very low and low risk areas are the most representative in the southern side of La Palma (24,905 ha in total, i.e. 81.68% of the entire area). Moderate risk areas represent 10.90% of the analysed area, while 6.31% is classified as high landslide risk. The comparative analyses shows that the event did not promote the susceptibility of the occurrence of landslide events in the area affected, even conferred a slight stabilization of the slope and land cover fundamental to mitigate the possibility of a landslide occurrence.Thirty-nine interferometric SAR images acquired during the post-eruption phase (from December 2021 to October 2022) by TerraSAR-X and PAZ satellites were processed to deliver no-standard Ground deformation analysis products (P12), i.e. LOS (Line Of Sight) displacement, coherence and interferogram products. Among these 39 results, two examples have been included in a Mapbook (P13), showing the LOS displacement all over the island, and detailed maps of the coherence and interferogram focused on the most affected area in the proximity of the volcano.