Evolution and Growth of Lava Deltas: Insights from the 2021 La Palma Eruption (Canary Islands)

During the 2021 eruption on La Palma Island, the predominant volcanic hazard was lava flows, while tephra fall and gas emission were significant concerns. Consequently, monitoring the expansion of the lava flow perimeter considering the variations in volcanic activity became fundamental. The interaction of lava with the sea water was also a major concern for emergency managers due to its associated hazards like gas emission and explosive activity due to interaction lava-water, leading to a specific focus on the formation and development of lava deltas.

Almost 10 days after the beginning of the eruption, the lava reached the sea, forming a main structure (south delta) that grew in different phases until nearly the end of the eruption, covering an area of approximately 83 ha. The south delta encroached upon the sea and additionally buried the northern part of a pre-existing lava delta from the 1949 San Juan eruption. About 1300 m from the northernmost tip of the south delta, a new lava flow entry to the sea occurred 64 days into the eruption, feeding a second lava delta (north delta) of about 5 ha over a 4-day period.

This study has made significant technical and scientific contributions, not only during the emergency but also in preparation for future recovery efforts on La Palma. Remotely Pilot Aircrafts (RPAs) provided valuable information about the lava-flow development and enhanced a deeper understanding of the formation and evolution of lava deltas and their potential hazards. Moreover, the study highlights the potential impact on new inhabited or economically exploited areas and is imperative its preservation for the geological heritage, including marine zones. Furthermore, it will play a crucial role in forecasting the behaviour of lava deltas and in the development of mitigation measures for potential future eruptions.