Lava deltas in the Canary Islands as geotourism resources: geoheritage value and risk-informed management in volcanic coastal environments

Lava deltas formed during monogenetic eruptions represent hazardous coastal environments due to rapid land construction, magma–water interactions, unstable lava fronts, gas emissions and recurrent gravitational collapses. While these processes pose significant dangers during eruptive phases, lava deltas commonly remain unstable for years to decades, resulting a source of post-eruptive volcanic and coastal hazards.

The 2021 eruption of the Tajogaite volcano on La Palma led to the formation of two new lava deltas on the western coast of Cumbre Vieja volcanic ridge, highlighting the rapid emergence of new hazardous environments. Notably, one of these deltas partially overlies a pre-existing lava delta formed during the 1949 eruption of the San Juan volcano, illustrating the superposition of eruptive events and the cumulative nature of lava-delta hazards over time. This diachronic coastal construction emphasises that lava-delta hazards are not confined to eruptive phases but persist well into post-eruptive periods coupled with the effects of sea level rise in the current climate change scenario.

Recent lava deltas coexist with emblematic historical and prehistoric examples across the Canary Islands, including, for instance, the lava delta formed during the 1706 eruption of the Arenas Negras volcano that affected the town of Garachico on Tenerife, the Pleistocene lava delta on which the city of Arrecife (Lanzarote) is currently built, and several lava deltas along the southern coast of El Hierro associated with Quaternary pahoehoe lava flows.

After the 2021 eruption, the two new lava deltas were requested in 2022 to be included as Natural Monuments for protection under Spanish Law 42/2007, being one of the best-preserved lava delta’s worldwide examples. Unfortunately, the lava deltas and other areas with high-scientific and cultural value remains unprotected and have already been damaged. In addition, these sites demonstrate the long-term persistence of structural instability, marine erosion and localised gas emissions, representing enduring sources of risk in inhabited or highly visited areas.

Within the framework of the “Canary Islands: Destination of Volcanoes” initiative, many of these lava deltas are included as geosites in the Spanish National Inventory of Geosites (IELIG). Notably, numerous tourist beaches in the Canary Islands archipelago are situated on these lava deltas, further enhancing their appeal and contributing significantly to the geosites’ tourist value. Beyond their scientific value, their designation as geosites offers significant potential for improving geological knowledge and enhancing risk perception among both visitors and local communities, particularly in post-eruptive landscapes where geohazards may be underestimated.

This contribution highlights lava deltas as key geosites but often underestimated eruptive and post-eruptive hazards in volcanic coastal environments and argues for the integration of volcanic and coastal hazard assessment with geoheritage recognition, land-use planning, and risk communication strategies in active volcanic regions.

Sub-Project 1 ‘Canary Islands, destiny of Volcanoes’ is funded by PROMOTUR SA through (Next Generation EU funds), PRTR. 2024krQ00nnn, carried out within the framework of the agreement between Promotur Turismo Canarias, S.A., and the CSIC, Univ. of La Laguna, Fundación Canaria General of the Univ. of La Laguna, and Univ. of Las Palmas de Gran Canaria.