What is it about?
When lava flows extend coasts into deeper water, they are attacked by waves. In this study led by Zhongwei Zhao, daily Pléiades satellite images of 0.5-m resolution were used to investigate the fronts of the two deltas emplaced during the 2021 eruption on La Palma, Canaries. One delta front was found to have retreated by 13 m within 400 days, becoming highly crenelated, whereas the other (a much thicker 'a'a delta) hardly changed at all. This confirms our other work suggesting that the resistance to erosion is an important factor.
Featured Image
Why is it important?
Within the Canary Islands, and other islands such as the Azores, old volcanic lava flows eventually develop soils and are used for agriculture. Knowing how long they are likely to survive from coastal erosion may be useful. How new volcanic coasts evolve could also be important for wave propagation, and hence geomorphologic change, at other adjacent coasts. Longer term longevity of islands may have affected the speciation in island groups. Hence, this is a subject that could be interesting to various researchers.
Perspectives
It would take some courage to predict exactly how far new coasts will retreat after they are emplaced in volcanic eruptions. However, we have found that they typically follow a simple equation (Figures 1 and 2), they are somewhat predictable. The slowing may occur for three reasons (unfortunately, we still do not know which of these is the more important). First, the coastal retreat leaves behind a nearshore shallow platform of eroded rock. Waves crossing such platforms are increasingly attenuated by bottom interaction as the platforms widen, protecting the coast. Second, progressive erosion exposes progressively deeper, more compacted and/or lithified rocks that were more resistant to erosion. Third, because the land rises away from the coast, sea cliffs become taller with time, leading to larger debris fields from cliff collapses, which protect cliff bases from wave impacts for longer periods before being removed by the sea. Over time and with more examples of new volcanic coasts, it will hopefully become possible to understand these factors more quantitatively.
Dr Neil C. Mitchell
University of Manchester
Read the Original
This page is a summary of: Rapid changes of the lava‐delta coastlines formed by the 2021 volcanic eruption on La Palma, Canary Islands, Earth Surface Processes, May 2026, Wiley,
DOI: 10.1002/esp.70318.
You can read the full text:
Contributors
The following have contributed to this page
