Geokolloqium, Dr. Harri Geiger

- GEOWISSENSCHAFTLICHES KOLLOQUIUM -

Explosive Ocean Island Volcanism Explained by High Magmatic Water Content Determined Through Nominally Anhydrous Minerals

Presentation from Dr. Harri Geiger
Universität Freiburg

Explosive eruptions are generally considered exceptional on ocean islands, where basaltic magmas are thought to contain little water and typically erupt effusively. Yet, several volcanic islands in the Atlantic and Pa-
cific record episodes of explosive volcanism, hinting at transient changes in magma dynamics that remain poorly understood. We explore new evidence from El Hierro in the Canary Islands, where unusually crystal-rich
basalts erupted shortly after a major sector collapse. Using mineral-scale volatile records, we revisit long-held assumptions about the volatile budgets of ocean island magmas and the processes that enable their explosive behaviour. The results point to deep-seated reservoirs of volatile-rich magma that may become eruptible when external forces - such as rapid unloading following landslides - disturb the magmatic plumbing system. These findings invite a broader reconsideration of how magmatic volatiles, crustal architecture, and surface instability interact to shape the evolution and hazards of ocean islands.