Controls on Water-Magma Interactions at Hydraulically-Charged Volcanic Islands

Abstract

[Abstract] The interaction of rising magma with groundwater can produce phreatomagmatic explosions, which, given their enhanced explosivity and unpredictability, increase the hazard potential of volcanic eruptions. To investigate the link between groundwater occurrence and phreatomagmatism, we compare the volcanic record of Flores Island (Azores) with regional climate reconstructions. Flores is an ideal case study as it experienced multiple magmatic and phreatomagmatic eruptions during the Holocene and Pleistocene. Our results show that at a broader scale (>10 ka), magmatic volcanism prevailed during dry/colder periods, whereas phreatomagmatism preferentially occurred during wet/warm periods. At a shorter timescale (<10 ka), however, water-magma interactions were primarily controlled by variations in eruption rates, with rainfall variability having a secondary role, as phreatomagmatism occurred even during low precipitation periods. This study reinforces that on island volcanoes with perched aquifers and prone to monogenetic volcanism, eruption rates rather than short-term hydroclimate changes control the triggering of phreatomagmatism.