Phreatic eruptions at Whakaari Volcano driven by hydrothermal mineralisation and magmatic gas input

Phreatic eruptions are a potentially lethal type of volcanic activity that is notoriously difficult to forecast. Understanding the complex processes that make eruptions more likely is a key step towards detecting precursory signals. Here, we employ 3-dimensional numerical models of heat and fluid flow based on field and laboratory data from Whakaari/White Island Volcano in New Zealand to explore the thermal, hydraulic, and geologic conditions that promote phreatic eruptions. Our results show that hydrothermally mineralised low-permeability seals can trap rising steam and magmatic gases until the pressure exceeds the tensile strength of the rock within days to months. Changes in persistent degassing through secondary vents can provide valuable insights into when the main sealed conduit is building to eruption. This study provides new insights into the timescales and mechanisms promoting phreatic eruptions, and a starting point to quantitatively interpret volcanic signals in terms of subsurface activity and eruptive potential. Phreatic eruptions at Whakaari volcano are influenced by subsurface pressurisation magnitudes and timescales, which are significantly influenced by hydrothermal mineralisation and magmatic gas input rates, according to 3-dimensional numerical modelling of volcanic hydrothermal systems.