Phys.org  April 20, 2022 Even with real-time geophysical monitoring, forecasting sudden eruptions is difficult, because their precursors are hard to recognize and can vary between volcanoes. An international team of researchers (New Zealand, Belgium) has described a general seismic precursor signal for gas-driven eruptions, identified through correlation analysis of 18 well-recorded eruptions in New Zealand, Alaska, and Kamchatka. The precursor manifested in the displacement seismic amplitude ratio between medium (4.5–8 Hz) and high (8–16 Hz) frequency tremor bands, exhibited a characteristic rise in the days prior to eruptions. They interpreted this as formation of a hydrothermal seal that enables rapid pressurization of […]