Fifteen minutes before the massive January 2022 eruption of the Hunga Tonga-Hunga Ha'apai volcano, a seismic wave was recorded by two distant seismic stations. The researchers propose that the seismic wave was caused by a fracture in a weak area of oceanic crust beneath the volcano's caldera wall. That fracture allowed seawater and magma to pour into and mix together in the space above the volcano's subsurface magma chamber, explosively kickstarting the eruption.