The rocks had a temperature of about when they were erupted, with the "Dacite 1" being hotter than the "Dacite 2". Their formation may have been stimulated by the entry of mafic magmas into the magmatic system; such an entry of new magma in a volcanic system is often the trigger for explosive eruptions. The magmas erupted early during the 1600 event (in the first stage of the eruption) appear to have originated from depths of more than ; petrological analysis indicates that some magmas came from depths greater than and others from shallower depths of about . An older hypothesis by de Silva and Francis held that the entry of water into the magmatic system may have triggered the eruption. A 2006 study argues that the entry of new dacitic magma into a pre-existent dacitic magma system triggered the 1600 eruption; furthermore movement of deep andesitic magmas that had generated the new dacite produced movements within the volcano.