A large amount of sulfur appears to have been carried in a volatile phase associated with the magma rather than in the magma proper. An even larger amount of sulfur may have originated from a relic hydrothermal system that underpins the volcano, and whose accumulated sulfur would have been mobilized by the 1600 eruption; some contradictions between the sulfur yield inferred from ice core data and these inferred from the magma composition can be resolved this way. The amount of volatiles in the magma appears to have decreased during the 1600 eruption, indicating that the magmas originated either in two separate magma chambers or from one zoned magma chamber. This compositional change may explain changes in the eruption phenomena during the 1600 activity as the "Dacite 1" rocks erupted early during the 1600 event were more buoyant and contained more gas and thus drove a Plinian eruption, while the latter "Dacite 2" rocks were more viscous and only generated Vulcanian eruptions. Crustal interactions and crystal fractionation processes were involved in the genesis of the magmas as well, with the so-called "Dacite 1" geochemical suite forming deep in the crust, while the "Dacite 2" geochemical suite appears to have interacted with the upper crust.