Fumarole and on the surfaces of lava flows and of thick deposits of pyroclastic flows. A fumarole field is an area of thermal springs and gas vents where magma or hot igneous rocks at shallow depth release gases or interact with groundwater. When they occur in freezing environments, fumaroles may cause fumarolic ice towers. Fumaroles may persist for decades or centuries if located above a persistent heat source; or they may disappear within weeks to months if they occur atop a fresh volcanic deposit that quickly cools. The Valley of Ten Thousand Smokes, for example, was formed during the 1912 eruption
Magma (the extrusive equivalents of gabbro, diorite and granite, respectively). During a volcanic eruption the magma that leaves the underground is called lava. Lava cools and solidifies relatively quickly compared to underground bodies of magma. This fast cooling does not allow crystals to grow large, and a part of the melt does not crystallize at all, becoming glass. Rocks largely composed of volcanic glass include obsidian, scoria and pumice. Before and during volcanic eruptions, volatiles such as CO and HO partially leave the melt through a process known as exsolution. Magma with low water content becomes increasingly viscous. If massive exsolution