Classification and quantification of volcanic eruptions

The eruptive style of volcanoes is the result of a complex process, which begins at depth and ends with the arrival of magma with variable amount of volatiles at the Earth's surface. The amount of gas, the magma composition, and the supply rate are the main factors controlling the either effusive or explosive character of an eruption. Degassing during the ascent favors a non-explosive eruptive style. Magma may reside in crustal magma chambers for a long time and may be subject to cooling processes with differentiation and separation of batches having different physico-chemical properties. Eruptions may be the result either of a direct connection between a crustal magma chamber and the surface or the ascent of single batches detaching themselves from a larger reservoir, each with its own history of ascent and composition. The eruptive style is the result of the complex mechanism of ascent of magma from its generation to its arrival at the surface. In this paper, we revise earlier schemes of eruption classification. We propose a conceptual grid of classification of the style of volcanic eruptions comprising the main descriptive terms that have been used in the past. The scheme is based on the interplay of a limited number of controlling factors (composition, velocity of ascent and mechanism of supply) that are thought to affect the way in which a volcano may erupt more relevantly. We further provide a more rigorous definition of the magnitude and intensity of an eruption that can be used for the quantitative comparison of eruptions of different volcanoes.