DEVELOPMENT OF A CLASSIFICATION SYSTEM FOR EXPLOSIVE MAFIC ERUPTIONS

Small mafic vents on Earth often form scoria cones by the accumulation of ejected clasts during the eruption. Cone formation is usually accompanied by the eruption of lava flows from the base of the cone, and in some cases, more explosive phases of activity produce widespread tephra blankets. However, little work has been done to develop a classification system for explosive mafic eruptions that accounts for all three of these materials erupted at a single vent. Magma viscosity, ascent rate, initial water content, and degassing efficiency are important controls on the range of explosivity at mafic vents. Changes in erupted materials over time reflect changes in these controls, making a classification system based on the volumes of cone material, lava flows, and the tephra blanket a convenient way to categorize mafic eruptions. This classification system accounts for the range of materials erupted at mafic vents throughout all phases of activity, which generally show a trend from cone-building to effusive, sometimes with intervening or simultaneous explosive phases. Additionally, classification of individual vents based on eruptive style can be used for probabilistic assessment of hazards associated with mafic eruptions. We find that small volume eruptions tend to produce only scoria cones, probably at low to moderate mass eruption rates. In contrast, large volume eruptions of H₂O-rich mafic magma create widespread tephra blankets at high mass eruption rates, or widespread lava flows when magmatic degassing is efficient. Finally, since volumetric estimates of cone material, lava flows, and, for very young eruptions, tephra blankets can be made using DEMs or images acquired through remote sensing, this classification system could be used to describe the eruptive history of remote mafic vents on Earth as well as vents on Mars. The system thus provides a means of comparing eruptive controls at well-documented and historic vents such as Paricutin, Mexico, to eruptive controls at remote or non-terrestrial vents where sample collection is not feasible.