Tephra fallout and associated deposits (Encyclopedia of Volcanoes, 3rd edition, book chapter)

The lifecycle of volcanic fall deposits begins with explosive fragmentation, continues as particles rise through the atmosphere, and culminates with sedimentation on the ground. This chapter explores how fall deposits can reveal the unique eruption and transport processes that shaped them. While we can directly observe modern eruptions to understand their dynamics, unobserved volcanic events are reconstructed through their deposits. This process typically includes field and laboratory-based measurements of tephra dispersal, grain size, componentry, composition, and clast textures. Advances in modern observational techniques and numerical modeling have also enhanced our understanding of tephra transport and forecasting of the hazards related to airborne ash. Using a combination of these approaches to link field deposits with their sub-visible equivalents in the distal realm (cryptotephra) provide key chrono-stratigraphic markers for records of eruption history on regional to global scales.