This study will systematically characterize the origins of volcanic breccias and their constituent fragments, and thus develop a new genetic classification scheme using mostly field-based observational criteria. Integrated field and laboratory studies will be undertaken in two phases. Phase I studies will focus on well- exposed breccias, mostly on Quaternary volcanoes, where field relationships permit relatively unambiguous interpretation of deposit and particle origins. These reference sites will emphasize those types of volcanic breccias that are least well understood. Phase II investigations will take place on well-exposed, accessible, and mapped volcanoes (one active, one Tertiary in age) to evaluate how breccias of different types are distributed within volcanic edifices, and the role that breccias play in the growth of the volcano.