Deep-Sea Tephra from the Azores during the past 300,000 Years: Eruptive Cloud Height and Ash Volume Estimates

Abstract

Background and Purposes Deep-sea tephra has been studied intensively because of its diverse geological uses. Tephra studies provide information on petrochemistry and petrogenesis, volcanicity and regional tectonism, possible climatic variation, magnetic properties, ambient wind directions and velocities, regional tephrochronology, depositional processes and origin of volcanogenic sediments, eruptive cloud heights, chemical correlation of tephra layers between land and abyssal regions, and micro-morphological indications on glass shards of eruptive cloud heights. Hitherto, deep-sea tephrochronology was based solely on visible ash layers in cores, Limiting Identification to a downwind distance of, 1,000 km. By using our technique for the separation and counting of deep-sea dispersed tephra (Huang and others, 1975a), we have obtained evidence that a single ash layer can be correlated between cores 3,000 km apart at high latitudes in the South Pacific (Huang and others, 1973, 1975b). The downwind particle-size variations can be used to estimate eruptive cloud heights and paleoexplosivities (Shaw and others, 1974; Huang and others, 1975b).