Temporal evolution of the Minoan eruption (Santorini, Greece), as recorded by its Plinian fall deposit and interlayered ash flow beds

• Published in: Journal of volcanology and geothermal research 2001-09, Vol.109 (4), p.299-317
• Main Authors: Taddeucci, Jacopo, Wohletz, Kenneth H.
• Format: Article
• Language: English
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; fragmentation; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Plinian-type eruptions; Santorini; tephra
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/S0377-0273(01)00197-4

The Plinian fall deposit of the Minoan eruption (Santorini, Greece) and its interlayered ash flow beds show textural, componentry and chemical trends indicative of their temporal evolution and conditions that lead to the ash-flow emplacement. The deposits have been sampled in detail at a selected locality, and the following features have been analyzed: (i) maximum clast size; (ii) grain size distribution; (iii) componentry; (iv) lithic types; (v) pumice morphology; (vi) pumice types; and (vii) pumice crystal abundance. Stratigraphic variations of these features are assumed to record changes that occurred during the eruption, including changes in eruptive plume height, nature and relative efficiency of the magma fragmentation process, conduit stability, and magma flow in the conduit. Based upon the inferred temporal changes, we propose the following eruption reconstruction. The sustained Plinian column activity reached its climax (in terms of mass eruption rate and plume altitude) soon after the beginning of the eruption, and subsequently began to gradually subside. As a result of eruption waning, the conduit walls began to collapse, causing an increase in the shear stress in the flowing vesicular magma and an increase in the efficiency of the magma fragmentation process. Eventually the conduit closed or became too narrow to support a high-standing eruption column, leading to ash flow eruption as a result of the collapse of what was left of the eruptive plume, and/or directly from emission of an overpressured jet. Subsequent conduit pressure increases led to conduit re-opening and a Plinian column with associated pumice fallout began anew. The eruptive magma fragmentation process is proposed to have been of a brittle nature and linked to the shear stress generated by conduit wall friction. Fragmentation efficiency is recorded by grain size distributions and free crystal contents of the deposits.