Four-Stage Dynamics of the Minoan Ash Cloud and Revised VolumetricParameters: The Critical Bayır Tephra from the Yatağan Basin, Türkiye

The Minoan eruption's extensive tephra deposits across the Eastern Mediterranean have been constrained by limited terrestrial data, particularly from the Anatolian mainland. This study presents the first documentation of the Bayır Tephra (BT), discovered in colluvial deposits 260 km E-NE of Santorini near the Yatağan Fault. Geochemically correlated with Minoan pyroclastics, the BT comprises two bimodal layers: BT-01 (8 cm white, micropumice-dominant, linked to the Plinian phase) and BT-02 (56 cm grey, non-vesicular glass shard-dominant, linked to the Co-ignimbrite phase). Using the BT data and an updated Anatolian dataset, a new isopach map was produced using the Radial Basis Function (RBF) method. Analysis of the tephra distribution yields a new Four-Stage Model for ash cloud dynamics: T ₁ ) Initial eastward drift toward Rhodes; T ₂ ) N-NE deflection near Rhodes creating a Bifurcation mechanism and the separation of a weak SE lobe due to crosswind effects; T ₃ ) Continued N-NE movement with crosswinds forming an Aeolian Ashfall Edge to the East; and T ₄ ) Final widespread ash drift towards the Black Sea. This model proposes that the bilobate tephra distribution (SE and NE) is controlled primarily by wind dynamics, rather than separation between Plinian and Co-ignimbrite plume axes. The ashfall volume is calculated as 59.3 km ³ (35 km ³ DRE), mass as 7.4 x 10 ¹³ kg, and the Eruption Magnitude is updated to 7.1. These precise parameters are essential for accurate future risk and hazard assessments.