Abstract

The Minoan eruption of Santorini produced the following sequence of deposits: a plinian pumice fall deposit, interbedded surtseyan-type ash fall and base surge deposits, mud-flow deposits and ignimbrite interbedded with very coarse, well-sorted flood deposits. The variation of thickness and grain size in the plinian deposit indicates a vent 1 km west of Thera town. The base surges and surtseyan-type activity is interpreted as the result of sea water entering the magma chamber. The poorly sorted mud-flow deposits and ignimbrite are distinguished on their grain size, temperature and morphological characteristics, which indicate substantial rheo-logical contrasts in the mass flows which produced them. Grain size analyses show wide ranges in the lithic contents of the different types of deposit: ignimbrite (35–60%), mud-flows (20–30%) and the pyroclastic fall and base surge deposits (4–15%). The ignimbrite is enriched in crystals, complemented by depletion in fine air-fall ash beds that interstratify with the ignimbrite. The gas velocity of the plinian phase is estimated as 550 m/s, the eruption column height as greater than 20 km and it is shown that only particles of 2 mm could have reached Minoan Crete.