ALBERT

Description: The Minoan deposits show evidence offour eruptive phases and a fluvial/erosion stage. The eruption began with a plinian phase which generated a column up to 36 km (±5 km) high. The maximum discharge rate is estimated at 1.4-4.2 1()8 x kg/s and the plinian phase lasted several hours. The vent for the plinian phase opened up about 1 to 2 km south-west of Phira in a subaerial environment only slightly above sea-level. Phase 2 involved access of sea water either by enlargement of the vent or by new vents opening up. Phreatomagmatic activity generated base surges and well-stratified fall-out deposits. Variable emplacement temperaturt:s of the deposits and contemporaneous plinian activity indicate highly variable magma-water interaction during phase 2. Phase 3 deposits are predominantly massive and poorly sorted, consisting of many individual units. They adhered to steep slopes and carried /arge lithics and intraclasts (several metres in diameter). The deposits are interpreted as poorly fluidized, low temperature pyroclastic flows, some of which contained liquid water. The flows are envisaged to form by very /arge phreatomagmatic explosions from a wide funnel-shaped vent filled with a pyroclastic slurry. Phase 3 disrupted a young dacitic Java shield which had been constructed in a pre-Minoan caldera. Phase 4 produced the thick ignimbrite fans seen around the present islands, composed of numerous flow units. The pyroclastic flows of phase 4 were hot(250-400 °C),lithic-rich and fluidized, and could not adhere to steep slopes. Thick pyroclastic accumulations around the widening vent system of phase 3 may have formed a barrier to the sea. and enabled the eruption to return to high temperature magmatic activity. There is no clear evidence that major caldera subsidence had begun at the end of phase 4. Phase 5 consisted of flood events forming alluvial [ans on top of the ignimbrite. A valanches of unstable caldera walls may have generated repeated flood waves following subsidence.