Scientific evidence of an eruption

1. In nothern crete, mixed deposits of volcanic ash, building debris, cultural material, and marine fossils near the beach are compared to those found in coastal regions after what modern disaster?
2. What does a beach deposit of mixed ash, building debris, marine fossils, and pottery near palekastro prove?
3. What is the most scientific evidence of an eruption 3500 years ago on santorini