There is one thing we can deduce, and that is that this was not a sudden eruption, for the ruins at Akrotiri indicate that the Minoan city had been completely evacuated of people and their belongings. That this occured shows that they knew what was going to happen, and that is likely because there had been a previous eruption. Earthquakes may have given them cause for alarm, but as we saw at Pompeii, they had no idea that a massive eruption would follow ten years later. If at some indeterminate time before the Thera eruption, but within living memory, or not too far back, there had been earthquakes followed by a minor eruption, next time it happened they didn't hang around and promptly evacuated. So we could have two events separated not too widely in time. And, who knows, if there had not been two events at Thera, but by coincidence there may have been an event like the Chelyabinsk meteor, and something like that would have scared them to death, but that's just speculation.