So, suppose we have a very large island. Exactly how big it is doesn't matter too much, but it must be big enough to support a small country.
This is a volcanic island, and the volcanoes on this island erupt regularly and predictably. In this way, lava flows periodically cover parts of the island, enriching the soil with deep-earth minerals and nutrients. Suppose this happens once a decade or so.
The people living here know roughly when the volcanoes will erupt, and are able to respond to eruptions by moving to a safe location beforehand, and then immediately farming on the newly cooled volcanic ground to produce extremely fertile farmland.
How plausible is this scenario? What mechanism keeps the volcano erupting consistently, and how do the locals know when a given part of the island is about to be covered in lava? How do they know where the safe spots are to wait out the eruption? are there any other details that might prevent this, like toxic gasses?
The answer should only use known natural processes. No magic.