As far as I know there is no evidence for a distinct big event, but there were smaller migration movements over a longer time period.

Toll jetzt muss ich mein Schlaufon laminieren

Back then, there weren’t much of medical knowledge and medicine that prolong lifespans; people had much shorter lives and died young.

That seems a bit incorrect. Of course medicine made a big leap over the last two centuries, but it was not worthless before.

Also people had good chances to reach their 60ies or even 70ies once they survived their first 15 years.

Still an active volcano,.if it was dormant for just a hundred years:

An active volcano is a volcano that is currently erupting, or has the potential to erupt in the future.[1] Conventionally it is applied to any that have erupted during the Holocene (the current geologic epoch that began approximately 11,700 years ago).

https://en.m.wikipedia.org/wiki/Active_volcano

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