For those wondering about this:

It has been three hundred and twenty-three years since the country of magical Italy was ruined by one man's folly.

323 years before 1992, this happened:

Etna's most destructive eruption since 122 BC started on 11 March 1669 and produced lava flows that destroyed at least 10 villages on its southern flank before reaching the city walls of the town of Catania five weeks later, on 15 April. The lava was largely diverted by these walls into the sea to the south of the city, filling the harbour of Catania. A small portion of lava eventually broke through a fragile section of the city walls on the western side of Catania and destroyed a few buildings before stopping in the rear of the Benedictine monastery, without reaching the centre of the town.

That's probably also what's referenced later on:

There is much literary wisdom in those stories. It is born of harsh experience and cities of ash.

(though it's pretty likely that in HPMOR-verse, all volcano eruptions, earthquakes, tsunamis, etc. are caused by Magic Gone Wrong)