"A smaller but still sizable eruption was observed at the supervolcano in 1538. That event lasted eight days and created the mountain Monte Nuovo. But since then, the volcano has been quiet, slumbering for more than 500 years."

I'm going to assume it's 1538 AD and that this volcano has slumbered almost 500 years. And if create a "new mountain" was enough to relieve the pressure then, how do they distinguish a major eruption from a minor one when performing these forecasts?