Mount Aso is an active volcano, which means it has erupted multiple times throughout history. It's impossible to say "when Mount Aso volcano happened" because it's an ongoing process.

To be more specific, you could ask:

* When was the last eruption of Mount Aso? (The most recent eruption was in October 2021.)

* When was the most significant eruption of Mount Aso? (A major eruption occurred in 1958.)

* When was the first recorded eruption of Mount Aso? (The earliest documented eruption is from 1792.)

Please provide more context or specify what you're interested in learning about Mount Aso's eruptions.