Here's why:

* Volcanic Features: Mount Gambier exhibits classic volcanic features, including a maar crater, lava flows, and volcanic tuff.

* Age: The volcanic activity in the Mount Gambier area ceased around 5,000 years ago.

* No Recent Activity: There's no evidence of any volcanic activity in the region for thousands of years, indicating that it's no longer an active volcano.

However, while Mount Gambier is extinct, it's important to remember that volcanic activity can sometimes reawaken.