Here's why:

* Volcanic activity: Mount Pirongia last erupted around 2.5 million years ago.

* Geological evidence: The mountain's volcanic features, like lava flows and craters, are heavily eroded and covered in vegetation. This suggests a long period of inactivity.

* No recent seismic activity: There is no evidence of magma movement or seismic activity beneath the mountain.

While Mount Pirongia was once an active volcano, it has been dormant for a very long time, making it considered extinct.