"The more a volcano looks like a volcano, the smaller it really is"

Tranquil Lake Taupo has been an active volcano for more than 65,000 years. In that time it has shown a random pattern of exceptionally large eruptions interspersed with many smaller events.
The area around Taupo is covered in 10m of pumice deposited from eruptions in the last 22,000 years and a further 5m from it's largest eruption 26,500 years ago.

Taupo is not a large mountain because the eruptions have been so large and so violent that all material has been deposited far from the vent and subsequent collapse of the ground has formed a caldera (a collapsed volcano). Many of the lakes around Rotorua were formed in the same way.