Mangere Lagoon

Mangere Lagoon is an explosion crater about 700m across, with a 100m wide scoria cone in the middle of it. It is thought to have erupted not long before Mangere Mountain first became active, roughly 70,000 years ago. This was during the last ice age when sea levels were lower (due to the accumulation of ice at the poles and in the mountain ranges of the world). About 7500 years ago, the crater was flooded as sea levels rose to their present level and broke through the ring of tuff (volcanic ash) on the south-western side of the crater. Having been used as a place for sewage treatment over about 40 years, it has now been restored into a tidal lagoon again, and has a very pleasant walkway around it.

If you have little time, you can get a good view of the lagoon / crater from the walking track right next to the car park. Alternatively it is well worth doing the circular walkway to take in the view from all sides (about half an hour).