Mangere Mountain

Mangere Volcanism - Te Puiatanga o Te Pane o Mataoho

(The following text has been taken with permission from LEARNZ.org.nz)

Within the Auckland Volcanic Field (nga wahi puia o Tamaki Makaurau) is the volcanic group known as the Mangere - Ihumatao District. It is a bit like a complete volcanic field in miniature. All the volcanoes (nga puia) are small, but different from one another. There is an island volcano, Puketutu (Week's Island); castle and moat volcano, Mangere Lagoon; and Pukaki, which has most of its original tuff ring. Mangere Mountain is the most dominant of all of these volcanoes.

Mangere Mountain is 106m above sea level. It is also the most preserved volcanic cone (he koeko rangitoto) in the area. Half a million cubic metres of its lava (rangitoto) output has been quarried away. It has about 45 million cubic metres of lava output. Nearly all of Puketutu has been quarried away. Many of the other volcanic cones in Auckland have been quarried. The basalt is used for building.

Mangere Mountain erupted about 18,000 years ago. A piece of wood (rakau) from under Mangere Mountains lava flow (te ara rangitoto) was carbon dated. It was found to have died about 18,000 years ago. Mangere Mountain is one of the largest scoria cones (nga koeko rahoto) in Auckland's volcanic field.

Mangere Mountain probably erupted in the following sequence:

  • A bubble of magma started forcing its way through the crust;

  • This magma came in contact with ground water;

  • Violent explosions took place and a large explosion crater formed with a low tuff ring;

  • Fire fountaining (te ara taratihi) followed with lava bombs blasting up into the air and forming steep mounds;

  • Large amounts of lava came to the surface and flowed outwards through a breech in the crater;

  • When the fire fountaining finished, one of the vents (puaretanga) heated up and semi-fluid lava pushed upwards forming a tholoid (plug) in the middle of the main crater;

  • New vents blasted out more scoria within the crater; and

  • One vent in the crater rim (te puke ngutu) erupted very violently to produced a second, very steep crater.

Lava fields from Mangere Mountain spread in all directions except the south-east. They cover about 5 square kilometres. Ambury Park covers Mangere western lava field. Lava caves (nga rua rangitoto) and tunnels (nga aro raro whenua) are found in the park. Volcanic ash (pungarehu) covered all these fields. It spread in all directions except the south for about 8 kilometres. The soil (onemata) became very fertile and was used for gardening (mahi mara).