1 million years ago to present

DepositionErosion

Deposition

Covering upLater more explosive rhyolite eruptions in the Rotorua area (and

possibly within the Tauranga Basin) spread vast amounts of hot

rocks and ash – known as ignimbrite – out over large parts of

the land. Some ignimbrite deposits were relatively small - like the

Aongatete Ignimbrite which covered this area. Others were much

larger, such as the Waiteariki Ignimbrite which is up to 220 metres

thick. Local rhyolitic eruptions also formed hills like the Kaimai

Dome at the headwaters of the Wairoa River and Mt Maunganui

(Mauao) on the coast.

Lifting upStarting about 7 million years ago, massive tearing in the Earth’s

crust made what is now called the Hauraki Fault. Although it

took millions of years to form, most movement happened about

1-2 million years ago when the Kaimai volcanos on the east of the

Hauraki Fault were uplifted (in places up to 4 kilometres higher

than the west). As well as creating the mountain range, the

faulting also tilted the Waiteariki Ignimbrite to form the

gently-inclined fertile plateau of the Tauranga Basin.

Filling inOver the last million + years, the low land in and around what is

now Tauranga Harbour has been filled slowly with river

sediments, swamp deposits, dunes and volcanic ash up to 50 m

thick in places.

The low areas west of the Hauraki Fault were also filled up with

ignimbrites and sediments to form the Hauraki Plains.

TheKaimai

Range Making mountainsThe Kaimai Ranges are made up of a series of volcanos (mostly

andesitic-dacitic cones) which erupted between 4 and 5.6 million

years ago. They are the southern end (and youngest) of a line of

progressively older volcanos which extend up to the northernmost

tip of the Coromandel Peninsula.

3.9 - 2 million years ago

Aongatete ignimbrite

Waiteariki ignimbrite

coast

2 - 1.2 million years ago

Ignimbrite rock sample

Hauraki Fault

5.6 - 4 million years ago

Greywacke basement rocks

Kaimai Volcanos

Fact A New Zealand geologist

named this type of rock –

it means ‘fiery rock dust’

Ignimbrite

Andesite rock sample

FactThe names comes from ‘The

Andes’ in South America, where

this type of rock is common

Andesite

Ha

ura

ki P

lain

sH

au

rak

i F

au

lt

Ka

ima

i R

an

ges

Tuapiro F

ault

Whakamarama PlateauTilted 3-5o

YOU ARE HERE

Tauranga

Kaimai Dome

Mamaku Plateau

Wairo

a Riv

er

Aongatete RiverMount Maunganui

Papamoa Range

The big picture