Wanted: Oscar Obsidian - Auckland Museum

Background
Shapes of Auckland Volcanoes
Auckland's volcanoes come in a variety of landforms,
depending on the style of eruption. Each
volcano is formed by one eruption, or a short
series of eruptions lasting no longer than a few
months. Then a plug of lava solidifies in the vent,
and later bubbles of magma find another place
to erupt.
Fieldtrips Around Auckland's Volcanic Field
The following is a list of places which provide a
great opportunity to study Auckland's volcanic
field at first hand. The list does not include all the
possibilities.
Meola Reef, Pt Chevalier - Auckland's longest lava
flow, home to burgeoning mangrove swamps and
being redeveloped as a park.
Mt Eden, One Tree Hill, Mt Albert, Big King,
Mangere Mountain etc - Scoria cones, craters and
lava flows, also providing evidence of use by
Maori and Pakeha. Use the map to check out volcanoes
in your area.
Three styles of eruption were involved in building
the Auckland volcanic field. Each has produced its
own type of rock and landform. While some volcanoes
were created by one style, others were
created by a combination. The landforms and
eruption styles have been discussed previously, but
this chart provides a summary of the events in
forming Auckland's volcanoes.
Eruption Style Rock type Volcanic Shape Examples
Lava Flows and
Fields
Conditions:
Magma is free of gas and
oozes out of volcano rim or
side vent
Fire fountaining
Conditions:
Gas-rich magma reaches
surface without contact with
water
Explosive eruption
Conditions:
Rising magma meets
groundwater causing
superheated steam
Solid basalt
There are two types of
lava flow:
pahoehoe fluid, fast
flowing and smooth.
a'a thick, slowmoving and
rough
Auckland Museum 11
Shield Rangitoto
Auckland Domain - Tuff ring, Auckland's first
water supply and one of the earliest quarries,
evidence of layers in tuff ring.
Rangitoto - shield volcano, lava caves.
In addition many volcanoes
have lava flows but are
not shield volcanoes.
Meola reef is the longest
flow and was extruded
from the Three Kings
volcano.
Scoria Scoria cone Mt Eden, Three Kings, Mt
Albert, One Tree Hill etc
(these also exhibit other
eruption styles)
Tuff (ash and lapilli) Tuff ring Auckland Domain. Lake
Pupuke, Panmure Basin
Old Mt Eden Prison Quarry (Auckland Grammar
land) - basalt columns.
Takapuna Beach - fossil forest which was engulfed
by lava from Lake Pupuke.