Geology of New Zealand Field Trip Guidebook - ResearchGate

Day 0—Thursday 13 November. Transit from Australia to Auckland, New Zealand. Store
your extra luggage if you have any and catch your flight to Christchurch. If the weather is
clear, you will have a spectacular overview (literally) of New Zealand geology on your flight.
As you gain altitude out of Auckland, look back and notice the many small conical hills
scattered throughout the city. These are all small volcanoes. Although none, except
Rangitoto in the Auckland Harbor 1 , have erupted since humans arrived in New Zealand about
800 years ago, they are still considered active. As you fly southeast, you’ll cross a relatively
low and eroded landscape which was the setting of The Shire in Peter Jackson’s LOTR
movies. Then you’ll cross the line of volcanoes and volcanic calderas that mark the surficial
evidence of tectonic subduction far beneath the island. Note the contrast between the
rounded and conical volcanic mountains of the North Island, and the jagged fault block
mountains of the Southern Alps on the South Island.
Southeast of Christchurch (Fig. 4) is the Banks Peninsula, which is composed of two
extinct, overlapping and deeply-eroded basaltic volcanoes. The eastern of these is the Akaroa
volcano, the western is called Lyttelton. Both are examples of hot-spot volcanoes erupting
onto the interior of a plate (Sewall et al. 1992). Suggate (1978) describes them as “erosional
calderas” in which wind and rain have breached the weak, innermost lava and tephra deposits
that formerly composed the highest portions of the volcanoes, leaving large, bowl-shaped
structures, perfect for the harbors of Akaroa and Lyttleton and echoing the process evidenced
by the Tweed Volcano at Lamington National Park in Queensland. (These are very different
from the felsic collapse or explosive calderas that we will see in the Taupo Volcanic Zone on
the North Island.)
As you approach Christchurch, you’ll pass over the Canterbury Plain, a broad eastdipping
surface between the Banks Peninsula and the faulted and folded rocks of the
Southern Alps. The area is intensively farmed and provided the locations for Rohan in
LOTR. The landscape is underlain by Quaternary gravels deposited as coalescing
sedimentary fans by braided streams carrying sediment eastward from the Southern Alps. In
the last 2 Ma, the buildup of these deposits has shifted the eastern shoreline approximately 10
km. Both erosion and transport were enhanced during glacial times, when glaciers extended
down nearly to the western margin of the plains (Beanland 1987). In periglacial times, up to
60 m of windblown loess was deposited on top of the gravels, significantly increasing the
fertility of the area. With decreased sediment supply during the current interglacial, streams
like the Wimakariri River, which flows through Christchurch, are now cutting into the gravel
plain. If you get a good view of the plain from the air, you can imagine it being deposited as
a blanket of clastic debris spreading out from the rising mountains to the west.
You will have the evening free in Christchurch. You will be responsible for your
own food and hostelry until you meet the group tomorrow morning. After this time,
your housing, meals and transport will be covered until we return to Auckland after the
conclusion of the program.
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Day 1—Friday 14 November. We will rendezvous with the bus at 9 a.m. in Latimer Square,
on the corner of Hereford and Latimer streets. Please be there on time. We will take a head
count before we depart, but we will not wait for you if you are late. If you miss the bus, it
1 Rangitoto was born about 800 years ago. There are several places where human footprints are preserved in
the now-rock-hard volcanic ash. Therefore, we know the ancestors of the Maori had already arrived on the
North Island and had gone out to explore the new piece of land that popped up in their midst. Today this little
volcano is a park with some really wonderful hiking trails. If you plan to hang out in Auckland, it’s well worth
a day trip.
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