Physical Environment of the West Coast Coastal Marine Area
2.3 Physical Features and Processes Influencing the Marine and Coastal
Environment
2.3.1 Oceanic Currents and Freshwater InflowsThe movement of oceanic water masses has a large effect on the ecology of the West Coast’s marine and coastal environment. Key oceanographic features affecting the West Coast are shown in the map (Figure 2.3), and the italic numerals in brackets in the following discussion refer to the numbered features in the figure.
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Figure 2.3 Oceonography and Current of the West Coast (Source: Neale & Nelson 1998 and NIWA base map) Numbers refer to features described in the text, as follows: 1 = Subtropical Convergence 2 = Tasman Current 3 = Antarctic Circumpolar Current 4 = West Coast shelf surface currents 5 = Westland Current 6 = Southland Current 7 = Wind-generated oscillations in Cook Strait 8 = West Coast inshore zone 9 = Upwelling (not depicted) 1 0 = Freshwater inflows, = “Squirts” |
A regional forum (the West Coast Marine Protection Forum) has been established with people from the West Coast community and other stakeholders, to make recommendations on areas for marine protection. This is so that sites and protection measures can be identified by the same communities that will be using and enjoying the marine protected areas.
The West Coast lies near the southern limit of the subtropical oceanic
water mass, to the north of the Subtropical Convergence (1). Ocean surface
currents (2,3), driven primarily by wind systems, flow on either side of
this convergence. In the north of the West Coast, the Tasman Current (2)
is considered to be a broad, slow flow of warm northern water derived from
the East Australian Current that approaches the West Coast from across the
Tasman Sea10. To the south of the Subtropical Convergence,
the strong westerly winds of the “Roaring Forties” drive a cool
westerly ocean current (a component of the Antarctic Circumpolar Current
(3) that lies north of the Subantarctic Front), but this current does not
have a direct impact on the West Coast.
The New Zealand continental shelf and coastline act as a barrier to the
ocean currents, which are forced to flow around the landmass as surface
currents (4). On the West Coast, the current is fed mostly by the warmer
water derived from the Tasman Current. The direction of the surface current
along the coast is determined primarily by local winds (which prevail from
the south-west) and “coastal trapped waves” (see below). As
a result, the West Coast is washed by a northward-moving current (the Westland
Current (5)) on some occasions and a southward-moving current (the beginnings
of the Southland Current (6)) on others11. Over
most of the region, the mean flow moves weakly northward towards Taranaki
and Cook Strait12.
A pattern of very long wave formations runs along the West Coast, at least
as far south as Milford. These waves are generated by the combined effects
of the wind component parallel to the West Coast and the slow wind-generated
oscillation of water (7) in the northern Cook Strait/ Taranaki Bight region13.
Because these waves are often thousands of kilometres long and only a few
centimetres high, they are virtually imperceptible but can be measured by
sensitive tide gauges. The Earth’s rotation causes these “coastal-trapped
waves” to move southward down the West Coast, their speed of travel
modified by the slope of the sea bed. These waves in turn cause the West
Coast’s coastal surface current to speed up or slow down (and regularly
to change direction) every few days, much as normal sea waves will cause
a floating stick to rock back and forth on the surface.
The Southland Current (6) begins in the vicinity of Westland/ northern Fiordland14,
forming from southern subtropical water. It flows southward and around the
bottom of the South Island, and continues northward along the South Island’s
east coast as far as Canterbury/Marlborough, becoming less saline and cooler
through incorporation of subantarctic water. While the Southland Current
is relatively warm for those latitudes, the South Island east coast tends
to be cooler than the west coast, and this has a great effect on the comparative
ecology of the two coasts.
The water that probably most affects the ecology of the West Coast’s
shores is a distinct inshore zone (8) approximately 30 kilometres wide,
extending from the coastline out to depths of 100 to 200 metres. It comprises
relatively cool seawater with a lowered salinity15.
However, the subtropical water in this zone is impacted by both coastal
upwelling and river inflow. Coastal upwelling (9) occurs when cool water
rises to the surface from depths of up to 200 metres16,
and this can occur right along the West Coast under westerly or south-westerly
winds17.
The inflow of fresh water (10) from the West Coast’s many large rivers
is another key physical factor affecting the marine environment. The West
Coast of the South Island is one of the wettest regions in New Zealand,
with in excess of 2400 mm of rain annually (and annual precipitation as
high as an extraordinary 17,000 mm measured in parts of the mountainous
hinterland). Consequently, many major rivers drain out into the West Coast
continental shelf18 and their fresh water mixes
with the upwelling water to produce a shallow surface layer that readily
exchanges heat with the atmosphere, further decreasing the temperature of
the inshore zone19. The sediment content of the
inshore zone water is high compared to the oceanic waters because of two
physical processes: the load of suspended sediment arriving from the rivers
(particularly during floods), and the disturbance of sea bottom sediments
by waves as they approach shallow water. The marked hydrographical differences
between the inshore zone and the open sea inhibit mixing of these waters,
and the visual boundary between the two water masses is usually quite clear.
Another physical process of importance in exchanging coastal and oceanic
water across the continental shelf, and to the biological productivity of
the shelf, is water escaping the inshore zone in the form of transient plumes
or “squirts” (11) 20. These shallow
surface layers of low salinity water extend up to 75 kilometres seawards
and are associated with specific topographic features (e.g. Hokitika Canyon).
The plumes stabilise the surface layer, preventing the mixing of surface
phytoplankton to deeper levels in the water column21.
The water within the plumes eventually merges with the more saline seawater
offshore.
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| The inflow of freshwater (and suspended sediment) is a key physical factor affecting the marine environment. Waita River, South Westland. Photo: T. Hume, NIWA |
The windward shores of the West Coast are more exposed than those of eastern coasts, leading to a greater inter-tidal zone. Photo: D Neale, DOC |
2.3.2 Tides
Tides have a major role in determining the location of the zones of plant
and animal life on the shore. Tides vary in their physical character – their daily pattern, their energy, and the levels they reach on the shore.
The West Coast, like the rest of New Zealand, has a dominantly twice-daily
tide of a 12.4 hour cycle22. Due to the anticlockwise
movement of the tidal wave around the New Zealand coast, the West Coast’s
tides tend to become progressively later towards the south, with Jackson
Bay tides lagging those at Karamea by about 75 minutes. Spring tides at
Westport rise and fall by up to 3.7 metres, while the difference between
high and low water at neap tides is as little as 1.2 metres23.
The tidal range right along the West Coast is broadly similar to this, but
a NIWA model (Figure 2.4) indicates that the tidal range is significantly
greater in the north than in the south.
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| Figure 2.4 Tidal range of the West Coast (compared with the rest of NZ). Source: T. Hume, NIWA |
Figure 2.5 Significant wave height. Source: T.Hume, NIWA |
2.3.3 Exposure to Waves and Weather
Exposure to the weather and the sea has an important effect on the ecology
of rocky shores, and the West Coast is extremely dynamic in this regard.
Since New Zealand lies across a belt dominated by westerly winds, the West
Coast is on a windward shore. This causes wave conditions to be generally
rougher than on the eastern coasts and weather conditions to be generally
more humid. Such conditions typically increase the vertical widths of intertidal
zones, since organisms can satisfy their water requirements further up the
shore than they could on dry, sheltered shores.
Daily visual observations made at Punakaiki over ten years, from 1984 to
1994, give an indication of the sea wave climate along the shoreline along
the entire West Coast24. There, high energy wave
events (wave heights at the shore greater than 1.5 m) occur 36% of the time,
but waves seldom exceed 3.0m height. About twice as many high energy wave
events arrive from the south than from the north. A NIWA model (Figure 2.5)25shows
that the wave exposure along the coast is broadly similar along most of
the West Coast, ranging between 1.5 and 2.0 metres significant wave height,
but increasing slightly towards the south.
2.3.4 Surface Temperature
Inshore surface water temperature means in the summer (winter) range from
17.75° C (12.5° C) in the north to 16.25° C (12°C) in the
south26. Bottom water temperatures over the shelf
are warmer in winter than summer by about 1°C, probably reflecting increased
influence of the East Australian Current during winter27.
Mean sea surface temperature (SST) in February is shown in Figure 2.6. Note
the cooler nearshore water off the West Coast, most likely caused by the
inflow of river water and the northward movement of the Westland Current.
Figure 2.6
Average February (summer) sea surface temperatures (SST) in New Zealand waters.
Source: NIWA
2.3.5 Seabed Topography
The topography of the seabed off the West Coast is complex28.
In the north of the West Coast, the seabed is dominated by the continental
shelf that slopes gradually out to the Challenger Plateau which extends
well beyond the territorial limit. South from about Hokitika, the shelf
narrows considerably and becomes dissected by a series of submarine canyons
that extend to within the coastal marine area. The continental slope that
marks the edge of the shelf comes in closer to the coastline in the southern
parts of the region, forming the margins of the Tasman Basin lying to the
south of the Challenger Plateau. The extent of the continental shelf, the
continental slope, and the position of the main underwater canyons off the
West Coast are shown in the NIWA map (Figure 2.7). The boundary between
the continental shelf and the top of the continental slope is around the
200 m depth mark (see also depth classes in section 2.4.1).
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(Explanation: This figure shows the NIWA survey tracks concentrating on the two canyons, overlaid on the previously recorded (and less accurate) bathymetric contour lines.) |
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| Figure 2.7 Undersea landfrom features of the West Coast |
NIWA has recently completed multibeam swath mapping and sediment coring
in the vicinity of the Hokitika and Cook Canyons off the West Coast29.
This work was generally done for the purpose of assessing New Zealand’s
paleoclimatic conditions (climatic and tectonic conditions throughout geological
time), and is based on West Coast sediment dispersal from the Southern Alps
to the Tasman Basin. Some initial results of this work are presented in
Figure 2.8, and these very accurate and detailed charts of the seabed show
intricate submarine channel networks. This project has shown that the two
canyons are active features of the continental shelf, draining the longshore
drift of shelf sediments into deeper waters. Seabed mapping of other parts
of the West Coast coastal marine area is generally less detailed, and mostly
shown in the bathymetric charts produced by the Hydrographic Office and
New Zealand Oceanographic Institute (NZOI) dating back to the 1970s and
80s.
2.3.6 Geology and Geomorphology
The geology and landforms of a region create the basic physical structure
on which its habitats and ecosystems are to be found. They also influence
the natural physical processes that affect the marine and coastal environment.
The West Coast contains a wide variety of geological formations, ranging
from some of New Zealand’s most ancient pre-Cambrian rocks to more
recent glacial formations and Holocene beach deposits30.
This section summarises the region’s geology and landforms, especially
as they relate to the coastal and marine environment.
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Softer, younger (Tertiary age) sedimentary rocks are a feature of the Punakaiki coastline. Photo: P. Ryan, DOC |
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| Typical ancient basement rocks are exposed in the Charleston locality Photo: D Neale, DOC |
Basement Geology – the oldest rocks
The basement rocks of the West Coast were formed from ocean sediments of
the ancient Gondwana ‘supercontinent’ between 300 million and
540 million years ago.31 Basement rocks appear
in coastal exposures on parts of the Kahurangi and Foulwind-Paparoa coasts,
along with metamorphic rocks like gneiss.
Sedimentary rocks – ‘Tertiary’ geology
In many places the oldest ‘basement’ rocks have been overlain
by younger (less than 65 million years old) sedimentary rocks (which are
usually softer and often calcareous). The coast from Kahurangi Point to
Punakaiki has several areas of limestone shoreline, with coastal ‘karst’
features (of soluble rock types like limestone), the most spectacular being
the ‘pancake rocks’ and blowholes at Dolomite Point near Punakaiki.
The coast between Barrytown and Greymouth presents a geologically informative
time-sequence of Tertiary-age sedimentary rock types. Included in this sequence
are softer mudstone and sandstone shorelines, features which are also present
in parts of South Westland.
Further out at sea, the rocks of the continental shelf seabed are mostly
Cretaceous-Tertiary sedimentary rocks32, but these
are mainly covered by a blanket of recent sediments derived from the West
Coast river discharges. In a study of the West Coast’s continental
shelf north of the Waiau (Waiho) River, Norris (1978) identified a complex
variety of fault lines, shorelines, channels and glacial features that are
almost all buried beneath the mantle of present-day shelf sediments.
Tectonic Uplift
The active uplifting of the West Coast has played a large part in shaping
the physical structure of the coastal and marine environment – a process
which continues today. Many large rivers flowing from the mountainous hinterland
carry down massive amounts of sediment from the naturally-eroding uplifted
mountains, forming long beaches of sand and gravel, while the finer mud
and silt-sized particles are swept out to settle as fine sediments on the
sea floor. In places, tectonic uplift of the landscape has left steep bluffs
leading down to rocky shorelines.
As well as the obvious signs of uplift on the land, there are a series of
ancient fault lines and other formations on the seabed right along the West
Coast33. These have helped to shape the structure
of the seabed, but are now mostly smothered by the fine sediments of the
continental shelf (see above). These features are most easily detected by
seismic and coring surveys that reach below the seabed surface.
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Below: Looking south across the mouth of the Cook/Weheka River. The lateral moraines straddling each side of the path of the former Cook Glacier have subsequently been truncated by wave erosion, leaving bluffs and boulder shores at Otorokua Point (foreground) and Cook Bluff (middle distance). Photo: T. Hume, NIWA.  |
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| Above: Plate movement around the Alpine Fault has played a major role in shaping the physical structure of the coastal and marine environment. Looking north-east along the faultline in the Jackson Valley, towards Jackson Bay/Okahu and the Haast coastline in the distance. Photo: D.L. Homer, GNS |
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Ice Age Glaciations
Historic glaciation has had a major effect on the geomorphology of the West
Coast shoreline. During the last (Otiran) glaciation (10 000+ years ago),
glaciers extended out beyond most of the present coastline from Hokitika
south to Fiordland (though the sea level at that time was 100 to 200 metres
lower than present)34. Rock deposits of glacial
origin (moraines) show that glaciers once extended well beyond the present
shoreline, especially in the southern parts of the West Coast and in Fiordland.
Coastal landforms such as the Cascade Plateau and all of the moraine headlands
between Hokitika and Paringa are the remains of deposits laid by these glaciers.
Since that time, sequences of coastal lowland outwash terraces and sandplains
have been formed from sediments brought down by the rivers. Today, the coast
between Hokitika and Paringa consists of many long beaches at the mouths
of rivers with glaciated catchments. These beach and dune deposits are intersected
by lateral moraines that have been truncated into steep bluffs and boulder
shores by the eroding sea (see photo bottom left). South of Paringa, the
Haast Glacier Tongue 14,000 years ago extended out around 10 km beyond the
present-day coastline between Ship Creek and Jackson Head; but today these
catchments of the Haast, Waiatoto and Arawhata contain only remnant glaciers
in their headwaters.
Beyond the coast, old shorelines, channels, moraines and other glacial features
buried by silt have been found to occur at several locations, such as off
the Waitaha, Whataroa and Waiau (Waiho) Rivers35.
These date back to the Pleistocene ‘Ice Age’ times when the
sea level was up to 200 metres lower than it is today. Offshore beds of
old river gravels are also mostly covered by silt, but are sometimes exposed
in a few places such as indicated by a 1983 study of the ‘Harvester
Prospect’ area near the head of the Hokitika Canyon36.
Sedimentation and River Discharges
Sedimentation – the movements of organic material, mud, silt, sand,
gravel and boulders – affects the West Coast’s marine environment
in many ways. The effects of sediments depend on a variety of factors: the
size of the sediment particles (texture), the nature of the seabed, and
the ability of currents to move them. Consider the mobility and effects
of the following sediment classes (in diminishing particle size):
(a) boulders mostly enter the coastal marine area by falling from eroding
coastal bluffs, forming ‘ramps’ that create fairly stable surfaces
and broken terrain on the shore.
(b) cobbles, gravels and coarse sands mostly come from river-borne sediments
or from the erosion of deposits left behind on the seabed or shoreline during
(or soon after) the ice ages. They form beaches, river beds and seabeds
that are generally less suitable for burrowing animals, and the scouring
they cause with wave action can greatly affect the survival of bottom-dwelling
plants and animals.
(c) fine sands tend to occur at the mouths of some estuaries, and a little
offshore beyond the direct impact of waves; they can similarly contribute
to sand scouring, but provide a generally more suitable habitat for the
likes of surf clams and other seabed species.
(d) very fine silts and muds settle in low energy areas like the upper reaches
of estuaries or the outer continental shelf. They are a habitat for some
species of shellfish, worms, crabs and saltmarsh plants. The prevalence
of these very fine sediments in West Coast waters also has a major effect
on water clarity, most clearly seen during flood and storm events when the
inshore waters of the coastal marine area become laden with suspended silt,
reducing underwater visibility and light penetration.
When such sediments reach the dynamic coastal system, they are moved around
and broken down to smaller sizes by the abrasive action of waves and other
energy sources.
| The size and shape of coastal and marine sediment varies widely: | |
 Boulders Photo: D. Neale, DOC |
 Cobbles Photo: T. Hume, NIWA |
 Gravel Photo: L.F. Molloy. |
 Sand and Gravel Photo: T. Hume, NIWA |
Timber and other plant materials are washed from forested land into the sea on the West Coast in considerable volumes. While wood is not known to be the dominant component of the substrate at any location, it is present as driftwood on intertidal shores and at the sea surface, and as sunken logs on the seabed of the shelf37 and in deeper waters38.
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Driftwood on Hunts Beaach, typical of many intertidal shores. Photo: T. Hume, NIWA |
Suspended sediment discharge models for river catchments indicate that the major rivers of the central and southern West Coast have some of the highest sediment loads in New Zealand (see Table 2.1 below)39. South Westland rivers originate in schist rock catchments and transport a higher proportion of sandy sediment and less gravel to the coast40. The high sediment loads contribute to low seawater clarity and the high amounts of mud, sand, gravel and boulders accumulating on the beaches and continental shelf.
Table 2.1
Suspended sediment loads of West Coast rivers (in million tonnes per year).
Derived from Hicks and Shankar 2003.)
| River | Mt/yr |
| Karamea | 0.1 5 |
| Mokihinui | 0.29 |
| Buller | 2.70 |
| Grey/Mawheranui | 2. 0 |
| All other rivers between Grey R & Farewell Spit | 1.26 |
| Total northern West Coast | 6.50 |
| Taramakau | 2.20 |
| Hokitika | 6.20 |
| Waitaha | 2.80 |
| Whataroa | 4.80 |
| Waiau (Waiho) | 3.40 |
| Haast | 5.90 |
| Arawhata | 7.20 |
| All other rivers between Taramakau R & Big Bay | 29.50 |
| Total southern West Coast | 62.00 |
| Total West Coast | 68.50 |
The surface sediments on the West Coast shelf are mostly derived from these
recent river sediments. In the northern parts of the shelf there is a simple
correlation of sediment texture with depth; that is, the seabed sediments
become finer as one goes from the shoreline to the outer shelf. Considerable
attention has been focused on beach sands and shelf sediments because of
their economic potential, such as the presence of gold, ilmenite and other
heavy minerals.41
Although sediment thickness on the continental shelf may reach 300 metres
or more in some places, the most typical situation is of a lens-shaped prism
of sediment about 20 to 70 metres thick lying on older faulted and folded
rocks. The lens of sediment is typically thickest in water depths of about
50-60 metres. It thins to about 20-40 metres thick both toward shore and
toward the shelf edge.42 (see Figure 2.9).
Figure 2.9
Example of a ‘typical’ sediment profile off the West Coast, showing the ‘lens’ of recent sediment beds covering older glacial and marine sediments and the underlying ‘basement’ rocks.
Source: adapted from a profile off Greymouth in Norris 1978.
Geopreservation Inventory
The New Zealand Geopreservation Inventory43 “aims
to list the best examples of the wide diversity of natural physical features
and processes that together characterise each part of New Zealand and document
its long and complex geological history, the formation of its landforms
and evolution of its unique biota.” The inventory gives a rating for
each site according to its geological importance for scientific, educational
or aesthetic values, and its vulnerability to human activity. The inventory
lists a number of West Coast coastal features as being of international,
national or regional importance. Two coastal locations of international
significance are listed in the inventory (Gillespies Beach, the type locality
for the mineral, huttonite and the fossil deposits at Perpendicular Point).
Geopreservation Inventory sites that extend into or near the coastal marine
area are shown in the sections of Chapter 5.
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Fossil Oysters at Perpendicular Point. Photo: DOC |
2.3.7 Coastal Margins and River Catchments
The hinterlands (coastal margins and catchments) of the coastal and marine
area are beyond the immediate scope of the West Coast Marine Protection
Forum. Nevertheless, the nature of the hinterland has a considerable influence
over the marine environment. The major landscape feature of the hinterland
is the Southern Alps/Ka Tiritiri o te Moana and their associated ranges,
from which a large number of rivers flow out to the coast. These rivers
carry large volumes of water and sediment to the coast, providing important
physical and ecological linkages between their catchments and the sea. Smaller
rivers and streams arise in lowland areas and coastal ranges, while the
coastline itself can be bounded by a variety of landforms, like sand plains,
coastal terraces, headlands, coastal wetlands, and dune systems.
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Left: The coastline in the northern part of the West Coast has diverse geology and no history of glaciation. Te Miko locality north of Punakaiki. Photo: D. Neale, DOC.
Centre: The coastline of the central part of the West Coast is influenced by past and present-day glacial activity and has murky seawatercaused by high silt discharges from rivers; tidal estuaries and lagoons are also prominent features. Looking south across the mouth of the
Whataroa River to Okarito Lagoon and the Southern Alps/Ka Tiritiri o te Moana. Photo: T. Hume, NIWA.
Left: In the southern part of the West Coast, the sea is often clearer close inshore and islands and stacks are less affected by sand scour. Looking south-east across Jackson Head to Jackson Bay/Okahu. Photo: D.L. Homer, GNS.
2.3.8 Variation in Physical Character from North to South
Research44 indicates that the physical character
of the West Coast marine and coastal environment changes from north to south,
especially in terms of its geological history, topography, and rock types.
In the north, from Kahurangi Point to Point Elizabeth, there is diverse
geology but no glacial history. The shores consist of both bedrock and coastal
sediments that enclose tidal flat estuaries on some of the coastal plains.
Beyond the surf zone, the continental shelf is relatively flat and shallow,
and coastal currents are mostly towards the north (commonly known as the ‘Westland Current’).
In the central area south to about Heretaniwha Point, there are more biologically
rich and relatively unmodified tidal wetlands and estuaries. Here, the shore
has been, and still is, very much dominated by glacial activity and high
discharge of sediments from the rivers. In common with the northern area,
this central area is dominated by species adapted to the heavy action of
the rough wave conditions, murky silt-laden water and moving sand. The continental
shelf in this central area is dissected by two major submarine canyons –
the Cook and the Hokitika – and coastal current directions vary between
northward- and southward-moving.
Further south to Awarua Point, there is a history of glaciation, but the
sediments now reaching the shore are predominantly from non-glaciated catchments.
Consequently, ‘glacial flour’ has a lesser influence and the
sea is often quite clear close inshore. Large river mouths are common in
the south and are often associated with slower-flowing tidal lagoons. Several
offshore islands, rock stacks and reefs provide habitats less affected by
sand scour. Further offshore, the continental shelf is much narrower than
further north, and it is heavily dissected by five main submarine canyons
– the Moeraki, Haast, Arawata, Jackson and Cascade. Coastal currents
are mostly towards the south, forming the beginnings of the ‘Southland
Current’.
10 Heath 1985
11 Stanton 1976
12 Heath 1982
13 Cahill et al. 1991
14 Heath 1973
15 Moore & Murdoch 1993
16 Shirtcliffe et al. 1990
17 Heath & Ridgway 1985
18 Heath 1982
19 Moore & Murdoch 1993
20 Moore & Murdoch 1993; Vincent et al. 1991
21 Moore & Murdoch 1993
22 Stevens & Chiswell 2007
23 OceanFun 2006
24 Jones 1994
25 Reproduced with permission from T Hume, NIWA
26 Dept of Conservation 2004
27 Booth et al 2005
28 e.g. see CANZ 1996, Carter 1981, Norris 1979, Norris & van der Linden
1972
29 P Barnes pers comm 2006, publication pending
30 e.g. see geological maps and reports such as Suggate & Waite 1999,
Rattenbury et al 1998 and Nathan 1996
31 Morton 2004
32 Carter 1975
33 Norris 1978
34 Soons & Selby 1992
35 Norris 1978
36 Price 1983b
37 I McKenzie pers comm 2006
38 Arnold 2003
39 Hicks & Shankar 2003
40 Goff et al 2003, p167
41 e.g. Carter 1975, Price 1983a, b
42 Norris 1978
43 Hayward & Kenny 1999
44 e.g. Roberts et al 2005, Dept of Conservation 2004, Neale & Nelson
1998, Shears in prep, Grange 1990, RNZN (various), Carter 1981, Eade 1972,
Norris 1979, Norris & van der Linden 1972,