Zealand (Fig. 1.2). Hence the New Zealand land surface
comprises a wide variety of loose or unconsolidated
deposits, such as the thick mantles of tephra beds in central
North Island along with extensive loess, alluvium, landslide
debris, and peat, as well as consolidated rocks, both ‘hard’
and ‘soft’. The ‘soft’ rocks, such as the papa mudstones of
the east coast and Rangitikei regions, are less indurated (not
as hard) and more readily broken down or eroded than the
so-called ‘hard’ rocks.
The topography of New Zealand is characterised by
complexity, ranging from flat plains, rolling and hilly land,
to steep land and alpine environments, as a consequence of
the uplift (and subsidence in places such as the Rangitaiki
Plains in Bay of Plenty) caused by New Zealand’s active
plate tectonic setting. New Zealand comprises about 39%
flat to undulating land ( 7° slopes), 36% rolling to hilly
land (7–25°), and about 25% steep to very steep land (>25°).
The steeper hilly and mountain lands are prone to erosion by
mass movement especially land-sliding. In the eastern North
Island, the uplifted calcareous (soft rock) mudstones are
especially vulnerable to landslide erosion.
Important regional geomorphic features include the
Southern Alps; the hill country of the east coast and lower
North Island; the volcanoes and associated landforms of the
central North Island and Taranaki, along with other intraplate volcanoes scattered throughout New Zealand such as
the Auckland Volcanic Field; the alluvial plains and terraces,
especially the widespread gravelly plains of Hawke’s Bay,
Wairarapa, Canterbury, and Otago; and the glacially gouged
valleys, lakes, and fjords of South Westland and Otago.
In hill and mountainous country, slope and aspect (the
downhill direction of the slope) are important factors
influencing soil processes and site microclimates. The
interactions between slope and aspect, and the resultant
microclimate and vegetation, impact many soil processes,
and thus the soils that form. For example, steeper slopes are
more prone to rainfall runoff and erosion than flatter areas
which may be sites of accumulation of material derived from
further upslope. Slopes with a northerly aspect tend to be
warmer and drier than those with a southerly aspect because
north-facing slopes receive more incoming solar radiation.
Frost and snow may prevail for longer on cooler southerly
slopes. In many regions slopes with a westerly aspect are
more exposed to prevailing north-westerly winds, which
enhance evapotranspiration rates and directly impact on
vegetation establishment and survival, and thus the development of the associated soil.
1.2.2 New Zealand’s Climate
The climate of New Zealand is moderated by the surrounding ocean and the mid-latitudinal location, with the
three main islands extending from 34° to 47° south. Thus
compared with many other regions, New Zealand generally
has a ‘goldilocks’ climate, that is, not too hot, not too cold,
not too wet, and not too dry. However, marked climatic
contrasts and extremes occur over short distances and the
regional variations have a marked influence on the soil
pattern. Mean annual temperature near sea level ranges from
about 15 °C in Northland to 9 °C in Southland (Fig. 1.3)
with cooler temperatures at higher altitudes. Basins in the
Central Otago region, situated inland, and in the rain shadow
of the Southern Alps, and basins in the inland Kaikoura
Range, are the nearest any part of New Zealand gets to a
continental climate. New Zealand’s warmest recorded temperature of 42.4 °C was measured simultaneously, on 7
February 1973, in both Rangiora (Canterbury) and Jordan
(Marlborough). New Zealand’s record coldest temperature
of −25.6 °C was recorded in Ranfurly in Central Otago on
17 July 1903. Nelson, Blenheim, and Whakatane are the
sunniest regions of New Zealand with over 2300 annual
sunshine hours. Rain-prone Westland has about 1800 sunshine hours per year while lowest annual sunshine hours
(about 1700 h) are recorded in Southland and coastal Otago.
The prevailing wind in New Zealand is from the west.
Cold fronts can bring strong southerly winds to the central
part of the country. Much of New Zealand is located within
the ‘roaring forties’, the latitudinal zone of 40° S–50° S that
is particularly prone to strong north-westerly winds, especially in the lower North Island, Marlborough, and Canterbury regions. (During the Last Glaciation, the zone of strong
westerly dominated winds shifted northwards to about 30°
S.) The hot dry nor’wester sucks moisture from plants and
soils, and can readily erode soils that are not protected by
vegetation.
The surrounding oceans, in combination with prevailing
westerly winds, mean that much of New Zealand has a relatively high and consistent rainfall in many regions
(Fig. 1.3). However, the main hill and mountain ranges,
especially the Southern Alps, cause a strong rainfall gradient
across New Zealand from west to east as wet ocean air
coming in from the west is forced up over the mountain
ranges. With uplift, the air cools and the water vapour
condenses releasing rain on the west and in the mountains.
As the air continues down the eastern sides of the ranges it
warms and becomes drier, bringing dry conditions (a rain
shadow effect), especially in Central Otago and the
McKenzie Basin, and also across the eastern areas of coastal
Otago, Canterbury, Wairarapa, Hawke’s Bay, and the Gisborne region.
The Northland, Coromandel, and Bay of Plenty regions
are sometimes subjected to the effects of subtropical cyclones that occasionally track southwards, bringing intense
rainfalls and strong winds. Most regions of New Zealand
receive between 600 and 1600 mm of rain per year, with
1.2 The Environmental (Soil-Forming) Factors …
5
comprises a wide variety of loose or unconsolidated
deposits, such as the thick mantles of tephra beds in central
North Island along with extensive loess, alluvium, landslide
debris, and peat, as well as consolidated rocks, both ‘hard’
and ‘soft’. The ‘soft’ rocks, such as the papa mudstones of
the east coast and Rangitikei regions, are less indurated (not
as hard) and more readily broken down or eroded than the
so-called ‘hard’ rocks.
The topography of New Zealand is characterised by
complexity, ranging from flat plains, rolling and hilly land,
to steep land and alpine environments, as a consequence of
the uplift (and subsidence in places such as the Rangitaiki
Plains in Bay of Plenty) caused by New Zealand’s active
plate tectonic setting. New Zealand comprises about 39%
flat to undulating land ( 7° slopes), 36% rolling to hilly
land (7–25°), and about 25% steep to very steep land (>25°).
The steeper hilly and mountain lands are prone to erosion by
mass movement especially land-sliding. In the eastern North
Island, the uplifted calcareous (soft rock) mudstones are
especially vulnerable to landslide erosion.
Important regional geomorphic features include the
Southern Alps; the hill country of the east coast and lower
North Island; the volcanoes and associated landforms of the
central North Island and Taranaki, along with other intraplate volcanoes scattered throughout New Zealand such as
the Auckland Volcanic Field; the alluvial plains and terraces,
especially the widespread gravelly plains of Hawke’s Bay,
Wairarapa, Canterbury, and Otago; and the glacially gouged
valleys, lakes, and fjords of South Westland and Otago.
In hill and mountainous country, slope and aspect (the
downhill direction of the slope) are important factors
influencing soil processes and site microclimates. The
interactions between slope and aspect, and the resultant
microclimate and vegetation, impact many soil processes,
and thus the soils that form. For example, steeper slopes are
more prone to rainfall runoff and erosion than flatter areas
which may be sites of accumulation of material derived from
further upslope. Slopes with a northerly aspect tend to be
warmer and drier than those with a southerly aspect because
north-facing slopes receive more incoming solar radiation.
Frost and snow may prevail for longer on cooler southerly
slopes. In many regions slopes with a westerly aspect are
more exposed to prevailing north-westerly winds, which
enhance evapotranspiration rates and directly impact on
vegetation establishment and survival, and thus the development of the associated soil.
1.2.2 New Zealand’s Climate
The climate of New Zealand is moderated by the surrounding ocean and the mid-latitudinal location, with the
three main islands extending from 34° to 47° south. Thus
compared with many other regions, New Zealand generally
has a ‘goldilocks’ climate, that is, not too hot, not too cold,
not too wet, and not too dry. However, marked climatic
contrasts and extremes occur over short distances and the
regional variations have a marked influence on the soil
pattern. Mean annual temperature near sea level ranges from
about 15 °C in Northland to 9 °C in Southland (Fig. 1.3)
with cooler temperatures at higher altitudes. Basins in the
Central Otago region, situated inland, and in the rain shadow
of the Southern Alps, and basins in the inland Kaikoura
Range, are the nearest any part of New Zealand gets to a
continental climate. New Zealand’s warmest recorded temperature of 42.4 °C was measured simultaneously, on 7
February 1973, in both Rangiora (Canterbury) and Jordan
(Marlborough). New Zealand’s record coldest temperature
of −25.6 °C was recorded in Ranfurly in Central Otago on
17 July 1903. Nelson, Blenheim, and Whakatane are the
sunniest regions of New Zealand with over 2300 annual
sunshine hours. Rain-prone Westland has about 1800 sunshine hours per year while lowest annual sunshine hours
(about 1700 h) are recorded in Southland and coastal Otago.
The prevailing wind in New Zealand is from the west.
Cold fronts can bring strong southerly winds to the central
part of the country. Much of New Zealand is located within
the ‘roaring forties’, the latitudinal zone of 40° S–50° S that
is particularly prone to strong north-westerly winds, especially in the lower North Island, Marlborough, and Canterbury regions. (During the Last Glaciation, the zone of strong
westerly dominated winds shifted northwards to about 30°
S.) The hot dry nor’wester sucks moisture from plants and
soils, and can readily erode soils that are not protected by
vegetation.
The surrounding oceans, in combination with prevailing
westerly winds, mean that much of New Zealand has a relatively high and consistent rainfall in many regions
(Fig. 1.3). However, the main hill and mountain ranges,
especially the Southern Alps, cause a strong rainfall gradient
across New Zealand from west to east as wet ocean air
coming in from the west is forced up over the mountain
ranges. With uplift, the air cools and the water vapour
condenses releasing rain on the west and in the mountains.
As the air continues down the eastern sides of the ranges it
warms and becomes drier, bringing dry conditions (a rain
shadow effect), especially in Central Otago and the
McKenzie Basin, and also across the eastern areas of coastal
Otago, Canterbury, Wairarapa, Hawke’s Bay, and the Gisborne region.
The Northland, Coromandel, and Bay of Plenty regions
are sometimes subjected to the effects of subtropical cyclones that occasionally track southwards, bringing intense
rainfalls and strong winds. Most regions of New Zealand
receive between 600 and 1600 mm of rain per year, with
1.2 The Environmental (Soil-Forming) Factors …
5