terraces at the bottom of Lake Rotomahana) were formed of
silica sinter. However, as is evident in the photo of Pohutu
(Fig. 13.5), sulphur may also be deposited and accumulate.
Where the yellow sulphur deposit interacts with water, sulphuric acid will form, imparting a very low pH. In contrast,
areas of boiling mud are defined as acid-steam features. Here
the pH is likely to be extremely low and the acidic, boiling,
mud provides one of the most hostile environments for most
living organisms.
Sandy Raw Soils occur predominantly on beaches and
coastal sand dunes. Ninety-mile beach in Northland and
Farewell Spit at the north-western tip of the South Island are
two outstanding areas that have formed from sand being
carried along the west coast of New Zealand. The Manawatu
sand country, which extends from about Levin northward to
the outlet of the Rangitikei River, is the largest dune field in
New Zealand.
The prevailing strong westerly winds in the Manawatu
have carried sand inland, forming a distinct series of dunes
ranging in age from active dunes to some over 5000 years
old. Raw Soils occur on the current beaches and active dunes
adjacent to the coast. Pockets of Raw Soils also occur further
inland where dunes have been reactivated and the sand has
been eroded and redeposited. The rate of weathering and soil
formation has been widely studied in sand in the Manawatu
environment with pioneering work by Des Cowie. Raw Soils
are associated with the Waiterere dune phase which are
dunes formed in the last 150 years or so. Recent Soils (with
A horizons at least 5 cm thick) are recognised on the Motuiti
dune phase which has been dated at about 500–1000 years
old. In the Foxton dune phase (1600–6500 years old) the
Recent Soils have yellow-brown B horizons in addition to
topsoils.
Within the Manawatu sand country there is also a clear
soil-landscape pattern between the droughty dunes and the
wetland areas where drainage is cut off by dunes, with Sandy
Raw Soils on the youngest dunes and Sandy Gley Raw Soils
in the adjacent low-lying areas of high water table between
the dunes (Fig. 13.6). Near the coast, in the low-lying
coastal wetlands the water table is controlled by the tide,
rising and falling over the course of a day.
Fluvial Raw Soils occur on river flood plains (Fig. 13.1)
where the sediment deposited in flood events is deep
enough, and/or frequent enough, to prevent a Recent Soil
from developing. Thus the Fluvial Raw Soils tend to occur
in thin strips on river banks, river levees, and riparian margins. They are associated with Recent Soils on slightly
higher ground where flood deposits are thinner, and with
Gley Raw Soils where water tables are high. The largest
areas of Fluvial Raw Soils are associated with rivers that
flow from the erosion-prone mudstone hill country in the
Rangitikei/Whanganui area and on the east coast of the
North Island from the Wairarapa northward to East Cape.
Such rivers periodically carry extremely high sediment loads
of material eroded from the mudstone hills, and deposit it on
the river flood plains during storm/flood events. Murray
Hicks and others calculated the suspended sediment yields
from the East Cape area (from East Cape to Mahia Peninsula) to be *69 Mt/yr, with the two main rivers, Waiapu
and Waipaoa, delivering 35 Mt/yr and 15 Mt/yr, respectively. Their combined yield represents 42% of the yield
from the North Island and 24% of the total yield to the entire
New Zealand coast. The yield from the southwest coast of
North Island (taking in the Rangitikei/Whanganui hinterland) is also relatively high at *12 Mt/yr.
Gley Raw Soils often occur in association with Fluvial
Raw Soils in the lower lying areas on river flood plains. The
more unusual, but increasingly recognised, Gley Raw Soils
are those of tidal mud flats where the material was deposited
in water and has never dried out and thus, has never been
exposed to oxygen (Fig. 13.7). Such sites often comprise
Fluid Gley Raw Soils which have low weight bearing
capacity so that a person may sink into the ‘mud’ if
attempting to walk across the area. The Fluid Gley Raw
Soils merge into the sea/estuary floor on their seaward
boundary (i.e. non-soils), and often into Sandy or Saline
Gley Raw Soils on the margins where the soil material has
built to a depth above sea level on the coastal margin.
Tephric Raw Soils occur in unconsolidated deposits of
explosive volcanic origin, collectively termed tephra, or in
reworked (secondary) tephric material. The tephra materials
include ash, lapilli, blocks and bombs, and pumice and
scoria (cinders), all of which originated via explosive
activity that generated (most commonly) fall deposits or
ground-hugging pyroclastic flow deposits. Hence Tephric
Raw Soils are prominent on very young, andesitic,
tephra-mantled surfaces or on older tephra deposits freshly
exhumed by recent erosion. Tephric Raw Soils are found:
• on Mounts Ruapehu, Tongariro, and Ngauruhoe in central North Island (Fig. 13.8);
• on exposed andesitic tephras around the steep peak of
Taranaki Maunga;
• on the summit and shoulder slopes of Mt Tarawera
(comprising a combination mainly of basaltic scoria
erupted on 10 June 1886 mixed with re-erupted clasts
of *1314 AD Kaharoa eruptives);
• on andesitic ash and other materials on Whakaari (White
Island); and
• on some of the steeper slopes of the 600-year-old basaltic
scoria cones near the summit of Rangitoto Island (amidst
sparse Tephric Recent Soils).
13.3 Soil-Landscape Relationships
205
silica sinter. However, as is evident in the photo of Pohutu
(Fig. 13.5), sulphur may also be deposited and accumulate.
Where the yellow sulphur deposit interacts with water, sulphuric acid will form, imparting a very low pH. In contrast,
areas of boiling mud are defined as acid-steam features. Here
the pH is likely to be extremely low and the acidic, boiling,
mud provides one of the most hostile environments for most
living organisms.
Sandy Raw Soils occur predominantly on beaches and
coastal sand dunes. Ninety-mile beach in Northland and
Farewell Spit at the north-western tip of the South Island are
two outstanding areas that have formed from sand being
carried along the west coast of New Zealand. The Manawatu
sand country, which extends from about Levin northward to
the outlet of the Rangitikei River, is the largest dune field in
New Zealand.
The prevailing strong westerly winds in the Manawatu
have carried sand inland, forming a distinct series of dunes
ranging in age from active dunes to some over 5000 years
old. Raw Soils occur on the current beaches and active dunes
adjacent to the coast. Pockets of Raw Soils also occur further
inland where dunes have been reactivated and the sand has
been eroded and redeposited. The rate of weathering and soil
formation has been widely studied in sand in the Manawatu
environment with pioneering work by Des Cowie. Raw Soils
are associated with the Waiterere dune phase which are
dunes formed in the last 150 years or so. Recent Soils (with
A horizons at least 5 cm thick) are recognised on the Motuiti
dune phase which has been dated at about 500–1000 years
old. In the Foxton dune phase (1600–6500 years old) the
Recent Soils have yellow-brown B horizons in addition to
topsoils.
Within the Manawatu sand country there is also a clear
soil-landscape pattern between the droughty dunes and the
wetland areas where drainage is cut off by dunes, with Sandy
Raw Soils on the youngest dunes and Sandy Gley Raw Soils
in the adjacent low-lying areas of high water table between
the dunes (Fig. 13.6). Near the coast, in the low-lying
coastal wetlands the water table is controlled by the tide,
rising and falling over the course of a day.
Fluvial Raw Soils occur on river flood plains (Fig. 13.1)
where the sediment deposited in flood events is deep
enough, and/or frequent enough, to prevent a Recent Soil
from developing. Thus the Fluvial Raw Soils tend to occur
in thin strips on river banks, river levees, and riparian margins. They are associated with Recent Soils on slightly
higher ground where flood deposits are thinner, and with
Gley Raw Soils where water tables are high. The largest
areas of Fluvial Raw Soils are associated with rivers that
flow from the erosion-prone mudstone hill country in the
Rangitikei/Whanganui area and on the east coast of the
North Island from the Wairarapa northward to East Cape.
Such rivers periodically carry extremely high sediment loads
of material eroded from the mudstone hills, and deposit it on
the river flood plains during storm/flood events. Murray
Hicks and others calculated the suspended sediment yields
from the East Cape area (from East Cape to Mahia Peninsula) to be *69 Mt/yr, with the two main rivers, Waiapu
and Waipaoa, delivering 35 Mt/yr and 15 Mt/yr, respectively. Their combined yield represents 42% of the yield
from the North Island and 24% of the total yield to the entire
New Zealand coast. The yield from the southwest coast of
North Island (taking in the Rangitikei/Whanganui hinterland) is also relatively high at *12 Mt/yr.
Gley Raw Soils often occur in association with Fluvial
Raw Soils in the lower lying areas on river flood plains. The
more unusual, but increasingly recognised, Gley Raw Soils
are those of tidal mud flats where the material was deposited
in water and has never dried out and thus, has never been
exposed to oxygen (Fig. 13.7). Such sites often comprise
Fluid Gley Raw Soils which have low weight bearing
capacity so that a person may sink into the ‘mud’ if
attempting to walk across the area. The Fluid Gley Raw
Soils merge into the sea/estuary floor on their seaward
boundary (i.e. non-soils), and often into Sandy or Saline
Gley Raw Soils on the margins where the soil material has
built to a depth above sea level on the coastal margin.
Tephric Raw Soils occur in unconsolidated deposits of
explosive volcanic origin, collectively termed tephra, or in
reworked (secondary) tephric material. The tephra materials
include ash, lapilli, blocks and bombs, and pumice and
scoria (cinders), all of which originated via explosive
activity that generated (most commonly) fall deposits or
ground-hugging pyroclastic flow deposits. Hence Tephric
Raw Soils are prominent on very young, andesitic,
tephra-mantled surfaces or on older tephra deposits freshly
exhumed by recent erosion. Tephric Raw Soils are found:
• on Mounts Ruapehu, Tongariro, and Ngauruhoe in central North Island (Fig. 13.8);
• on exposed andesitic tephras around the steep peak of
Taranaki Maunga;
• on the summit and shoulder slopes of Mt Tarawera
(comprising a combination mainly of basaltic scoria
erupted on 10 June 1886 mixed with re-erupted clasts
of *1314 AD Kaharoa eruptives);
• on andesitic ash and other materials on Whakaari (White
Island); and
• on some of the steeper slopes of the 600-year-old basaltic
scoria cones near the summit of Rangitoto Island (amidst
sparse Tephric Recent Soils).
13.3 Soil-Landscape Relationships
205