| Code | Name | Description | Synonyms and subtypes |
|---|---|---|---|
| Mt | Mountains | Steep to very steep, high relief (>300 m), fixed and well connected stream channels, often deep | Alps, Volcanoes, Mountain country |
| Hi | Hills | Gentle to very steep, moderately high to high relief (90-300 m), fixed and well connected stream channels, shallow to deep | Hillscapes, hill country, hilly land |
| Up | Uplands | Gentle to very steep, low relief (30-90 m) but relatively high elevation, fixed and well connected stream channels, shallow valleys and plateaus, located among hills and mountains | Piedmont |
| Ll | Lowlands | Gentle to very steep, low relief (30-90 m) and elevation, fixed and well connected stream channels, shallow to deep | Downlands |
| Te | Terraces | Former plains, uplifted and sometimes covered by loess. Flat to gently undulating upper surfaces bounded by distinctive drop-offs on their downhill end, often backing on to lowlands, hills or mountains at their uphill end. | Marine benches |
| Pl | Plains | Level to very gentle surfaces created by fluvial and/or airfall tephra deposition. | Floodplains, ringplains |
| Sc | Sand country | Extensive dune and sandplain areas. Low relief and elevation, gentle to steep slopes, and active stream channels, often with interrupted connectivity | Dunefields |
| Cs | Coasts | On- and near-shore features created by the interaction of the ocean with the land, including beaches, deltas, lagoons and estuaries | Coastlines |
4 Geomorphology
Geomorphology limits the range of soils than can occur at specific locations on the basis of slope, relief, aspect, and drainage. Geomorphology can be described at multiple scales, which break down into progressively simpler shapes. The system described in this chapter helps the pedologist to do that consistently. In this system, the chosen scales are Province (Section 4.1), Landscape (Section 4.2), and Landform (Section 4.3) as described below. Some additional, highly local geomorphology parameters are captured when describing the land surface at a site (Chapter 11).
4.1 Province
Provinces identify major geomorphic zones in New Zealand, expressive of large-scale lithological associations, tectonic regime, and climate. Table 4.1 lists their names and Figure 4.1 shows their general distribution. Full definitions of the provinces are in Appendix F.
Given their very broad extent, province does not need to be recorded in the field. However, the province boundaries are not currently strictly defined so an understanding of their conceptual basis (Appendix F) is required before a confident allocation can be made.
4.2 Landscape
The landscape around a soil observation comprises a distinct geomorphological pattern with repeating elements. The scale of observation varies but commonly extends from a few hundred to a few thousand meters (Heck 2017). Landscapes nest within Provinces but are not exclusive to one or another.
4.2.1 Parameterising landscapes
A landscape can be described in terms of a short list of parameters: relief, characteristic slope, drainage pattern, and the landforms contained within the landscape.
4.2.1.1 Relief
Relief is the degree of separation between high and low points in a landscape. As described in National Committee on Soil and Terrain (2024, p. 36), relief can be visualised by picturing two surfaces roughly parallel to the land surface - one passing through local crests and one through local depressions. The median vertical distance between the two surfaces is the relief.
add a diagram here
Relief is usually best determined from a DEM, but can be estimated in the field. Record in whole meters if estimating, e.g. 55 m. Relief classes may be applied to the recorded data; see Section 22.3.
4.2.1.2 Characteristic slope
The characteristic slope is the most common range of slopes within a regional landscape. These are often controlled by local geology.
Characteristic slope is usually best determined from zonal analysis of a DEM-derived slope dataset, but can be estimated in the field. Estimate in the field as a median and range, in whole degrees, e.g. 25° (20-28). Slope classes may be applied to the recorded data; some options are presented in Section 22.1.
Note 4.1: Multiple characteristic slopes
Some landscapes may have two or more distinct characteristic slopes, e.g. the fronts and tops of alluvial terrace elements. In this case the median will describe the dominant surface while the range will capture the steeper areas. Recording multiple characteristic slopes at landscape scale is not considered useful, as adequate context is provided by naming the landscape and its component landforms.
4.2.1.3 Stream channels
Natural stream channel patterns are relevant to understanding landscape development, but are best observed remotely. They do not need to be recorded in the field. If desired, assess the landscape drainage pattern using available data sources and define it using the stream channel attributes given in (2024, p. 38–41).
4.2.1.4 Landscape description
Few controlled vocabularies for landscapes exist. The schema given in Table 4.2 below is provisional and based on terms seen in common use in New Zealand environmental datasets.
4.2.1.5 Composition
A breakdown of the major landforms expected within the landscape should be included (see Section 4.3 below) along with an estimate of their relative dominance (e.g. Cs: Bc 80%, Du 10%, Cl 10% for a coastal landscape comprising steep cliffs fronted by a narrow beach system with some limited dune development in places where the beach is wide enough to allow it).
4.3 Landform
A landform is a component of the landscape, and again can have a variable extent - usually 10’s to 100’s of meters. A landform has a relatively simple shape and is not itself composed of multiple repeating elements in the way that a landscape is. A landform has a characteristic range of slopes and aspects. Landforms also have distinctive composition in terms of geology/parent materials and are usually restricted to particular locations within a landscape.
4.3.1 Naming Landforms
Few controlled vocabularies for landforms exist. The schema given in Table 4.3 below is provisional and based on terms seen in common use in New Zealand environmental datasets and related publications.
| Code | Name | Description | Synonyms and subtypes |
|---|---|---|---|
| Natural | |||
| Ba | Bar | A ridge-like accumulation of sand, gravel, or other alluvial material formed in the channels, along the banks, or at the mouth of a stream where a decrease in velocity induces deposition | sandbar, channel bar, meander bar |
| Bc | Beach | Low-slope, shorefront accumulation of unconsolidated sediment (usually sand to cobble sized) | |
| Bo | Bog | Rainfall-fed, peat-accumulating freshwater wetland with low pH and nutrient availability and restricted water flow | peat bog, domed bog |
| Ca | Caldera | Large hollow in the top of a volcano | volcanic crater |
| Cl | Cliff | Steep to vertical slope with more than 10 m local relief | |
| Cn | Cone | Moderate to steep, usually isolated hill built up by volcanic activity | |
| Cr | Crest | A locally high area, from which the surface slopes downwards in opposite directions | Apex, Summit |
| Dl | Delta | A fan-shaped accumulation of alluvial sediment, usually with several water channels, at a river or stream mouth. | River mouth |
| Du | Dune | Accumulation of windblown sand into an elongated ridge or crescent shape | |
| Ew | Ephemeral wetland | Wetland subject to pronounced seasonal drying. Non-peaty, with neutral pH and moderate nutrient status. Usually in a closed depression | |
| Fl | Flat | Level area created by deposition | Tidal flat, intertidal flat, supratidal flat, infill |
| Fn | Fan | Gently sloping, flat to convex depositional slope, often at the foot of a steeper area and built up by a stream or by colluvial action | |
| Fe | Fen | Rainfall and groundwater-fed peaty freshwater wetland with low to moderate pH and nutrient availability, and slightly fluctuating water table | |
| Go | Gorge | A valley 10 m or more deep with over three-quarters of its sides sloping at more than 25°, and half or more of its sides formed by cliffs, and less than 5 times as wide as it is deep over half or more of its length, and everywhere less than 10 times as wide as it is deep | Ravine |
| Lv | Levee | An embankment of flood alluvium built up alongside a river and typically with lower-lying land behind | |
| Ma | Marsh | Wetlands with large periodic water table fluctuations, relatively high pH and nutrient content, and mainly mineral substrate | |
| Mh | Hummocky moraine | Low, roughly undulating deposits of glacial till | |
| Mo | Mound | A small hill with moderate to steep sides, often somewhat isolated | Lahar mound, knoll, hillock |
| Mr | Moraine ridge | Low ridges comprising glacial till | |
| Pk | Pakihi and gumland | Wetland in highly leached soils with low pH and nutrient availability. Sometimes periodically dry and usually without peat | |
| Pl | Plain | Level to gently undulating area built up by alluvial, aeolian, or volcanic deposition | Alluvial plain, backplain, sand plain, outwash plain |
| Pt | Plateau | Any comparatively flat extensive and elevated area, often dissected and with a steep dropoff on at least one side | Tableland |
| Ri | Riser | The vertical or steeply sloping surface of one of a series of natural, step-like landforms, as those of a glacial stairway or of successive stream terraces | |
| Rt | Tread | The flat or gently sloping broadly planar surface of one of a series of natural step-like landforms, as those of a glacial stairway or of successive stream terraces | Bench |
| Sa | Saddle | A low point (dip) along a ridge or the lowest point between two adjacent elevated areas. In one axis along the ridge or between the elevated areas the land slopes up in both directions and in the other axis, typically at right angles to the first, the land slopes down in both directions | |
| Se | Seepage | Sloped area carrying a slow but steady flow of groundwater | Flushes |
| Sm | Swamp | Rainfall and groundwater-fed, somewhat peaty freshwater wetland with high pH and nutrient availability, and seasonally fluctuating water table | Backswamp |
| Sw | Swale | A low-lying depression between adjacent ridges | Interdune, dune slack |
| Sl | Slope | Very gentle to very steep inclined surfaces | Backslope, midslope, toeslope, footslope, dip slope, flank, headslope, talus slope |
| St | Saltmarsh | Wetlands with saline water supply, usually in tidally influenced areas | Estuary, mudflat |
| Vl | Valley-bottom | Open depression between parallel facing slopes | |
| Human-induced | |||
| Cs | Cut-surface | Flat excavated by human activity | |
| Cf | Cut-face | Slope excavated by human activity | |
| Em | Embankment | Ridge or slope built up by human activity | |
| Fi | Fill-top | Flat built up by human activity | |
4.3.2 Describing landforms
Where available landforms are unsatisfactory or a more detailed parameterisation of the landform is desired, the landform can optionally be described in terms of its slope, orientation and element.
4.3.2.1 Slope
Record the characteristic slope of the major part of the landform as median and range in whole degrees, e.g. 5° (4-6) for a low-angle fan. Slope classes may be applied to the recorded data; some options are presented in Section 22.1.
4.3.2.2 Orientation
For simpler sloping landforms, record orientation as the characteristic aspect of the major part of the landform. Record median and range in whole degrees, e.g. 315 (300-330) for a roughly northwest direction. For complex landforms with a range of aspects, record the orientation of the landform’s longest axis, looking downslope (e.g. the direction in which a valley bottom is descending). Some landforms may not have an identifiable orientation (e.g. cones, saddles), in which case record NA.
Aspect classes may be applied to the recorded data; some options are presented in Section 22.2.
4.3.2.3 Landform element
The following is adapted from (2024, p. 19–25).
A landform element is the simplest component of a landform, and some landforms are made up of only one element. Landform elements are first assigned to a morphological type - one of a series of simple shapes - at the scale of observation. These are given in Table 4.4 below.
| Code | Name | Description |
|---|---|---|
| Cr | Crest | A local high area |
| Ri | Ridge | A linear high area |
| Sl | Slope | A sloping area |
| Fl | Flat | A non-sloping area |
| Do | Open depression | a linear low area |
| Dc | Closed depression | a locally low area |
Note that these are paired mirror images, e.g. a closed depression is the opposite of a crest. Each morphological type extends to a break of slope or point of 0-curvature.
Slopes can be further refined by including information about their relationship to their neighbouring elements. Up and down slope, four options are available.
| Code | Name | Description |
|---|---|---|
| X | Waxing | Element upslope is gentler, element downslope is steeper. |
| N | Waning | Element upslope is steeper, element downslope is gentler. |
| A | Maximal | Element upslope is gentler, element downslope is gentler. |
| I | Minimal | Element upslope is steeper, element downslope is steeper. |
Three more are available across the slope.
| Code | Name | Description |
|---|---|---|
| L | Enclosed | Adjacent slope elements face towards each other |
| E | Exposed | Adjacent slope elements face away from each other |
| O | Open | Adjacent slope elements face the same direction |
This combination of properties gives rise to more complex shapes. For example, an open hollow could be described as an enclosed maximal slope (SL A L). A shoulder would be an exposed waxing slope (SL X E). Adding further information about slope and aspect can define a complete element. For instance, for a gently sloping, northeast facing fan - 5 40 SL N E.
TODO add graphics
4.4 Other terrain parameters
The following terrain parameters may be useful in particular contexts.
4.4.1 Slope length
Slope length is used in assessments of erosion vulnerability. Length is measured from the point at which a slope becomes steep enough to lose soil to erosion processes (see Section 11.8.1), to where it levels out enough to receive soils (or to a drainage channel). This is usually impractical to measure in the field, but can be determined computationally given an appropriately detailed DEM. Alternatively, the slope length can be manually traced in GIS.
4.4.2 Mesoscale topographic index
The Mesoscale Topographic Index (MTI, Hurst et al. (2022), p. 15) is a measure of how sheltered or exposed a location is within a landscape. To measure in the field, use a compass and clinometer to measure angle to the horizon at the 8 cardinal compass bearings. Record positive values if looking up and negative when looking down. The average of the eight values defines the index, with high values signifying a sheltered area and low values signifying exposure.
4.4.3 Terrain shape index
Terrain shape index (TSI, Hurst et al. (2022), p. 15) is a localised version of MTI, where slope angles are measured at cardinal compass points 20 m from the point of observation, rather than to the horizon.