This chapter was prepared by the Landform Mapping Systems
Subcommittee of the Canada Soil Survey Committee, 1976: D.F.
Acton (chairman), N.F. Alley, R. Baril, A.T. Boydell, J.H.
Day, R.J. Fulton, P.K. Heringa, T.M. Lord, J.I. MacDougall,
J.L. Nowland, W.W. Pettapiece, E.W. Presant, B. Rochefort,
J.A. Shields, R.E. Smith, and M.D. Sudom.
A system of landform classification for soil mapping has been
desired by soil scientists in Canada for a long time. The
Canada Soil Survey Committee (CSSC) adopted a system at a
meeting held at the University of Guelph in February 1976.
Many aspects of the system came from mapping schemes used by
the Geological Survey of Canada for mapping surficial geology.
The system also embodies concepts developed initially by R.J.
Fulton and later by N.F. Alley while doing terrain mapping in
British Columbia. However, the needs of the soil scientist for
a terrain or landform classification system are not necessarily
compatible with those of the geologist. A national system
without any constraints that might be inherent in the system
developed for British Columbia was needed. Consequently, the
Landform Classification Subcommittee of the CSSC wanted to
ensure that the system devised to meet the soil survey
requirements in British Columbia, Terrain Classification
System (Environment and Land Use Committee Secretariat
1976), was acceptable for soil surveys throughout Canada.
The system of landform classification, developed and presented
here, is categorical in nature but does not involve any rigid
hierarchy. It is intended to be a field classification system
rather than a theoretical taxonomic one.
Landforms in this system are considered to include materials
and form. The system emphasizes objectivity whereby the two
basic attributes are recognized in terms of their inherent
properties rather than on inferred genesis. Genetic terms
are frequently used to denote materials and, in some instances,
a knowledge of the genesis of a material or form may be
required to accurately classify it. The system also attempts
to map comprehensively all landforms rather than stress
prominent features of importance in interpreting glacial
history as is sometimes the case in surficial geological
mapping.
The system applies to "local" landforms that are
readily represented on maps at scales of 1:50 000 to l:500 000.
These local forms contrast to "regional" landforms
that can be represented at scales of 1:1 000 000 or smaller.
In many respects the system is still conceptual in scope and
is not parametric because it generally lacks precise limits on
the boundaries between classes. It is anticipated that, with
further development, parameters can be applied to define
classes more rigidly.
The Material category recognizes four groups of materials:
unconsolidated mineral, organic, consolidated, and ice. A
number of classes of unconsolidated mineral and organic
materials have been established, but classes of consolidated
materials (bedrock) and ice have not been recognized. Textures
of unconsolidated mineral and fiber content of organics are
recognized in a category called Material Qualifiers.
Surface Expression, or form, associated with a material or
deposit is considered first based on the primary depositional
form. Postdepositional forms, essentially erosional, as well
as secondary processes are recognized by a category called
Modifying Processes.
Finally, a category called Qualifying Descriptors makes
possible further qualification of the kinds of materials
and the current state of processes as to whether they are
active or inactive.
- To provide a standard glossary of local landform
terminology for the needs of a soil survey. Other
geological terms are defined in the references cited
(American Geological Institute 1960a and
b).
- To provide a system for field collection of landform
information in soil surveys involving scales of l:50 000
and smaller.
- To provide a system for cataloging local landform
information (on-file maps, data banks).
- To provide a system for recognizing the landform
component of the mapping unit used by soil surveys.
Materials are classified according to their essential
properties within a general framework of their mode of
formation. Four groups (components) of materials have been
recognized to facilitate further characterization of the
texture and the surface expression of the materials. They
are unconsolidated mineral, organic, consolidated, and ice
components. These groups and the classes established within
them are presented below (see Figs. 44-49)1.
1 = Some examples of materials and surface expression are shown in Figures 44-71. The photographs were made
available through the courtesy of: C.J. Acton (58, 63); D.F. Acton (45, 47, 49, 50, 52, 53, 57, 62); N.F. Alley (44, 46, 64);
P. Baurdeau (48); R. Marcoux (56, 67); K. Michalica (66); J.L. Nowland (51); B. Rochefort (65); J.A. Shields (54, 59, 60,
61); C. Tarnocai (68, 69, 70, 71); C. Wang (55).
The unconsolidated mineral component consists of clastic
sediments that may or may not be stratified, but whose
particles are not cemented together. They are essentially
of glacial or postglacial origin but include poorly
consolidated and weathered bedrock. The classes and their
definitions follow:
| A-Anthropogeni |
|
M-Morainal |
| C-Colluvial |
|
S-Saprolite |
| E-Eolian |
|
V-Volcanic |
| F-Fluvial |
|
W-Marine |
| L-Lacustrine |
|
U-Undifferentiated |
These materials are artificial or modified by people and
include those associated with mineral exploitation and waste
disposal.
They include materials constructed or deposited by people
or geological materials modified by people so that their
physical properties (structure, cohesion, compaction) have
been drastically altered. These materials commonly possess
a wide range of textures. The process is assumed to be active.
Examples: areas of landfill, spoil heaps, and open-pit mines.
On-site symbols are used for anthropogenic sites where the
zone of disturbance is too small to be mapped as an areal
unit (see
Fig. 72).
These sediments are massive to moderately well stratified
and nonsorted to poorly sorted with any range of particle
sizes, from clay to boulders, and blocks that have reached
their present position by direct, gravity-induced movement
(see
Fig. 44).
They are restricted to products of mass-wasting whereby the
debris is not carried by wind, water, or ice (excepting snow
avalanches). Processes include slow displacements such as
creep and solifluction and rapid movements such as earth flows,
rockslides, avalanches and falls. The process is assumed to be
active.
Where colluvial materials are derived from an unconsolidated
deposit but overlie a different unit or form a discrete
surface expression, they are mapped as colluvial. Colluvial
material, which is derived from unconsolidated Quaternary
sediments, that overlies and resembles its parent unit is
mapped as the parent unit. Colluvial materials exclude those
materials deposited at the base of steep slopes by
unconcentrated surface runoff or sheet erosion.
Examples: creep, solifluction, earth flows, rockslides,
avalanches and falls are processes that produce colluvial
material.
These sediments generally consist of medium to fine sand and
coarse silt. They are well sorted, poorly compacted, and may
show internal structures such as cross bedding or ripple
laminae, or may be massive. Individual grains may be rounded
and show signs of frosting (see
Fig. 45).
These materials have been transported and deposited by wind
action. In most cases the process is assumed to be inactive.
Examples: dunes, veneers and blankets of sand and coarse silt,
and loess but not tuffs.
These sediments generally consist of gravel and sand with a
minor fraction of silt and rarely of clay. The gravels are
typically rounded and contain interstitial sand. Fluvial
sediments are commonly moderately to well sorted and display
stratification, but massive, nonsorted fluvial gravels do
occur. These materials have been transported and deposited
by streams and rivers (see
Fig. 46).
The process is assumed to be inactive.
Examples: channel deposits, overbank deposits, terraces,
alluvial fans, and deltas.
These sediments generally consist of either stratified fine
sand, silt, and clay deposited on a lake bed; or moderately
well sorted and stratified sand and coarser materials that
are beach and other nearshore sediments transported and
deposited by wave action (see
Fig. 47).
These materials have either settled from suspension in
bodies of standing fresh water or have accumulated at
their margins through wave action. The process is assumed
to be inactive.
Examples: lake sediments and beaches.
These sediments generally consist of well-compacted material
that is nonstratified and contains a heterogeneous mixture of
particle sizes. It commonly comprises a mixture of sand, silt,
and clay that has been transported beneath, beside, on, within,
and in front of a glacier and not modified by any intermediate
agent (see
Fig. 49).
Examples: basal till (ground moraine), lateral and terminal
moraines, rubbly moraines of cirque glaciers, hummocky
ice-disintegration moraines, and preexisting, unconsolidated
sediments reworked by a glacier so that their original
character is largely or completely destroyed.
This material is rock and contains a high proportion of
residual silts and clays formed by alteration, chiefly by
chemical weathering.
The rock remains in a coherent state, interstitial grain
relationships are undisturbed, and no downhill movement due
to gravity has occurred. The process is assumed to be active.
Examples: rotten rock containing corestones.
The deposits consist of unconsolidated pyroclastic sediments.
The process is assumed to be inactive.
Examples: volcanic dust, ash, cinders, and pumice.
These unconsolidated deposits of clay, silt, sand, or gravel
are well to moderately well sorted and well to moderately
stratified (in some places containing shells). They have
settled from suspension in salt or brackish water bodies
or have accumulated at their margins through shoreline
processes such as wave action and longshore drift
(see
Fig. 48).
Nonfossiliferous deposits may be judged marine, if they are
located in an area that might reasonably be considered to have
contained salt water at the time the deposits were formed. The
process is assumed to be inactive.
This classification is used for a layered sequence of more
than three types of genetic material outcropping on a steep
erosional escarpment.
This complex class is used where units relating to individual
genetic materials cannot be delimited separately at the scale
of mapping. It may include colluvium derived from various
genetic materials and resting upon a scarp slope.
The organic component consists of peat deposits containing
>17% organic C (>30% organic matter) by weight. These
deposits may be as thin as 10 cm if they overlie bedrock but
are otherwise greater than 40 cm and generally greater than
60 cm thick. The classes and their definitions follow:
B-Bog (sphagnum or forest peat)
N-Fen (fen or sedge peat)
O-Organic, undifferentiated
S-Swamp (forest peat)
These deposits consist of sphagnum or forest peat formed in
an ombrotrophic environment caused by the slightly elevated
nature of the bog. They tend to be disassociated from
nutrient-rich ground water or surrounding mineral soils.
Near the surface the materials are usually undecomposed
(fibric), yellowish to pale brown in color, loose and spongy
in consistence, and entire sphagnum plants are readily
identified. These materials are extremely acid (pH <4.5),
and have low bulk density (<0.075 mg cm-3)
and very high fiber content (>85% unrubbed and ≥40%
rubbed). At depths they become darker in color, compacted,
and somewhat layered. Bogs are associated with slopes or
depressions with a water table at or near the surface in
the spring and slightly below it during the remainder of
the year. They are usually covered with sphagnum, but sedges
may also grow on them. Bogs may be treed or treeless and are
frequently characterized by a layer of ericaceous shrubs.
These deposits consist of sedge peat derived primarily from
sedges with inclusions of partially decayed stems of shrubs
formed in a eutrophic environment due to the close association
of the material with mineral-rich waters.
It is usually moderately well to well decomposed, dark brown
in color, with fine- to medium-sized fibers but may be well
decomposed and black with fine fibers. Decomposition often
becomes greater at lower depths. Fen materials are medium acid
to weakly alkaline (pH 5.5-7.5), relatively low in fiber
(20-80% unrubbed and 2-25% rubbed), and relatively dense
(0.075-0.195 mg cm-3). They are associated with
relatively open peat lands with a mineral-rich water table
that persists seasonally at or very near the surface. The
materials are covered with a dominant component of sedges,
but grasses and reeds may be associated in local pools.
Sphagnum is usually subordinate or absent and the more
exacting mosses are common. Often there is much low to medium
height shrub cover and sometimes a sparse layer of trees.
This class is used for forest peat-covered or forest
peat-filled areas where the water table is at or above
the peat surface. The dominant peat materials are shallow
to deep mesic to humic forest and fen peat formed in a
eutrophic environment resulting from strong water movement
from the margins or other mineral sources.
The peat is usually moderately well to well decomposed and
has a dark brown to reddish brown matrix; the more decomposed
materials are black in color. It has an amorphous or very fine
fibered structure and somewhat layered macrostructure and
contains a random distribution of coarse- to medium-sized
woody fragments. There may be layers of larger woody particles
consisting of stems, roots, and trunks of coniferous tree
species. Forest peat materials are usually base saturated
and medium acid to weakly alkaline (pH 5.5-7.5); the matrix
material is relatively dense (≥0.075 mg cm-3)
and density increases with depth. The fiber content is
intermediate between sphagnum and fen peats (about 55%
unrubbed and 10% rubbed). These materials are associated with
stream courses, lake edges, subsurface drainage, glacial
depressions, and bog margins. Standing to gently flowing
waters occur seasonally or persist for long periods on the
surface. The substrate is usually continually waterlogged.
The vegetation cover may consist of coniferous or deciduous
trees, tall shrubs, herbs, and mosses. In some regions
sphagnum mosses may abound.
The consolidated component consists of tightly packed,
indurated materials of bedrock origin. The materials include
igneous, metamorphic, sedimentary, and consolidated volcanic
rocks. The only class is bedrock (R), which is
undifferentiated.
The ice component includes areas of snow and ice where
evidence of active glacier movement is present within the
boundary of the defined unit area. Ice movement is indicated
by features such as crevasses, supraglacial moraines, icefalls,
and ogives. The only class is ice (I) which is
undifferentiated. The process is assumed to be active.
Examples: cirque glaciers, mountain icefields, valley
and piedmont glaciers.
Material modifiers are used to qualify unconsolidated mineral
and organic deposits. Particle-size classes serve to indicate
the size, roundness, and sorting of unconsolidated mineral
deposits. Fiber classes indicate the degree of decomposition
and fiber size of organic materials.
The particle-size clases and definitions for unconsolidated
materials are as follows:
| a-Blocky |
|
l-Loamy |
| b-Bouldery |
|
p-Pebbly |
| c-Clayey |
|
r-Rubbly |
| k-Cobbly |
|
s-Sandy |
| g-Gravelly |
|
si-Silty |
An accumulation of angular particles greater than 256 mm in
size.
An accumulation of rounded particles greater than 256 mm
in size.
An accumulation of particles where the fine earth fraction
contains 35% or more clay (≤0.002 mm) by weight and
particles greater than 2 mm are less than 35% by volume.
An accumulation of rounded particles having a diameter of
64-256 mm.
An accumulation of rounded particles ranging in size from
pebbles to boulders.
An accumulation of particles of which the fine earth fraction
contains less than 35% clay (≤0.002 mm) by weight and less
than 70% fine sand and coarser particles. Particles coarser
than 2 mm occupy less than 35% by volume.
An accumulation of rounded particles having a diameter of
2-64 mm.
An accumulation of angular fragments having a diameter of
2-256 mm.
An accumulation of particles of which the fine earth fraction
contains more than 70% by weight of fine sand or coarser
particles. Particles greater than 2 mm occupy less than 35%
by volume.
An accumulation of particles of which the fine earth fraction
contains less than 15% of fine sand or coarser particles and
has less than 35% clay. Particles greater than 2 mm occupy
less than 35% by volume.
Well-sorted materials are generally described using a single
particle-size term; less well sorted and poorly sorted
materials are described using two particle-size terms. A
subordinate textural component is not generally shown if it
constitutes less than 35% of the total volume of the deposit.
The amount of fiber and its durability are important
characterizing features of organic deposits in that they
reflect on the degree of decomposition of the material.
The prevalence of woody materials in peats is also of prime
importance. The fiber classes and definitions for organic
materials are as follows:
f-Fibric
m-Mesic
h-Humic
w-Woody
The least decomposed of all organic materials; large amounts
of well-preserved fiber(s) are present that are readily
identifiable as to their botanical origin. Fibers retain
their character upon rubbing.
Organic material in an intermediate stage of decomposition;
intermediate amounts of fiber are present that can be
identified as to their botanical origin.
Highly decomposed organic material; small amounts of fiber
are present that can be identified as to their botanical
origin. Fibers can be easily destroyed by rubbing.
Organic material containing more than 50% woody fibers.
The surface expression of genetic materials is their form
(assemblage of slopes) and pattern of forms. Form as applied
to unconsolidated deposits refers specifically to the product
of the initial mode of origin of the materials. When applied
to consolidated materials, form refers to the product of their
modification by geological processes. Surface expression also
indicates how unconsolidated genetic materials relate to the
underlying unit. Examples of surface expressions of genetic
materials are presented in Figures 50-71.
The classes and definitions for unconsolidated and consolidated
mineral components are as follows:
| a-Apron |
|
m-Rolling |
| b-Blanket |
|
r-Ridged |
| f-Fan |
|
s-Steep |
| h-Hummocky |
|
t-Terraced |
| i-Inclined |
|
u-Undulating |
| l-Level |
|
v-Veneer |
A relatively gentle slope at the foot of a steeper slope and
formed by materials from the steeper, upper slope (see
Figs.
50
and
53).
Examples: two or more coalescing fans, a simple slope.
A mantle of unconsolidated materials thick enough to mask
minor irregularities in the underlying unit but still
conforming to the general underlying topography (see
Fig.
56
and
67).
Examples: lacustrine blanket overlying hummocky moraine.
A fan-shaped form similar to the segment of a cone and
having a perceptible gradient from the apex to the toe
(see
Fig. 52).
Examples: alluvial fans, talus cones, some deltas.
A very complex sequence of slopes extending from somewhat
rounded depressions or kettles of various sizes to irregular
to conical knolls or knobs. The surface generally lacks
concordance between knolls or depressions. Slopes are
generally 9-70% (5-35°) (see Figs.
51,
57,
and
62).
Examples: hummocky moraine, hummocky glaciofluvial.
A sloping, unidirectional surface with a generally constant
slope not broken by marked irregularities. Slopes are 2-70%
(1-35°). The form of inclined slopes is not related to
the initial mode of origin of the underlying material.
Examples: terrace scarps, river banks.
A flat or very gently sloping, unidirectional surface with a
generally constant slope not broken by marked elevations and
depressions. Slopes are generally less than 2% (1°)
(see
Fig. 63).
Examples: floodplain, lake plain, some deltas.
A very regular sequence of moderate slopes extending from
rounded, sometimes confined concave depressions to broad,
rounded convexities producing a wavelike pattern of moderate
relief. Slope length is often 1.6 km or greater and gradients
are greater than 5% (3°) (see
Fig. 59).
Examples: bedrock-controlled ground moraine, some drumlins.
A long, narrow elevation of the surface, usually sharp
crested with steep sides. The ridges may be parallel,
subparallel, or intersecting (see Figs.
54
and
58).
Examples: eskers, crevasse fillings, washboard moraines,
some drumlins.
Erosional slopes, greater than 70% (35°), on both
consolidated and unconsolidated materials. The form of
a steep erosional slope on unconsolidated materials is
not related to the initial mode of origin of the underlying
material.
Examples: escarpments, river banks, and lakeshore bluffs.
A scarp face and the horizontal or gently inclined surface
(tread) above it (see
Fig. 64).
Example: alluvial terrace.
A regular sequence of gentle slopes that extends from
rounded, sometimes confined concavities to broad rounded
convexities producing a wavelike pattern of low local relief.
Slope length is generally less than 0.8 km and the dominant
gradient of slopes is 2-5% (1-3°) (see Figs.
55,
60,
and
65).
Examples: some drumlins, some ground moraine, lacustrine
veneers and blankets over morainal deposits.
Unconsolidated materials too thin to
mask the minor irregularities of the underlying
unit surface. A veneer ranges from 10-100 cm
in thickness and possesses no form typical of
the material's genesis (see Figs.
61,
66
and
67).
Examples: shallow lacustrine deposits overlying glacial
till, loess cap.
Figure 44:
Colluvial material
Figure 45:
Eolian material
Figure 46:
Fluvial material
Figure 47:
Lacustrine material
Figure 48:
Thin marine sands over marine clays in the background have
been deranged by progressive rotational flow slides in the
foreground
Figure 49:
Morainal material
Figure 50:
Colluvial apron at the base of Nahanni Butte, N.W.T.
Figure 51:
Hummocky eolian material, active and stabilized sand
dunes in Prince Edward Island
Figure 52:
Fluvial fan in the foreground, Carcajou Lake, N.W.T.
Figure 53:
Fluvial apron in the midground, Carcajou Canyon, N.W.T.
Figure 54:
Ridged and hummocky glaciofluvial material, Kamloops, B.C.
Figure 55:
Undulating glaciofluvial material, eastern New Brunswick
Figure 56:
Morainal blanket over undulating bedrock, eastern Quebec
Figure 57:
Hummocky and ridged morainal material in the midground and
background, Kamloops, B.C.
Figure 58:
Ridged morainal material. The lines of trees mark the swales
between parallel ridges, southern Ontario
Figure 59:
Rolling morainal material, southeastern Alberta
Figure 60:
Undulating morainal material, southern Sask
Figure 61:
Morainal veneer over rolling bedrock, Vancouver Island, B.C.
Figure 62:
Hummocky glaciolacustrine material, Biggar, Sask
Figure 63:
Level lacustrine material, southwestern Ontario
Figure 64:
A lacustrine terrace dissected by streams between a river
and hills, Kamloops, B.C.
Figure 65:
Undulating marine landform marks the remnants of ancient
clay flow slides, Pontiac County, Que.
Figure 66:
Thin marine veneer over level bedrock, Grande-Anse, N.B.
Figure 67:
Marine veneer and blanket over hummocky bedrock, Montmagny, Que.
Figure 68:
The domed bog in the midground has mainly sphagnum
vegetation, Sibbeston Lake, N.W.T.
Figure 69:
Plateaus in this bog are marked by the light brown
vegetation with sparse tree cover. The flat, reddish brown
areas are sedge-covered fens, Norman Wells, N.W.T.
Figure 70:
The horizontal fen in the foreground is dominated by sedge
vegetation, Manitoba
Figure 71:
The ribbed fen has sedge vegetation broken by low ridges
where spruce trees grow, Fort Simpson, N.W.T.
The classes and definitions for organic components are as
follows:
| b-Blanket |
|
h-Horizontal |
| o-Bowl |
|
p-Plateau |
| d-Domed |
|
r-Ribbed |
| f-Floating |
|
s-Sloping |
A mantle of organic materials that is thick enough to mask
minor irregularities in the underlying unit but still
conforms to the general underlying topography.
Example: blanket bog.
A bog or fen occupying concaveshaped depressions.
Example: bowl bog.
A bog with an elevated, convex, central area much higher
than the margin. Domes may be abrupt (with or without a
frozen core) or gently sloping or have a stepped surface
(see
Fig. 68).
Examples: palsa, peat mound, raised bog.
A level organic surface associated with a pond or lake and
not anchored to the lake bottom.
Example: floating fen.
A flat peat surface not broken by marked elevations and
depressions (see
Fig. 70).
Examples: flat bog, horizontal fen.
A bog with an elevated, flat, central area only slightly
higher than the margin (see
Fig. 69).
Examples: peat plateau, bog plateau, polygonal peat plateau.
A pattern of parallel or reticulate low ridges associated
with fens (see
Fig. 71).
Examples: string fen, ribbed fen, net fen.
A peat surface with a generally constant slope not broken by
marked irregularities.
Example: sloping fen.
A set of slope classes has been provided to make it possible
to quantify the dominant but not necessarily most abundant
slopes within a mapped unit of a local landform. There are
10 slope classes. Each is defined in terms of percent and
degrees. Measurements are to the nearest tenth in the two
lowest classes.
| 1 |
0-0.5 |
0 |
level |
| 2 |
>0.5-2 |
0.3-1.1 |
nearly level |
| 3 |
>2-5 |
>1.1-3 |
very gentle slopes |
| 4 |
>5-10 |
>3-5 |
gentle slopes |
| 5 |
>10-15 |
>5-8.5 |
moderate slopes |
| 6 |
>15-30 |
>8.5-16.5 |
strong slopes |
| 7 |
>30-45 |
>16.5-24 |
very strong slopes |
| 8 |
>45-70 |
>24-35 |
extreme slopes |
| 9 |
>70-100 |
>35-45 |
steep slopes |
| 10 |
>100 |
>45 |
very steep slopes |
Terms that describe the geological processes that have
modified or are currently modifying genetic materials and
their surface expression are considered within the modifying
processes category of the system.
These modifiers are to be used where a relatively large part
of the map unit is modified. On-site symbols can be used to
indicate that only a relatively small part of a map unit is
modified.
The assumed common process status (active, inactive) is
specified in the definition of each modifier. Where this
status varies from the assumed state, it must be qualified
in the description.
| A-Avalanched |
|
K-Karst modified |
| B-Beveled |
|
N-Nivated |
| C-Cryoturbated |
|
P-Piping |
| D-Deflated |
|
S-Soliflucted |
| E-Eroded (channeled) |
|
V-Gullied |
| F-Failing |
|
W-Washed |
| H-Kettled |
|
|
Describes slopes modified by frequent avalanche activity.
An avalanche is a large mass of snow, ice, soil, or rock, or
mixtures of these materials, falling or sliding rapidly
under the force of gravity. The process is assumed to be
active.
Examples: avalanche cones, avalanche tracks or chutes.
Describes a surface cut or planed by running water but not
underlain by fluvial materials.
Beveled applies to river-cut terraces in bedrock and river
terraces cut into till or lacustrine silts. The process is
assumed to be inactive.
Example: river-cut terrace in bedrock.
Describes a surface modified by processes of frost action.
It includes surfaces produced by the stirring, churning,
modification and other disturbances of soil that result
from frost action. This involves frost heaving and
differential and mass movements, which produce patterned
ground. The process is assumed to be active. Processes
involving downslope movements of material overlying a
frozen layer are excluded from this modifier and considered
more specifically as soliflucted.
Examples: sorted nets, stripes, unsorted circles, earth
hummocks.
Describes a surface modified by the sorting out, lifting,
and removal of loose, dry, fine-grained particles (clay and
silt sizes) by the turbulent, eddy action of the wind. The
process is assumed to be inactive.
Example: deflated lacustrine terrace.
Describes a surface modified by a series of abandoned
channels.
The term applies to fluvial plains, terraces, and fans. The
process is assumed to be inactive.
Example: abandoned channels on alluvial terrace.
Describes a surface modified by the formation of tension
fractures or by large consolidated or unconsolidated masses
moving slowly downslope.
Colluvial processes resulting in shallow surface movements
are not described as failing. The process is only active.
Example: slumps.
Describes a surface, deposit, or feature modified by
depressions left by melting ice blocks.
Depressions can be formed by the melting blocks of ice
buried in glaciofluvial, glaciolacustrine, or glacial
till materials. Kettle depressions usually have steep
sides and are bound by an abrupt convex break of slope.
They occur in a variety of shapes and sizes from round basins
to branching valleys. The process is assumed to be inactive.
Examples: pitted outwash and lacustrine, knob and kettle
topography.
Describes a modification of carbonate and other rocks whose
surfaces are marked by features of collapse and solution and
also where the rocks are overlain by unconsolidated materials
that show posthumous collapse depressions. The process is
assumed to be active.
Examples: sinkholes, dolines, uvalas.
Describes a surface modified by frost action, erosion, and
mass wasting beneath and around a snowbank so as to produce
transverse, longitudinal, and circular hollows.
Examples: nivation terraces in colluvium, nivation hollow.
Describes a surface modified by small hollows, commonly
aligned along routes of subsurface drainage, and resulting
from the subsurface removal of particulate matter in
unconsolidated materials.
It occurs most commonly in lake silts but may also affect
alluvium, loess, and volcanic ash. The process is assumed
to be active.
Example: piping in silty lacustrine terrace.
Describes a surface modified by the process of slow
gravitational movement downslope of saturated, nonfrozen
earth material behaving apparently as a viscous mass over
a surface of frozen ground.
Soliflucted surfaces are commonly associated with processes
of cryoturbation and nivation occurring in alpine and
subalpine areas. The process is assumed to be active.
Examples: lobes, stripes, sheets, terracettes.
Describes a surface modified by fluvial erosion resulting
in the development of parallel and subparallel, steep-sided,
and narrow ravines in both consolidated and unconsolidated
materials. The process is assumed to be active.
Example: gullied lacustrine terrace.
Describes a surface, deposit, or feature modified by wave
action in a body of standing water resulting in lag deposits,
beaches of lag materials, and wave-cut platforms.
Washed surfaces occur most commonly in areas of former
marine inundation or glacial lakes. Active washing occurs
along present shorelines. The process is assumed to be active.
Example: terrace or beach that is cut or deposited on a
morainal blanket.
A number of descriptors have been introduced to qualify
either the genetic materials or the modifying process terms.
The descriptors add information about the mode of formation
or depositional environment. They also qualify the status of
the genetic and modifying processes. Included in the
definitions of the categories are statements concerning
the commonly assumed status of their processes. Where the
process status is contrary to the common assumption, it is
indicated.
G Glacial, Glaciofluvial, etc.
A Active, I Inactive
Used to qualify nonglacial genetic materials or process
modifiers where there is direct evidence that glacier ice
exerted a strong but secondary or indirect control upon the
mode of origin of the materials or mode of operation of the
process. The use of this qualifying descriptor implies that
glacier ice was close to the site of the deposition of a
material or the site of operation of a process.
Used only where fluvial materials show clear evidence of
having been deposited either directly in front of, or in
contact with, glacier ice. At least one of the following
characteristics must be present:
- kettles, or an otherwise irregular (possibly hummocky or
ridged) surface that resulted from the melting of buried
or partially buried ice, e.g., pitted outwash, knob and
kettle topography
- either slump structures or their equivalent topographic
expression, or both, indicating partial collapse of a
depositional landform due to melting of supporting ice,
e.g., kame terrace, delta kame
- ice-contact and molded forms such as gravelly or sandy
crevasse fillings and eskers
- nonsorted and nonbedded gravel of an extreme range of
particle sizes, such as results from very rapid
aggradation at an ice front, e.g., ice-contact gravels
- flowtills.
Used where there is evidence that the lacustrine materials
were deposited in contact with glacial ice. One of the
following characteristics must be present:
- kettles or an otherwise irregular surface that is
neither simply the result of normal settling and
compaction in silt nor the result of piping
- slump structures resulting from loss of support caused
by melting of retaining ice
- presence of numerous ice-rafted stones in the lacustrine
silts.
Used only where it is clear that materials of glacial origin
were laid down in a marine environment, i.e., deposits
settled through the waters from melting, floating ice and
ice shelves. Sediments may be poorly sorted and poorly
stratified to nonsorted and massive; shells present will
generally be whole and in growth positions.
Used to indicate the presence of glacial meltwater channels
in a unit where they are either too small or too numerous,
or both, to show individually by an on-site symbol.
Used to indicate any evidence of the recurrent nature of a
modifying process or of the contemporary nature of the
process forming a genetic material.
Used to indicate that there is no evidence of the modifying
process recurring and that the processes that formed the
genetic materials have ceased.
The following example illustrates a system for ordering
symbols used in map edits. It assumes that all components of
the system (genetic materials and their particle-size or
fiber class, surface expression and related slope, modifying
processes, and qualifying descriptors) are to be used.
t GQ eQ is the dominant (>50%)
surficial material and t GQ eQ 1 -
PQ is the subdominant material. Rarely will
materials occupying less than 15% of the map area be
recognized in the edit. (On-site symbols
[Fig. 72]
provide a
mechanism for depicting many of these).
| t |
genetic material modifier (particle
size of clastic materials and fiber content of organic
materials). |
| G |
genetic materials |
| e |
surface expression |
| l |
slope qualifiers (numeric) |
| P |
modifying processes |
| Q |
qualifying descriptor (superscript) |
| GQe |
in the denominator represents an
underlying stratigraphic unit. |
Figure 72:
On-site landform symbols.
Not all terrain can be presented as simple units because
terrain units commonly occur that are of small areal extent
and cannot be delimited individually at the scale of mapping.
Consequently, a system of composite units is employed whereby
up to three types of terrain may be designated within a common
unit boundary. The relative amounts of each terrain type are
indicated by the use of the symbols =, /, and //. The
components are always indicated in decreasing order of
abundance.
| = |
components on either side of this symbol
are about equal; each represents 45-55% of the area. |
| / |
the component in front of this symbol is
more abundant than the one that follows; the first
represents 55-70% of the area and the second 30-45%. |
| // |
the component in front of this symbol
is considerably more abundant than the one that
follows; the first represents 70-90% of the area
and the second 10-30%. |
Stratigraphic data may be presented to supplement the
surficial data. Stratigraphic information should be given
for veneers and blankets. Also, where the depth of the
surface unit is such that the nature of the underlying
unit may be important or where it is deemed necessary to
show the character of the underlying unit, or both, then
stratigraphic information should be shown.
For map presentation a horizontal bar is used to separate
the components that are arranged in stratigraphic order.
Surface expressions may be attached to underlying units if
appropriate.
If the type of unconsolidated material underlying a blanket
of different genetic material is not known, then only the
surface expression of that underlying material is given. For
example, Mb/h indicates hummocky unconsolidated material of
unknown specific type underlying a blanket of morainal
materials.
On-site symbols or map symbols (see
Fig. 72)
are used to
describe features or processes in the terrain that express
either a limited (by scale), areal function or are simply
point observations. These may be linear features such as
eskers or moraine ridges, site-specific information such
as gravel locations or kettle holes, or to add details of
Quaternary history such as striae, glacial meltwater channels,
or abandoned shorelines.
The size of the on-site symbols varies with the type of
symbol. For example, the symbols that connote an areal extent
such as failing or block fields vary in size, whereas those
that are point observations and have no relation to areal
extent, such as fossil locality or karst, will be of a
standard size. The symbols that have linear connotations,
such as eskers, gullying, or end moraines, vary in length
but are of standard width.
|