Geomorphological Process Terms and Symbols
Application of Geomorphological Processes
Definitions of Erosional Processes
Definitions of Fluvial Processes
Definitions of Mass Movement Processes
Definitions of Periglacial Processes
Definitions of Deglacial Processes
Definitions of Hydrologic Processes
Back to Table of Contents

Geomorphological processes are natural mechanisms of weathering, erosion and deposition that result in the modification of the surficial materials and landforms at the earth's surface.

The status of all geomorphological processes in this classification is assumed to be "active," except for the geomorphological processes "channeled by meltwater" and "kettled," which have an assumed status of "inactive." The status of activity of a geomorphological process is indicated on a terrain map only if it is contrary to the assumed state defined for each process. Status is indicated as "active" or "inactive" by the use of the qualifiers: superscript "I" (inactive) and "A" (active)*. For further details refer to "Qualifiers."

*Note: Computer-drafted maps can show normal upper-case letters, not superscripts.

GEOMORPHOLOGICAL PROCESS TERMS AND SYMBOLS

Back to Geomorphological Processes

APPLICATION TO GEOMORPHOLOGICAL PROCESSES

• Geomorphological process symbols are applied where a relatively large portion (area) of a polygon is being modified by a process (e.g., solifluction), or where several sites within the polygon are being affected (e.g., rapid mass movement processes). The areal proportion or number of sites that is required is not normally stated, however, it may be defined in the map legend at the mapper's discretion.
  
  
• Up to three geomorphological processes may be used in a terrain symbol. They are placed after a dash at the end of the symbol for both simple and composite terrain symbols (see Terrain Symbols ).

Examples:	simple terrain symbol	sLGt-V
	composite terrain symbol	zgFGt/zLGt-V

• On-site symbols can be used for certain geomorphological processes to indicate modification of a relatively small portion of a map unit or where the specific location of a process needs to be shown. The available on-site symbols are indicated in the descriptions of the geomorphological process terms.
  
  
• Where two or three geomorphological process symbols are used, they are written in order of decreasing visible areal extent. No information about frequency and intensity of events is intended.

Erosional processes involve the erosion of earth materials by either flowing water (on or below the land surface), or by the action of wind, or through the chemical solution of rocks such as limestone.

Application and Examples:

• Most likely to apply in areas that are sparsely vegetated due to aridity, cold temperatures or recent deposition of surface materials. Features such as deflation hollows, exposed roots and the presence of nearby dunes, and gravel lag deposits are indicative of this process.

Example:	deflated glaciolacustrine terrace	zLGt-D

Application and Examples:

• Applied to carbonate and other rocks whose surfaces are marked by features such as sinkholes, uvalas, caves, surface etching, and limestone pavements.

Example:	limestone outcrop with caves and sinkholes	Ru-K

• Applied to depressions in surficial material that result from solution and subsidence in the underlying bedrock.

Example:	till blanket with depressions due to collapse of underlying bedrock

• Large and small karst depressions may be shown by on-site symbols.

Application and Examples:

• Applied to surfaces exhibiting modification in the form of small hollows (collapse depressions) irregularly arranged, or aligned along routes of subsurface drainage (beaded gullies); these features occur most commonly in glaciolacustrine silts (Figure 19).

Example:	piping in a glaciolacustrine terrace	zLt-P

• Piping may also occur in alluvium, volcanic ash, till and colluvium, as evidenced by pipes in cross-sectional exposures.
  
  
• Depression resulting from piping may be shown by an on-site symbol.

Figure 19. Gullied terrace of glaciolacustrine silt undergoing modification by piping as indicated by the circular and semi-circular depressions (arrows) on the surface of the terrace (map symbol: zL^Gt-VP) (location of photo: Okanagan Valley, southern British Columbia).

Application and Examples:

• Gullies may have either steep or gently sloping sides, and either steep or gently sloping longitudinal profiles. They are much smaller than valleys but larger than rills, and occur on various type of terrain such as steep mountain slopes, escarpments and terraces (Figure 20).

Examples:	a till mantle overlying steep bedrock dissected by gullies
	glaciolacustrine terrace dissected by gullies	LGt-V

• Individual gullies may be indicated by on-site symbols.

Figure 20. Gullied till in the Coast Mountains of British Columbia (map symbol: Ms-V).

Application and Examples:

• Commonly applied in areas of former glacial lakes, marine inundation, or areas of meltwater runoff. Active washing occurs along present shorelines.
  
  
• The process generally results in the formation of a thin lag gravel; thicker, water-deposited gravels (e.g., beaches) should be mapped as discrete units of surficial material.

Examples:	gravel pavement (lag) on till plain due to wave action in an ancient lake	Mp-WI
	marine beach gravels overlying a till plain (no process needed)

The behavior of a river is a complex function of discharge, sediment load and gradient. Analysis of these parameters is beyond the scope of terrain mapping, however over time, a particular kind of river behavior results in a characteristic set of features, such as the type and distribution of floodplain sediments and floodplain vegetation, floodplain and channel zone morphology, and channel pattern. These features are amenable to air photo interpretation and can be mapped and interpreted as part of terrain analysis. The classification of fluvial processes is based primarily on channel patterns as these provide a useful basis for the interpretation of fluvial hazards and other river characteristics. The following symbols apply only to rivers on floodplains. See also Subclasses for Fluvial Processes.*

*Note: Fluvial Subclasses are new (1997).

Back to Geomorphological Processes

Application and Examples:

• Most commonly applied to active floodplains and fluvial fans, and to distributary channels on deltas (Figure 21).

Example:	braiding channel on active floodplain	sgFAp-B

• Braided channels on abandoned fluvial surfaces are classified as inactive.

Example:	braided channel on former outwash plain	sgFGp-BI

Figure 21. An example of a braiding channel at moderate to low flow (map symbol: sgF^Ap-B) (location of photo: Southgate River).

Application and Examples:

• Applicable only to active floodplains and fluvial fans (Figure 22).

Example:	fluvial fan with irregularly sinuous channel	gFAf-I

Figure 22. An irregularly sinuous channel; note there is a single clearly defined main channel although there are many backchannels (map symbol: sgF^Ap-I) (location of photo: Bella Colla River).

Application and Examples:

• Applicable only to active floodplains and fluvial fans (Figure 23).
  
  
• Most Anastomosing rivers occupy gravel channels; islands consist of relatively thick sequences of overbank silt and sand which overlie gravel at low-water level.

Example:	gravel channel with islands of silty sand overlying gravel

Figure 23. The Stikine River in the Coast Mountains, an example of Anastomosing channel (map symbol: F^Ap-J).

Application and Examples:

• Applied to active floodplains that display features ranging from meander scars and cut-offs (ox-bow lakes) to regular scroll patterns (Figure 24). Zoned (i.e., linear pattern) successional vegetation may be present on point bars. Channel may be bounded by lev&#eacute;es.

Example:	floodplain with a meandering channel	sFAp-M

Figure 24. A meandering channel; note uniform size of meanders (and cutoffs) (map symbol: F^Ap-M) (location of photo: Kahntah River).

DEFINITIONS FOR MASS MOVEMENT PROCESSES

Mass movement processes involve the downslope movement, due to gravity, of surficial materials, bedrock fragments, and snow and ice, often mixed with vegetation debris. This classification distinguishes three types of mass movement based on the rate of movement and the presence of snow and/or ice. Subclass symbols may be used with these categories in order to indicate specific processes (see Subclasses for Mass Movement Processes and Snow Avalanches).*

Application and Examples:

• Applied to terrain with snow avalanche initiation zones, tracks, and runout zones (Figure 25).

Example:	avalanche cone	Cc-A

• Commonly associated with areas of high local relief and moderate to heavy snowfall. Below treeline, slopes modified by snow avalanches are characterized by linear vegetation patterns: avalanche tracks with deciduous shrubs and young conifers are demarcated from mature forest by a sharp treeline. Above the treeline avalanche paths are not well marked.

Example:	steep rocky slope modified by avalanches	Rs-A

• Applied to terrain affected by falling ice from glaciers.
  
  
• Specific avalanche paths can be indicated by on-site symbols.

Figure 25. A valley side of till and colluvium subject to snow avalanches; note the varying length of the runout zones (map symbol: Mb/Cv-A).

Application and Examples:

• Applied to terrain that includes the initiation, transportation, and depositional zones of slow mass movement. Includes slow earthflows, rotational slumps, rock glaciers, and lateral spreads. Terrain affected by slow mass movement usually displays irregular, chaotic or hummocky topography bounded upslope by an arcuate headscarp; lateral margins may be marked by lev&#eacute;-like ridges, and seepage or small ponds may be present (Figure 26). Also includes soil creep; in steep mountainous terrain where soil creep is a common process, the symbol should only be applied to sites showing significant alteration by creep processes.
  
  
• Applied to terrain units that consist entirely of unstable material, or to terrain units which include small areas where failure is occurring.

Examples:	earthflow	dmChr-F
	scarp of glaciolacustrine terrace with several small slumps	zLGt-F

• Slow movement may be indicated by the presence of tension cracks, tilted or jackstrawed trees, and displacement of man-made features such as roads and fence lines.

Example:	tension cracks indicating incipient failure of bedrock	Rst-F

• On-site symbols can be used to delineate specific failure headwall scars and paths.
  
  
• Additional information regarding specific slow mass movement processes can be indicated by subclass symbols (see Subclasses For Geomorphological Processes).

Figure 26. Hummocky and irregular topography of lower portion of the Pavilion earthflow - an example of slow mass movement (map symbol: Chr-F) (location of photo: near Pavilion, central British Columbia).

Application and Examples:

• Applied to terrain that includes the initiation, transportation, and depositional zones of rapid mass movement (Figure 27). Includes rock and earth falls; rock slides; debris slides, flows and torrents. These processes result in features that range from small linear tracks (bare or vegetated) that terminate at fans or cones (e.g., debris flow) to large accumulations of debris characterized by lobate, hummocky or ridged topography with an arcuate slide scar upslope (e.g., rockslide).

Examples:	till slope modified by debris slides	Mbv-R
	talus slope derived from rockfall	arCa-R
	large rockslide deposit	aChr-RI

• On-site symbols can be used to delineate specific failure headwall scars and paths. See On-Site Symbols.
  
  
• Additional information regarding specific rapid mass movement processes can be indicated by subclass symbols (see Subclasses and Subtypes).

Figure 27. Recent debris slides and flows (rapid mass movements) on steep slopes made up of till and colluvium; recent failures appear as white linear scars whereas older failures can be identified by their uniform revegetation pattern (arrow) (map symbol: Mb/Cv-R) location of photo: west coast of Vancouver Island).

DEFINITIONS FOR PERIGLACIAL PROCESSES

Application and Examples:

• Applied to areas of patterned ground where features such as sorted circles, and earth hummocks result from freeze-thaw processes (Figure 28).

Example:	stone polygons on morainal blanket	Mb-C

Figure 28. Patterned ground: evidence of cyroturbation in till (map symbol: Mb-C) (location of photo: northern British Columbia).

Application and Examples:

• Applied to areas where transverse, longitudinal, circular and/or irregular nivation hollows occur.

Example:	nivation hollows on rolling till plain	Mm-N

Application and Examples:

• Applied to areas where solifluction lobes, sheets and terraces are widespread (Figure 29).

Example:	solifluction lobes in a colluvial blanket	zrCb-S

• Material transported by solifluction is classified according to its source material, although technically solifluction material is colluvium.

Example:	solifluction lobes on till	Mb-S

Figure 29. Solifluction lobes (highlighted by the dark tones) in till in the alpine zone (map symbol: Mb-S) (location of photo: Omineca Mountains).

Application and Examples:

• Commonly used for small scale and generalized mapping and is applied instead of "-CNS".

Example:	moderately sloping alpine area of till on small scale map	Mb-Z

Processes controlled by the presence of permafrost, and permafrost aggradation or degradation. "Permafrost" is earth material whose temperature remains below 0°C continuously for two years or longer.

Application and Examples:

• Applied to terrain where any of the following features are present: ice-wedge polygons; thaw lakes or other thermokarst features; surficial materials containing interstitial or segregated ice (ice lenses); palsas and pingos.

Examples:	bog with palsas	Op-X
	lacustrine plain with ice wedge polygons	Lp-X

• Permafrost cannot be identified on the basis of a single (at one point in time) observation. If during field work, frozen ground is encountered during late summer or fall, it may be permafrost, however, if no permafrost landforms are present the permafrost symbol should not be used. Instead, the site should be identified with the frozen ground on-site symbol.
  
  
• See also Subclasses for Permafrost Processes.

DEFINITIONS FOR DEGLACIAL PROCESSES

Application and Examples:

• Applied to terrain dissected by meltwater channels (Figure 30); channels vary in length and range from broad, shallow channels to deeply-incised, steep-sided, flat-bottomed valleys. Channels may run across or along slope contours and presently may be dry, poorly drained or contain a stream (often a misfit stream) or small lake.

Example:	till-covered slope dissected by several lateral meltwater channels	Mbv-E

• Specific small and large meltwater channels may be indicated by on-site symbols (see Glacial Features).

Figure 30. Lateral meltwater channels developed on a slope made up of till; the channels formed during the last deglaciation (map symbol: Mb-E) (location of photo: Spatzizi Plateau, northwest British Columbia).

Back to Geomorphological Processes

Kettled

Map Symbol: H

Status: inactive

Depressions in surficial materials resulting from the melting of buried or partially buried glacier ice.

Application and Examples:

• Kettles are depressions characterized by steep sides bounded by abrupt, convex breaks in slope. They occur in a variety of shapes from round to irregular forms (Figure 31).

Example:	pitted outwash terrace	sgFGt-H

• Individual small and large kettle holes can be indicated by on-site symbols (see Glacial Features).

Figure 31. Pitted or kettled topography made up sandy gravel glaciofluvial eskers and kames (map symbol: sgF^Grhd-H) (location of photo: Liard Plain, northeast British Columbia).

DEFINITIONS FOR HYDROLOGIC PROCESSES

Application and Examples:

• Commonly applied to ephemeral lakes whose floors are mapped as terrain units, and to surficial materials with seasonally high watertables that result in local flooding for a continuous and significant time period (greater than one month).

Example:	ephemeral lake on lacustrine plain	Lp-U

Application and Examples:

• Applied to terrain units where seepage zones are much more common than in adjacent polygons of similar terrain.

Example:	toe of avalanche cone with abundant seepage	xCj-LA

We hope you find this service useful and welcome your comments at: Ian.Webster@gems1.gov.bc.ca Information Disclaimer and Copyright Notice