SURFACE EXPRESSION

• Not applied to till or colluvium or other material on bedrock-controlled slopes.

Example:

colluvial veneer overlying moderately sloping smooth bedrock

Definition of Surface Expression Terms

A layer of unconsolidated material thick enough to mask minor irregularities of the surface of the underlying unit, but still conforms to the general underlying topography. A blanket is greater than 1 metre thick and possesses no constructional forms typical of the materials' genesis; outcrops of the underlying unit are rare.

Figure 13. Schematic cross-sections that illustrate and distinguish the surface expression terms blanket, veneer, and mantle of variable thickness.

• The surface expression of the blanket is expressed by either the surface expression of the underlying unit, or by the contour lines of the topographic map (Figures 13 and 14).
  
  
• If the underlying unit is unconsolidated material, its presence is indicated in a stratigraphic symbol (see Stratigraphic Symbols).

Example:	till blanket overlying hummocky glaciofluvial gravels

• If the underlying unit is bedrock, no stratigraphic information need be supplied, except where the contours of the topographic map do not adequately depict the land surface.

Examples:	till blanket overlying bedrock with surface shape shown by contours (bedrock-controlled topography)	Mb
	till blanket overlying bedrock with surface shape not shown by contours (bedrock-controlled topography)

Figure 14. Schematic cross-sections to illustrate the use of stratigraphic symbols with the surface expression terms blanket, veneer, and mantle of variable thickness. In (d), "Mb" is used alone because contours indicate the long, convex hillside.

Definition of Surface Expression Terms

A cone or segment of a cone with a relatively smooth slope gradient from apex to toe greater than 15° (26%), and a longitudinal profile that is either straight, concave or convex.

Application and Examples:

• A cone is distinguished from a fan on the basis of slope gradient (Figure 15). Refer to FAN.
  
  
• Typically applied to talus cones, avalanche cones, coalescing cones where individual cones can be distinguished and volcanic cones of pyroclastic materials.

Examples:	talus cones	rCc
	avalanche cones	arCc-A
	cinder cone	rVc

• Small volcanic cones may be indicated by on-site symbols (see Other Landforms and Features).

Figure 15. Block diagrams that illustrate the surface expression terms cone (a) and fan (b).

Circular or irregular area of lower elevation (hollow) than the surrounding terrain and marked by an abrupt break in slope; side slopes within the depression are steeper than the surrounding terrain; depressions are two or more metres in depth.

Application and Examples:

• Typically used when mapping deposits containing kettle holes, karst depressions, or depressions caused by piping.
  
  
• If map scale permits, the term depression may be applied to a single enclosed depression.

Example:	a large kettle in ice-contact materials	gsFGd

• The origin of the depression, when known, should be indicated by the use of a "Geomorphological Process" symbol (see Geomorphological Process Terms and Symbols).

Examples:	a kettle hole	gsFGd-H
	pitted outwash plain	sgFGpd-H
	glaciolacustrine terrace with depressions caused by piping	mLGtd-P

• On-site symbols for kettles, piping depressions, and karst depressions should be used instead of "d" where occurrence is of limited extent in relation to the whole map unit.

Definition of Surface Expression Terms

A fan is a relatively smooth sector of a cone with a slope gradient from apex to toe, up to, and including 15° (26%), and a longitudinal profile that is either straight, concave or convex.

Application and Examples:

• A fan is distinguished from a cone on the basis of slope gradient (Figure 16). Refer to CONE.
  
  
• Typically applied to fluvial (alluvial) fans, colluvial fans, or glaciofluvial fans.

Examples:	active colluvial fan	rCf
	"relict" fluvial fan	sgFf

• Applied to coalescing fans where individual fans are distinguishable.

Definition of Surface Expression Terms

Steep sided hillock(s) and hollow(s) with multidirectional slopes dominantly between 15 and 35° (26 to 70%) if composed of unconsolidated materials; bedrock slopes may be steeper. Local relief is greater than 1 metre. In plan, an assemblage of non-linear, generally chaotic forms that are rounded or irregular in cross-profile.

Application and Examples:

• Hummocky unconsolidated materials are sufficiently thick to mask the surface irregularities of the underlying unit (Figure 17).
  
  
• Hummocky topography is distinguished from undulating topography on the basis of the predominant slope angles. Refer to UNDULATING TOPOGRAPHY.
  
  
• Commonly applied to knob-and-kettle topography, some landslide deposits, and hummocky bedrock.

Examples:	kame-and-kettle glaciofluvial sediments	gsFGh-H
	landslide debris	mdCh
	till mantle of variable thickness overlying hummocky bedrock (till is thin on crests and thicker in depressions)

An unidirectional (planar) surface with a slope gradient greater than 3° , to and including 15° (5 to 26%), and a smooth, longitudinal profile that is either straight, concave or convex; local surface irregularities generally have a relief of less than 1 metre.

Application and Examples:

• Does not include the surface expression fan. Refer to FAN.
  
  
• Applied to constructional slopes underlain by till or glaciofluvial materials, gently sloping beaches, and the floodplains of steep creeks.

Examples:	floodplain of a steep creek	bgFAj
	thick till with gentle slopes and minor surface irregularities	dmMj

• Not applied to till or colluvium, or other material on bedrock-controlled slopes.

Example:

till 2-3 m thick covering gently sloping bedrock

Figure 16. Examples of the surface expression terms rolling, ridged, undulation and hummocky. (a) Rolling till plain made up of low, gently sloping drumlinoid features on the Nahlin Plateau in the northwest corner of British Columbia (map symbol: Mm). (b) Drumlinized till plain on the McGregor Plateau; the drumlins are linear features characterized by steep slopes (map symbol: Mr). (c) Undulating glaciomarine deposit in the Fraser Valley characterized by gentle slopes and irregularly distributed swales (map symbol: W^Gu). (d) Till hummocks with steep slopes in the Interior of British Columbia (map symbol: Mh).

Moderately Steep Slope

Map Symbol: k

Definition of Surface Expression Terms

An unidirectional (planar) surface with a slope gradient greater than 26° , to and including 35° (50 to 70%), and a smooth, longitudinal profile that is either straight, concave or convex; local surface irregularities generally have a relief of less than 1 metre.

Application and Examples:

• Does not include the surface expression cone. Refer to CONE.
  
  
• Applied to constructional and erosional slopes in unconsolidated materials, such as scarps resulting from stream erosion, gully side-scarps, ice-contact slopes and talus slopes.

Examples:	scarp of glaciofluvial terrace	gFGk
	side-slopes of gully eroded into till	Mk

• Applied to erosional slopes in bedrock, and to rock where rock controlled slopes are covered by till, colluvium or other materials.

Examples:	moderately steep sloping bedrock	Rk
	colluvial veneer overlying moderately steep, smooth bedrock

Definition of Surface Expression Terms

Elongate hillock(s) with slopes dominantly between 3 and 15° (5 to 26%) with local relief greater than 1 metre. In plan, an assemblage of parallel or sub-parallel linear forms with subdued relief.

Application and Examples:

• Rolling topography is distinguished from ridged topography on the basis of predominatly gentler slopes (Figure 17). Refer to RIDGE(S).
  
  
• Rolling unconsolidated materials are sufficiently thick to mask the surface irregularities of the underlying material.
  
  
• Commonly applied to fluted till plains, swell-and-swale topography, and subdued, beach and bedrock ridges.

Examples:	"washboard" moraine	Mm
	beach strandlines	Wm

• Where rolling topography is the result of glaciation and reflects former ice-flow direction, the appropriate on-site symbols should be applied to the terrain map (e.g., drumlins, flutings, and roches moutonnées. See Glacial Features).

Example:

grooved till plain

Mm (with appropriate on-site symbol)

Definition of Surface Expression Terms

A level or very gently sloping, unidirectional (planar) surface with gradients up to, and including 3° (5%); local surface irregularities generally have a relief of less than 1 metre.

Application and Examples:

• Commonly applied to floodplains, deep organic deposits, lacustrine and marine plains, and the level portions of terraces and deltas (Figure 18).

Examples:	active floodplain	sgFAp
	thick organic deposit	Op
	silty lacustrine plain	zLp

Figure 17. Level to very gently sloping (<3°) active delta deposit (map symbol: sgF^Ap) (location of photo: Port Hardy, Vancouver Island).

Definition of Surface Expression Terms

Elongate hillock(s) with slopes dominantly between 15 and 35° (26 to 70%) if composed of unconsolidated materials; bedrock slopes may be steeper. Local relief is greater than 1 metre. In plan, an assemblage of parallel or sub-parallel linear forms.

Application and Examples:

• Ridged unconsolidated materials are sufficiently thick to mask the irregularities of the underlying material surface.
  
  
• Ridged topography is distinguished from rolling topography on the basis of predominatly steeper slopes (Figure 17). Refer to ROLLING.
  
  
• Commonly applied to drumlinized till plains, eskers, morainal ridges, crevasse fillings and ridged bedrock.

Examples:	sandy gravel esker	sgFGr
	till mantle of variable thickness overlying bedrock ridges

• Where ridged topography is the result of glaciation and reflects former ice-flow direction, the appropriate on-site symbols should be applied to the terrain map (e.g., drumlins, flutings, and roche moutonnées. See Glacial Features).

Example:	drumlinized till plain	Mr (with appropriate on-site symbol)

Steep Slope

Map Symbol: s

Definition of Surface Expression Terms

An unidirectional (planar) surface with gradients greater than 35° (70%), and a smooth longitudinal profile that is either straight, concave or convex; local surface irregularities generally have a relief of less than 1 metre; bedrock slopes may be more irregular.

Application and Examples:

• Most commonly applied to steep erosional slopes of unconsolidated materials, such as terrace scarps, river banks and lake shore bluffs, steep bedrock slopes such as cliffs and steep slopes overlain with colluvium.

Examples:	cirque headwall	Rs
	lakeshore bluff	LGs
	escarpment of a river terrace	Fs
	steep-sided gully in thick till (gully comprises entire polygon	Ms-V

• Where the map scale does not permit the delineation of a scarp, an on-site symbol should be applied to indicate the scarp location and extent (see Other Landforms and Features).

Example:	multiple fluvial terraces with narrow scarps	Ft (with scarp symbols)

Definition of Surface Expression Terms

A single or assemblage of step-like forms where each step-like form consists of a scarp face and a horizontal or gently inclined surface (tread) above it.

Application and Examples:

• Terrace is applied to both the scarp and the flat tread, that is, to the whole feature in the landscape; includes river and lake terraces, kame terraces and structurally-controlled, stepped topography (Figure 18).

Examples:	river terrace	gsFt
	stepped bedrock topography	Rt

• In units comprising more than one terrace, individual terrace scarps can be designated by a scarp on-site symbol (see Other Landforms and Features).

Figure 18. Terraces made up of thick Quaternary sediments (map symbol: F^Gt) (location of photo: Churn Creek near the Gang Ranch).

Definition of Surface Expression Terms

Gently sloping hillock(s) and hollow(s) with multidirectional slopes generally up to 15° (26%); local relief is greater than 1 metre. In plan, an assemblage of non-linear, generally chaotic forms that are rounded or irregular in cross-profile.

Application and Examples:

• Undulating topography made up of unconsolidated materials sufficiently thick to mask the surface irregularities of the underlying material.
  
  
• Undulating topography is distinguished from hummocky topography on the basis of the predominantly gentler slopes (Figure 17). Refer to HUMMOCK(S).
  
  
• Commonly applied to undulating till plains, some landslide and dune deposits, and some ice-contact deposits.

Examples:	undulating till plain	Mu
	dunes on river terrace
	discrete areas of kame hummocks and undulations	FGhu

Veneer

Map Symbol: v

Definition of Surface Expression Terms

A mantle of unconsolidated materials too thin to mask the minor irregularities of the surface of the underlying material. It is between about 10 cm to 1 metre in thickness and possesses no constructional form typical of the material genesis.

Application and Examples:

• The surface topography of the veneer is indicated by either the surface expression of the underlying unit, or as expressed by the contour lines of the topographic map (Figures 13 and 14).
  
  
• When the underlying unit is unconsolidated material, its presence must be indicated by stratigraphic information, (see Stratigraphic Units).

Example:	sandy eolian veneer overlying river terrace gravels

• If the underlying unit is bedrock, no stratigraphic information need be supplied, except where the contours of the topographic map do not adequately depict the land surface.

Examples:	colluvial veneer overlying bedrock with surface shape shown by contours	Cv
	colluvial veneer overlying bedrock with surface shape not shown by contours

• If veneer (v) and thin veneer (x) are used together, e.g., Cvx, then v indicates material 20 cm to 1 m thick, and x indicates material thinner than 20 cm.

Mantle of Variable Thickness*

Map Symbol: w

Definition of Surface Expression Terms

A layer or discontinuous layer of surficial material of variable thickness (typically 0 to 3 m) that fills or partly fills depressions in an irregular substrate. It is generally too thin to mask prominent irregularities in the underlying material (see figure 14c).

Application and Examples:

• Similar to blanket and veneer.
  
  
• Mantle of variable thickness is draped over the underlying material and has no constructional form of its own.

Examples:	mantle of variable thickness over hummocky rock (Figure 13c)
	mantle of glaciolacustrine sediments over hummocky till (Figure 14b)

Thin Veneer*

Map Symbol: x

Definition of Surface Expression Terms

A very thin layer of unconsolidated material about 2-20 cm in thickness.

Application and Examples:

• Similar to veneer. Intended primarily for bioterrain mapping that is to be used as the basis for ecosystem mapping.
  
  
• If veneer (v) and thin veneer (x) are used together, e.g., Cvx, then v indicates material 20 cm to 1 m thick, and x indicates material thinner than 20 cm.

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