Soils of the - Agriculture and Agri-Food Canada

SURFICIAL GEOLOGIC DEPOSITS
Several glaciations, marine submergence and rebound, postglacial fluvial action and eolian depositio n
have produced a wide variety of surficial geologic deposits (soil parent materials) in the map area . They vary i n
texture, form and extent, and range from mostly colluvial and morainal materials in the mountains to comple x
fluvial and glaciofluvial, marine and glaciomarine, lacustrine and glaciolacustrine, organic and eolian depôsit s
in the valleys . The general characteristics of the various materials, in the context of the map area, are briefl y
described in the following paragraphs . The individual soils developed on each deposit are shown in Table 2 .
(1) Morainal (glacial till) deposits are materials laid down by glacier ice . They are common above abou t
150 m elevation and are mainly strongly or steeply sloping . They consist of compact, slowly permeable ,
heterogeneous mixtures of boulders, stones, gravel, sand, silt and clay derived mainly from th e
associated granitic bedrock . Textures are moderately coarse, sometimes varying to medium, wit h
gravelly sandy loam or sandy loam being most common . The deposits are generally deeper than 1 m
and usually conform topographically to the underlying bedrock . In the eastern part of the map area th e
morainal deposits are usually capped by a veneer of eolian material mostly less than 100 cm thick .
Here, the surface textures are silt loam or loam .
(2) Colluvial deposits are common in the mountains and occupy relatively small areas elsewhere . The y
occur mostly on or at the base of steep slopes and on ridge tops and consist of materials originatin g
from nearby sources which have been redeposited by the action of gravity. The deposits are usuall y
loose, moderately to rapidly permeable and variable in depth to bedrock . Usual textures are gravell y
sandy loam with a high proportion of stones and cobbles . They tend to be unstable and in some area s
are still actively accumulating . In the eastern part of the map area, mainly on Sumas and Vedde r
mountains and near Mission, silty eolian material is mixed into the colluvium .
(3) Glaciofluvial deposits were laid down by flowing water during glacial advance and recession an d
are most common below 250 m elevation . They consist mainly of stratified gravels and sands, contai n
varying amounts of stones, and are usually rapidly permeable . The land surfaces are mostly level o r
gently undulating terraces and plains, although sometimes, they may be kettled or hummocky ,
particularly in ice-contact areas . Where glacial deltas predominate the deposits are usually gently o r
moderately sloping . Most deposits are relatively deep (well in excess of 2 m) and textures in or near
the surface usually vary from gravelly sandy loam or loam to sand and gravel . In the eastern part of th e
map area, relatively large areas of glaciofluvial deposits are capped by a silty eolian veneer . Here th e
surface textures are loam or silt loam .
(4) Fluvial deposits consist of materials deposited by flowing water since glacial time . They have eithe r
been relatively recently deposited or are still in the process of deposition . Several groups of fluvia l
deposits have been identified in the Langley-Vancouver map area .
(i) Deltaic deposits occur where moving water carrying sediment discharges into a relatively stil l
water body. In the case of the Langley-Vancouver map area, the main receiving waters are Georgi a
Strait and Mud Bay. Most of Richmond and Delta Municipalities and the Serpentine-Nicomekl Rive r
valley of Surrey Municipality are composed of these deposits with the sediment mainly bein g
provided by the Fraser River in the first two instances . The surface deposits are stone-free an d
variable in texture, ranging from sand to silty clay, with the finer textures being most common . Th e
deposits have high groundwater tables and the mostly sandy subsoils (below 1 to 2 m depth) ar e
saline . High contents of sulphurous compounds are also common in the subsurface and subsoi l
layers (Clark, Gobin and Sprout, 1961) . These mixed, marine and non-marine deltaic deposits"all li e
below 5 m elevation and, where not dyked, are subject to periodic flooding, either by high tid ės o r
river overflow. Surface topography varies from level to gently rolling .
(ii) Floodplain deposits of the Fraser and other rivers comprise much of the lowlands of the Langléy -
Vancouver map area . The deposits mostly lie below 10 m elevation, have level to gently rollin g
topography and include both lateral and vertical accretions . Textures range from sandy to clayey i n
the surface and usually grade to sand at depths of 0 .5 to 2 m . Most areas are affected by hig h
groundwater tables and many areas are poorly drained . Periodic flooding during freshet period s
occurs in undyked areas .
(iii) Alluvial deposits, variable in nature, have been laid down by several local streams and smalle r
rivers flowing across the uplands and lowlands and in mountain valleys . These include levees ,
floodplains and terraces which range in texture from gravel and sand to silty clay depending on th e
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