GeoVancouver

Objectives

To explore the impact of Gradational / Denudational Processes on the Greater Vancouver area.

Let's look at the impact of Gradational / Denudational Processes on the Greater Vancouver area.

GeoVancouver

The following information and images are courtesy of the Geological Survey of Canada.

Authors: Robert J.W. Turner and John J. Clague
Design and Production: David Lemieux

Vancouver's Landscape

Flood Hazard

This map provides a generalized interpretation of hazard based on the distribution of modern flood deposits. Low-lying areas adjacent to rivers and the sea shore are coloured red. These areas are underlain by modern flood and coastal storm deposits. The red zone includes floodplains of the Fraser River and its tributaries, and gently sloping fans at the mouths of the Chilliwack, Coquitlam, Seymour, Capilano rivers. This zone also includes poorly drained areas in the Nicomekl and Serpentine river valleys. Although most of these areas have been dyked to protect people and property, they are still at risk from rare, exceptionally large river floods. Low-lying shorelines exposed to waves and strong winds can also be flooded during exceptional storms if the winds push water inland. Localized flooding can occur at the front of the Fraser delta when a storm or high tide coincides with a Fraser River flood. In both the red and black zones on the map, small streams, which are not shown at this scale, can also overflow their banks. These relatively small floods are triggered by heavy rainstorms.

Moderate to High (modern lowland sediments)
Low - except adjacent to small streams (uplands and mountains)

Slopes and Landslides

The slope of the land surface ranges from nearly horizontal on floodplains to more than 20 degrees through much of the Coast and Cascade Mountains and on escarpments bordering uplands in the Fraser Valley. Why is slope important? First, it affects surface drainage -- in a general sense, drainage improves as the land surface steepens. Second, slope is an important factor in the stability of the land surface -- most landslides in the Vancouver area occur on slopes that are steeper than 20degrees (red areas on this map). Locations of many of the landslides that have occurred in this century in the Fraser Valley are plotted on the map (landslides in the Coast and Cascade Mountains are not included). Most landslides in the Fraser Valley involve Ice Age sediments and are triggered by intense rainstorms. In contrast, many of the landslides in the Coast and Cascade Mountains are in bedrock (rockfalls and rockslides). A common type of landslide in both regions is rapid flows of water-saturated debris (debris flows).

<10 degrees
10 - 20 degrees
> 20 degrees
landslide

Locations of landslides from Armstrong and Hicock 1979, 1980 (see ADDITIONAL INFORMATION) and G.H. Eisbacher and J.J. Clague, 1981, Urban landslides in the vicinity of Vancouver, British Columbia, with special reference to the December 1979 rainstorm, Canadian Geotechnical Journal, v.18, pp. 205-216. Slope data derived from British Columbia government Terrain Resource Information Management (TRIM) data.

Groundwater and Aquifers

Aquifers are bodies of sediment or rock that are saturated and sufficiently permeable to provide subsurface water to wells. Most groundwater in the Fraser Valley is derived from aquifers in modern and Ice Age sediments. These aquifers are a major source of high-quality water for drinking and other uses. The British Columbia Ministry of Environment, Lands and Parks has classified 71 aquifers in the Fraser Valley according to current levels of use and vulnerability to contamination. Almost two-thirds of the aquifers are shallow and can be easily contaminated by downward infiltration of waters laced with agricultural fertilizers and pesticides, manure, septic effluent, or gas and oil from leaking storage tanks. The most heavily utilized of these highly vulnerable aquifers occur in the Abbotsford and Langley/Brookswood areas. Less developed, but highly vulnerable aquifers occur in sediments below the floodplain and delta of the Fraser River. Deeper aquifers overlain by silts, clays, or tills of low permeability are less vulnerable to contamination. The most important of these deep aquifers occur in the Aldergrove area; others underlie the uplands of Vancouver, Burnaby, Surrey, and Langley, and the lowland of the Nicomekl and Serpentine rivers. Some groundwater is also pumped from fractured bedrock, for example, at Grant Hill, Mission, and Belcarra. The thin soil cover over these bedrock aquifers makes them highly vulnerable to contamination. Some aquifers, in both sediments and bedrock, have poor water quality due to elevated levels of naturally occurring substances such as chloride, iron, sulphur, and fluoride.

Aquifers not assessed
Aquifers in Bedrock (high vulnerability)

Aquifers in Sediment
high vulnerability / heavy use
moderate to high vulnerability / low to moderate use
low vulnerability/ low to heavy use

Map based on R. Kreye and M. Wei, 1994, A proposed aquifer classification system for groundwater management in British Columbia, British Columbia Ministry of Environment, Lands, and Parks, Water Management Division, Hydrology Branch, Groundwater Section, 67 p.

Earthquake Liquefaction

During an earthquake loose water-saturated silts and sands at shallow depth may lose their strength and transform into a fluid (liquefaction). Deeper sediments are more consolidated, have higher confining pressures, and consequently are less likely to liquefy. When sand beneath a layer of silt or clay liquefies, the capping layer may "glide" laterally under the influence of gravity towards a slope, such as the bank of a nearby river channel, causing ground cracking. Foundations of highways, bridges, and buildings, as well as buried sewer and gas lines, can be damaged by such movements. Liquefaction can also trigger landslides at the front of the Fraser delta. The red zone shows areas of relatively loose, saturated lowland sediments (i.e. lowlands). Liquefaction is likely to occur during a strong earthquake in those parts of the red zone where there is shallow subsurface sand and coarse silt, for example the Fraser delta.

Moderate to High (modern lowlands sediments)
Low (Ice Age upland sediments)
Nil (bedrock)

This map provides only a generalized interpretation of liquefaction susceptibility during an earthquake and should not be used for local geotechnical evaluation.

Geomap Vancouver

Physiography

Assignment Work

Note: E-mail your responses to your instructor as a word document attachment. Remember to respond in complete sentences. This assignment is worth 10 marks.

Flood Hazard
1a) Which communities are most vulnerable to flooding and why?
b) Why do you think so many people have settled in these communities although they are vulnerable to flooding?

Slopes and Landslides
2) What do most landslides in the Fraser Valley involve and how are they triggered?

Groundwater and Aquifers
3a) What are aquifers?
b) Why are the Brookswood and Abbotsford aquifers so vulnerable to contamination?
c) List four contaminants that are a threat to these aquifers.

Earthquake Liquefaction
4a) Define liquefaction.
b) List three communities most vulnerable to this effect and what could be consequences?

Geomap Vancouver
5) Construct a table to organize your answers to the following questions (you may answer in point form):

a) List the dominant geological materials for each of the following communities - Delta, Surrey, Vancouver, and West Vancouver?

b) Give the origin of the geological materials (i.e. how did it get there?).

c) Indicate whether the origin is reflective of gradational or tectonic processes at work.

Physiography
6a) What type of bedrock dominates under Richmond and Delta along the A to A' cross-section?

b) What type of bedrock dominates under the Abbotsford and Mission area along the B to B' cross-section?

c) Why is there a difference?

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