THE INFLUENCE OF THE QUATERNARY GEOLOGY OF CANADA ON MAN'S ENVIRONMENT

responsible for many of these landslides are still active to-day and consequently most landslides areas are presently active (Christiansen, 1983; Sauer, 1983).
One of the most extensive areas of landslides within the region, and perhaps anywhere in Canada, occurs along the Manitoba Escarpment which rises in places 300 m in 10 km. Evidence of slumping is present along much of the escarpment but it is best displayed along the east and northeast side of Porcupine Hills (Wickenden, 1945; Scott and Brooker, 1968; Fig. 12.14). The disturbed zone is estimated to be 200 km2 and appears to consist of four separate land-slides. Individual landslides are typically 5 km wide across the slip planes and 10 km parallel to them. The upper one-third to one-half of each landslide consists of a series of parallel grabens, commonly containing long narrow lakes. The lower parts of the slides are hummocky and comprise mixed black Cretaceous shale and Pleistocene sediments. Cretaceous shales of the Favel and Vermilion River Formations, both containing layers of bentonite, occur along the base of the escarpment. Springs and seepage zones were observed in the toe area of minor slope failures that had occurred along valley walls of creeks that drain the northern part of the slide area (Scott and Brooker, 1968). The age and specific cause of the landslides are not known. The toe of the failure truncates the lower Campbell Beach of glacial Lake Agassiz, however, and thus a maximum age of 9.3 ka can be assigned to the failure. It is possible that the presence of bentonite seams and groundwater discharge may have contributed to instability. In addition, drawdown of water levels associated with the early Holocene draining of Lake Agassiz, may have been a significant triggering factor.
Flood hazards
Spring snowmelt is the main source of runoff and erosion in the Prairie region except for local, intense thunderstorms during summer months. Flooding is not a general problem because of the topographic configuration largely developed in response to Quaternary processes and events. Most large rivers are deeply incised and many areas are dotted with undrained sloughs which maximize groundwater recharge and minimize overland runoff. Risk of flooding, however, occurs in valley bottoms and in the lowlands of Manitoba where Red and Assiniboine rivers drain across the flat-floored Lake Agassiz Basin. Past floods in this basin have caused millions of dollars damage and loss of life. Flood risk potential is greatest during the spring and depends upon winter snow accumulation, rate of snowmelt, and precipitation during the snowmelt period. Governments have spent millions of dollars on the construction and maintenance of dykes, dams, and flood control programs.
The most impressive flood diversion project to date has been the Red River Floodway. It was excavated to carry floodwater around the city of Winnipeg and back into Red River near Lockport. The channel is 56.7 km long and construction involved moving 764 X 106 m3 of material. The floodway is designed to carry a flow of 850 m3/s which should protect Winnipeg from floods with a recurrence frequency of 1 in 160 years (Table 12.5). Since the beginning of operational use of the floodway in 1968 flood damage to the City of Winnipeg has been eliminated.
The Lake Agassiz plain has been further protected by a floodway between Assiniboine River and Lake Manitoba. This protects the city of Portage La Prairie, several villages,

and a 90 km strip of flat farmland between Portage La Prairie and Winnipeg.
The Federal and Provincial Governments, in 1975, initiated a flood damage reduction program aimed at identifying flood risk areas and discouraging further development in areas subjected to periodic flooding. The program involves mapping of flood risk areas, flood forecasting systems, land use planning, works to control flows, and acquisition of property or easements to control further development in flood risk areas.
Solution collapse
Solution collapse is a potential hazard over wide areas of the Prairies that are underlain by evaporites. For example, southern Saskatchewan is underlain by about 250 000 km2 of Devonian salt which is up to 200 m thick (Pearson, 1963). Dissolution of these salt beds has been a continuous process since their deposition, resulting in the formation of col-lapsed structures in overlying beds (Gendzwill and Hajnal, 1971). Crater Lake in southeastern Saskatchewan, the youngest known collapse structure, dates possibly at 13.6 ka (Christiansen, 1971). The lack of abundant collapse structures in the present surface suggests that this process does not pose a significant hazard.
GEOLOGICAL HAZARDS IN CENTRAL AND EASTERN CANADA
Jacques Locat and Jean-Yves Chagnon
Quaternary geology finds similar applications to civil engineering, mining, and hydrology in Ontario, Quebec, and the Atlantic Provinces as it does in the Prairies. Differing physiography and Quaternary histories, especially during the Late Wisconsinan glaciation, however, make for divergent geological hazards between these two regions. It is the management of these hazards that is emphasized in the following discussion of Quaternary geology and planning in east-ern Canada.
A geological hazard is defined as a possible event or unpredicted geological condition that is unwanted or undesired. It excludes such things as foundation settlement problems, disposal of toxic wastes, or groundwater supply problems. Natural hazards encountered in Ontario, Quebec, and the Atlantic Provinces are predominantly related to crustal deformation, mass movement, flooding, and erosion. Submarine processes, such as iceberg scour and coastal erosion, are considered in Volume 2 of the Geology of Canada (Keen and Williams, 1989).
Pertinent Quaternary events
In eastern Canada, many geological hazards are directly related to the Quaternary geological history of the area. The preglacial physiography and the processes of glaciation have

Locat, J. and Chagnon, J-Y.
1989: Geological hazards in central and eastern Canada; in Chapter 12 of Quaternary Geology of Canada and Greenland, R.J. Fulton (ed.); Geological Survey of Canada, Geology of Canada, no. 1 (also Geological Society of America, The Geology of North America, v. K-1).

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controlled the emplacement of the Quaternary deposits and these play a large role in determining the location of many hazards.
The downwarping of the crust, caused by the weight of the Laurentide Ice Sheet, depressed areas such as St. Lawrence and lower Ottawa valleys below sea level so that
Table 12.5. Maximum discharge and return period for the fifteen greatest floods on record on Red River at Winnipeg
	Date of	Estimated maximum
maximum	discharge at Redwood	Probable return
period (years)	
	discharge	Bridge (1000 m3/s)		
1826 May 21	6.37	E	667	
1852 May 21	4.67	E	147	
1861 May 8	3.54	E	45	
1979 May 10	3.00	"	26	
1950 May 19	2.93		23	
1974 April 24	2.93	*	23	
1966 April 14	2.50		14	
1970 May 3	2.26	*	10	
1882 May 3	2.26		10	
1969 May 1	2.17	*	9	
1916 April 22	2.02		8	
1948 April 30	1.95		7	
1956 April 27	1.95		7	
1904 April 24	1.87		6	
1897 April 27	1.83			
E - Estimated
computed natural flow without existing control works

upon retreat of the ice they were submerged by the sea. Ice damming and differential uplift during glacier retreat resulted in development of many large glacial lakes (e.g., lakes Iroquois, Algonquin, Ojibway). These basins were the loci of fine grained sedimentation. Crustal unloading initiated isostatic uplift (Quinlan, 1984) as evidenced by the emergence above sea level of most coastal areas of eastern Canada, and St. Lawrence and lower Ottawa valleys. Isostatic uplift of lake and marine basins led to stream incision of fine grained marine and lacustrine sediments, which in turn has triggered landsliding (Locat, 1977). Even where these deposits have not been incised, they remain metastable and create problems for the engineering of buildings and road foundations (Smalley, 1979; Quigley, 1980; Torrance, 1983; Locat et al., 1984).
Vertical movement has also caused faulting of Quaternary sediments and a reactivation of ancient vertical faults (Adams, 1981). In some areas, such as the Hudson Bay Lowland (Hardy, 1976; Andrews and Peltier, 1989) crustal uplift continues today.
Tectonic activity and seismicity
Earthquakes are frequent in eastern Canada (Leblanc, 1981; Basham and Adams, 1984). Major ones were noted as early as 1534-1535 (Smith, 1962) and tremors of greater than magnitude 7 on the Richter scale have occurred periodically during the last 300 years. A well known example is the Grand Banks Earthquake of 1929 (Basham and Adams, 1982; Keen et al., 1989) which triggered an enormous land-slide on the continental slope off Newfoundland. Table 12.6 lists recent major earthquakes in eastern Canada and Figure 12.15 shows locations of seismic activity. Additional information on zones of intense earthquake activity such as

Table 12.6. Major earthquakes of eastern Canada
Date	Epicentre	Intensity	Magnitude	Remarks	
1534-1535	Les Eboulements	IX - X			
June 1638	St. Lawrence Valley	IX		Near mouth of Saguenay River	
Feb. 1663	La Malbaie	X		Greatest ground shaking episode
recorded in Quebec	
Sept. 1732	Montreal	VIII	5.6-6.0	Resulted in one death and
damage or destruction of
300 homes	
Dec. 1791	Baie-St-Paul	VIII			
Oct. 1860	Riviere-Ouelle	VIII-IX		Vibrations felt over an area	
				of 1.8 x 106 km2	
Oct. 1870	Baie-St-Paul	IX			
28 Feb. 1925	La Malbaie	IX		Caused considerable damage in
Quebec, Trois-Rivieres, and
Shawinigan	
18 Nov. 1929	Grand Banks		7		
9 Jan. 1982	Miramichi		5.7		

the Mount Tremblant and Miramichi areas are available in Horner et al. (1979) and Basham and Adams (1984), respectively. These earthquakes are expressions of tectonic activity believed to be partly related to plate tectonic movements and possibly also to vertical uplift resulting from the stress relief caused by the melting of the last ice sheet. This strain energy appears to be dissipating in zones of crustal weakness. For example, the Charlevoix area of Quebec was the locus of a meteorite impact 350 Ma ago (Rondot, 1968; Roy and Duberger, 1983). The strain energy imparted by this impact is coupled with the regional tectonic stress to induce in situ principal stress ratios greater than 1 (o-h/o•v, v<1) in many areas. These deviatoric stresses can exceed the shear strength of the rock, resulting in popouts (White et al., 1974; Durand and Ballivy, 1974). Compilations of seismicity and neotectonism in eastern Canada have been made by Adams (1981) and Chagnon and Locat (1984), and a new compilation is being prepared by Adams for the neotectonics volume of the Geological Society of America's Geology of North America series.
Mass movement
Many landslides have occurred and will continue to occur in the fine grained sediments of eastern Canada. The most re-cent major ones are listed in Table 12.7. Loss of life has resulted in many cases from these mass movements. In the last

two decades major studies were undertaken to shed more light on the causes of landslides and to attempt some measure of prediction (Chagnon, 1968; Tavenas et al., 1971; Mitchell and Markell, 1974; Quigley, 1980; Lebuis et al., 1983; Locat et al., 1984; Lefebvre, 1984). Natural mass movements are not entirely restricted to Quaternary sediments but also occur locally in rock materials (Dionne, 1969a).
Landslides in soft clay
Landslides of more than one type occur in soft sediments (Fig. 12.16-12.18). Depending on soil properties, deposit stratigraphy, and underlying topography, failures can be a simple block rotation or a large earthflow. Stability analysis of the first rupture can be carried out easily as a routine measure (Lefebvre, 1981), but much remains to be done in the prediction of landslides in time and space (Locat et al., 1984). Mapping techniques for areas prone to landslide failure have been developed for Ontario (Klugman and Chung, 1976) and Quebec (Lebuis et al., 1983). Carson and Bovis (1989) also discuss flowslides in marine clay in another part of this volume.
The major landslides of eastern Canada are found in the so-called sensitive clays located primarily in St. Lawrence, lower Ottawa, and adjacent tributary valleys.

Figure 12.15. Locations of earthquake epicentres and magnitude of earthquakes in eastern Canada and adjacent United States (from Geophysics Division, Geological Survey of Canada).