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

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 
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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 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.

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).

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

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
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.

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		

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).