C h a p t e r 2 : Physical Geography of Ontario David J. B. Baldwin1, Joseph R. Desloges2, and Lawrence E. Band3 Introduction Table 2.1 Ontario, the second largest province of Canada, covers English as a Second Language (ESL) enrolment by approximately 1 million km2 and extends approximately School District, 1993-94. from 42°N to 57°N latitude and from 75°W to 95°W longitude. The major patterns of geoclimatic features ESL as Percent across the province are strongly interrelated and form of Total District School District ESL Enrolment Enrolment the foundation for the biotic and natural disturbance processes of Ontario’s many different landscapes. In this Vancouver 25,960 48% chapter, we describe the spatial distribution of the abi- Richmond 8,686 39% otic factors, including bedrock, surficial geology, climate, Surrey 5,775 12% soils and hydrology, that influence and interact with Burnaby 3,599 17% the biotic systems. The relationships among these ele- Coquitlam 2,571 9% North Vancouver 1,892 11% ments, and the various biotic and natural disturbance Abbotsford 1,073 6% processes at work across the province, are the subject Victoria 1,043 4% of subsequent chapters in Sections I and II of this book. In keeping with the focus of this book on Ontario’s Source: BCTF (1994). northern managed forest landscape, we do not describe the southern, settled portion of the province, but refer cent of the province is underlain by Precambrian rock the reader to well-known summaries of that region, such of the Canadian Shield (Thurston 1991). In the Phan- as Chapman and Putnam (1984). erozoic age, sedimentary rocks developed in marine basins along the northern border of the Shield, form- Geology and Terrain ing the Hudson Bay lowlands, and in the Great Lakes The geology and terrain of Ontario are best understood Basins in the south (Figure 2.1). The Shield can be di- by first examining the foundation of bedrock geology vided into three major geological and physiographic underlying the surficial deposits and landforms. Table regions, from the oldest in the northwest to the young- 2.1 provides a summary of the geologic time scale rel- est in the southeast. The northwestern region, known evant to Ontario’s bedrock and surficial geology. as the Superior Province, is more than 2.5 billion years The bedrock geology of Ontario is variable in lithol- old. This region, which can be described as lying north ogy, structure and age, although approximately 61 per- and west of the present city of Sudbury, is composed 1 Ontario Forest Research Institute, Ontario Ministry of Natural 3 Department of Geography, University of North Carolina, CB# Resources, 1235 Queen Street East, Sault Ste. Marie, Ontario 3220 Chapel Hill, North Carolina, USA. 27599 P6A 2E5 2 Department of Geography, University of Toronto, 100 George Street, Toronto, Ontario M5S 3G3 2 Physical Geography of Ontario Table 2.1 Geologic periods relevant to Ontario’s bedrock and surficial geology. (Adapted from Trenhaile 1998 and Webber and Hoffman 1970) Physical Geography of Ontario 3 mainly of felsic intrusive rocks forming the rocky Sev- across most of Ontario have low total relief and de- ern and Abitibi uplands (Bostock 1970). The central ranged drainage patterns from glaciation, both of which region, known as the Grenville Province, is 1.0 to 1.6 result in poor drainage. billion years old. This region lies to the south of Sudbury, All of Ontario underwent a set of major glacial ad- and is dominated by metasedimentary rocks that form vances and retreats during the last major glacial stade, the Laurentian highlands. The Penokean hills, a fold up to 12,000 years BP. Northern parts of the province belt, and the Cobalt plain, an embayment, constitute were still covered with ice 8000 years BP (Hardy 1977, the Southern Province, which is a narrow region ap- Ritchie 1989). The Hudson Ice, a distinct domain within proximately 1.8 to 2.4 billion years old extending from the Laurentide Ice Sheet, had a number of separate Sault Ste. Marie in the west approximately to Kirkland lobes, one extending northeastward up the St. Lawrence Lake in the east. River, a second westward into Lake Huron, and a third To the north of the Shield, in the area generally re- east-to-northeastward out of Lake Superior (Dyke et ferred to as the Hudson Bay lowlands, the bedrock is com- al. 1989). The retreat of the ice was neither uniform posed of carbonate sedimentary formations. These nor continuous. Isolated re-advances, such as the formations date primarily from the Silurian period, but Cochrane surge, occurred during the period of final there are significant areas from the Ordovician and deglaciation. Figure 2.3 provides an overview of the Devonian periods as well. Other sedimentary rocks occur major features and surficial materials across the prov- near the city of Ottawa, in an area referred to as the ince. During the retreat, streams formed along the mar- Ottawa embayment, as well as throughout areas north gins of the ice sheets and created oblique, linear patterns of Lakes Erie and Ontario (Dyke et al. 1989). The clas- of deposition. Glaciofluvial complexes that occur in vari- tic and marine carbonate bedrock of southern Ontario ous parts of the province (for example, the Oak Ridges is interrupted by the Frontenac Axis, a southern exten- complex in southern Ontario, and the Burntwood-Knife sion of the Shield, which intersects the St. Lawrence and Harricana-Lake McConnell complexes in central Seaway east of Kingston. The Frontenac Axis has dif- Ontario, each extending hundreds of kilometres, pro- ferent forest cover and land use patterns than areas to vide evidence of the massive scale of the convergent either the west or east, owing to its uneven terrain and ice lobes and catastrophic meltwater discharges shallow, acidic soils, both characteristic of the Cana- (Brennand and Shaw 1994) beneath the ice sheets and dian Shield. at their forward margins. The topography of Ontario varies from flat plains to The retreating ice sheet fed a series of large meltwa- low, rolling uplands having 60 m to 90 m of relative ter lakes. Glacial Lake Algonquin covered much of the relief, to dissected uplands with ridges, escarpments and area from Sudbury to Huntsville. The Champlain Sea cuestas as high as 200 m above the adjacent terrain. flooded well above the current levels of the Ottawa This variation in topography originates from the bed- River Valley and of Lake Ontario. Lake Barlow-Ojibway rock structure; from extensive pre-Quaternary erosion, covered a large area south of James Bay over what is which is estimated at more than 6000 m since the last now referred to as the Claybelt. The Tyrrell Sea lay mountain-building episode (Card et al. 1972); and from over the Hudson Bay lowlands. In the northwest, Lake Quaternary glaciations that both eroded and filled the Agassiz covered virtually one-third of the province, pre-Quaternary surface. The significant relief that is joining with the Tyrrell Sea to the east for a short pe- present elsewhere in eastern North America is absent riod (Teller 1985). Neither the postglacial lakes nor from Ontario. The highest point in the province, Maple the Tyrrell Sea had fully receded until about 6000 BP. Mountain near Temagami, is 693 m. The most rugged The general northward retreat of the Laurentide Ice and fragmented surfaces occur in a band extending from Sheet left a predominately sandy to silty till cover over the north shore of Lake Superior, across the Algoma the southern part of the Shield and over southern On- highlands, through the Sudbury region and north of tario, in contrast to the silty and clayey till and clay- Manitoulin Island, and across the Madawaska highlands. rich lake and marine deposits that dominate the This height of land forms a continental divide between northern half of the province (Dredge and Cowan the Great Lakes and Arctic drainage of Hudson Bay; 1989). Low-lying and poorly-drained glacial deposits north of this line, the elevation falls off monotonically have become covered with peat and other organic de- (Figure 2.2). The large river basins that flow to the north posits (Figure 2.3). 4 Physical Geography of Ontario Figure 2.2 Topography of Ontario, generated from a 1-km digital elevation model. (Data from Mackey et al. 1994) Physical Geography of Ontario 5 Figure 2.3 Surficial geology of Ontario. (Adapted from Forest Landscape Ecology Program 1996) 6 Physical Geography of Ontario Figure 2.4 Temperature characteristics of Ontario: (a) annual mean daily temperature; (b) mean daily minimum temperature for January; (c) mean daily maximum temperature for July; and (d) growing-degree-days over 5oC. Temperatures interpolated from 30 years of data from more than 400 AES stations. (Adapted from Watson and MacIver 1995) Physical Geography of Ontario 7 Together, glaciation and postglacial deposition largely areas as far south as Kirkland Lake. The result is a sub- account for the present landscape of the province. The stantial reduction in growing-degree-days, relative to ice sheets sculpted or rounded the land and generally other locations in Canada at similar latitudes. For ex- reduced its elevation, removed the original topsoils, and ample, Winnipeg, Manitoba lies at approximately the exposed the bedrock. Deposits laid down by glacial same latitude as Cochrane, Ontario, but has about 1000 streams and lakes have strongly influenced soil devel- more growing-degree-days. Lake Superior and the Lake opment and, consequently, the composition of present- Huron moderate the winter temperature, “bending” the day forests (Thompson 2000, this volume). isolines around their shores (Figure 2.4b).