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GEOG 2RC3 (90)
Lecture

2 The Physical Environment.docx

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Department
Geography
Course
GEOG 2RC3
Professor
Walter Peace
Semester
Winter

Description
The Physical Environment Niagara Falls – Then and Now -since the end of the last Ice Age (12000 ya), Niagara Falls has retreated about 8km up the Niagara River -since Father Louis Hennepin saw the falls in 1678, retreat = 300m -explanation for the retreat/recession – geologic composition of Niagara Escarpment The Physical Environment -“why is Canada‟s physical geography so essential to an understanding of its regional geography?” -physical landscapes differ in terms of: -landforms -geology -climate -vegetation -soils -hydrology Definitions -physiographic region: an area with distinct surface landform features (geomorphology) and underlying rock structure (geology) -geomorphology: the study of landforms and the process(es) of their genesis (from Greek root words: geo – earth; and morpho – form) Geology -three basic rock types 1) Igneous: rocks formed when minerals crystallize during the cooling of molten liquids (ex: granite) -heat 2) Sedimentary: rocks formed through the layering of mineral particles (ex: limestone) -deposition 3) Metamorphic: existing rocks are altered through heat/pressure (ex: shale transformed into slate) -heat/pressure Landform Processes -erosional processes (water, ice, wind) -depositional processes (water, ice, wind) -challenges – imagining/understanding the ability of these processes to alter the physical landscape (force and time) Canada‟s Physiographic Regions -geographical evolution of North America featured three major developments 1) Formation of the Shield -early Pre-Cambian era -600 million-3.5 billion years ago -metamorphic and igneous rocks -„core‟ of North America 2) Formation of mountains -Appalachian Uplands – eastern North America; Paleozoic era -Arctic Uplands – north; Paleozoic era -Western Cordillera – west coast; Cenozoic era -these periods of „orogenesis‟ between 250 and 600 million years ago 3) Epeiric seas -shallow, sub-tropical seas covering the interior of North America during Ordovician and Silurian periods -deposition of sediments – Interior Plains, Hudson Bay Lowlands, and Great Lakes-St. Lawrence Lowlands Canadian Shield -p 36-38 -underlies more than half of Canada -har, crystalline rocks (metamorphic), mostly granite -rocks of western Slave Province, NWT, dated 4.06 billion years ago -image/identity of Canada – prototypical Canadian landscape -rocks, lakes, forests Western Cordillera -p 38-39 -Pacific Ocean – „Ring of Fire‟ (plate tectonics) -volcanic eruptions and earthquakes common here -16% of Canada‟s land mass -2 parallel systems of mountains -Rocky Mountains -Coast Range Mountains -separated by Intermontane Plateau Interior Plains -p 39-40 -20% of Canada‟s land mass -sedimentary rocks -low „relief‟ (difference between the highest and lowest points) – flat landscape -elevation increases from east to west Hudson Bay Lowlands -p 41-42 -3.5% of Canada‟s land mass -low-lying, poorly drained landscape (muskeg) -typical of lowlands -abundance of water -underlain by sedimentary rocks -difficult to build settlements Arctic Lands (Achipelago) -p 42-43 -10% of Canada‟s land mass -pre-Cambrian crystalline (igneous) rocks overlain by Paleozoic sedimentary rock -Ellesmere Island -top of the world -location was very different in the past (was closer to the equator) – climate allowed trees -rough, not flat landscape -Pangaela: original continent (before they split up to what we know today) -India was separate from Asia, eventually collided – creation of Himalayan Mountains Appalachian Uplands -p 43-44 -2% of Canada‟s land mass -very old, heavily-eroded mountains (Taconic Mountains – original mountains) -geologically complex (sedimentary, igneous, and metamorphic rocks) as a result of 2 periods of orogenesis (440 mya and 350 mya) -continues into the US Great Lakes – St. Lawrence Lowlands -p 44-45 -<2% of Canada‟s land mass -smallest physiographic region (110,000 sq km) -most heavily populated region (more than half of Canadians) -underlain by Paleozoic sedimentary rocks -Niagara Escarpment Summary -given Canada‟s enormous size, there is considerable variation in physical environments -all of Canadian landscape influenced by glaciation -links between physical and human geographies of Canada Physical Environment: Ice Age The Pleistocene Epoch -began 2.6mya, ended 12000ya -several advances (glacial periods) and retreats (interglacial periods) of continental ice sheets in the northern hemisphere beginning a million years BP (before present) up to 10000 years BP -Holocene Epoch: the current period on the geologic time scale -began 10,000 years ago -most recent glacial period – Wisconsin Ice Age -began 67,000ya and ended 12,500ya -maximum extent – 18-25,000ya -previous Ice Ages (named after the most southerly point reached): -Illinoian -Kansan -Nebraskan -scientific knowledge regarding ice ages is quite recent -early theories proposed by Louis Agassiz and Charles Lyell, 1830-1860 -coincides with many other important discoveries about the world -Darwin‟s Origin of Species published in 1859 -theories regarding the causes of Ice Ages focus on the factors which cause variation in the amount and distribution of sunlight (solar energy) reaching the Earth‟s surface -in each case, these factors affect the Earth‟s orbit, which in turn affects incoming solar radiation -these are natural factors (not human-induced) -three cycles of the Earth‟s orbit 1) Precession -Earth‟s orbit around the sun changes from more elliptical to less elliptical (more oval) -more oval – closer to the sun sometimes, further away sometimes -affects the timing of the seasons -cycle lasts approximately 19,000 years 2) Tilt -the Earth rotates on a tilted axis -the angle of the tilt varies slightly around 23 degrees -cycles lasts approximately 41,000 years 2) Eccentricity -the shape of the Earth‟s rotation on its axis varies from more circular to more elliptical (wobbles) -cycle lasts approximately 100,000 years -maximum extent of the Wisconsin Ice Sheet -into American mid-west south of Great Lakes -reached 18-25,000 years ago -ice depth – 3200m at the center, 1,600m at southern edge -ice melted out of southern Ontario 15-10,000ya -advance of ice (during a glacial period) associated with cooler temperatures and an increase in the volume of snow/ice -retreat of ice (during an interglacial period) associated with warmer temperatures and a decrease in the volume of snow and ice -pressure on the earth‟s crust causes it to compress; when released, it eventually springs back Glacial Landforms -result from various processes (or a combination): -erosion by ice -deposition by ice -erosion by meltwater -deposition by meltwater -glacial drift: material or debris (including clay, rocks, sand, silt, gravel) deposited in situ by melting glacial ice -materials may be sorted/stratified by glacial meltwater or they can be a heterogeneous mixture deposited by ice without water transport -moraines: ridges or mounds of glacial material deposited at/close to the ice margin -often associated with very irregular/uneven topography (hence the term “knob and kettle topography” -ex: Oak Ridges Moraine -several types – terminal, recessional, interlobate moraines -eskers: sinuous ridges of gravel, sand, and cobbles deposited by meltwater streams flowing in a tunnel inside a glacier -scale – up to 50m in height, 150m in width, length ranges from a few hundred meters to several hundred kilometers -drumlins: streamlined hills shaped like the inverted bowl of a spoon -5-50m in height, up to 3km long -long axis – parallel to direction of ice movement -usually many in an area (hence the term “basket of eggs topography”) -examples: Guelph, Westover, Caledonia, Peterborough -erratics: deposited by retreating glacial ice -rocks that are geographically and geologically foreign to their present location -sometimes referred to as “haystack boulders” -largest erratic in southern Ontario – Bleasbell Boulder (3km north of Trenton) – 8m high, 33,000 tons Glacial Landforms – Hamilton and Vicinity -Westover drumlin field -Waterdown and Vinemount moraines -Iroquois bar (shoreline of post-glacial Lake Iroquois) -gorges in Niagara Escarpment formed by erosion associated with glacial meltwater (misfit streams) The Niagara Escarpment -dominant physiographic (landform) feature in Great Lakes – St. Lawrence Lowlands -designated as a UNESCO World Biosphere Reserve in 1990 (12 in Canada) -first large-scale environmental land u
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