The Physical Regioims OfWester a Canada

Our country has a difficultlandscape. Its mountains andplains, its massive Shield,

and its harsh lands in the Northhave made the development ofCanada a challenge. The physicalgeography of western Canada isdominated by the presence of theCanadian Shield, the Interior Plains,and the Western Mountains. Each ofthese regions has distinct geologicalfeatures, landforms, and climaticconditions. The Canadian Shield isthe oldest region; the Interior Plainshave the most uniform physical

characteristics; and the WesternMountains have the most complexphysical structure.

The Canadian ShieldCanada is a young country in politi¬cal years but one of the oldest ingeologic years. Large masses of rock,known as shields, are the oldestparts of the Earth. They are hard,rigid blocks around which theyounger areas of the continents haveformed.

geological: having to dowith geology, the studyof the history of theEarth as found in rocks

topography: the shapeof the land

Figure 3-7 The physicalregions of western Canadaare based primarily on theage and type of rock andon topography.

Igneous and metamorphic rock layers

INTERIOR PLAIN

Sedimentary Rock Layers

CORDILLERAYoung Fold Mountains

CANADIAN SHIELD

Ancient shields

ErosionHHHBSRi

GEOGRAPHY OF WESTERN CANADA 99

DID YOU KNOW?The most recent volcanicactivity in British Columbiaoccurred in the Northwestin 1750, when a volcaniceruption destroyed someNisga'a villages.

Figure 3-9 The farms of theInterior Plains

Figure 3-8 The worn-down landscape of the Shield is evident in this photo.

Much of this rock has been changedby heat and/or pressure into meta-morphic rock. This process also cre¬ated the Shield's vast storehouse ofminerals, such as copper, gold, lead,and nickel. The exposed rock, how¬ever, makes the land unsuitable foragriculture and large-scale settlement.

The Interior PlainsIn Canada, the Interior Plains regionstretches from the Canadian Shieldto the Rocky Mountains. It coversalmost all of Alberta. The InteriorPlains were formed as eroded mater¬ial from the Canadian Shield wasdeposited in layers at its edges.These generally horizontal layers ofsedimentary rock make up theplains. Millions of years ago, whenthe area had a tropical climate andwas covered by water, occasional

flooding left deposits of plants andanimals. Over time, these depositswere compressed between the sedi¬mentary layers to form deposits offossil fuels, such as oil and naturalgas, and evaporites, such as potash.

igneous rock: rock thathas been formed bythe solidification ofmolten material

metamorphic rock: rockchanged from itsoriginal form intoanother form throughheat and pressure

sedimentary rock: rockmade up of sedimentlaid down in layerswhich have growntogether

The Canadian Shield stretchesfrom the Arctic islands aroundHudson Bay to the AdirondackMountains in the United States, andeast across Labrador. The Shield wasonce a volcanic mountain range as

high as the Himalayas. Over mil¬lions of years, weathering and ero¬sion wore it down into a landscapeof exposed rock and lakes. TheShield was originally made up ofigneous rock from its volcanic state.

100 CHAPTER 3

WESTERN

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DID YOU KNOW?

Figure 3-10 The Rocky Mountains near Banff

The Western MountainsThe Western Mountains are madeup of parallel mountain ranges thatare separated by a series of plateausand valleys. Mountain ranges of thistype are known as a "cordillera."

The Rocky and Coast mountainranges and the Interior Plateau wereformed when plate collision causedthe Earth's crust to buckle, whichlifted sections of it into the air. Thepressure of plate tectonics alsocaused the terrain to form valleys,plateaus, and trenches. Erosion from

rivers and glaciers sculpted therugged, mountainous landscape thatwe know today. Sediments carriedoff by rivers, called "alluvium,"formed fertile river valleys, such asthe Eraser River Valley. The area isalso rich in minerals, such as copper,gold, molybdenum, and coal.

The mountain-building processcontinues today in the St. EliasRange, where British Columbia,the Yukon, and Alaska meet Theforce of plate collision is pushingup these mountains, includingCanada's highest, Mount Logan,at a rate of 4 centimetres a year.

CORDILLERA REGION

fossil fuel: a natural fuelformed by geologicalforces from the residueof living organisms

evaporite: a type ofsedimentary rock thatoriginates by theevaporation of seawater

plate: a slab of theEarth's crust. Plates areunderneath all thecontinents and oceans.They regularly moveaway from, and collidewith, each other.

tectonics: the study offorces within the Earththat form its surfacefeatures, such asmountain ranges andocean basins

GREAT PLAINS

3] Mountains,foothills

I . I Plateaus,basins

I Lowlands,plains andtrenches

Figure 3-11 The diverse landscapes of BritishColumbia form six parallel regions. This hasmade east-west travel in BC particularly difficult.

NTER OR

QUEENCHARLOTTE

SOUND

PACIFICOCEAN

Victoria