Plate tectonics is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of the Earth's lithosphere, since tectonic processes began on Earth between 3 and 3.5 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century; the geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s. The lithosphere, the rigid outermost shell of a planet, is broken into tectonic plates; the Earth's lithosphere is composed of many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, oceanic trench formation occur along these plate boundaries; the relative movement of the plates ranges from zero to 100 mm annually. Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust.
Along convergent boundaries, subduction, or one plate moving under another, carries the lower one down into the mantle. In this way, the total surface of the lithosphere remains the same; this prediction of plate tectonics is referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual expansion of the globe. Tectonic plates are able to move because the Earth's lithosphere has greater mechanical strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from spreading ridges due to variations in topography and density changes in the crust. At subduction zones the cold, dense crust is "pulled" or sinks down into the mantle over the downward convecting limb of a mantle cell. Another explanation lies in the different forces generated by tidal forces of the Moon; the relative importance of each of these factors and their relationship to each other is unclear, still the subject of much debate.
The outer layers of the Earth are divided into the asthenosphere. The division is based on differences in mechanical properties and in the method for the transfer of heat; the lithosphere is more rigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heat by conduction, whereas the asthenosphere transfers heat by convection and has a nearly adiabatic temperature gradient; this division should not be confused with the chemical subdivision of these same layers into the mantle and the crust: a given piece of mantle may be part of the lithosphere or the asthenosphere at different times depending on its temperature and pressure. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like asthenosphere. Plate motions range up to a typical 10–40 mm/year, to about 160 mm/year; the driving mechanism behind this movement is described below. Tectonic lithosphere plates consist of lithospheric mantle overlain by one or two types of crustal material: oceanic crust and continental crust.
Average oceanic lithosphere is 100 km thick. Because it is formed at mid-ocean ridges and spreads outwards, its thickness is therefore a function of its distance from the mid-ocean ridge where it was formed. For a typical distance that oceanic lithosphere must travel before being subducted, the thickness varies from about 6 km thick at mid-ocean ridges to greater than 100 km at subduction zones. Continental lithosphere is about 200 km thick, though this varies between basins, mountain ranges, stable cratonic interiors of continents; the location where two plates meet is called a plate boundary. Plate boundaries are associated with geological events such as earthquakes and the creation of topographic features such as mountains, mid-ocean ridges, oceanic trenches; the majority of the world's active volcanoes occur along plate boundaries, with the Pacific Plate's Ring of Fire being the most active and known today. These boundaries are discussed in further detail below; some volcanoes occur in the interiors of plates, these have been variously attributed to internal plate deformation and to mantle plumes.
As explained above, tectonic plates may include continental crust or oceanic crust, most plates contain both. For example, the African Plate includes the continent and parts of the floor of the Atlantic and Indian Oceans; the distinction between oceanic crust and continental crust is based on their modes of formation. Oceanic crust is fo
Canada is a country in the northern part of North America. Its ten provinces and three territories extend from the Atlantic to the Pacific and northward into the Arctic Ocean, covering 9.98 million square kilometres, making it the world's second-largest country by total area. Canada's southern border with the United States is the world's longest bi-national land border, its capital is Ottawa, its three largest metropolitan areas are Toronto and Vancouver. As a whole, Canada is sparsely populated, the majority of its land area being dominated by forest and tundra, its population is urbanized, with over 80 percent of its inhabitants concentrated in large and medium-sized cities, many near the southern border. Canada's climate varies across its vast area, ranging from arctic weather in the north, to hot summers in the southern regions, with four distinct seasons. Various indigenous peoples have inhabited what is now Canada for thousands of years prior to European colonization. Beginning in the 16th century and French expeditions explored, settled, along the Atlantic coast.
As a consequence of various armed conflicts, France ceded nearly all of its colonies in North America in 1763. In 1867, with the union of three British North American colonies through Confederation, Canada was formed as a federal dominion of four provinces; this began an accretion of provinces and territories and a process of increasing autonomy from the United Kingdom. This widening autonomy was highlighted by the Statute of Westminster of 1931 and culminated in the Canada Act of 1982, which severed the vestiges of legal dependence on the British parliament. Canada is a parliamentary democracy and a constitutional monarchy in the Westminster tradition, with Elizabeth II as its queen and a prime minister who serves as the chair of the federal cabinet and head of government; the country is a realm within the Commonwealth of Nations, a member of the Francophonie and bilingual at the federal level. It ranks among the highest in international measurements of government transparency, civil liberties, quality of life, economic freedom, education.
It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many other countries. Canada's long and complex relationship with the United States has had a significant impact on its economy and culture. A developed country, Canada has the sixteenth-highest nominal per capita income globally as well as the twelfth-highest ranking in the Human Development Index, its advanced economy is the tenth-largest in the world, relying chiefly upon its abundant natural resources and well-developed international trade networks. Canada is part of several major international and intergovernmental institutions or groupings including the United Nations, the North Atlantic Treaty Organization, the G7, the Group of Ten, the G20, the North American Free Trade Agreement and the Asia-Pacific Economic Cooperation forum. While a variety of theories have been postulated for the etymological origins of Canada, the name is now accepted as coming from the St. Lawrence Iroquoian word kanata, meaning "village" or "settlement".
In 1535, indigenous inhabitants of the present-day Quebec City region used the word to direct French explorer Jacques Cartier to the village of Stadacona. Cartier used the word Canada to refer not only to that particular village but to the entire area subject to Donnacona. From the 16th to the early 18th century "Canada" referred to the part of New France that lay along the Saint Lawrence River. In 1791, the area became two British colonies called Upper Canada and Lower Canada collectively named the Canadas. Upon Confederation in 1867, Canada was adopted as the legal name for the new country at the London Conference, the word Dominion was conferred as the country's title. By the 1950s, the term Dominion of Canada was no longer used by the United Kingdom, which considered Canada a "Realm of the Commonwealth"; the government of Louis St. Laurent ended the practice of using'Dominion' in the Statutes of Canada in 1951. In 1982, the passage of the Canada Act, bringing the Constitution of Canada under Canadian control, referred only to Canada, that year the name of the national holiday was changed from Dominion Day to Canada Day.
The term Dominion was used to distinguish the federal government from the provinces, though after the Second World War the term federal had replaced dominion. Indigenous peoples in present-day Canada include the First Nations, Métis, the last being a mixed-blood people who originated in the mid-17th century when First Nations and Inuit people married European settlers; the term "Aboriginal" as a collective noun is a specific term of art used in some legal documents, including the Constitution Act 1982. The first inhabitants of North America are hypothesized to have migrated from Siberia by way of the Bering land bridge and arrived at least 14,000 years ago; the Paleo-Indian archeological sites at Old Crow Flats and Bluefish Caves are two of the oldest sites of human habitation in Canada. The characteristics of Canadian indigenous societies included permanent settlements, complex societal hierarchies, trading networks; some of these cultures had collapsed by the time European explorers arrived in the late 15th and early 16th centuries and have only been discovered through archeological investigations.
The indigenous population at the time of the first European settlements is estimated to have been between 200,000
Canada–United States border
The Canada–United States border known as the International Boundary, is the longest international border in the world between two countries. It is shared between Canada and the United States, the second- and fourth/third largest countries by area, respectively; the terrestrial boundary is 8,891 kilometres long, of which 2,475 kilometres is Canada's border with Alaska. Eight Canadian provinces and territories, thirteen U. S. states are located along the border. The Treaty of Paris of 1783 ended the American Revolutionary War between Great Britain and the United States. In the second article of the Treaty the parties agreed on all of the boundaries of the United States, including but not limited to the boundary with British North America to the north; the agreed boundary included the line from the northwest angle of Nova Scotia to the northwesternmost head of Connecticut River, proceeded down along the middle of the river to the 45th parallel of north latitude. That parallel had been established in the 1760s as the boundary between the provinces of Quebec and New York.
It was surveyed and marked by John Collins and Thomas Valentine from 1771 to 1773. The Saint Lawrence River and the Great Lakes became the boundary further west. Northwest of Lake Superior, the boundary followed rivers to the Lake of the Woods. From the Lake of the Woods, the boundary was agreed to go straight west until it met the Mississippi River. In fact that line never meets the river; the Jay Treaty of 1794 created the International Boundary Commission, charged with surveying and mapping the boundary. It provided for removal of British military and administration from Detroit and other frontier outposts on the U. S. side. It was superseded by the Treaty of Ghent concluding the War of 1812, which included pre-war boundaries; the Rush–Bagot Treaty of 1817 provided a plan for demilitarizing the two combatant sides in the War of 1812 and laid out preliminary principles for drawing a border between British North America and the United States. Westward expansion of both British North America and the United States saw the boundary extended west along the 49th parallel from the Northwest Angle at Lake of the Woods to the Rocky Mountains under the Treaty of 1818.
That treaty extinguished British claims south of that latitude to the Red River Valley, part of Rupert's Land. The treaty extinguished U. S. claims to land north of that line in the watershed of the Missouri River, part of the Louisiana Purchase. Along the 49th parallel, the border vista is theoretically straight but in practice follows the 19th-century surveyed border markers and varies by several hundred feet in spots. Disputes over the interpretation of the border treaties and mistakes in surveying required additional negotiations resulting in the Webster–Ashburton Treaty of 1842; the treaty resolved the dispute known as the Aroostook War over the boundary between Maine on the one hand, New Brunswick and the Province of Canada on the other. The treaty redefined the border between New Hampshire and New York on the one hand, the Province of Canada on the other, resolving the Indian Stream dispute and the Fort Blunder dilemma at the outlet to Lake Champlain; the part of the 45th parallel that separates Quebec from the U.
S. states of Vermont and New York had first been surveyed from 1771 to 1773 after it had been declared the boundary between New York and Quebec, it was surveyed again after the War of 1812. The U. S. federal government began to construct fortifications just south of the border at Rouses Point, New York, on Lake Champlain. After a significant portion of the construction was completed, measurements revealed that at that point, the actual 45th parallel was three-quarters of a mile south of the surveyed line; this created a dilemma for the United States, not resolved until a provision of the treaty left the border on the meandering line as surveyed. The border along the Boundary Waters in present-day Ontario and Minnesota between Lake Superior and the Northwest Angle was redefined. An 1844 boundary dispute during U. S. President James K. Polk's administration led to a call for the northern boundary of the U. S. west of the Rockies to be latitude 54° 40' north, but the United Kingdom wanted a border that followed the Columbia River to the Pacific Ocean.
The dispute was resolved in the Oregon Treaty of 1846, which established the 49th parallel as the boundary through the Rockies. The Northwest Boundary Survey laid out the land boundary, but the water boundary was not settled for some time. After the Pig War in 1859, arbitration in 1872 established the border between the Gulf Islands and the San Juan Islands; the International Boundary Survey, called the Northern Boundary Survey in the United States, began in 1872. Its mandate was to estab
The Canadian Shield called the Laurentian Plateau, or Bouclier canadien, is a large area of exposed Precambrian igneous and high-grade metamorphic rocks that forms the ancient geological core of the North American continent. Composed of igneous rock resulting from its long volcanic history, the area is covered by a thin layer of soil. With a deep, joined bedrock region in eastern and central Canada, it stretches north from the Great Lakes to the Arctic Ocean, covering over half of Canada. Human population is sparse, industrial development is minimal, while mining is prevalent; the Canadian Shield is a physiographic division, consisting of five smaller physiographic provinces: the Laurentian Upland, Kazan Region, Davis and James. The shield extends into the United States as the Superior Upland; the Canadian Shield is U-shaped and is a subsection of the Laurentia craton signifying the area of greatest glacial impact creating the thin soils. The Canadian Shield is more than 3.96 billion years old.
The Canadian Shield once had jagged peaks, higher than any of today's mountains, but millions of years of erosion have changed these mountains to rolling hills. The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of the Proterozoic Eon that were progressively amalgamated during the interval 2.45 to 1.24 Ga, with the most substantial growth period occurring during the Trans-Hudson orogeny, between ca. 1.90 to 1.80 Ga. The Canadian Shield was the first part of North America to be permanently elevated above sea level and has remained wholly untouched by successive encroachments of the sea upon the continent, it is the Earth's greatest area of exposed Archean rock. The metamorphic base rocks are from the Precambrian and have been uplifted and eroded. Today it consists of an area of low relief 300 to 610 m above sea level with a few monadnocks and low mountain ranges eroded from the plateau during the Cenozoic Era. During the Pleistocene Epoch, continental ice sheets depressed the land surface creating Hudson Bay, scooped out thousands of lake basins, carried away much of the region's soil.
When the Greenland section is included, the Shield is circular, bounded on the northeast by the northeast edge of Greenland, with Hudson Bay in the middle. It covers much of Greenland, most of Quebec north of the St. Lawrence River, much of Ontario including northern sections of the Ontario Peninsula, the Adirondack Mountains of New York, the northernmost part of Lower Michigan and all of Upper Michigan, northern Wisconsin, northeastern Minnesota, the central/northern portions of Manitoba away from Hudson Bay, northern Saskatchewan, a small portion of northeastern Alberta, the mainland northern Canadian territories to the east of a line extended north from the Saskatchewan/Alberta border. In total, the exposed area of the Shield covers 8,000,000 km2; the true extent of the Shield is greater still and stretches from the Western Cordillera in the west to the Appalachians in the east and as far south as Texas, but these regions are overlaid with much younger rocks and sediment. The Canadian Shield is with regions dating from 2.5 to 4.2 billion years.
The multitude of rivers and lakes in the entire region is caused by the watersheds of the area being so young and in a state of sorting themselves out with the added effect of post-glacial rebound. The Shield was an area of large tall mountains with much volcanic activity, but over hundreds of millions of years, the area has been eroded to its current topographic appearance of low relief, it has some of the oldest volcanoes on the planet. It has over 150 volcanic belts; each belt grew by the coalescence of accumulations erupted from numerous vents, making the tally of volcanoes reach the hundreds. Many of Canada's major ore deposits are associated with Precambrian volcanoes; the Sturgeon Lake Caldera in Kenora District, Ontario, is one of the world's best preserved mineralized Neoarchean caldera complexes, 2.7 billion years old. The Canadian Shield contains the Mackenzie dike swarm, the largest dike swarm known on Earth. Mountains float on the denser mantle much like an iceberg at sea; as mountains erode, their roots are eroded in turn.
The rocks that now form the surface of the Shield were once far below the Earth's surface. The high pressures and temperatures at those depths provided ideal conditions for mineralization. Although these mountains are now eroded, many large mountains still exist in Canada's far north called the Arctic Cordillera; this is a vast dissected mountain range, stretching from northernmost Ellesmere Island to the northernmost tip of Labrador. The range's highest peak is Nunavut's Barbeau Peak at 2,616 metres above sea level. Precambrian rock is the major component of the bedrock; the North American craton is the bedrock forming the heart of the North American continent and the Canadian Shield is the largest exposed part of the craton's bedrock. The Canadian Shield is part of an ancient continent called Arctica, formed about 2.5 billion years ago during the Neoarchean era. It was s
The Great Plains is the broad expanse of flat land, much of it covered in prairie and grassland, that lies west of the Mississippi River tallgrass prairie in the United States and east of the Rocky Mountains in the U. S. and Canada. It embraces: The entirety of the U. S. states of Kansas, North Dakota, South Dakota Parts of the states of Colorado, Minnesota, New Mexico, Oklahoma and Wyoming The southern portions of the Canadian provinces of Alberta and SaskatchewanThe region is known for supporting extensive cattle ranching and dry farming. The Canadian portion of the Plains is known as the Prairies, it covers much of Alberta and southern Saskatchewan, a narrow band of southern Manitoba. Despite covering a small geographic area, the Prairies are home to the majority of each of the three provinces' respective populations; the term "Great Plains" is used in the United States to describe a sub-section of the more vast Interior Plains physiographic division, which covers much of the interior of North America.
It has currency as a region of human geography, referring to the Plains Indians or the Plains States. In Canada the term is little used. There is no region referred to as the "Great Plains" in The Atlas of Canada. In terms of human geography, the term prairie is more used in Canada, the region is known as the Prairie Provinces or "the Prairies." The North American Environmental Atlas, produced by the Commission for Environmental Cooperation, a NAFTA agency composed of the geographical agencies of the Mexican and Canadian governments, uses the "Great Plains" as an ecoregion synonymous with predominant prairies and grasslands rather than as physiographic region defined by topography. The Great Plains ecoregion includes five sub-regions: Temperate Prairies, West-Central Semi-Arid Prairies, South-Central Semi-Arid Prairies, Texas Louisiana Coastal Plains, Tamaulipas-Texas Semi-Arid Plain, which overlap or expand upon other Great Plains designations; the region is about 500 mi east to 2,000 mi north to south.
Much of the region was home to American bison herds until they were hunted to near extinction during the mid/late-19th century. It has an area of 500,000 sq mi. Current thinking regarding the geographic boundaries of the Great Plains is shown by this map at the Center for Great Plains Studies, University of Nebraska–Lincoln; the term "Great Plains", for the region west of about the 96th and east of the Rocky Mountains, was not used before the early 20th century. Nevin Fenneman's 1916 study Physiographic Subdivision of the United States brought the term Great Plains into more widespread usage. Before that the region was invariably called the High Plains, in contrast to the lower Prairie Plains of the Midwestern states. Today the term "High Plains" is used for a subregion of the Great Plains; the Great Plains are the westernmost portion of the vast North American Interior Plains, which extend east to the Appalachian Plateau. The United States Geological Survey divides the Great Plains in the United States into ten physiographic subdivisions: Coteau du Missouri or Missouri Plateau, glaciated – east central South Dakota and eastern North Dakota and northeastern Montana.
The Great Plains consist of a broad stretch of country underlain by nearly horizontal strata extends westward from the 97th meridian west to the base of the Rocky Mountains, a distance of from 300 to 500 miles. It extends northward from the Mexican boundary far into Canada. Although the altitude of the plains increases from 600 or 1,200 ft on the east to 4,000–5,000 or 6,000 feet near the mountains, the local relief is small; the semi-arid climate opens far-reaching views. The plains are by no means a simple unit, they are of various stages of erosional development. They are interrupted by buttes and escarpments, they are broken by valleys. Yet on the whole, a broadly extended surface of moderate relief so prevails that the name, Great Plains, for the region as a whole is well-deserved; the western boundary of the plains is well-defined by the abrupt ascent of the mountains. The eastern boundary of the plains is more climatic than topographic; the line of 20 in. of annual rainfall trends a little east of northward near the 97th meridian.
If a boundary must be drawn where nature presents only a gradual transition, this rainfall line may be taken to divide the drier plains from the moister prairies. The plains may be described in northern, intermediate and southern sections, in relation to certain peculiar features; the northern section of the Great Plains, north of latitude 44°, including eastern Montana, north-eastern Wyomi
The Arctic Cordillera is a vast dissected chain of mountain ranges extending along the northeastern flank of the Canadian Arctic Archipelago from Ellesmere Island to the northeasternmost part of the Labrador Peninsula in northern Labrador and northern Quebec, Canada. It spans most of the eastern coast of Nunavut with high glaciated peaks rising through icefields and some of Canada's largest ice caps, including the Penny Ice Cap on Baffin Island, it is bounded to the east by Baffin Bay, Davis Strait and the Labrador Sea while its northern portion is bounded by the Arctic Ocean. The range is located in Nunavut but extends southeast into the northernmost tip of Labrador and northeastern Quebec; the system is divided with mountains reaching heights more than 2,000 m. The highest of the group is Barbeau Peak on Ellesmere Island at 2,616 m, the highest point in eastern North America; the system is one of Canada's three mountain systems, the others being the Western Cordillera of Western Canada and the Canadian extension of the Appalachian Mountains into the Gaspé Peninsula and Atlantic Provinces.
The landscape is dominated by massive polar icefields, alpine glaciers, inland fjords, large bordering bodies of water, distinctive of many similar arctic regions in the world. Although the terrain is infamous for its unforgiving conditions, humans maintained an established population of 1000 people – 80% of which were Inuit. In addition, the landscape is 75% covered by ice or exposed bedrock, with a continuous permafrost that persists throughout the year, making plant and animal life somewhat scarce; the temperature of the Arctic Cordillera ranges from 6 °C in summer, down to −16 °C in winter. Vegetation is absent in this area due to permanent ice and snow; the Arctic Cordillera is a narrow ecozone compared to other Canadian ecozones. The majority of this ecozone borders the Northern Arctic, while the small segment within Labrador borders the Taiga Shield. However, bordering the Taiga Shield seems to affect neither itself nor the ecozones it borders because their biological properties appear to be opposites.
While the Arctic Cordillera mountain system includes most of the Arctic islands and regions such as Bathurst Island, Cornwall Island, Amund Ringnes Island, Ellef Ringnes Island, Ellesmere Island, Baffin Island, Bylot Island and Labrador, the Arctic Cordillera Ecozone only covers Ellesmere Island, Baffin Island, Axel Heiberg Island, Bylot Island and Labrador. The Arctic Cordillera contains numerous regions. Much of Ellesmere Island is covered by the Arctic Cordillera, making it the most mountainous in the Canadian Arctic Archipelago, it is considered part of the Queen Elizabeth Islands, with Cape Columbia being the most northerly point of land in Canada. It encompasses an area of 196,235 km2, making it the world's tenth largest island and Canada's third largest island; the first inhabitants of Ellesmere Island were small bands of Inuit drawn to the area for Peary caribou and marine mammal hunting about 1000–2000 BC. Axel Heiberg Island is one of the several members of the Canadian Arctic Archipelago and the largest of the Sverdrup Islands.
It has been inhabited in the past by Inuit people but was uninhabited by the time it was named by Otto Sverdrup, who explored it around 1900. In 1959, scientists from McGill University explored Expedition Fiord in central Axel Heiberg Island; this resulted in the establishment of the McGill Arctic Research Station, constructed 8 km inland from Expedition Fjord in 1960. Baffin Island is the largest island in Canada and the fifth largest island in the world, with an area of 507,451 km2; the largest uninhabited island on Earth, Devon Island is the second-largest of the Queen Elizabeth Islands, the 27th largest island in the world and Canada's 6th largest island. An outpost was established at Dundas Harbour in August 1924 as part of a government presence intended to curb foreign whaling and other activity. Much of Bylot Island is covered by the Arctic Cordillera. At 11,067 km2 it is ranked 71st largest island in Canada's 17th largest island. While there are no permanent settlements on this Canadian Arctic island, Inuit from Pond Inlet and elsewhere travel to it.
More than one-fifth of Ellesmere Island is protected as Quttinirpaaq National Park, which includes seven fjords and a variety of glaciers, as well as Lake Hazen, the world's largest lake north of the Arctic Circle. Barbeau Peak, the highest mountain in Nunavut is located in the British Empire Range on Ellesmere Island; the most northern mountain range in the world, the Challenger Mountains, is located in the northwest region of the island. The northern lobe of the island is called Grant Land. In July 2007, a study noted the disappearance of habitat for waterfowl and algae on Ellesmere Island. According to John P. Smol of Queen's University in Kingston and Marianne S. V. Douglas of the University of Alberta in Edmonton, warming conditions and evaporation have caused low water level changes in the chemistry of ponds and wetlands in the area; the researchers noted, "In the 1980s they needed to wear hip waders to make their way to the ponds...while by 2006 the same areas were dry enough to burn.
Sirmilik National Park in northern Baffin Island harbours large populations of thick-billed murres, black-legged kittiwakes and greater snow geese. The park comprises Bylot Island, Oliver Sound and the Borden Peninsula. Auyuittuq National Park, located on Baffin Island's Cumberland Peninsula, features the many terrains of Arctic wilderness such as fjords and ice
North American Cordillera
The North American Cordillera is the North American portion of the American Cordillera, a mountain chain along the western side of the Americas. The North American Cordillera covers an extensive area of mountain ranges, intermontane basins, plateaus in western North America, including much of the territory west of the Great Plains, it is sometimes called the Western Cordillera, the Western Cordillera of North America, or the Pacific Cordillera. The precise boundaries of this cordillera and its subregions, as well as the names of its various features, may differ depending on the definitions in each country or jurisdiction, depending on the scientific field; this cordillera extends from the U. S. state of Alaska to the southern border of Mexico. The North American Cordillera includes some of the highest peaks on the continent, its mountain ranges run north to south along three main belts: the Pacific Coast Ranges in the west, the Nevadan belt in the middle, the Laramide belt in the east. These three orogenic belts arose due to the engagement of tectonic plates which deformed the Earth's lithosphere.
For example, the Laramide orogeny changed the topography of the central Rocky Mountains and adjoining Laramide regions during the Late Cretaceous 80 million years ago. Prior to this time the Rocky Mountain region was occupied by a broad basin. Further topographical evolution occurred during the Eocene and Oligocene, but since that time the region has been stable. Speaking, it will be convenient here to consider these three belts going west to east, north to south. In Alaska, south of the Interior Plains area, is the Rocky Mountain System the Intermontane Basins and Ranges, in the southern part of the state are the Pacific Mountains and Valleys. In the Alaska panhandle, the mainland mountain ranges and offshore islands are extensions of respective ranges further south. In Canada, the North American Cordillera is divided into three physiographic regions: the western system, the interior system, the eastern system; the western system includes the Coast Mountains, the interior system includes the Columbia Mountains, the eastern system includes the Canadian Rockies.
At its midsection between San Francisco and Denver, the North American Cordillera is about 1,000 miles wide, its physiographic provinces at this midpoint are as follows, going from west to east: the Pacific Coast Ranges, the Central Valley, the Sierra Nevada, the Basin and Range Province, the Colorado Plateau, the Rocky Mountains. In the United States, another major feature of the Cordillera is the Columbia Plateau, located north of California between the Cascade Range —, a northern extension of the Sierra Nevada — and the Rocky Mountains. In Mexico, the Sierra Madre Occidental, the Sierra Madre Oriental further east, surround the Mexican Plateau. To the west of the Sierra Madre Occidental, the Peninsular Ranges border the Pacific Ocean, the Sierra Madre del Sur is the southern extension of the Peninsular Ranges. Sierra Madre means "Mother Range" in Spanish; the Nevadan belt runs down the middle of the North American Cordillera. Therefore, the intermontane areas of the cordillera can be divided up into the areas east of the Nevadan belt, those west of the Nevadan belt.
The Pacific Coast Ranges, comprising the Pacific Coast Belt, parallel the North American Pacific Coast, comprise several mountain systems. Along the British Columbia and Alaska coast, the mountains intermix with the sea in a complex maze of fjords, with thousands of islands. Off the Southern California coast the Channel Islands archipelago of the Santa Monica Mountains extends for 160 miles. In southern Alaska, the primary mountain ranges are the Alaska Range, Wrangell Mountains, Saint Elias Mountains, Kenai Mountains, Chugach Mountains, Talkeetna Mountains; the Yukon Ranges comprise the mountains in the southeastern part of the U. S. state of Alaska and most of the Yukon, Canada. This range has an area of 364,710 km2; the Coast Mountains run from the lower Fraser River and the Fraser Canyon northwestward, separating the Interior Plateau from the Pacific Ocean. Their coastal flank is characterized by an intense network of fjords and associated islands similar to the Norwegian coastline, while their inland side against the plateau they transition to the high plateau in dryland valleys notable for a series of large lakes similar to the alpine lakes of southern Switzerland, beginning in deep mountains and ending in flatland.
They are subdivided in three main groupings, the Pacific Ranges between the Fraser and Bella Coola, the Kitimat Ranges from there northwards to the Nass River and the Boundary Ranges from there to their terminus in the Yukon Territory at Champagne Pass and Chilkat Pass northwest of Haines, Alaska. The Saint Elias Mountains lie to their west and northwest, while the Yukon Ranges and Yukon Basin lie to their north. On the inland side of the Boundary Ranges are the Tahltan and Tagish Highlands and the Skeena Mountains, part of the Interior Mountains system, which extend southwards on the inland side of the Kitimat Ranges; the terrain of the main spine of the Coast Mountains is typified by heavy glaciation, including several large icefields of varying elevation. Of the three subdivisions, the Pacific Ranges are the highest and are crowned by Mount Waddington