The Coast Mountains (french: La chaîne Côtière) are a major

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have ari ...

in the Pacific Coast Ranges of western

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

, extending from southwestern

Yukon Yukon (; ; formerly called Yukon Territory and also referred to as the Yukon) is the smallest and westernmost of Canada's three territories. It also is the second-least populated province or territory in Canada, with a population of 43,964 as ...

through the Alaska Panhandle and virtually all of the

Coast of British Columbia , settlement_type = Region of British Columbia , image_skyline = , nickname = "The Coast" , subdivision_type = Country , subdivision_name = Canada , subdivision_type1 = Province , subdivision_name1 = British ...

south to the

Fraser River The Fraser River is the longest river within British Columbia, Canada, rising at Fraser Pass near Blackrock Mountain in the Rocky Mountains and flowing for , into the Strait of Georgia just south of the City of Vancouver. The river's annual ...

. The mountain range's name derives from its proximity to the sea coast, and it is often referred to as the Coast Range. The range includes volcanic and non-volcanic mountains and the extensive ice fields of the Pacific and Boundary Ranges, and the northern end of the

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...

system known as the

Cascade Volcanoes The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern ...

. The Coast Mountains are part of a larger mountain system called the Pacific Coast Ranges or the Pacific Mountain System, which includes the Cascade Range, the Insular Mountains, the

Olympic Mountains The Olympic Mountains are a mountain range on the Olympic Peninsula of the Pacific Northwest of the United States. The mountains, part of the Pacific Coast Ranges, are not especially high – Mount Olympus is the highest at ; however, the easte ...

, the Oregon Coast Range, the

California Coast Ranges The Coast Ranges of California span from Del Norte or Humboldt County, California, south to Santa Barbara County. The other three coastal California mountain ranges are the Transverse Ranges, Peninsular Ranges and the Klamath Mountains. ...

, the

Saint Elias Mountains The Saint Elias Mountains (french: Chaîne Saint-Élie) are a subgroup of the Pacific Coast Ranges, located in southeastern Alaska in the United States, Southwestern Yukon and the very far northwestern part of British Columbia in Canada. The r ...

and the

Chugach Mountains The Chugach Mountains of southern Alaska are the northernmost of the several mountain ranges that make up the Pacific Coast Ranges of the western edge of North America. The range is about long and wide, and extends from the Knik and Turnaga ...

. The Coast Mountains are also part of the

American Cordillera The American Cordillera is a chain of mountain ranges ( cordilleras) that consists of an almost continuous sequence of mountain ranges that form the western "backbone" of North America, Central America and South America, with Aconcagua as the ...

a Spanish term for an extensive chain of mountain rangesthat consists of an almost continuous sequence of mountain ranges that form the western backbone of

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

and

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

. The Coast Mountains are approximately long and average in width. The range's southern and southeastern boundaries are surrounded by the

and the Interior Plateau while its far northwestern edge is delimited by the Kelsall and Tatshenshini Rivers at the north end of the Alaska Panhandle, beyond which are the Saint Elias Mountains, and by Champagne Pass in the

Yukon Territory Yukon (; ; formerly called Yukon Territory and also referred to as the Yukon) is the smallest and westernmost of Canada's three territories. It also is the second-least populated province or territory in Canada, with a population of 43,964 as ...

. Covered in dense

temperate rainforest Temperate rainforests are coniferous or broadleaf forests that occur in the temperate zone and receive heavy rain. Temperate rain forests occur in oceanic moist regions around the world: the Pacific temperate rain forests of North American ...

on its western exposures, the range rises to heavily glaciated peaks, including the largest temperate-latitude ice fields in the world. On its eastern flanks, the range tapers to the dry Interior Plateau and the subarctic boreal forests of the Skeena Mountains and

Stikine Plateau The Stikine Plateau is a plateau in northern British Columbia, Canada. It lies between the Boundary Ranges of the Coast Mountains on the west and southwest and the Cassiar Mountains along its northeast, and between the Skeena Mountains on its south ...

. The Coast Mountains are part of the

Pacific Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a region around much of the rim of the Pacific Ocean where many volcanic eruptions and earthquakes occur. The Ring ...

the ring of volcanoes and associated mountains around the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...

and contain some of British Columbia's highest mountains.

Mount Waddington Mount Waddington, once known as Mystery Mountain, is the highest peak in the Coast Mountains of British Columbia, Canada. Although it is lower than Mount Fairweather and Mount Quincy Adams, which straddle the United States border between Ala ...

is the highest mountain of the Coast Mountains and the highest that lies entirely within British Columbia, located northeast of the head of Knight Inlet with an elevation of .

Geography

The Coast Mountains consists of three subdivisions known as the

Pacific Ranges , photo = Mount Garibaldi (50997016501).jpg , photo_size = 280px , photo_caption = Mount Garibaldi massif as seen from Squamish , map = , map_image = South BC-NW USA-relief PacificRanges.png , ...

, the

Kitimat Ranges , photo = Lax Kw'alaams.jpg , photo_size = 280px , photo_caption = Lax Kw'alaams backdropped by Mount McNeil , map = , map_image = BC-relief_Kitimatranges.png , map_caption = Kitimat Range ...

, and the Boundary Ranges. The Pacific Ranges are the southernmost subdivision of the Coast Mountains, extending from the lower stretches of the

to Bella Coola. Included in this subdivision is four of the five major coastal icecaps in the southern Coast Mountains. These are the largest temperate-latitude icecaps in the world and fuel a number of major

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...

s. Other than logging and a large ski resort at the resort town of Whistler, most of the land in the range is completely undeveloped.

, the highest mountain of the Coast Mountains, lies in the Waddington Range of the Pacific Ranges. Just north of the Pacific Ranges lies the central subdivision known as the Kitimat Ranges. This subdivision extends from the

Bella Coola River The Bella Coola River is a major river on the Pacific slope of the Coast Mountains in southern British Columbia. The town of Bella Coola is at its mouth on North Bentinck Arm. Bella Coola Indian Reserve No. 1 the location of the main community ...

and Burke Channel in the south to the Nass River in the north. A040, Coast Mountains, Alaska Panhandle, USA, 2002

The third and northernmost subdivision of the Coast Mountains is the Boundary Ranges, extending from the Nass River in the south to the Kelsall River in the north. It is also the largest subdivision of the Coast Mountains, spanning the British Columbia-Alaska border and northwards into

flanking the west side of the Yukon River drainage as far as Champagne Pass, north of which being the

Yukon Ranges The Yukon Ranges are a mountain range comprising the mountains in the southeastern part of the U.S. state of Alaska and most of the Yukon in Canada. Named after the Yukon, this range has area of .Juneau Icefield between

Juneau, Alaska The City and Borough of Juneau, more commonly known simply as Juneau ( ; tli, Dzánti K'ihéeni ), is the capital city of the state of Alaska. Located in the Gastineau Channel and the Alaskan panhandle, it is a unified municipality and the ...

and Atlin Lake in British Columbia, and the

Stikine Icecap The Stikine Icecap (sometimes referred to as the Stikine Icefield) is a large icefield straddled on the Alaska– British Columbia boundary in the Alaska Panhandle region. It lies in the Boundary Ranges of the Coast Mountains. Within the Unite ...

, which lies between the lower Stikine River and the

Whiting River The Whiting River is a stream, about long, in the U.S. state of Alaska and the Canadian province of British Columbia. It enters the waters of Stephens Passage at the Borough of Juneau in the Alaska Panhandle between the mouths of the Taku and St ...

. Because the Coast Mountains are just east of the

, they have a profound effect on British Columbia's climate by forcing moisture-laden air off the Pacific Ocean to rise, dropping heavy rainfalls on the western slopes where lush forests exist. This precipitation is among the heaviest in North America. The eastern slopes are relatively dry and less steep and protect the

British Columbia Interior , settlement_type = Region of British Columbia , image_skyline = , nickname = "The Interior" , subdivision_type = Country , subdivision_name = , subdivision_type1 = Province , subdivi ...

from the Pacific weather systems, resulting in dry warm summers and dry cold winters. Beyond the eastern slopes is a plateau occupying the southern and central portions of British Columbia called the Interior Plateau. Included within the Interior Plateau is a coalescing series of layered flood basalt lava flows. These sequences of fluid volcanic rock cover about of the Interior Plateau and have a volume of about , forming a large

volcanic plateau A volcanic plateau is a plateau produced by volcanic activity. There are two main types: lava plateaus and pyroclastic plateaus. Lava plateau Lava plateaus are formed by highly fluid basaltic lava during numerous successive eruptions thro ...

constructed atop of the Interior Plateau. North of the Interior Plateau on the range's northeastern slopes lies a huge mountainous area known by geographers as the

Interior Mountains The Interior Mountains or Northern Interior Mountains are the semi-official names for an expansive collection of mountain ranges that comprises much of the northern half of the Canadian province of British Columbia and a large area of southern Y ...

, which includes the neighbouring Skeena, Cassiar and Hazelton Mountains.

Geology

Origins and growth

The Coast Mountains consists of deformed

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

and metamorphosed structurally complex pre-

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

rocks. These originated in diverse locations around the globe: the area is built of several different

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its ow ...

s of different ages with a broad range of tectonic origins. In addition,

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic ...

under the

is being subducted at the southern portion of the range to form a north–south line of volcanoes called the

Garibaldi Volcanic Belt The Garibaldi Volcanic Belt is a northwest–southeast trending volcanic chain in the Pacific Ranges of the Coast Mountains that extends from Watts Point in the south to the Ha-Iltzuk Icefield in the north. This chain of volcanoes is located in ...

, a northern extension of the

in the northwestern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

, and contains the most explosive young volcanoes in Canada. Further north the northwesterly structural trend of the Coast Mountains lies partly in a large continental rift responsible for the creation of several volcanoes. These volcanoes form part of the Northern Cordilleran Volcanic Province, the most volcanically active area in Canada.

Insular and Omineca Arc eruptive periods

The first event began 130 million years ago when a group of active volcanic islands approached a pre-existing

continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

and coastline of North America. These volcanic islands, known as the

Insular Islands The Insular Islands were an extended chain of volcanic islands forming an arc in what is now the Pacific Ocean during the Paleozoic and Mesozoic eras. The islands formed by subduction and melting of the Farallon Plate along a fragment (or micr ...

by geoscientists, were formed on a pre-existing tectonic plate called the

Insular Plate The Insular Plate was an ancient oceanic plate that began subducting under the west-coast of North America around the early Cretaceous period. The Insular Plate had a chain of active volcanic islands that were called the Insular Islands. These vol ...

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

of the former Farallon Plate to the west during the early

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ...

era. This subduction zone records another subduction zone to the east under an ancient ocean basin between the Insular Islands and the former continental margin of North America called the Bridge River Ocean. This arrangement of two parallel subduction zones is unusual in that very few twin subduction zones exist on Earth; the Philippine Mobile Belt off the southeastern coast of

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

is an example of a modern twin subduction zone. As the Insular Plate drew closer to the pre-existing continental margin by ongoing subduction under the Bridge River Ocean, the Insular Islands drew closer to the former continental margin and coastline of western North America, supporting a pre-existing volcanic arc on the former continental margin of North America called the

Omineca Arc The Omineca Arc or Omineca Belt was a Jurassic through Cretaceous volcanic arc terrane in western North America, extending from Alaska through Yukon and British Columbia to Washington. The Omineca is bounded by the Foreland Belt to the east an ...

. As the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Paci ...

drifted west and the Insular Plate drifted east to the old continental margin of western North America, the Bridge River Ocean eventually closed by ongoing subduction under the Bridge River Ocean. This subduction zone eventually jammed and shut down completely 115 million years ago, ending the Omineca Arc and the Insular Islands collided, forming the

Insular Belt The Insular Belt is a physiogeological region on the north western North American coast. It consists of three major island groups and many smaller islands and stretches from southern British Columbia into Alaska and the Yukon. It represents the L ...

. Compression resulting from this collision crushed, fractured and folded rocks along the old continental margin. The Insular Belt then welded onto the pre-existing continental margin by magma that eventually cooled to create a large mass of

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...

, creating a new continental margin. This large mass of igneous rock is the largest

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

outcropping in North America.

Coast Range Arc eruptive period

The final event began when the Farallon Plate continued to subduct under the new continental margin after the Insular Plate and Insular Islands collided with the old continental margin, supporting a new continental volcanic arc called the

Coast Range Arc The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon. The Coast Range Arc lies along the western margin of the North American Plate in the ...

about 100 million years ago during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

period. Magma rising from the Farallon Plate under the new continental margin ascended through the newly accreted Insular Belt, injecting huge quantities of granite into older igneous rocks of the Insular Belt. At the surface, new volcanoes were built along the continental margin. Named after the Coast Mountains, the basement of this arc was likely Early Cretaceous and Late Jurassic intrusions from the Insular Islands. One of the major aspects that changed early during the Coast Range Arc was the status of the northern end of the Farallon Plate, a portion now known as the

Kula Plate The Kula Plate was an oceanic tectonic plate under the northern Pacific Ocean south of the Near Islands segment of the Aleutian Islands. It has been subducted under the North American Plate at the Aleutian Trench, being replaced by the Pacific ...

. About 85 million years ago, the Kula Plate broke off from the Farallon Plate to form a

mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a div ...

known to geoscientists as the

Kula-Farallon Ridge The Kula-Farallon Ridge was an ancient mid-ocean ridge that existed between the Kula and Farallon plates in the Pacific Ocean during the Jurassic period. There was a small piece of this ridge off the Pacific Northwest 43 million years ago. The ...

. This change apparently had some important ramifications for regional geologic evolution. When this change was completed, Coast Range Arc volcanism returned and sections of the arc were uplifted considerably in latest Cretaceous time.Geology of a Transpressional Orogen Developed During Ridge-Trench ... - Google Books
Books.google.ca. Retrieved on 2013-07-21. This started a period of mountain building that affected much of western North America called the

Laramide orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the ...

. In particular a large area of dextral transpression and southwest-directed thrust faulting was active from 75 to 66 million years ago. Much of the record of this deformation has been overridden by

age structures and the zone of Cretaceous dextral thrust faulting appears to have been widespread. It was also during this period when massive amounts of molten granite intruded highly deformed ocean rocks and assorted fragments from pre-existing island arcs, largely remnants of the Bridge River Ocean. This molten granite burned the old oceanic sediments into a glittering medium-grade

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...

called

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...

. The older intrusions of the Coast Range Arc were then deformed under the heat and pressure of later intrusions, turning them into layered metamorphic rock known as

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

. In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite, appearing to have been nearly melted in the procedure. Volcanism began to decline along the length of the arc about 60 million years ago during the Albian and Aptian faunal stages of the Cretaceous period. This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Thou ...

. Instead of subducting beneath the Pacific Northwest, the Kula Plate began subducting underneath southwestern Yukon and Alaska and during the early

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

period. Volcanism along the entire length of the Coast Range Arc shut down about 50 million years ago and many of the volcanoes have disappeared from erosion. What remains of the Coast Range Arc to this day are outcrops of granite when magma intruded and cooled at depth beneath the volcanoes, forming the present Coast Mountains. During construction of intrusions 70 and 57 million years ago, the northern motion of the Kula Plate might have been between and per year. However, other geologic studies determined the Kula Plate moved at a rate as fast as per year.

High-prominence peaks

Mountain ranges

References

{{Authority control Pacific Coast Ranges Mountain ranges of British Columbia Mountain ranges of Yukon Mountain ranges of Alaska Coast of British Columbia