| Coast Mountains | |
|---|---|
| Coast Range | |
 Coast Mountains taken from theInternational Space Station from outer space. TheCanadian Rockies can be seen at the right. | |
| Highest point | |
| Peak | Mount Waddington, British Columbia |
| Elevation | 4,019 m (13,186 ft) |
| Coordinates | 51°22′30″N125°15′30″W / 51.37500°N 125.25833°W /51.37500; -125.25833 |
| Dimensions | |
| Length | 1,600 km (990 mi) north–south |
| Width | 300 km (190 mi) east–west |
| Area | 336,962 km2 (130,102 sq mi) |
| Geography | |
 Locator map of the Coast Mountains | |
| Countries | Canada andUnited States |
| Region(s) | Alaska,British Columbia andYukon |
| Range coordinates | 54°N128°W / 54°N 128°W /54; -128 |
| Parent range | Pacific Coast Ranges |
TheCoast Mountains (French:La chaîne Côtière) are a majormountain range in thePacific Coast Ranges of westernNorth America, extending from southwesternYukon through theAlaska Panhandle and virtually all of theCoast of British Columbia south to theFraser River.[1] The mountain range's name derives from its proximity to the sea coast, and it is often referred to as theCoast Range.[2] The range includes volcanic and non-volcanic mountains and the extensiveice fields of thePacific andBoundary Ranges, and the northern end of thevolcanic system known as theCascade Volcanoes. The Coast Mountains are part of a larger mountain system called thePacific Coast Ranges or the Pacific Mountain System, which includes theCascade Range, theInsular Mountains, theOlympic Mountains, theOregon Coast Range, theCalifornia Coast Ranges, theSaint Elias Mountains and theChugach Mountains. The Coast Mountains are also part of theAmerican Cordillera—a Spanish term for an extensive chain of mountain ranges—that consists of an almost continuous sequence of mountain ranges that form the western backbone ofNorth America,Central America,South America andAntarctica.
The Coast Mountains are approximately 1,600 kilometres (1,000 mi) long and average 300 kilometres (190 mi) in width.[2] The range's southern and southeastern boundaries are surrounded by theFraser River and theInterior Plateau while its far northwestern edge is delimited by theKelsall andTatshenshini Rivers at the north end of the Alaska Panhandle, beyond which are the Saint Elias Mountains, and byChampagne Pass in theYukon Territory.[3][4] Covered in densetemperate rainforest on its western exposures, the range rises to heavilyglaciated 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 subarcticboreal forests of theSkeena Mountains andStikine Plateau.
The Coast Mountains are part of thePacific Ring of Fire—the ring of volcanoes and associated mountains around thePacific Ocean—and contain some of British Columbia's highest mountains.Mount Waddington is the highest mountain of the Coast Mountains and the highest that lies entirely within British Columbia, located northeast of the head ofKnight Inlet with an elevation of 4,019 metres (13,186 ft).[5]
The Coast Mountains consists of three subdivisions known as thePacific Ranges, theKitimat Ranges, and theBoundary Ranges. The Pacific Ranges are the southernmost subdivision of the Coast Mountains, extending from the lower stretches of theFraser River toBella 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 majorrivers. Other than logging and a large ski resort at theresort town ofWhistler, most of the land in the range is completely undeveloped.Mount Waddington, the highest mountain of the Coast Mountains, lies in theWaddington Range of the Pacific Ranges.
Just north of the Pacific Ranges lies the central subdivision known as the Kitimat Ranges. This subdivision extends from theBella Coola River andBurke Channel in the south to theNass River in the north.
The third and northernmost subdivision of the Coast Mountains is theBoundary Ranges, extending from the Nass River in the south to theKelsall River in the north. It is also the largest subdivision of the Coast Mountains, spanning the British Columbia-Alaska border and northwards intoYukon flanking the west side of theYukon River drainage as far asChampagne Pass, north of which being theYukon Ranges. The Boundary Ranges include several large icefields, including theJuneau Icefield betweenJuneau, Alaska, andAtlin Lake in British Columbia, and theStikine Icecap, which lies between the lowerStikine River and theWhiting River.
Because the Coast Mountains are just east of thePacific Ocean, 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.[2] This precipitation is among the heaviest in North America.[2] The eastern slopes are relatively dry and less steep and protect theBritish Columbia Interior from the Pacific weather systems, resulting in dry warm summers and dry cold winters.[2]
Beyond the eastern slopes is a 154,635 km2 (59,705 sq mi) plateau occupying the southern and central portions of British Columbia called theInterior Plateau. Included within the Interior Plateau is a coalescing series of layeredflood basalt lava flows. These sequences of fluidvolcanic rock cover about 25,000 km2 (9,700 sq mi) of the Interior Plateau and have a volume of about 1,800 km3 (430 cu mi), forming a largevolcanic plateau 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 theInterior Mountains, which includes the neighbouringSkeena,Cassiar andHazelton Mountains.
The Coast Mountains consist of deformedigneous andmetamorphosed structurally complex pre-Tertiary rocks. These originated in diverse locations around the globe: the area is built of several differentterranes of different ages with a broad range of tectonic origins. In addition,oceanic crust under thePacific Ocean is beingsubducted at the southern portion of the range to form a north–south line of volcanoes called theGaribaldi Volcanic Belt, a northern extension of theCascade Volcanoes in the northwesternUnited States, and contains the most explosive young volcanoes in Canada. Further north the northwesterly structural trend of the Coast Mountains lies partly in a large continentalrift responsible for the creation of several volcanoes. These volcanoes form part of theNorthern Cordilleran Volcanic Province, the most volcanically active area in Canada.
The first event began 130 million years ago when a group of active volcanic islands approached a pre-existingcontinental margin and coastline of North America.[6] These volcanic islands, known as theInsular Islands by geoscientists, were formed on a pre-existingtectonic plate called theInsular Plate bysubduction of the formerFarallon Plate to the west during the earlyPaleozoic era.[6] This subduction zone records another subduction zone to the east under an ancientocean basin between the Insular Islands and the former continental margin of North America called theBridge River Ocean.[6] This arrangement of two parallel subduction zones is unusual in that very few twin subduction zones exist on Earth; thePhilippine Mobile Belt off the southeastern coast ofAsia is an example of a modern twin subduction zone.[6] 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 theOmineca Arc.[6] As theNorth American Plate 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.[6] This subduction zone eventually jammed and shut down completely 115 million years ago, ending the Omineca Arc and the Insular Islands collided, forming theInsular Belt.[6] Compression resulting from this collision crushed, fractured andfolded rocks along the old continental margin.[6] The Insular Belt then welded onto the pre-existing continental margin by magma that eventually cooled to create a large mass ofigneous rock, creating a new continental margin.[6] This large mass of igneous rock is the largestgranite outcropping in North America.[6]
The final event began when theFarallon 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 theCoast Range Arc about 100 million years ago during theLate Cretaceous period.[7] 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.[6] At the surface, new volcanoes were built along the continental margin.[6] Named after the Coast Mountains, the basement of this arc was likely Early Cretaceous andLate Jurassic intrusions from the Insular Islands.[7]
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 theKula Plate.[6] About 85 million years ago, the Kula Plate broke off from the Farallon Plate to form amid-ocean ridge known to geoscientists as theKula-Farallon Ridge.[6] 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.[8] This started a period of mountain building that affected much of western North America called theLaramide orogeny.[9] In particular a large area of dextral transpression and southwest-directed thrust faulting was active from 75 to 66 million years ago.[8] Much of the record of this deformation has been overridden byTertiary age structures and the zone of Cretaceous dextral thrust faulting appears to have been widespread.[8] 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.[6] This molten granite burned the old oceanic sediments into a glittering medium-grademetamorphic rock calledschist.[6] 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 asgneiss.[6] 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 asmigmatite, appearing to have been nearly melted in the procedure.[6]
Volcanism began to decline along the length of the arc about 60 million years ago during theAlbian andAptianfaunal stages of the Cretaceous period.[7] This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along thePacific Northwest.[6] Instead of subducting beneath the Pacific Northwest, the Kula Plate began subducting underneath southwestern Yukon and Alaska and during the earlyEocene period.[6] 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.[6] 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.[6] During construction of intrusions 70 and 57 million years ago, the northern motion of the Kula Plate might have been between 140 mm (6 in) and 110 mm (4 in) per year.[10] However, other geologic studies determined the Kula Plate moved at a rate as fast as 200 mm (8 in) per year.[10]
| Range Name | Parent | Region(s) | Country |
|---|---|---|---|
| Boundary Ranges | Coast Mountains | British Columbia, Yukon, Alaska | Canada, United States |
| Boundary Range | Boundary Ranges | British Columbia, Alaska | Canada, United States |
| Adam Mountains | Boundary Ranges | Alaska | United States |
| Ashington Range | Boundary Ranges | British Columbia | Canada |
| Burniston Range | Boundary Ranges | British Columbia | Canada |
| Dezadeash Range | Boundary Ranges | Yukon | Canada |
| Florence Range | Boundary Ranges | British Columbia | Canada |
| Halleck Range | Boundary Ranges | Alaska | United States |
| Juneau Icefield | Boundary Ranges | British Columbia, Alaska | Canada, United States |
| Sawtooth Range | Juneau Icefield | Alaska | United States |
| Kakuhan Range | Boundary Ranges | Alaska | United States |
| Lincoln Mountains | Boundary Ranges | Alaska | United States |
| Longview Range | Boundary Ranges | British Columbia | Canada |
| Peabody Mountains | Boundary Ranges | Alaska | United States |
| Rousseau Range | Boundary Ranges | Alaska | United States |
| Seward Mountains | Boundary Ranges | Alaska | United States |
| Snowslide Range | Boundary Ranges | British Columbia | Canada |
| Spectrum Range | Boundary Ranges | British Columbia | Canada |
| Stikine Icecap | Boundary Ranges | British Columbia, Alaska | Canada, United States |
| Chechidla Range | Stikine Icecap | British Columbia | Canada |
| Cheja Range | Stikine Icecap | British Columbia | Canada |
| Kitimat Ranges | Coast Mountains | British Columbia | Canada |
| Bare Top Range | Kitimat Ranges | British Columbia | Canada |
| Countess of Dufferin Range | Kitimat Ranges | British Columbia | Canada |
| Kitlope Range | Kitimat Ranges | British Columbia | Canada |
| North Coastal Archipelago | Kitimat Ranges | British Columbia | Canada |
| Bell Range | North Coastal Archipelago | British Columbia | Canada |
| Burnaby Range | North Coastal Archipelago | British Columbia | Canada |
| Cape Range | North Coastal Archipelago | British Columbia | Canada |
| Chismore Range | North Coastal Archipelago | British Columbia | Canada |
| Murphy Range | North Coastal Archipelago | British Columbia | Canada |
| Richardson Range | North Coastal Archipelago | British Columbia | Canada |
| Spiller Range | North Coastal Archipelago | British Columbia | Canada |
| Williams Range | North Coastal Archipelago | British Columbia | Canada |
| Wimbledon Range | North Coastal Archipelago | British Columbia | Canada |
| Tenaiko Range | Kitimat Ranges | British Columbia | Canada |
| Pacific Ranges | Coast Mountains | British Columbia | Canada |
| Ashlu-Elaho Divide | Pacific Ranges | British Columbia | Canada |
| Bazalgette Range | Pacific Ranges | British Columbia | Canada |
| Bendor Range | Pacific Ranges | British Columbia | Canada |
| Bridge-Lillooet Divide | Pacific Ranges | British Columbia | Canada |
| Broughton Archipelago | Pacific Ranges | British Columbia | Canada |
| Calliope Range | Broughton Archipelago | British Columbia | Canada |
| Georgina Range | Broughton Archipelago | British Columbia | Canada |
| Bunster Range | Pacific Ranges | British Columbia | Canada |
| Cadwallader Range | Pacific Ranges | British Columbia | Canada |
| Caren Range | Pacific Ranges | British Columbia | Canada |
| Charlotte Alplands | Pacific Ranges | British Columbia | Canada |
| Douglas Ranges | Pacific Ranges | British Columbia | Canada |
| Chilcotin Ranges | Pacific Ranges | British Columbia | Canada |
| Camelsfoot Range | Chilcotin Ranges | British Columbia | Canada |
| Dickson Range | Chilcotin Ranges | British Columbia | Canada |
| Leckie Range | Chilcotin Ranges | British Columbia | Canada |
| Pantheon Range | Chilcotin Ranges | British Columbia | Canada |
| Potato Range | Chilcotin Ranges | British Columbia | Canada |
| Shulaps Range | Chilcotin Ranges | British Columbia | Canada |
| Clendinning Range | Pacific Ranges | British Columbia | Canada |
| Colville Range | Pacific Ranges | British Columbia | Canada |
| Conical Range | Pacific Ranges | British Columbia | Canada |
| Earle Range | Pacific Ranges | British Columbia | Canada |
| Edwards Range | Pacific Ranges | British Columbia | Canada |
| Florence Range | Pacific Ranges | British Columbia | Canada |
| Franklyn Range | Pacific Ranges | British Columbia | Canada |
| Fraser Range | Pacific Ranges | British Columbia | Canada |
| Garibaldi Ranges | Pacific Ranges | British Columbia | Canada |
| Garibaldi Névé | Garibaldi Ranges | British Columbia | Canada |
| Fitzsimmons Range | Garibaldi Ranges | British Columbia | Canada |
| McBride Range | Garibaldi Ranges | British Columbia | Canada |
| Spearhead Range | Garibaldi Ranges | British Columbia | Canada |
| Golden Ears | Garibaldi Ranges | British Columbia | Canada |
| Misty Icefield | Garibaldi Ranges | British Columbia | Canada |
| Bastion Range | Garibaldi Ranges | British Columbia | Canada |
| Gastineau Range | Pacific Ranges | British Columbia | Canada |
| Ha-Iltzuk Icefield | Pacific Ranges | British Columbia | Canada |
| Homathko Icefield | Pacific Ranges | British Columbia | Canada |
| Koeye Range | Pacific Ranges | British Columbia | Canada |
| Lewis Range | Pacific Ranges | British Columbia | Canada |
| Lillooet Icecap | Pacific Ranges | British Columbia | Canada |
| Compton Névé | Lillooet Icefield | British Columbia | Canada |
| Lillooet Ranges | Pacific Ranges | British Columbia | Canada |
| Cantilever Range | Lillooet Ranges | British Columbia | Canada |
| Cayoosh Range | Lillooet Ranges | British Columbia | Canada |
| Mission Ridge | Pacific Ranges | British Columbia | Canada |
| Monarch Icefield | Pacific Ranges | British Columbia | Canada |
| North Shore Mountains | Pacific Ranges | British Columbia | Canada |
| Fannin Range | North Shore Mountains | British Columbia | Canada |
| Britannia Range | North Shore Mountains | British Columbia | Canada |
| Namu Range | Pacific Ranges | British Columbia | Canada |
| Nicholl Range | Pacific Ranges | British Columbia | Canada |
| Niut Range | Pacific Ranges | British Columbia | Canada |
| Pemberton Icefield | Pacific Ranges | British Columbia | Canada |
| Pembroke Range | Pacific Ranges | British Columbia | Canada |
| Powell Divide | Pacific Ranges | British Columbia | Canada |
| Sir Harry Range | Pacific Ranges | British Columbia | Canada |
| Squamish-Cheakamus Divide | Pacific Ranges | British Columbia | Canada |
| Tantalus Range | Pacific Ranges | British Columbia | Canada |
| The Tahumming | Pacific Ranges | British Columbia | Canada |
| Tottenham Range | Pacific Ranges | British Columbia | Canada |
| Unwin Range | Pacific Ranges | British Columbia | Canada |
| Waddington Range | Pacific Ranges | British Columbia | Canada |
| Wharncliffe Range | Pacific Ranges | British Columbia | Canada |
| Whitemantle Range | Pacific Ranges | British Columbia | Canada |
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