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The Coast Mountains are a major mountain range of western North America, extending from southwestern Yukonmarker through the Alaska Panhandlemarker and virtually all of the Coast of British Columbia. They are so-named because of their proximity to the sea coast, and are often referred to as the Coast Range. It includes volcanic and non-volcanic mountains and the huge icefields of the Pacific and Boundary Ranges, and the northern end of the notable volcanic system known as the Cascade Volcanoes. 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 Oregon and California Coast Ranges and the Saint Eliasmarker and Chugach Mountains.

The Coast Mountains are approximately long and average in width. Its southern and southeastern boundaries are surrounded by the Fraser River and the Interior Plateaumarker while its far northwestern edge is delimited by the Kelsallmarker and Tatshenshini Riversmarker at the north end of the Alaska Panhandle, beyond which are the Saint Elias Mountains, and by Champagne Passmarker in the Yukon Territorymarker. Covered in dense temperate rainforest on its western exposures, the range rises to heavily glaciated peaks, including the largest temperate-latitude icefields in the world. It then tapers to the dry Interior Plateau on its eastern flanks, or to the subarctic boreal forest of the Skeena Mountains and Stikine Plateaumarker.

The Coast Mountains are part of the Pacific Ring of Fire, the ring of volcanoes and associated mountains around the Pacific Oceanmarker. It contains some of British Columbia's highest mountains. Mount Waddingtonmarker, northeast of the head of Knight Inletmarker with an elevation of , is the highest mountain of the Coast Mountains and the highest that lies entirely within British Columbia.

Geography

The Coast Mountains consists of three subdivisions known as the Pacific Ranges, the Kitimat Rangesmarker, and the Boundary Ranges. The Pacific Ranges are the southernmost subdivision of the Coast Mountains, extending from the lower stretches of the Fraser River to Bella Coolamarker. 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 rivers. Other than logging and a large ski resort at the resort town of Whistlermarker, most of the land in the range is completely undeveloped. Mount Waddingtonmarker, 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 Rivermarker and Burke Channel in the south to the Nass River in the north.

The third and northernmost subdivision of the Coast Mountains is the Boundary Ranges, extending from the Nass River in the south to the Kelsall Rivermarker in the north. It is also the largest subdivision of the Coast Mountains, spanning the British Columbia-Alaska border and northwards into Yukonmarker flanking the west side of the Yukon Rivermarker drainage as far as Champagne Pass, north of which being the Yukon Ranges. The Boundary Ranges include several large icefields, including the Juneau Icefieldmarker between Juneau, Alaskamarker and Atlin Lakemarker in British Columbia, and the Stikine Icecapmarker, which lies between the lower Stikine Rivermarker and the Whiting Rivermarker.

Because the Coast Mountains are just east of the Pacific Oceanmarker, 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 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 Plateaumarker. 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 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, which includes the neighboring Skeena, Cassiarmarker and Hazelton Mountainsmarker.

Geology

Origins and growth

The Coast Mountains consists of deformed igneous and metamorphosed structurally complex pre-Tertiary rocks. These originated in diverse locations around the globe: the area is built of several different terranes of different ages with a broad range of tectonic origins. In addition, oceanic crust under the Pacific Oceanmarker is being subducted at the southern portion of the range to form a north-south line of volcanoes called the Garibaldi Volcanic Belt, a northern extension of the Cascade Volcanoes in the northwestern United Statesmarker, 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 Bridge River Ocean between North America and the Insular Islands
The first event began 130 million years ago when a group of active volcanic islands approached a pre-existing continental margin and coastline of North America. These volcanic islands, known as the Insular Islands by geoscientists, were formed on a pre-existing tectonic plate called the Insular Plate by subduction of the former Farallon Plate to the west during the early Paleozoic period. This subduction zone records another subduction zone to the east under an ancient ocean basin between the Insular Islands and the former continential 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 is an example of a modern twin subduction zone. As the Insular Plate drew closer to the pre-existing continential margin by ongoing subduction under the Bridge River Ocean, the Insular Islands drew closer to the former continential margin and coastline of western North America, supporting a pre-existing volcanic arc on the former continential margin of North America called the Omineca Arc. As the North American Plate drifted west and the Insular Plate drifted east to the old continential 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. 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, creating a new continental margin. This large mass of igneous rock is the largest granite outcropping in North America.

Plate tectonics of the Coast Range Arc 100 million years ago.


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 about 100 million years ago during the Late Cretaceous period. Magma ascending from the Farallon Plate under the new continential margin burned their way upward through the 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.

Plate tectonics of the Coast Range Arc about 75 million years ago
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. About 85 million years ago, the Kula Plate broke off from the Farallon Plate to form a mid-ocean ridge known to geoscientists as the Kula-Farallon Ridge. 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. """This started a period of mountain building that affected much of western North America called the Laramide orogeny.""" In particular a large area of dextral transpression and southwest-directed thrust """faulting""" was active from 75 to 65 """million years ago.""" Much of the record of this deformation has been """overridden""" by Tertiary """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 called schist. 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. 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 patters 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. Instead of subducting beneath the Pacific Northwest, the Kula Plate began subducting underneath southwestern Yukon and Alaska and during the early Eocene 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

The North Shore Mountains near Vancouver.
View of the Juneau Icefield.


Mountain/Peak Height (metres) Prominence (metres) Location
Mount Waddingtonmarker 4019 3289

Monarch Mountainmarker 3555 2930

Skihist Mountainmarker 2968 2463

Mount Ratzmarker 3090 2430

Mount Queen Bessmarker 3298 2355

Razorback Mountain 3183 2253

Wedge Mountainmarker 2892 2249

Otter Mountain 2692 2242

Mount Silverthronemarker 2860 974

Kwatna Peak 2290 2225

Scud Peak 2987 2172



Mountain ranges

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 Rangemarker Boundary Ranges Alaska United States
Juneau Icefieldmarker Boundary Ranges British Columbia, Alaska Canada, United States
Sawtooth Rangemarker Juneau Icefield Alaska United States
Kakuhan Rangemarker Boundary Ranges Alaska United States
Lincoln Mountainsmarker Boundary Ranges Alaska United States
Longview Range Boundary Ranges British Columbia Canada
Peabody Mountainsmarker Boundary Ranges Alaska United States
Rousseau Rangemarker Boundary Ranges Alaska United States
Seward Mountainsmarker Boundary Ranges Alaska United States
Snowslide Range Boundary Ranges British Columbia Canada
Spectrum Rangemarker Boundary Ranges British Columbia Canada
Stikine Icecapmarker Boundary Ranges British Columbia, Alaska Canada, United States
Chechidla Rangemarker Stikine Icecap British Columbia Canada
Cheja Rangemarker Stikine Icecap British Columbia Canada
Kitimat Rangesmarker 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 Rangemarker 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 Rangemarker Pacific Ranges British Columbia Canada
Bendor Range Pacific Ranges British Columbia Canada
Bridge-Lillooet Divide Pacific Ranges British Columbia Canada
Broughton Archipelagomarker 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 Rangemarker 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 Rangemarker 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 Névémarker Garibaldi Ranges British Columbia Canada
Fitzsimmons Rangemarker 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 Icefieldmarker Garibaldi Ranges British Columbia Canada
Bastion Range Garibaldi Ranges British Columbia Canada
Gastineau Range Pacific Ranges British Columbia Canada
Ha-Iltzuk Icefieldmarker Pacific Ranges British Columbia Canada
Homathko Icefieldmarker Pacific Ranges British Columbia Canada
Koeye Range Pacific Ranges British Columbia Canada
Lewis Range Pacific Ranges British Columbia Canada
Lillooet Icecapmarker Pacific Ranges British Columbia Canada
Compton Névémarker 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 Ridgemarker Pacific Ranges British Columbia Canada
Monarch Icefieldmarker 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 Rangemarker Pacific Ranges British Columbia Canada
Pemberton Icefieldmarker 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


See also



References

  1. [1]



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