The Coast Mountains are a major mountain range
in the Pacific Coast Ranges
of western North America
, extending from southwestern Yukon
through the Alaska Panhandle
and virtually all of the Coast of British Columbia
south to the Fraser River
. 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 field
s of the Pacific
and Boundary Ranges
, and the northern end of the 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 Olympic Mountains
, the Oregon Coast Range
, the California Coast Ranges
, the Saint Elias Mountains
and the Chugach Mountains
. The Coast Mountains are also part of the American Cordillera
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 North America
, Central America
, South America
The Coast Mountains are approximately long and average in width.
The range's southern and southeastern boundaries are surrounded by the Fraser River
and the Interior Plateau
while its far northwestern edge is delimited by the Kelsall
and Tatshenshini River
s at the north end of the Alaska Panhandle, beyond which are the Saint Elias Mountains, and by Champagne Pass
in the Yukon Territory
. Covered in dense temperate rainforest
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 Coast Mountains are part of the Pacific Ring of Fire
the ring of volcanoes and associated mountains around the Pacific 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 of Knight Inlet
with an elevation of .
The Coast Mountains consists of three subdivisions known as the Pacific Ranges
, the Kitimat Ranges
, 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 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
s. Other than logging and a large ski resort at the resort town
, most of the land in the range is completely undeveloped. Mount Waddington
, 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
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 River
in the north. It is also the largest subdivision of the Coast Mountains, spanning the British Columbia-Alaska border and northwards into Yukon
flanking the west side of the Yukon River
drainage as far as Champagne Pass
, north of which being the Yukon Ranges
. The Boundary Ranges include several large icefields, including the Juneau Icefield
between Juneau, Alaska
and Atlin Lake
in British Columbia, and the Stikine Icecap
, which lies between the lower Stikine River
and the Whiting River
Because the Coast Mountains are just east of the Pacific 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.
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 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
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 neighbouring Skeena
and Hazelton Mountains
Origins and growth
The Coast Mountains consists of deformed igneous
structurally complex pre-Tertiary
rocks. These originated in diverse locations around the globe: the area is built of several different terrane
s of different ages with a broad range of tectonic origins. In addition, oceanic crust
under the Pacific Ocean
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 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 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
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
of the former Farallon Plate
to the west during the early Paleozoic
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
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
As the North 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.
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.
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
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
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.
[Geology of a Transpressional Orogen Developed During Ridge-Trench ... - Google Books](_blank)
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
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 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
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 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 stage
s 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
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.
*Coast Range Arc
*Geography of British Columbia
*Geology of British Columbia
*Volcanism of Canada
*Volcanism of Western Canada
*List of mountain ranges
Category:Pacific Coast Ranges
Category:Mountain ranges of British Columbia
Category:Mountain ranges of Yukon
Category:Mountain ranges of Alaska
Category:Coast of British Columbia