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54-716: The Pacific Ranges include 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 very major rivers (by volume, not length). One of these contains Mount Waddington , the highest summit entirely within British Columbia . Also within this region is Hunlen Falls , among the highest in Canada , located in Tweedsmuir South Provincial Park . Other than logging and various hydroelectric developments, and

108-417: A convergent plate boundary . Most of the material in the accretionary wedge consists of marine sediments scraped off from the downgoing slab of oceanic crust , but in some cases the wedge includes the erosional products of volcanic island arcs formed on the overriding plate. An accretionary complex is a current (in modern use) or former accretionary wedge. Accretionary complexes are typically made up of

162-481: A mountain-building event. The piecemeal addition of these accreted terranes has added an average of 600 km (370 mi) in width along the western margin of the North American continent. The topographic expression of the accretionary wedge forms a lip, which may dam basins of accumulated materials that, otherwise, would be transported into the trench from the overriding plate. Accretionary wedges are

216-753: A NE-strike, parallel to strike of the South China Sea slope. Analysis shows that the pre-orogenic mechanical/crustal heterogeneities and seafloor morphology exert strong controls on the thrust-belt development in the incipient Taiwan arc-continent collision zone. In accretionary wedges, seismicity activating superimposed thrusts may drive methane and oil upraising from the upper crust. Mechanical models that treat accretionary complexes as critically tapered wedges of sediment demonstrate that pore pressure controls their taper angle by modifying basal and internal shear strength. Results from some studies show that pore pressure in accretionary wedges can be viewed as

270-497: A decrease in stable taper angle from 8.4°–12.5° to <2.5–5°. In general, low-permeability and thick incoming sediment sustain high pore pressures consistent with shallowly tapered geometry, whereas high-permeability and thin incoming sediment should result in steep geometry. Active margins characterized by a significant proportion of fine-grained sediment within the incoming section, such as northern Antilles and eastern Nankai , exhibit thin taper angles, whereas those characterized by

324-642: A dynamically maintained response to factors which drive pore pressure (source terms) and those that limit flow (permeability and drainage path length). Sediment permeability and incoming sediment thickness are the most important factors, whereas fault permeability and the partitioning of sediment have a small effect. In one such study, it was found that as sediment permeability is increased, pore pressure decreases from near-lithostatic to hydrostatic values and allows stable taper angles to increase from ~2.5° to 8°–12.5°. With increased sediment thickness (from 100–8,000 m (330–26,250 ft)), increased pore pressure drives

378-781: A full listing of rivers in the Pacific Ranges, see List of rivers of the Pacific Ranges . Coast Mountains The Coast Mountains ( French : La chaîne Côtière ) 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

432-402: A higher proportion of sandy turbidites, such as Cascadia , Chile , and Mexico , have steep taper angles. Observations from active margins also indicate a strong trend of decreasing taper angle (from >15° to <4°) with increased sediment thickness (from <1 to 7 km). Rapid tectonic loading of wet sediment in accretionary wedges is likely to cause the fluid pressure to rise until it

486-704: 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. 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

540-571: A large ski resort at Whistler , most of the land in the range is completely undeveloped. Historically, in the southern part of the range, mining was important at various times in the Lillooet, Bridge River and Squamish areas, and large pulp and paper mills at Powell River, Port Mellon and Woodfibre. The largest hydroelectric development in the Pacific Ranges is the Bridge River Power Project , though smaller hydro plants are on

594-482: A mix of turbidites of terrestrial material, basalts from the ocean floor , and pelagic and hemipelagic sediments . For example, most of the geological basement of Japan is made up of accretionary complexes. Accretionary wedges and accreted terranes are not equivalent to tectonic plates, but rather are associated with tectonic plates and accrete as a result of tectonic collision. Materials incorporated in accretionary wedges include: Elevated regions within

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648-539: 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 era. This subduction zone records another subduction zone to the east under an ancient ocean basin between

702-414: Is sufficient to cause dilatant fracturing. Dewatering of sediment that has been underthrust and accreted beneath the wedge can produce a large steady supply of such highly overpressured fluid. Dilatant fracturing will create escape routes, so the fluid pressure is likely to be buffered at the value required for the transition between shear and oblique tensile (dilatant) fracture, which is slightly in excess of

756-432: Is the major control on the geometry of frontal structures. The preexisting South China Sea slope that lies obliquely in front of the advancing accretionary wedge has impeded the advancing of frontal folds resulting in a successive termination of folds against and along strike of the South China Sea slope. The existence of the South China Sea slope also leads the strike of impinging folds with NNW-trend to turn more sharply to

810-756: The British Columbia Interior from the Pacific weather systems, resulting in dry warm summers and dry cold winters. Beyond the eastern slopes is a 154,635 km (59,705 sq mi) 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 25,000 km (9,700 sq mi) of

864-1219: 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 ranges—that consists of an almost continuous sequence of mountain ranges that form the western backbone of North America , Central America , South America and Antarctica . The Coast Mountains are approximately 1,600 kilometres (1,000 mi) long and average 300 kilometres (190 mi) in width. The range's southern and southeastern boundaries are surrounded by

918-696: The Fraser River 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 . Covered in dense temperate rainforest on its western exposures, the range rises to heavily glaciated peaks, including the largest temperate-latitude ice fields in

972-682: The Late Cretaceous 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

1026-552: The Silverthrone Caldera , which lie 140 and 190 km northwest of the main volcanic belt. The Cascadia subduction zone is a 680 mi (1,094 km) long fault , running 50 mi (80 km) off the west-coast of the Pacific Northwest from northern California to Vancouver Island . The plates move at a relative rate of over 0.4 inches (10 mm) per year at a somewhat oblique angle to

1080-727: 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

1134-507: The Waddington Range these are also considered to be " ranges " but are listed separately here because of their unique character). List is incomplete Some Protected areas, recreation areas and other non-park preservation areas are not listed. Many relatively unknown rivers of considerable size along the coastal flank of the range are not listed, partly because they are largely unknown and also very difficult to access. For

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1188-498: The ocean basins such as linear island chains, ocean ridges , and small crustal fragments (such as Madagascar or Japan), known as terranes , are transported toward the subduction zone and accreted to the continental margin. Since the Late Devonian and Early Carboniferous periods, some 360 million years ago, subduction beneath the western margin of North America has resulted in several collisions with terranes, each producing

1242-711: 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

1296-544: 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

1350-630: The Cascade Range contributes to further obscuring the presence of a trench. However, in common with most other subduction zones, the outer margin is slowly being compressed, similar to a giant spring . When the stored energy is suddenly released by slippage across the fault at irregular intervals, the Cascadia subduction zone can create very large earthquakes , such as the 8.7–9.2 M w   Cascadia earthquake of 1700 . Many smaller ranges and subranges are not listed at present. (Other than

1404-661: The Coast Mountains and the highest that lies entirely within British Columbia, located northeast of the head of Knight Inlet with an elevation of 4,019 metres (13,186 ft). 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

1458-513: 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

1512-577: 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

1566-646: 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

1620-612: The Interior Plateau and have a volume of about 1,800 km (430 cu mi), 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 , Cassiar and Hazelton Mountains . The Coast Mountains consist of deformed igneous and metamorphosed structurally complex pre- Tertiary rocks. These originated in diverse locations around

1674-900: 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

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1728-851: The Stave River-Alouette Lake system in Mission and Maple Ridge, the Daisy Lake-Squamish River division of the Cheakamus Powerhouse, and another power dam and power plant at Clowhom . Although the range was extensively surveyed for possible rail routes, only that of the Pacific Great Eastern (now part of CN) was eventually built; the Homathko River-Bute Inlet route, however, was one of the two main choices in

1782-438: The cohesive strength of the weak sediment layer that acts as the basal detachment. These assumptions allow the application of a simple plastic continuum model, which successfully predicts the observed gently convex taper of accretionary wedges. Pelayo and Weins have postulated that some tsunami events have resulted from rupture through the sedimentary rock along the basal decollement of an accretionary wedge. Backthrusting of

1836-592: The deliberations of the CPR's routing. The Pacific Ranges are part of the southern portion of the Coast Plutonic Complex and has been characterized by rapid rates of uplift over the past 4 million years, which has led to relatively high rates of erosion . The Garibaldi Volcanic Belt is within the Pacific Ranges, which is a volcanic belt formed by the subduction of the Juan de Fuca Plate (a remnant of

1890-420: 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,

1944-549: 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 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

1998-606: 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

2052-419: The home of mélange , intensely deformed packages of rocks that lack coherent internal layering and coherent internal order. The internal structure of an accretionary wedge is similar to that found in a thin-skinned foreland thrust belt. A series of thrusts verging towards the trench are formed with the youngest most outboard structures progressively uplifting the older more inboard thrusts. The shape of

2106-588: 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

2160-421: The load pressure if the maximum compression is nearly horizontal. This in turn buffers the strength of the wedge at the cohesive strength, which is not pressure-dependent, and will not vary greatly throughout the wedge. Near the wedge front the strength is likely to be that of the cohesion on existing thrust faults in the wedge. The shear resistance on the base of the wedge will also be fairly constant and related to

2214-417: 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 rivers . Other than logging and a large ski resort at the resort town of Whistler , most of the land in the range is completely undeveloped. Mount Waddington ,

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2268-477: The middle Jurassic Period, roughly 170 million years ago, in an extensional regime within either a back-arc or a forearc basin. It was later accreted to the continental margin of Laurasia. Longitudinal sedimentary tapering of pre-orogenic sediments correlates strongly with curvature of the submarine frontal accretionary belt in the South China Sea margin, suggesting that pre-orogenic sediment thickness

2322-575: 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. The first event began 130 million years ago when a group of active volcanic islands approached

2376-797: The much larger Farallon Plate ) under the North American Plate along the Cascadia subduction zone . The belt is the northern extension of the Cascade Volcanic Arc in the United States (which includes the volcanoes Mount St. Helens and Mount Baker ) and contains the most explosive young volcanoes in Canada. The eruption styles in the belt range from effusive to explosive , with compositions from basalt to rhyolite . Morphologically, centers include calderas , cinder cones , stratovolcanoes and small isolated lava masses. Due to repeated continental and alpine glaciations, many of

2430-434: The northern motion of the Kula Plate might have been between 140 mm (6 in) and 110 mm (4 in) per year. However, other geologic studies determined the Kula Plate moved at a rate as fast as 200 mm (8 in) per year. Download coordinates as: Accretionary wedge An accretionary wedge or accretionary prism forms from sediments accreted onto the non- subducting tectonic plate at

2484-548: The overriding plate are said to be obducted . Where this occurs, rare slices of ocean crust, known as ophiolites , are preserved on land. They provide a valuable natural laboratory for studying the composition and character of the oceanic crust and the mechanisms of their emplacement and preservation on land. A classic example is the Coast Range ophiolite of California, which is one of the most extensive ophiolite terranes in North America. This oceanic crust likely formed during

2538-513: The rear of the accretionary wedge, arcward over the rocks of the forearc basin, is a common aspect of accretionary tectonics. An older assumption that backstops of accretionary wedges dip back toward the arc, and that accreted material is emplaced below such backstops, is contradicted by observations from many active forearcs that indicate (1) backthrusting is common, (2) forearc basins are nearly ubiquitous associates of accretionary wedges, and (3) forearc basement, where imaged, appears to diverge from

2592-539: 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 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

2646-408: The subduction zone. Unlike most subduction zones worldwide, there is no oceanic trench present along the continental margin in Cascadia . Instead, terranes and the accretionary wedge have been uplifted to form a series of coast ranges and exotic mountains. A high rate of sedimentation from the outflow of the three major rivers ( Fraser River , Columbia River , and Klamath River ) which cross

2700-630: The volcanic deposits in the belt reflect complex interactions between magma composition, topography, and changing ice configurations. The most recent major catastrophic eruption in the Garibaldi Volcanic Belt was from the Mount Meager massif 2,350 BP , which is Canada's most recent major catastrophic eruption. The Garibaldi Volcanic Belt contains two extra volcanic fields, the Franklin Glacier Complex and

2754-462: The wedge is determined by how readily the wedge will fail along its basal decollement and in its interior; this is highly sensitive to pore fluid pressure . This failure will result in a mature wedge that has an equilibrium triangular cross-sectional shape of a critical taper . Once the wedge reaches a critical taper, it will maintain that geometry and grow only into a larger similar triangle . The small sections of oceanic crust that are thrust over

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2808-401: 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

2862-431: 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

2916-475: 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 66 million years ago. Much of the record of this deformation has been overridden by Tertiary age structures and

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