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Big Raven Plateau

Coordinates: 57°42′49″N 130°45′06″W / 57.71361°N 130.75167°W / 57.71361; -130.75167
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Big Raven Plateau
Volcanic plateau
An overhead view of a barren, rocky plateau with a glaciated mountain in the middle.
Satellite image of the Big Raven Plateau
Big Raven Plateau is located in British Columbia
Big Raven Plateau
Big Raven Plateau
Location in British Columbia
Coordinates: 57°42′49″N 130°45′06″W / 57.71361°N 130.75167°W / 57.71361; -130.75167[1]
LocationCassiar Land District, British Columbia, Canada[2]
RangeTahltan Highland[2]
Part ofMount Edziza complex[3]
Age7.4 Ma to less than 20 ka[4][5]
Formed byVolcanic activity[6]
GeologyTrachybasalt, trachyte, hawaiite, tristanite, mugearite, comendite, benmoreite, pantellerite, alkali basalt[5]
EtymologyBig Raven (Tse'sketco)[1][7]
Defining authorityBC Geographical Names office in Victoria, British Columbia[1][8]
Dimensions
 • LengthApproximately 35 km (22 mi)[2]
 • WidthApproximately 20 km (12 mi)[2]
ElevationAbove 910 m (3,000 ft)[2]
Last eruptionLess than 2,000 years ago[9]
Topo mapNTS 104G10 Mount Edziza[1]
DesignationMount Edziza Provincial Park[2]
Drained byTsecha Creek, Tennaya Creek, Tenchen Creek, Taweh Creek, Sorcery Creek, Shaman Creek, Sezill Creek, Pyramid Creek, Nido Creek, Kadeya Creek, Elwyn Creek, Cook Creek[2][5]
Borders onChakima Creek valley (south)[2]
Walkout Creek valley (south)[2]
Klastline River valley (north)[2]
Kakiddi Creek valley (east)[2]
Mess Creek valley (west)[2]
Map Location in Mount Edziza Provincial Park

The Big Raven Plateau is an intermontane plateau in Cassiar Land District of northwestern British Columbia, Canada. It lies on the Tahltan Highland and is surrounded by several valleys, including those of Mess Creek, Kakiddi Creek, Chakima Creek, Walkout Creek and the Klastline River. The plateau is drained by many small streams that flow into these neighbouring valleys and, unlike the valleys, it is relatively barren of vegetation. Stream erosion has resulted in the creation of canyons with intervening ridges on the eastern and western sides of the plateau, resulting in the creation of rugged terrain. The plateau is in Mount Edziza Provincial Park which is one of the largest provincial parks in British Columbia. Access to the Big Raven Plateau is mainly by aircraft or by a network of footpaths from surrounding roads.

The Big Raven Plateau is volcanic in origin, consisting mostly of basaltic lava flows of the Mount Edziza volcanic complex that were erupted in the last 7.5 million years. These lava flows are interbedded with rhyolite and trachyte which are in the form of rock fragments produced and ejected by explosive eruptions. The dominant feature on the Big Raven Plateau is Mount Edziza, an ice-covered stratovolcano reaching an elevation of 2,786 metres (9,140 feet). Its composition is more diverse, consisting of alkali basalt, hawaiite, trachybasalt, tristanite, mugearite, benmoreite, trachyte and rhyolite which are in the form of lava flows and rock fragments. The Big Raven Plateau is subdivided into at least 10 geological formations, each being the product of a distinct period of volcanic activity.

Geography and geomorphology

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Location

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The Big Raven Plateau is on the Tahltan Highland east of the Zagoddetchino massif and west of the mountainous Klastline Plateau in Cassiar Land District. Between the Zagoddetchino massif and the Big Raven Plateau is Mess Creek valley which extends more than 60 kilometres (37 miles) to the south where it separates the Boundary Ranges of the Coast Mountains in the west from the Spectrum Range and Arctic Lake Plateau in the east. Between the Big Raven and Klastline plateaus is the north–south trending Kakiddi Creek valley which includes a number small lakes such as Nuttlude Lake, Kakiddi Lake, Mowchilla Lake and Mowdade Lake. The northern end of the Big Raven Plateau is bounded by the Klastline River valley while the southern end is bounded by two relatively small east–west trending valleys; a mountain ridge extends south of the Big Raven Plateau between these valleys.[2]

This roughly 35-kilometre-long (22-mile) and 20-kilometre-wide (12-mile) plateau lies at the northern end of the Mount Edziza volcanic complex which also includes the Arctic Lake and Kitsu plateaus, as well as the Spectrum Range to the south.[2][3] This volcanic complex consists of a group of overlapping shield volcanoes, stratovolcanoes, lava domes and cinder cones that have formed over the last 7.5 million years. It contains four central volcanoes along its north–south trending axis; from north to south they are Mount Edziza, Ice Peak, Armadillo Peak and the Spectrum Range.[6]

Drainage

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As a part of the Mount Edziza volcanic complex, the Big Raven Plateau is drained entirely by streams within the Stikine River watershed.[2][10] The northeastern portion of the Big Raven Plateau is drained by Tsecha Creek which flows to the northeast.[2] Draining the eastern side of the plateau are a series of east-flowing streams choaked with glacial and landslide debris from rapidly eroding headwalls; from north to south these are Pyramid Creek, Tenchen Creek, Nido Creek, Tennaya Creek, Sorcery Creek and Shaman Creek.[2][5][11] Transportation of the glacial and landslide debris into Kakiddi Creek valley has resulted in the formation of several large alluvial fans behind which Nuttlude Lake, Kakiddi Lake, Mowdade Lake and Mowchilla Lake have ponded.[11] Nido Creek and Tennaya Creek flow into Nuttlude Lake while Sorcery Creek and Shaman Creek flow into Kakiddi Lake.[2] Both lakes are expansions of Kakiddi Creek which flows north into the Klastline River, a tributary of the Stikine River.[2][12][13]

Elwyn Creek and its tributary, Kadeya Creek, drain the northwestern portion of the plateau; Elwyn Creek flows westward while Kadeya Creek flows to the northwest.[2][14] Northwest-flowing Taweh Creek and its tributary, the westward-flowing Sezill Creek, drain the southwestern and western portions of the plateau, respectively.[2][15][16] Elwyn Creek and Taweh Creek are tributaries of Mess Creek which flows northwestward into the Stikine River.[2][17] The northern end of the Big Raven Plateau is drained by small, unnamed streams which flow north into the Klastline River; these streams are shallowly incised into the plateau.[2][11] At the southern end of the Big Raven Plateau is a drainage divide between Chakima Creek, flowing east into the Kakiddi drainage and Walkout Creek flowing west, via Raspberry Creek into Mess Creek.[2][18]

Structure

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The Big Raven Plateau is roughly oval in structure, largely covered with colluvium and relatively barren of vegetation which contrasts with the surrounding valleys.[2][5] Colluvium on the plateau consists of felsenmeer, till, glacial and fluvial outwash, as well as solifluction deposits.[5] In contrast to the northern end of the Big Raven Plateau which is relatively smooth and uneroded, the eastern side has undergone extensive erosion which has resulted in the creation of steep spurs with intervening valleys.[2][11] A handful of these spurs are named on the southeastern side of the plateau; from north to south they are Idiji Ridge, Sorcery Ridge and Cartoona Ridge. Idiji Ridge extends east from the northern end of Tencho Glacier and is the namesake of Idiji Glacier which exists to the northwest. Sorcery Ridge, which shares its name with adjacent Sorcery Creek, extends east from the southern end of Tencho Glacier. Cartoona Ridge lies between Chakima and Shaman creek valleys and shares its name with Cartoona Peak at the westernmost end of the ridge.[5]

The western side of the Big Raven Plateau has been moderately dissected by stream erosion which has resulted in the formation of steep-sided canyons; Elwyn, Sezill and Taweh creek canyons are the most extensive.[2][11] Elwyn and Sezill creek canyons contain hot springs with recorded water temperatures of 36 degrees Celsius (97 degrees Fahrenheit) and 46 degrees Celsius (115 degrees Fahrenheit), respectively. Discharge at these hot springs may be linked to shallow hydrothermal systems driven by residual magmatic heat as they are adjacent to recently active volcanic centres on the plateau.[5][19] Forming the southwestern edge of the Big Raven Plateau is the Mess Creek Escarpment which extends at least 25 kilometres (16 miles) to the south where it forms the western edge of the Kitsu Plateau.[2][3]

Landforms

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The flat-topped summit of a snow-covered mountain with a rocky and snow-covered cliff in the foreground.
The summit crater of Mount Edziza

The Big Raven Plateau is dominated by the ice-covered stratovolcano of Mount Edziza which rises to an elevation of 2,786 metres (9,140 feet) from the middle of the plateau.[2][20][21] Immediately north of Mount Edziza is the Desolation Lava Field which covers an area of more than 150 square kilometres (58 square miles) and mostly issued from cinder cones near the northern trim line of Mount Edziza's ice cap.[22] The Snowshoe Lava Field immediately southwest of Mount Edziza covers an area of about 40 square kilometres (15 square miles) and mostly issued from cones on the southwestern flank of Ice Peak.[23]

Smaller features on the Big Raven Plateau include Hoia Bluff at the southwestern end of the plateau along Taweh Creek, Kaia Bluff and Cartoona Peak at the southeastern end of the plateau, Camp Hill near the southwestern edge of the plateau, Kana Cone on the extreme northern side of the plateau, Klastline Cone on the eastern side of the plateau near the head of Pyramid Creek, Tsekone Ridge at the northwestern end of the plateau near the head of Elwyn Creek canyon and Ornostay and Koosick bluffs near the middle of the plateau adjacent to the head of Sezill Creek canyon.[2][5][24]

Mount Edziza

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Mount Edziza is a nearly symmetrical volcanic cone containing a nearly flat summit with an ice-filled, 2-kilometre (1.2-mile) in diameter crater.[6][25] The symmetry of the volcano is broken by several steep-sided lava domes, including Sphinx Dome, Glacier Dome, Triangle Dome and The Pyramid.[26][27] Surrounding the summit crater is a circular ridge that is breached to the east by active cirques where the remains of several lava lakes are exposed inside the crater.[6] The ridge is partially exposed above the ice cap as a discontinuous series of spires and serrated nunataks; spires forming the southern end of the ridge are the highest. Although the eastern side of Mount Edziza has been deeply dissected by glacial erosion, less dissection has taken place on the southern and northwestern flanks of the volcano.[26] Extending northwest from the northwestern flank of Mount Edziza is Pillow Ridge which is named after its exposures of pillow lava.[28]

About 3 kilometres (1.9 miles) south of the summit is Ice Peak, the southern peak of Mount Edziza.[5][29] This prominent pyramid-shaped horn has an elevation of 2,500 metres (8,200 feet) and is the glacially eroded remains of an older stratovolcano whose northern flank is buried under the younger edifice of Mount Edziza.[6][10][29] The southern and western flanks of Ice Peak are approximal to those of the original stratovolcano whereas the eastern flank has been almost completely destroyed by headward erosion of glacial valleys.[11] At its climax, the stratovolcano had a symmetrical profile and contained a small crater at its summit; the current summit is an erosional remnant etched from the eastern crater rim.[6][30]

Desolation Lava Field

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An overhead view of a barren, rocky plateau with a glaciated mountain in the middle.
Satellite image of the Big Raven Plateau showing the locations of Mount Edziza, Ice Peak and Cocoa and Coffee craters in the Snowshoe Lava Field

The Desolation Lava Field at the northern end of the Big Raven Plateau consists of blocky basaltic lava flows and wind-sculptured ash beds that erupted from at least 10 cinder cones, most of which are clustered near the northern base of Mount Edziza.[5][31] Lava flows in the Desolation Lava Field range in elevation from more than 1,370 metres (4,490 feet) to 820 metres (2,690 feet) on the shore of Buckley Lake and 670 metres (2,200 feet) inside the Klastline River valley.[32] The largest lava flow is about 14 kilometres (8.7 miles) long and travelled to the northeast into the Kakiddi Creek and Klastline River valleys where it temporarily blocked both streams.[33]

From oldest to youngest, the cinder cones in this lava field are Sleet Cone, Storm Cone, the three Triplex Cones, Sidas Cone, Twin Cone, Moraine Cone, Eve Cone and Williams Cone which range in elevation from 2,135 to 1,430 metres (7,005 to 4,692 feet).[27][34] Williams Cone is the largest, reaching 1.2 kilometres (0.75 miles) wide at its base and rising about 275 metres (902 feet) on the northeastern side of Mount Edziza.[35][36] Eve Cone contains a bowl-shaped crater at its summit and is one of the most symmetrical and best preserved cinder cones in Canada, rising about 150 metres (490 feet) above the central portion of the Desolation Lava Field.[35][37]

Snowshoe Lava Field

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The Snowshoe Lava Field at the southern end of the Big Raven Plateau consists of blocky basaltic lava flows that issued from at least 12 separate vents, most of which are associated with a cinder cone.[5][38] Nearly all of these vents are adjacent to the lower edges of broad glaciers projecting from Mount Edziza's ice cap and occur at elevations greater than 1,800 metres (5,900 feet).[39] Although most of the lava in the Snowshoe Lava Field ponded as thick flows on the gently sloping surface of the Big Raven Plateau, some flowed into the upper canyon of Sezill Creek and into the head of Taweh Creek, as well as into the narrow tributary valleys of Walkout and Shaman creeks.[40]

Tennena Cone, Cocoa Crater, Coffee Crater, Keda Cone and The Saucer are the only named volcanic features in the Snowshoe Lava Field which are 2,350 to 1,920 metres (7,710 to 6,300 feet) in elevation.[5][27] The oldest named feature, Tennena Cone, is a subglacial volcano that formed on the upper western flank of Ice Peak during the Last Glacial Maximum between 23,000 and 18,000 years ago, under an expansion of Mount Edziza's ice cap during the Younger Dryas between 12,900 and 11,600 years ago or during a more recent glacial advance.[41][42][43][44] Cocoa Crater, Coffee Crater and Keda Cone are subaerial cinder cones while The Saucer is a low, nearly circular mound of lava roughly 500 metres (1,600 feet) in diameter.[5][45]

Geology

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Stratigraphy

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The Big Raven Plateau is subdivided into at least 10 geological formations, each being the product of a distinct period of volcanic activity.[5][4] These periods of volcanic activity occurred during five magmatic cycles of the Mount Edziza volcanic complex; each cycle began with the effusion of alkali basalt and culminated with the eruption of lesser volumes of felsic magma.[46] The two oldest geological formations comprising the Big Raven Plateau are the Raspberry and Armadillo formations which were deposited by volcanic eruptions during the first magmatic cycle between 7.5 and 6 million years ago. Overlying these two geological formations are the Nido and Pyramid formations which were deposited between 6 and 1 million years ago during the second magmatic cycle. The fifth, sixth and seventh oldest geological formations comprising the Big Raven Plateau are the Ice Peak, Pillow Ridge and Edziza formations which were deposited during the third magmatic cycle between about 1 and 0.8 million years ago. Volcanic eruptions during the fourth magmatic cycle between 0.8 and 0.2 million years ago deposited the Klastline and Kadiddi formations while the Big Raven Formation, the youngest geological formation comprising the Big Raven Plateau, was deposited during the fifth magmatic cycle in the last 20,000 years.[5][4]

Raspberry Formation

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An overhead view of an oval-shaped, snow-covered plateau with a snow-covered mountain in the middle.
Snow-covered Big Raven Plateau

The Raspberry Formation is exposed at the base of prominent escarpments on the western, southwestern and southeastern sides of the Big Raven Plateau.[5] It has an elevation of less than 1,310 metres (4,300 feet) along the Mess Creek Escarpment and consists of flat-lying basaltic lava flows interbedded with scoria.[47] More than 180 metres (590 feet) of Raspberry lava flows are exposed in the Mess Creek Escarpment, most of which were erupted from a shield volcano that formed on a Late Miocene erosion surface.[48][49] These lava flows travelled westward into the ancestral valley of Mess Creek while those exposed on and around Cartoona Ridge at the southeastern end of the Big Raven Plateau most likely issued from a smaller volcanic centre northeast of the Raspberry shield.[5][48][49] A minimum age for the timing of Raspberry volcanism is 7.4–6.2 million years.[50]

Armadillo Formation

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Basaltic lava flows of the 6.3-million-year-old Armadillo Formation are exposed in Kadeya Creek canyon on the northwestern side of the Big Raven Plateau, in Sezill Creek canyon on the western side of the plateau and along the Mess Creek Escarpment on the southwestern side of the plateau where they overlie basaltic lava flows of the Raspberry Formation.[2][51] Armadillo basalt flows form up to 180-metre-thick (590-foot) units at these locations and are interbedded with air-fall pumice and ash flows of trachytic and comenditic compositions.[52][53] They were highly fluid and mobile at the time of their eruption as evidenced by their extreme persistence and relatively narrow thicknesses; individual basalt flows are normally less than 3 metres (9.8 feet) thick. The source of these flows was probably a cluster of vents further to the east called Sezill Volcano.[53] In contrast, the air-fall pumice and ash flows probably originated from the more than 4-kilometre-in diameter (2.5-mile) Armadillo Peak caldera south of the Big Raven Plateau.[6][52]

Nido Formation

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The Tenchen Member is the only stratigraphic unit of the Nido Formation comprising the Big Raven Plateau.[5] It consists of basaltic lava flows and pyroclastic rocks which were erupted 4.4 million years ago from three major volcanoes and several smaller eruptive centres; these eruptive centres have since been deeply dissected by erosion.[54] A lower unit of alkali basalt with minor hawaiite is exposed at the southern, southeastern and southwestern ends of the Big Raven Plateau where it is in the form of lava flows, flow breccia and agglutinate. Alkali basalt and minor hawaiite of the Alpha Peak, Beta Peak and associated satellitic eruptive centres are exposed on Sorcery Ridge and Idiji Ridge on the southwestern side of the plateau. They are in the form of lava flows, agglutinate, flow breccia, tuff breccia, pillow lava and pillow breccia which are intercalated with gravel.[5] Alkali basalt of the Gamma Peak eruptive centre is in the form of lava flows, tuff breccia and pillow lava which occur in the upper canyon of Elwyn Creek at the northwestern end of the Big Raven Plateau and overlie alkali basalt of the lower unit at the southeastern end of the plateau.[5][55] Cartoona Peak and Kaia Bluff at the southeastern end of the Big Raven Plateau both consist of alkali basalt erupted from the Gamma Peak eruptive centre.[2][56]

Pyramid Formation

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Exposures of the 1.1-million year-old Pyramid Formation are limited only to the northeastern, eastern and southeastern ends of the Big Raven Plateau where it is in the form of rhyolite and trachyte domes, flows and pyroclastic breccia.[5][57] The Pyramid at the northeastern end of the plateau consists of a roughly 366-metre-high (1,201-foot) trachyte dome whose base is slightly more than 1 kilometre (0.62 miles) wide.[2][58] Unlike other domes of the Pyramid Formation which have been either buried under younger lavas or greatly modified by erosion, The Pyramid has only been moderately eroded and is completely isolated from adjacent rocks.[59] Sphinx Dome is a partially buried rhyolite dome adjacent to The Pyramid whose southern edge has been largely destroyed by headward stream erosion.[60] Isolated remnants of the rhyolitic Pharaoh Dome occur along the eastern and southeastern ends of the Big Raven Plateau between Tennaya Creek in the north and Cartoona Ridge in the south.[5][61] A series of basaltic lava flows up to 65 metres (213 feet) thick overlies a pyroclastic surge deposit of trachytic composition south and east of The Pyramid, both of which are also part of the Pyramid Formation.[5][62]

Ice Peak Formation

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An overhead view of two flat-topped, steep-sided rocky hills on a barren surface.
Ornostay and Koosick bluffs are part of the Ice Peak Formation

The Ice Peak Formation is the most compositionally diverse geological formation of the Big Raven Plateau, having mostly erupted from the Ice Peak stratovolcano about one million years ago.[5][63] Most of the Ice Peak rocks are subdivided into two distinct stratigraphic units called the lower and upper assemblages. The lower assemblage consists of alkali basalt, hawaiite and minor mugearite, tristanite and trachybasalt which are in the form of subaerial lava flows and pyroclastic breccia, as well as tuff breccia, pillow lava and pillow breccia that formed in an ice-contact environment. It is widespread throughout the Big Raven Plateau but is largely buried under colluvium such as glacial till and glacial and fluvial outwash.[5]

Alkali basalt, trachybasalt, tristanite, mugearite, benmoreite and trachyte of the upper assemblage are in the form of lava flows, domes and pyroclastic breccia. They comprise the summit of Ice Peak and are exposed to the south and northeast along the southeastern and eastern sides of the Big Raven Plateau.[5] Ornostay and Koosick bluffs on the western flank of Ice Peak consist of thick lobes of trachyte of the upper assemblage and project onto the Big Raven Plateau.[5][64] Both bluffs are similar in composition and owe their thickness from the ponding of trachyte lava against glacial ice.[64][65]

An isolated occurrence of Ice Peak Formation rocks on the Big Raven Plateau forms Camp Hill which consists of basaltic tuff breccia, pillow breccia, lava flows and tephra.[5][66] Lava from Camp Hill extends to the northwest along the southwestern edge of the plateau but it is almost completely buried under colluvium deposits. Small exposures of this lava occur along the Mess Creek Escarpment and along Taweh Creek valley just south of Hoia Bluff.[5]

Pillow Ridge Formation

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The 0.9-million-year-old Pillow Ridge Formation is limited to Pillow Ridge and Tsekone Ridge at the northern end of the Big Raven Plateau. Pillow Ridge consists of alkali basalt that is in the form of tuff breccia, pillow breccia, pillow lava and minor subaerial lava flows.[5][4] The tuff breccia is crudely bedded and comprises much of the lower and central portions of the ridge.[67] Overlying the tuff breccia is an outer mantle of tubular pillow lava and subaerial lava flows; the pillow lava occurs at the northwestern and southeastern ends of Pillow Ridge while the subaerial lava flows occur only at the southeastern end.[5][67] In contrast, Tsekone Ridge consists of a lower and central unit of tuff breccia and an upper unit of fractured, closely jointed pillows and lava tubes of hawaiitic composition.[5][68] All of the Tsekone Ridge units are cut by vertical north-trending dikes which fed the tuff breccia and pillow lava comprising the ridge. Pillow Ridge and Tsekone Ridge are both products of subglacial volcanism but they differ in glass alteration and vesicular texture, suggesting that they both formed under slightly different conditions.[68]

Edziza Formation

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A glaciated, flat-topped, gently-sloping mountain shadowed by clouds with a much lower barren mountain in the right foreground.
Mount Edziza as seen from Mount Glenora in the northwest

The Edziza Formation is a 0.9-million-year-old trachyte formation mainly comprising the younger central stratovolcano of Mount Edziza and satellitic domes.[5][69] The stratovolcano overlies the northern flank of the older Ice Peak stratovolcano and consists of pyroclastic breccia as well as lahar and ash flow deposits.[5][70] These rocks are well exposed in 850-metre-high (2,790-foot) cliffs along the northern side of Tenchen Glacier where an active cirque has eroded the eastern side of the volcano.[5][26] Exposed at the head of this cirque is hydrothermally altered vent breccia of the central conduit which is overlain by the remains of at least four lava lakes that ponded inside the summit crater.[5][71] Each lava lake has a thickness of around 30 metres (98 feet) and are represented by at least four distinct cooling units.[72]

Satellitic domes of the Edziza Formation include Glacier Dome on the lower northeastern flank of Mount Edziza, Triangle Dome on the upper western flank of Mount Edziza and Nanook Dome on the southwestern rim of the summit crater, the latter of which is the largest dome of the Edziza Formation.[5][73] Glacier Dome was the source of a lava flow that travelled along the northern side of Pyramid Creek valley while Nanook Dome may have been the source of one or two of the lava lakes inside the summit crater.[74] An unnamed pyroclastic cone on the northwestern flank of Mount Edziza produced two trachyte flows that travelled onto the gently sloping surface of the Big Raven Plateau; they are both largely buried under ash and colluvium deposits.[5][75]

Klastline Formation

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The Klastline Formation consists of the remains of thick alkali basalt flows that issued from at least three vents on the northern and eastern sides of the Big Raven Plateau 0.62 million years ago.[5][76] A lobe of alkali basalt extends eastward from the northern end of the plateau to Buckley Lake as a series of scattered outcrops; much of the lobe is buried under colluvium deposits and younger lava flows.[5][77] The source of this lobe was probably a pyroclastic cone that has been eroded to a low grassy hill 1,220 metres (4,000 feet) in elevation.[77] Klastline Cone on the eastern side of the Big Raven Plateau near the head of Pyramid Creek was the main source of Klastline Formation lava flows in the Klastline River valley which have been reduced to small buttes and buttresses.[5][77]

Kakiddi Formation

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The 0.3-million-year-old Kakiddi Formation occurs east and west of Tencho Glacier on the southern flank of Ice Peak, consisting mainly of trachyte in the form of pyroclastic rocks and lava flows.[5][78] Punch Cone on the southwestern flank of Ice Peak is a roughly 1 kilometre (0.62 miles) long, steep-sided ridge composed of agglutinated Kakiddi spatter and breccia from which a largely buried lava flow extends westward onto the gently sloping surface of the Big Raven Plateau.[5][79] Erosional remnants of thick Kakiddi lava flows and pyroclastic rocks to the east occur on Ice Peak and in deeply incised valleys on the eastern side of the plateau; lava flow remnants on Ice Peak overlie older volcanic rocks of the Ice Peak Formation. The remnants on Ice Peak originated from a vent near its summit while those in the adjacent valleys originated from unknown vents, although Nanook Dome on the summit of Mount Edziza may have been a major source which consists of similar Edziza Formation trachyte.[5][80] Trachyte flows of the Kakiddi Formation erupted more fluidly than those of the Edziza Formation as evidenced by their greater extant on gently sloping terrain.[81]

Big Raven Formation

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A black cone-shaped mountain rising over glacial ice in the foreground.
Tennena Cone in the Snowshoe Lava Field from the northwest

Alkali basalt and hawaiite of the Big Raven Formation is widespread at the northern and southern ends of the Big Raven Plateau; the largest occurrence at the northern end is the Desolation Lava Field while the largest occurrence at the southern end is the Snowshoe Lava Field.[5] A radiocarbon date of 1340 ± 130 years has been obtained from willow twigs preserved within tephra from Williams Cone, the youngest pyroclastic cone in the Desolation Lava Field.[82] Kana Cone is an isolated pyroclastic cone on the extreme northern slope of the plateau and is the northernmost occurrence of Big Raven Formation alkali basalt and hawaiite; it was the source of lava flows that forced the Klastline River against the northern valley wall.[5][83]

The Walkout Creek centres on the extreme southern slope of the Big Raven Plateau consist of the remains of two small cinder cones and associated alkali basalt flows on the northern side of Walkout Creek valley.[5][84] Cinder Cliff, Icefall Cone and Ridge Cone are three isolated occurrences of Big Raven Formation alkali basalt on the eastern flank of Mount Edziza, the latter two of which are on the high eastern rim of Ice Peak and have been significantly modified by slumping, rockfalls and glaciation.[5][85] The Big Raven Formation also includes the Sheep Track Member, a pyroclastic fall deposit of unconsolidated comenditic trachyte pumice obscuring much of the surficial details of the Snowshoe Lava Field.[5][39]

Basement

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As a part of the Mount Edziza volcanic complex, the Big Raven Plateau is underlain by the Stikinia terrane.[3][86] This is a Paleozoic and Mesozoic suite of volcanic, sedimentary and metamorphic rocks that accreted to the continental margin of North America during the Jurassic.[5][86][87] The rocks of this terrane are exposed along the western side of the plateau in Mess Creek valley, the southern side of the plateau in Walkout and Chakima creek valleys, at the extreme northern end of the plateau as inliers and along the eastern side of the plateau where they comprise the lower units of Idiji Ridge, Sorcery Ridge and other neighbouring ridges.[5]

Also underlying the Big Raven Plateau are Cretaceous and Paleocene conglomerates, arkoses, sandstones, siltstones, shales and minor coal of the Sustut Group which are exposed along the western side of the plateau. Eocene leucogranite of the Elwyn Creek Pluton is exposed in Elwyn Creek canyon at the northwestern end of the Big Raven Plateau, as are Eocene rhyolite, dacite and andesite pyroclastic breccias and andesite lava domes and flows.[5] All of these Eocene rocks are part of the Sloko Group and were emplaced by the youngest documented magmatic event before the Mount Edziza volcanic complex started erupting in the Late Miocene.[5][88]

Name and etymology

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The name of the plateau was adopted 2 January 1980 on the National Topographic System map 104G after being submitted to the BC Geographical Names office by the Geological Survey of Canada.[1] It is named after Big Raven, a deity in Tahltan mythology whose name translates to Tse'sketco in the Tahltan language.[1][7] Several features on the Big Raven Plateau also have names with Tahltan roots that were adopted 2 January 1980 for geology reporting purposes, including Keda Cone, Sidas Cone, Kana Cone, Tennena Cone, Hoia Bluff, Kaia Bluff, Ornostay Bluff, Koosick Bluff, Cartoona Peak and Tsekone Ridge.[5][89][90][91][92][93][94][95][96][97][98]

Provincial park

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A gently sloping surface rising above vegetated slopes with mountains in the background and foreground.
Panoramic view of the Big Raven Plateau; Eve Cone is visible as a small dark hill to the right

The Big Raven Plateau lies at the northern end of Mount Edziza Provincial Park, a protected area founded in 1972 to showcase the volcanic landscape.[2][99] This remote wilderness area of northwestern British Columbia is not accessible by motorized vehicles to help protect the very sensitive environment. Instead, access is mainly via aircraft or unmaintained hiking trails that cross creeks.[99] Mount Edziza Provincal Park covers 266,180 hectares (657,700 acres), making it one of the largest provincial parks in British Columbia.[99][100] Hunting, camping, fishing, hiking, wildlife viewing and nature studying are some of the activities available in Mount Edziza Provincial Park.[99]

Wildlife in the area includes moose, caribou, mountain goats, stone sheep, wolves, bears, squirrels, owls, ptarmigans, ravens, gyrfalcons, grouse and migratory songbirds. The climate is characterized by warm summers and cold, snowy winters; temperatures are warmest in mid-summer during the day when they may hit the 30 degrees Celsius (86 degrees Fahrenheit) range. However, temperatures can drop below freezing during summer nights, making snow or freezing rain a possibility at any time of the year.[99]

Accessibility

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The closest roads to the Big Raven Plateau are the Stewart–Cassiar Highway to the southeast and the Telegraph Creek Road to the northwest, both of which extend within 40 kilometres (25 miles) of the plateau.[2][101] Extending from these roads are horse trails that provide access to the Big Raven Plateau.[102] From Telegraph Creek, the Buckley Lake Trail extends about 15 kilometres (9.3 miles) southeast along Mess Creek and Three Mile Lake. It then traverses about 15 kilometres (9.3 miles) northeast along Dagaichess Creek and Stinking Lake to the northeastern end of Buckley Lake where it meets with the Klastline River Trail and the Buckley Lake to Mowdade Lake Route, the latter of which climbs up onto the gently sloping northern side of the Big Raven Plateau.[101]

To the east, the roughly 50-kilometre-long (31-mile) Klastline River Trail begins at the community of Iskut on the Stewart–Cassiar Highway. It extends northwest and west along the Klastline River for much its length. The trail enters Mount Edziza Provincial Park at about 25 kilometres (16 miles) where Kakiddi Creek drains into the Klastline River. After entering Mount Edziza Provincial Park, the Klastline River Trail traverses northwest along the Klastline River for about 10 kilometres (6.2 miles) and then crosses the river north of the Big Raven Plateau. From there, the Klastline River Trail traverses west for about 15 kilometres (9.3 miles) to the northeastern end of Buckley Lake where it meets with the Buckley Lake Trail and Buckley Lake to Mowdade Lake Route junction.[101]

The Big Raven Plateau can also be accessed by float plane or helicopter, both of which are available for charter at the communities of Iskut and Dease Lake.[102] Buckley Lake to the northwest, Nuttlude Lake to the east and Kakiddi Lake, Mowchilla Lake and Mowdade Lake to the southeast are large enough to be used by float-equipped aircraft.[2][99][102] Landing on Buckley Lake and Mowchilla Lake with a private aircraft requires a letter of authorization from the BC Parks Stikine Senior Park Ranger. Private aircraft are prohibited from landing on lava flows that are 1,700 metres (5,500 feet) in elevation or higher.[99]

See also

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References

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  2. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj Telegraph Creek, Cassiar Land District, British Columbia (Topographic map) (3 ed.). 1:250,000. A502 (in English and French). Department of Energy, Mines and Resources. 1989. Archived from the original on 2021-05-02. Retrieved 2021-09-25.
  3. ^ a b c d Souther 1992, p. 32.
  4. ^ a b c d Souther 1992, p. 267.
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc Souther, J. G. (1988). "1623A" (Geologic map). Geology, Mount Edziza Volcanic Complex, British Columbia. 1:50,000. Cartography by M. Sigouin, Geological Survey of Canada. Energy, Mines and Resources Canada. doi:10.4095/133498.
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Sources

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