Spectrum Range

Last updated
Spectrum Range
Spectrum Mountains
Rainbow Mountains
MEVC satellite.jpg
Mount Edziza appears at the top of this image west of snow-covered Nuttlude and Kakiddi lakes. The snow-covered mountains at the right-centre, lying between the Mess Creek (left) and Little Iskut River (right) drainages, are in the Spectrum Range.
Highest point
Peak Kitsu Peak [1]
Elevation 2,430 m (7,970 ft) [2]
Coordinates 57°25′25″N130°41′24″W / 57.42361°N 130.69000°W / 57.42361; -130.69000 [3]
Geography
Canada British Columbia relief location map.jpg
Red triangle with thick white border.svg
Spectrum Range
Location in British Columbia
Country Canada [2]
Province British Columbia [2]
District Cassiar Land District [4]
Protected area Mount Edziza Provincial Park [4]
Range coordinates 57°24′N130°42′W / 57.400°N 130.700°W / 57.400; -130.700 [4]
Parent range Tahltan Highland [5]
Borders on Skeena Mountains (east) [6]
Coast Mountains (west) [6]
Arctic Plateau (southwest) [7]
Kitsu Plateau (northwest) [7]
Topo map NTS   104G7 Mess Lake [4]
Geology
Formed by Lava dome [1]
Age of rock 3.5–2.5 million years old [8] [9]
Type of rock Rhyolite, trachyte, basalt [1]
Volcanic region Northern Cordilleran Province [10]
Last eruption Unknown [2]
Spectrum Range Location in Mount Edziza Provincial Park

The Spectrum Range, formerly gazetted as the Spectrum Mountains and the Rainbow Mountains, is a small mountain range in Cassiar Land District of northwestern British Columbia, Canada. Located at the southern end of the Tahltan Highland, it borders the Skeena Mountains in the east and the Boundary Ranges of the Coast Mountains in the west. The Spectrum Range is surrounded by the Arctic Lake Plateau in the southwest and the Kitsu Plateau in the northwest, both of which contain volcanic features such as cinder cones. It lies at the southern end of the Mount Edziza volcanic complex which includes the two neighbouring plateaus as well as Mount Edziza and the Big Raven Plateau to the north. The mountain range is drained on all sides by streams within the Stikine River watershed and, unlike Mount Edziza to the north, contains relatively small separate glaciers. Mount Edziza Provincial Park is the main protected area surrounding the Spectrum Range.

Contents

The Spectrum Range is the eroded remains of a large lava dome whose original surface is only preserved as a few small remnants on the summits of the higher peaks. This dome formed between 3.5 and 2.5 million years ago during the second magmatic cycle of the Mount Edziza volcanic complex and was originally more than 25 kilometres (16 miles) wide. Much of the dome consists of massive rhyolite and trachyte lava flows but relatively minor basalt lava flows erupted later during the dome's formation. These lava flows form the nearly circular group of pyramidal peaks and long, narrow-crested ridges comprising the Spectrum Range; the basalt flows mainly cap the higher peaks. Volcanism in the last 2.5 million years has mainly occurred on the northwestern and southwestern sides of the Spectrum Range but the precise age of the latest eruption is unknown.

Names and etymology

The Spectrum Range was labelled as the Rainbow Mountains on a BC Lands map published in 1929 which was followed by renaming of the mountain range to the Spectrum Mountains in 1945. [4] In 1954, the form of name was changed to the Spectrum Range in accordance to the Geological Survey of Canada memoir 247 published in 1948. [4] [11] These names for the mountain range refer to its multi-coloured rocks; pale green, light grey and white rocks weather to bright hues of orange, yellow and red. [1]

Geography and geomorphology

Location

The Spectrum Range lies at the southern end of the Tahltan Highland east of the Boundary Ranges of the Coast Mountains and west of the Skeena Mountains in Cassiar Land District. [4] [6] To the southwest, the Spectrum Range is surrounded by the Arctic Lake Plateau which includes adjacent volcanic features such as Outcast Hill, Wetalth Ridge, Exile Hill, Nahta Cone and Tadekho Hill. [6] [12] The Kitsu Plateau surrounds the Spectrum Range to the northwest and includes the Mess Lake Lava Field which consists of geologically recent lava flows and tephra from three pyroclastic cones. [2] [13] To the north and northeast, the Spectrum Range is bounded by Raspberry Pass and Artifact Creek valley, respectively, the latter of which separates Artifact Ridge from the mountain range. [6] [14]

The Spectrum Range lies at the southern end of the Mount Edziza volcanic complex which includes the adjacent Arctic Lake and Kitsu plateaus, as well as Mount Edziza and the Big Raven Plateau to the north. [7] 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 an intermontane plateau that is overlain by four central volcanoes along its north–south trending axis; the Spectrum Range is the southernmost and third oldest central volcano. [8]

Structure

Extending outward from the central portion of this nearly circular group of pyramidal peaks and long, narrow-creasted ridges is a crudely radial drainage system characterized by deeply incised valleys. [15] Talus and felsenmeer deposits cover large portions of the valley slopes which rise to broad, rounded crests of the interfluvial ridges. [7] These ridges are the eroded remains of a once continuous lava dome whose original surface is only preserved as a few small remnants on the summits of the higher peaks. [15] The ridges and peaks decrease in elevation away from the central portion of the mountain range. [1] Among these peaks and ridges are Kitsu Peak, Yeda Peak, Kuno Peak, Kounugu Mountain, Obsidian Ridge and Yagi Ridge. [6]

The current, approximately 19-kilometre-wide (12-mile) dome comprising the Spectrum Range originally had a width of more than 25 kilometres (16 miles) as indicated by the existence of erosional remnants around its northern and southwestern edges. [1] It was also originally higher than its current elevation of 2,430 metres (7,970 feet) as evidenced by the thick, gently dipping lava flows comprising the summit of Kitsu Peak, the highest point of the Spectrum Range. [1] [2] The original volume of the Spectrum Dome is estimated to have been 101 cubic kilometres (24 cubic miles) based on restoration calculations of the original surface. [1]

Glaciation

The Mount Edziza volcanic complex was covered by a regional ice sheet during the Pleistocene which receded and advanced periodically until about 11,000 years ago when deglaciation was essentially complete in a steadily warming climate. [16] [17] This warming trend ceased about 2,600 years ago, causing glaciers to advance from the Spectrum Range and elsewhere along the volcanic complex as a part of the neoglaciation. The present trend towards a more moderate climate put an end to the neoglacial period in the 19th century which has resulted in rapid glacial recession throughout the Mount Edziza volcanic complex. This rapid glacial recession is apparent from the lack of vegetation on the barren, rocky ground between the glaciers and their trim lines which are up to 2 kilometres (1.2 miles) apart. [18]

Unlike Mount Edziza which has an approximately 70-square-kilometre (27-square-mile) ice cap, the Spectrum Range is covered with relatively small separate glaciers that occupy cirques on most peaks greater than 2,130 metres (6,990 feet) in elevation. [19] The largest glacier is Nagha Glacier which initiates just northwest of Yeda Peak and terminates at the head of the valley between Yagi Ridge and the Kitsu Plateau. [6] Yeda Glacier, an informally named glacier at the head of Ball Creek, existed south of Yeda Peak in 1988. [20]

Drainage

The Spectrum Range drains into the Stikine River via tributaries StikineRiverCanyon.JPG
The Spectrum Range drains into the Stikine River via tributaries

As a part of the Mount Edziza volcanic complex, the Spectrum Range is drained on all sides by streams within the Stikine River watershed. [6] [21] Kitsu Creek is a northwest-flowing stream originating from the northern side of Kitsu Peak. [22] It contains one named tributary, Nagha Creek, which also flows northwest from the Spectrum Range. [6] [23] Tadekho Creek originates from between Kuno and Yeda peaks and flows to the northwest. [6] Kitsu and Tadekho creeks both flow into Mess Creek which is a northwest-flowing tributary of the Stikine River. [6] [24]

The Little Iskut River originates from Little Ball Lake just south of Kounugu Mountain and flows to the northeast where it collects Stewbomb Creek flowing east from the Spectrum Range. Stewbomb Creek contains one named tributary, Artifact Creek, which originates adjacent to Kitsu Peak and flows through a valley between Artifact and Obsidian ridges. Ball and More creeks both flow south from the southern end of the Spectrum Range near Yeda Peak, the former of which contains an east-flowing tributary called Chachani Creek. [6] The Little Iskut River and Ball and More creeks are tributaries of the Iskut River which flows south and then west into the Stikine River. [6] [25]

Geology

Background

Map of the Mount Edziza volcanic complex showing the location of the Spectrum Range MEVC map.png
Map of the Mount Edziza volcanic complex showing the location of the Spectrum Range

The Spectrum Range is part of the Northern Cordilleran Volcanic Province, a broad area of volcanoes and lava flows extending from northwestern British Columbia northwards through Yukon into easternmost Alaska. [10] [26] The dominant rocks comprising these volcanoes are alkali basalts and hawaiites, but nephelinite, basanite and peralkaline phonolite, trachyte and comendite are locally abundant. These rocks were deposited by volcanic eruptions from 20 million years ago to as recently as a few hundred years ago. The cause of volcanic activity in the Northern Cordilleran Volcanic Province is thought to be due to rifting of the North American Cordillera driven by changes in relative plate motion between the North American and Pacific plates. [27]

Basement

Underlying nearly all of the Spectrum Range is the Kounugu Member of the Nido Formation, one of many stratigraphic units comprising the Mount Edziza volcanic complex. [28] Basaltic lava flows of this Pliocene geological member are exposed around the perimeter of the Spectrum Range and are limited only to the area south of the broad east–west valley of Raspberry Pass. [29] [30] They issued from at least four separate eruptive centres that have been either deeply eroded or have been completely destroyed by erosion. [29]

Also underlying the Spectrum Range are flat-lying basalt flows of the Raspberry Formation, the oldest unit of the Mount Edziza volcanic complex. [31] This geological formation is of late Miocene age and originated as a composite shield volcano that erupted lava from at least three locations near Raspberry Pass. [32] The Nido and Raspberry formations are underlain by the Stikinia terrane, a Paleozoic and Mesozoic suite of volcanic and sedimentary rocks that accreted to the continental margin of North America during the Jurassic. [33] [34]

Composition

The Spectrum Range consists mainly of trachyte, comendite and pantelleritic trachyte and rhyolite of the Spectrum Formation, the fifth oldest stratigraphic unit of the Mount Edziza volcanic complex. [35] More than 90% of these volcanic rocks were erupted as lava while less than 10% of them were erupted as pumice and pyroclastic flows; the lava is in the form of flows that individually reach thicknesses of up to 200 metres (660 feet). [36] These volcanic rocks are overlain locally by eroded remnants of Kitsu Member basaltic lava flows which preserve the unmodified upper surface of the original Spectrum Dome and cap the higher peaks of the Spectrum Range. [15] [36]

Caldera

In the middle of the Spectrum Range at the base of the volcanic pile is a buried depression that may be a caldera or an irregular collapse structure. It occurs within a roughly circular area about 10 kilometres (6.2 miles) in diameter and likely formed by collapse of a shallow magma chamber during eruption of the Spectrum Formation lavas. At least 1 kilometre (0.62 miles) of vertical caldera collapse may have resulted if the magma chamber was similar in diameter to this circular area, but poor exposure of the depression and of the bounding vertical faults has given fragmentary evidence. The southwestern side of a northwesterly-trending, nearly vertical fault adjacent to Stewbomb Creek has dropped at least 90 metres (300 feet) and is cut by parallel rhyolite dikes. [37]

Eruptive history

The rocks comprising the Spectrum Range were deposited by volcanic eruptions between 3.5 and 2.5 million years ago during the second magmatic cycle of the Mount Edziza volcanic complex. [8] [38] A relatively small initial eruption of pumice and ash was followed by the effusion of massive rhyolite flows that reached 13 kilometres (8.1 miles) long. [39] These rhyolite flows accumulated in rapid succession to form the broad Spectrum Dome which reached a thickness of at least 750 metres (2,460 feet) and a width of more than 25 kilometres (16 miles). [40] The predominantly rhyolitic eruptions were later replaced by the effusion of trachyte lava as deeper parts of the underlying magma chamber were tapped. [41] Formation of the Spectrum Dome was followed by evacuation of the magma chamber, resulting in the creation of the caldera which was eventually buried by lava from subsequent eruptions. [42]

Paleogeological map of the Spectrum Formation showing the current extent of the Spectrum Dome Spectrum Formation.png
Paleogeological map of the Spectrum Formation showing the current extent of the Spectrum Dome

Yeda Peak, a 2,240-metre-high (7,350-foot) pinnacle in the middle of the Spectrum Range, was the site of a subsequent explosive eruption that resulted in the formation of a crater. [6] [43] Some of the ejecta accumulated around the vent to form a low volcanic cone while the more volatile, pumice-rich phases of the eruption sent ash flows down the slopes of the Spectrum Dome. [41] Renewed volcanism at Exile Hill 8 kilometres (5.0 miles) to the west on the Arctic Lake Plateau produced a similar but much smaller eruption that created a roughly 200-metre-wide (660-foot) breccia pipe. [6] [44] Late-stage volcanism also deposited alkali basalt flows of the Kitsu Member which likely issued from multiple eruptive centres on the dome's summit that have since been removed by erosion. [45] These lava flows travelled over a layer of polymict gravel that overlies older volcanic rocks of the Spectrum Formation. [36]

Following construction of the Spectrum Dome, lesser activity continued into the Quaternary from parasitic vents in and adjacent to the Spectrum Range. [2] [20] Volcanism during the Pleistocene created a number of small volcanoes on the southwestern flank of the mountain range that formed in subaerial and subglacial environments. [2] Subaerial lava fountaining at the extreme northern end of the Arctic Lake Plateau created the Outcast Hill cinder cone which blocked westerly flowing streams to create a temporary lake against its eastern side. [46] [47] About 4 kilometres (2.5 miles) to the south, Tadekho Hill formed on top of a 180-metre-high (590-foot) remnant of Spectrum Formation trachyte. Lava from this volcano spread onto the surrounding plateau surface to form a small shield volcano. [48] Subsequent subglacial volcanism near the central portion of the Arctic Lake Plateau formed the subglacial mound of Wetalth Ridge. [48] [49] All three Pleistocene volcanoes are basaltic in composition and are part of the Arctic Lake Formation which formed during a period of volcanic activity 0.71 million years ago. [50]

Volcanism during the Holocene created subaerial cinder cones and lava flows on the northwestern and southwestern sides of the Spectrum Range, all of which are part of the Big Raven Formation. [2] [20] The basaltic Mess Lake Lava Field on the northwestern flank issued from three cinder cones adjacent to the edge of the Mess Creek Escarpment. [2] [51] Lava from the two oldest cones flowed to the west and probably cascaded over the escarpment into Mess Creek valley. [51] The youngest cinder cone, The Ash Pit, formed at the south end of the Mess Lake Lava Field and was the source of a northeasterly-trending tephra deposit on the Kitsu Plateau. [52] An eruption near the northern edge of the Arctic Lake Plateau created the isolated Nahta Cone on the southwestern flank of the Spectrum Range which was the source of a narrow, 3-kilometre-long (1.9-mile) basaltic lava flow that travelled northward into the head of Nahta Creek. [6] [53] Volcanic activity on the southern flank of Kuno Peak at the southwestern end of the Spectrum Range created a cinder cone that was subsequently destroyed by landsliding on Kuno Peak. [6] [54] This cinder cone also produced a basaltic lava flow but it was later buried under debris from the landsliding. [54] Although volcanic activity at the Spectrum Range continued into the current Holocene epoch, the last eruption is unknown. [2]

Fumarolic alteration

Alteration of Spectrum Formation rocks caused by fumarolic activity during the formation of the Spectrum Dome occurs at Yeda Peak and elsewhere throughout the Spectrum Range. [37] Fumarolic alteration at Yeda Peak occurs in the breccia pipe comprising this peak and along adjacent fractures; it likely resulted from fumarolic activity after the explosive eruption that formed the Yeda Peak crater. [55] Alteration elsewhere in the Spectrum Range was caused by fumarolic activity during the cooling and degassing of lava flows comprising the Spectrum Formation. In contrast to the fumarolic activity at Yeda Peak which was likely sourced by a deeper, hotter and longer lived hydrothermal system than elsewhere in the Spectrum Range, the lava flow fumaroles were small and relatively short-lived. [37] The multi-coloured rocks which give the Spectrum Range its name are partially the result of fumarolic alteration. [5] [56]

Subvolcanic intrusions

At the head of Ball Creek valley is a subvolcanic mass of granite with abnormally high soda content that probably intruded into the base of the Spectrum Dome during the explosive Yeda Peak breccia pipe eruption. It lies along the edge of the hypothetical caldera or irregular collapse structure and comprises a series of glacially rounded bluffs along the southwestern side of Ball Creek valley. The soda granite forming this subvolcanic intrusion is lustrous brown and medium to coarse-grained, consisting mostly of feldspar that is locally covered with iron and manganese oxides. [37]

Provincial park

Nahta Cone from the southeast with the Spectrum Range obscured by clouds in the background Nahta cone from southeast june 2006.jpg
Nahta Cone from the southeast with the Spectrum Range obscured by clouds in the background

The Spectrum Range lies at the southern end of Mount Edziza Provincial Park, a protected area founded in 1972 to showcase the volcanic landscape. [6] [14] 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. [14] Mount Edziza Provincial Park covers 266,180 hectares (657,700 acres), making it one of the largest provincial parks in British Columbia. [14] [57] Hunting, camping, fishing, hiking, wildlife viewing and nature studying are some of the activities available in Mount Edziza Provincial Park. [14]

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. [14]

Accessibility

The Spectrum Range can be accessed by float plane or helicopter, both of which are available for charter at the communities of Iskut and Dease Lake. [58] Private aircraft are prohibited from landing on the Kitsu Plateau lava flows. [14] Mess Lake northwest of the Spectrum Range, 180 Lake southeast of the Spectrum Range, Arctic Lake and Little Arctic Lake southwest of the Spectrum Range and Little Ball Lake just south of Kounugu Mountain at the southwestern end of the Spectrum Range are large enough to be used by float-equipped aircraft. [6] [14] [58] Landing on the latter two lakes with a private aircraft requires a letter of authorization from the BC Parks Stikine Senior Park Ranger. [14]

See also

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<span class="mw-page-title-main">Big Raven Formation</span> Geological formation in British Columbia, Canada

The Big Raven Formation is a stratigraphic unit of Quaternary age in northwestern British Columbia, Canada. It is the youngest and least voluminous geological formation of the Mount Edziza volcanic complex (MEVC); it overlies at least six older formations of this volcanic complex. The main volcanic rocks of the Big Raven Formation are alkali basalts and hawaiites, although a small volume of trachyte comprises the Sheep Track Member. These rocks were deposited by volcanic eruptions in the last 20,000 years during the latest magmatic cycle of the MEVC. Alkali basalt and hawaiite are in the form of lava flows and small volcanic cones while trachyte of the Sheep Track Member is mainly in the form of volcanic ejecta which covers an area of about 40 square kilometres.

<span class="mw-page-title-main">Volcanism of the Mount Edziza volcanic complex</span> Volcanic activity of the Mount Edziza volcanic complex, Canada

The Mount Edziza volcanic complex (MEVC) in British Columbia, Canada, has a long history of volcanism that spans more than 7 million years. It occurred during five cycles of magmatic activity, each producing less volcanic material than the previous one. Volcanism during these cycles has created several types of volcanoes, including cinder cones, stratovolcanoes, subglacial volcanoes, shield volcanoes and lava domes. The approximately 1,000-square-kilometre (400-square-mile) volcanic plateau forming the base of the MEVC owes its origin to successive eruptions of highly mobile lava flows. Volcanic rocks such as basalt, trachybasalt, benmoreite, tristanite, mugearite, trachyte and rhyolite were deposited by multiple eruptions of the MEVC; the latter seven rock types are products of varying degrees of magmatic differentiation in underground magma reservoirs. At least 10 distinct flows of obsidian were produced by volcanism of the MEVC, some of which were exploited by indigenous peoples in prehistoric times to make tools and weaponry. Renewed volcanism could produce explosive eruptions and block local streams with lava flows.

<span class="mw-page-title-main">Edziza Formation</span> Geological formation in British Columbia, Canada

The Edziza Formation is a stratigraphic unit of Pleistocene age in northwestern British Columbia, Canada. First described in 1984, the Edziza Formation was mapped as one of several geological formations of the Mount Edziza volcanic complex. It overlies at least four other geological formations of this volcanic complex that differ in age and composition. The main volcanic rock comprising the Edziza Formation is trachyte which was deposited by volcanic eruptions at the end of the third magmatic cycle of the Mount Edziza volcanic complex 0.9 million years ago.

Artifact Ridge is a mountain ridge extending southeast from the eastern side of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It is bounded on the north by Bourgeaux Creek valley, on the south by Artifact Creek valley, on the east by the Little Iskut River valley and on the west by the Kitsu Plateau. The ridge is at the southeastern end of Mount Edziza Provincial Park and gets its name from the knapping of obsidian tools and points by early Tahltan hunters. Destell Pass cuts north–south through the westernmost end of Artifact Ridge.

Yagi Ridge is a mountain ridge extending northwest from the middle of the Spectrum Range at the southern end of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It is bounded on the north by Nagha Glacier and Nagha Creek valley, on the south by Yeda Creek on the Arctic Lake Plateau and on the west by Mess Creek valley. Yagi Ridge reaches an elevation of 2,243 metres at the head of Nagha Glacier where its eastern end adjoins to the Spectrum Range just northwest of Yeda Peak.

Kitsu Peak is the highest summit of the Spectrum Range at the southern end of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It is bounded on the west by Nagha Creek valley, on the northwest by the Kitsu Plateau, on the northeast by Obsidian Ridge, on the east by Stewbomb Creek valley and on the southwest by Nagha Glacier and Yagi Ridge. It has an elevation of 2,430 metres and lies at the northern end of the Spectrum Range.

Kounugu Mountain is a mountain in the Spectrum Range at the southern end of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It is southeast of Yeda Peak, west and northwest of the Little Iskut River, south of Stewbomb Creek valley and just north of Little Ball Lake. It has an elevation of 2,267 metres and lies at the southeastern end of the Spectrum Range. The mountain is also at the southeastern end of Mount Edziza Provincial Park which is southeast of the community of Telegraph Creek.

Kuno Peak is a mountain peak in the Spectrum Range at the southern end of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It is south of Yagi Ridge, west of Yeda Peak, southeast of Outcast Hill, east of Exile Hill, northeast of Tadekho Hill and north of Little Arctic Lake, the latter four of which are on the northern end of the Arctic Lake Plateau. It has an elevation of 2,183 metres and lies at the southwestern end of the Spectrum Range. Tadekho Creek originates from the southern flank of the ridge connecting Kuno Peak with Yeda Peak.

References

  1. 1 2 3 4 5 6 7 8 Souther 1992, p. 113.
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Sources