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Spectrum Range
Spectrum Mountains
Rainbow Mountains
An overhead view of snow-covered mountains with intervening river valleys.
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
PeakKitsu Peak[1]
Elevation2,430 m (7,970 ft)[2]
Coordinates57°25′25″N 130°41′24″W / 57.42361°N 130.69000°W / 57.42361; -130.69000[4]
Geography
Spectrum Range is located in British Columbia
Spectrum Range
Spectrum Range
Location in British Columbia
CountryCanada[2]
ProvinceBritish Columbia[2]
DistrictCassiar Land District[3]
Protected areaMount Edziza Provincial Park[3]
Range coordinates57°24′N 130°42′W / 57.400°N 130.700°W / 57.400; -130.700[3]
Parent rangeTahltan Highland[5]
Borders onCoast Mountains (west)[5]
Skeena Mountains (east)[5]
Topo mapNTS 104G7 Mess Lake[3]
Geology
Formed byLava dome[1]
Type of rockRhyolite, trachyte, basalt[1]
Volcanic regionNorthern Cordilleran Province[6]
Last eruptionUnknown[2]
Map

The Spectrum Range is a mountain range in Cassiar Land District of northwestern British Columbia, Canada.











Names and etymology edit

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.[3] 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.[3][7] These names for the mountain range refer to its multicoloured rocks; pale green, light grey and white rocks weather to bright hues of orange, yellow and red.[1]

Geography and geomorphology edit

Location edit

The Spectrum Range lies east of the Boundary Ranges of the Coast Mountains and west of the Skeena Mountains at the southern end of the Tahltan Highland in Cassiar Land District.[3][5] 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.[5][8] The Kitsu Plateau surrounds the Spectrum Range to the northwest and includes the Mess Lake Lava Field which comprises geologically recent lava flows and tephra from three pyroclastic cones.[2][9] To the northeast, the Spectrum Range is surrounded by the Obsidian and Artifact ridges, which extend east from the Spectrum Range and Kitsu Plateau, respectively.[5]

The Spectrum Range is 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.[10] This volcanic complex of Miocene-to-Holocene age comprises a broad, steep-sided, intermontane plateau that rises from a base elevation of 760 to 816 metres (2,500 to 2,675 feet).[11][12][13] The plateau is dotted with several cinder cones and contains four central volcanoes along its north–south trending axis; the Spectrum Range is the southernmost and third oldest central volcano.[11]

Structure edit

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.[14] Talus and felsenmeer deposits cover large portions of the valley slopes which rise to broad, rounded crests of the interfluvial ridges.[10] 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.[14] The ridges and peaks decrease in elevation away from the central portion of the mountain range.[1]

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 about 101 cubic kilometres (24 cubic miles) based on restoration calculations of the original surface.[1]

Glaciation edit

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.[15][16] This warming trend ceased about 2,600 years ago, causing glaciers to advance from the Spectrum Range and elsewhere along the volcanic complex as 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.[17]

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.[18] 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.[5] Yeda Glacier, an informally named glacier at the head of Ball Creek, existed south of Yeda Peak in 1988.[19]

Drainage edit

 
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.[5][20] Kitsu Creek is a northwest-flowing stream originating from the northern side of Kitsu Peak.[21] It contains one named tributary, Nagha Creek, which also flows northwest from the Spectrum Range.[5][22] Tadekho Creek originates from between Kuno and Yeda peaks and flows to the northwest.[5] Kitsu and Tadekho creeks both flow into Mess Creek which is a northwest-flowing tributary of the Stikine River.[5][23]

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.[5] 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.[5][24]

Geology edit

Background edit

The Spectrum Range is part of the Northern Cordilleran Volcanic Province, a broad area of shield volcanoes, lava domes, cinder cones and stratovolcanoes extending from northwestern British Columbia northwards through Yukon into easternmost Alaska.[6][25] The dominant rocks comprising these volcanoes are alkali basalts and hawaiites, but nephelinite, basanite and peralkaline[a] 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 edit

 
Map of the Mount Edziza volcanic complex showing the location of the Spectrum Range

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 edit

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]

Caldera edit

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 9.6 kilometres (6.0 miles) in diameter and likely formed by collapse of a shallow magma chamber during eruption of the Spectrum 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.[36]

Eruptive history edit

The rocks comprising the Spectrum Range were deposited by volcanic eruptions during the second magmatic cycle of the Mount Edziza volcanic complex 3.1 million years ago.[35]

Fumarolic alteration edit

Subvolcanic intrusions edit

Provincial park edit

The Spectrum Range lies at the southern end of Mount Edziza Provincial Park, a protected area founded in 1972 to showcase the volcanic landscape.[5][37]

Accessibility edit

See also edit

Notes edit

  1. ^ Peralkaline rocks are magmatic rocks that have a higher ratio of sodium and potassium to aluminum.[26]

References edit

  1. ^ a b c d e f g h Souther 1992, p. 113.
  2. ^ a b c d e f "Spectrum Range: General Information". Global Volcanism Program. Smithsonian Institution. Archived from the original on 2022-09-22. Retrieved 2022-10-03.
  3. ^ a b c d e f g "Spectrum Range". BC Geographical Names. Archived from the original on 2020-06-30. Retrieved 2021-09-26.
  4. ^ "Kitsu Peak". BC Geographical Names. Retrieved 2024-03-25.
  5. ^ a b c d e f g h i j k l m n 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.
  6. ^ a b "Stikine volcanic belt". Catalogue of Canadian volcanoes. Natural Resources Canada. 2008-02-13. Archived from the original on 2009-06-08. Retrieved 2024-03-28.
  7. ^ "Purcell Mountains". BC Geographical Names. Retrieved 2024-03-25.
  8. ^ Souther 1992, pp. 22, 23, 26, 32, 108.
  9. ^ Souther 1992, pp. 32, 234, 235.
  10. ^ a b Souther 1992, p. 32.
  11. ^ a b Wood, Charles A.; Kienle, Jürgen (1990). Volcanoes of North America: United States and Canada. Cambridge University Press. pp. 124, 125. ISBN 0-521-43811-X.
  12. ^ D.R. Piteau and Associates (1988). Geochemistry and Isotope Hydrogeology of the Mount Edziza and Mess Creek Geothermal Waters, British Columbia (Report). Open File 1732. Geological Survey of Canada. p. 3. doi:10.4095/130715.
  13. ^ Lakeman, Thomas R.; Clague, John J.; Menounos, Brian; Osborn, Gerald D.; Jensen, Britta J. L.; Froese, Duane G. (2008). "Holocene tephras in lake cores from northern British Columbia, Canada". Canadian Journal of Earth Sciences. 45 (8). NRC Research Press: 940. Bibcode:2008CaJES..45..935L. doi:10.1139/E08-035. ISSN 1480-3313.
  14. ^ a b Souther 1992, pp. 32, 113.
  15. ^ Souther 1992, pp. 18–20, 25.
  16. ^ Wilson & Kelman 2021, p. 10.
  17. ^ Souther 1992, p. 25.
  18. ^ Souther 1992, pp. 35, 36.
  19. ^ Souther, J. G. (1988). "1623A" (Geologic map). Geology, Mount Edziza Volcanic Complex, British Columbia. 1:50,000. Geological Survey of Canada. doi:10.4095/133498.
  20. ^ Souther 1992, p. 33.
  21. ^ "Kitsu Creek". Geographical Names Data Base. Natural Resources Canada. Retrieved 2024-03-30.
  22. ^ "Nagha Creek". BC Geographical Names. Archived from the original on 2021-10-01. Retrieved 2024-03-30.
  23. ^ "Mess Creek". BC Geographical Names. Archived from the original on 2021-08-20. Retrieved 2022-09-29.
  24. ^ "Iskut River". BC Geographical Names. Archived from the original on 2021-10-01. Retrieved 2024-03-30.
  25. ^ Edwards & Russell 2000, pp. 1280, 1281, 1283, 1284.
  26. ^ Imam, Naiyar (2003). Dictionary of Geology and Mineralogy. McGraw–Hill Companies. p. 253. ISBN 0-07-141044-9.
  27. ^ Edwards & Russell 2000, p. 1280.
  28. ^ Souther 1992, pp. 104, 113, 267.
  29. ^ a b Souther 1992, pp. 93, 104.
  30. ^ "Kounugu Member". Lexicon of Canadian Geologic Units. Government of Canada. Retrieved 2024-03-31.
  31. ^ Souther 1992, pp. 3, 4, 267.
  32. ^ Souther 1992, pp. 3, 47.
  33. ^ Souther 1992, p. 39.
  34. ^ Edwards & Russell 2000, pp. 1281, 1287.
  35. ^ a b Souther 1992, pp. 113, 267.
  36. ^ Souther 1992, p. 120.
  37. ^ "Mount Edziza Provincial Park". BC Parks. Archived from the original on 2023-01-23. Retrieved 2024-03-28.

Sources edit

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