Wikipedia

Tennena Cone

Tennena Cone, alternatively Icebridge Cone, is a small volcanic cone in Cassiar Land District of northwestern British Columbia, Canada. It has an elevation of 2,390 metres (7,840 feet) and lies on the western flank of Ice Peak, the prominent south peak of Mount Edziza. The cone is almost completely surrounded by glacial ice of Mount Edziza's ice cap which covers an area of around 70 square kilometres (27 square miles). Tennena Cone is 200 metres (660 feet) high, 1,200 metres (3,900 feet) long and up to 600 metres (2,000 feet) wide, its symmetrical structure resembling a black pyramid. The cone and the surrounding area lies in Mount Edziza Provincial Park which also includes the Spectrum Range to the south.

Tennena Cone
Icebridge Cone
A black cone-shaped mountain rising over glacial ice in the foreground.
Tennena Cone from the northwest
Highest point
Elevation2,390 m (7,840 ft)[1]
Coordinates57°41′03″N 130°39′44″W / 57.68417°N 130.66222°W / 57.68417; -130.66222[2]
Dimensions
Length1,200 metres (3,900 feet)[1]
Width600 metres (2,000 feet)[1]
Naming
EtymologyCombination of the Tahltan words ten and nena[2]
English translationIcebridge[2]
Geography
Tennena Cone is located in British Columbia
Tennena Cone
Tennena Cone
Location in British Columbia
CountryCanada[3]
ProvinceBritish Columbia[3]
DistrictCassiar Land District[2]
Protected areaMount Edziza Provincial Park[2]
Topo mapNTS 104G10 Mount Edziza[2]
Geology
Mountain typeSubglacial mound[4]
Type of rockAlkali basalt[5]
Volcanic regionNorthern Cordilleran Province[6]
Last eruptionPleistocene or Holocene age[4][7]
Map

Tennena Cone is part of the Mount Edziza volcanic complex, an intermontane plateau that has been volcanically active periodically for the last 7.5 million years. It overlies four older geological formations of this volcanic complex that formed during the Miocene, Pliocene and Pleistocene epochs, all of which consist of several types of volcanic rocks. Tennena Cone consists of alkali basalt pillow lavas, tuff breccias and lapilli tuffs of the younger Big Raven Formation which were deposited by a small eruption under glacial ice. The exact timing of this eruption is unknown but radiometric dating of volcanic rocks from Tennena Cone has yielded ages as old as 0.011 ± 0.033 million years.

Name and etymology

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The name of the volcanic cone was officially adopted on January 2, 1980, after being submitted to the BC Geographical Names office by the Geological Survey of Canada.[2] It was required for geology reporting purposes since Jack Souther, a volcanologist of the Geological Survey of Canada, was studying the area in detail between 1970 and 1992.[2][8][9] Tennena is a combination of the Tahltan words ten and nena, which mean ice and bridge, respectively.[5] It was chosen because Tennena Cone is almost completely surrounded by glacial ice in an alpine environment.[2][5] Tennena Cone and the associated volcanic rocks have been called the Tennena volcanic centre.[3]

Geography

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Tennena Cone is in Cassiar Land District of northwestern British Columbia, Canada, and resembles a symmetrical, 200-metre-high (660-foot), 1,200-metre-long (3,900-foot) and up to 600-metre-wide (2,000-foot) black pyramid.[2][7][10] Its northern, eastern and southern flanks are mantled by the roughly 70-square-kilometre (27-square-mile) Mount Edziza ice cap and rises about 150 metres (490 feet) above the ice surface.[5][11] Tennena Cone reaches an elevation of 2,390 metres (7,840 feet) on the upper western flank of Ice Peak and lies at the northern end of Tencho Glacier, the largest glacier of the Mount Edziza volcanic complex.[1][5][12]

At lower elevations, Tennena Cone is surrounded by Ornostay Bluff in the northwest and by Koosick Bluff in the southwest.[5] Between these two bluffs is the head of Sezill Creek which flows northwest from the surrounding Big Raven Plateau and then drains into Taweh Creek, a tributary of Mess Creek.[5][13][14] The Big Raven Plateau is the northernmost subdivision of the Mount Edziza volcanic complex which comprises a broad intermontane plateau that has been volcanically active periodically for the last 7.5 million years.[15] At the southwestern end of the Big Raven Plateau is the Snowshoe Lava Field, of which Tennena Cone is a part.[5]

Tennena Cone lies in Mount Edziza Provincial Park southeast of the community of Telegraph Creek.[2] With an area of 266,180 hectares (657,700 acres), Mount Edziza Provincial Park is one of the largest provincial parks in British Columbia and was established in 1972 to preserve the volcanic landscape.[16][17] It includes not only the Mount Edziza area but also the Spectrum Range to the south from which it is separated by Raspberry Pass.[17]

Geology

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Tennena Cone 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][18] 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.[19]

Lithology

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Tennena Cone consists mainly of Big Raven Formation alkali basalt that can be mapped into four subdivisions, all of which are exposed on the eastern, southern and western flanks of the cone.[5][20] The first subdivision is massive and crudely bedded tuff breccia exposed in near vertical cliffs on the flanks of Tennena Cone. Exposed in scarps on the eastern and southern flanks of Tennena Cone is lapilli tuff of the second subdivision which forms 10-to-30-centimetre-thick (3.9-to-11.8-inch) beds.[21] Two 1-metre-wide (3.3-foot) dikes comprise the third subdivision, both of which consist of fragmented plagioclase-phyric rock.[21] The first dike forms a 5-metre-high (16-foot) remnant and is exposed on the eastern flank of Tennena Cone while the second dike is exposed 50 metres (160 feet) to the south. In addition to occurring on the eastern flank, the second dike is also exposed on the western flank and along the summit ridge of Tennena Cone.[22] The fourth subdivision consists of pillow and fluidal lavas that overlie tuff breccia in the northern section of the cone.[23]

At the southwestern base of Tennena Cone are elongated mounds of pillow lava that cover about 0.45 square kilometres (0.17 square miles) of hummocky topography. They have a maximum basal diameter of 75 metres (246 feet) and range from 3 to 20 metres (9.8 to 65.6 feet) high, decreasing in height to the southwest.[24] Just west of these pillow lava mounds are massive non-pillowed lava flows which are exposed over an area of around 0.4 square kilometres (0.15 square miles) across gently sloping terrain.[25] Extending west of Tennena Cone north of the pillow lava mounds and massive non-pillowed lava flows is a 4.4-kilometre-long (2.7-mile) pillowed lava flow that terminates at the head of Sezill Creek valley.[26] It contains pillows that range from less than 1 metre (3.3 feet) to more than 1 metre (3.3 feet) in diameter, as well as vertically oriented pillow-like lava bodies.[27]

Formation

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Glacier of Mount Edziza with the summit of Tennena Cone obscured by clouds in the background

Tennena Cone was one of the first volcanoes to erupt during the fifth magmatic cycle of the Mount Edziza volcanic complex.[28] Its formation began when basaltic magma issued from a vent under 500–1,400 metres (1,600–4,600 feet) of glacial ice where it was quenched to create the pillow lavas, tuff breccias and lapilli tuffs comprising Tennena Cone.[3][29] This volcanic material accumulated inside a depression melted in the ice and did not breach the ice surface, resulting in the formation of a subglacial mound.[4][30] Lava flows from Tennena Cone travelled west through tunnels created by eruption-generated meltwater escaping at the base of the enclosing ice.[30]

The longest lava flow at the head of Sezill Creek valley 4.3 kilometres (2.7 miles) west of Tennena Cone travelled to the western edge of the enclosing ice, causing a violent steam explosion.[31][29] This explosive interaction between meltwater and lava spilled over the terminal moraine and spread onto the Big Raven Plateau beyond the ice.[5][29][32] Although the lava flow was quenched by meltwater throughout its entire length, it has a thickness of 2–4 metres (6.6–13.1 feet) and travelled into small depressions of the current topography. This suggests that the lava flow was relatively fluid at the time of eruption, resulting in higher mobility.[10]

The precise age of Tennena Cone is unknown but it may have formed during the Last Glacial Maximum when the Mount Edziza volcanic complex was covered by the Cordilleran Ice Sheet.[3] Another possibility is that Tennena Cone formed during a Younger Dryas expansion of the still-extant Mount Edziza ice cap or during the height of the neoglaciation when the ice cap was much larger in area than it is now.[3][29] Argon–argon dating of glassy pillows from Tennena Cone has yielded ages of 0.011 ± 0.033 million years and 0.005 ± 0.033 million years.[33]

Basement

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Tennena Cone and its eruptive products overlie the Armadillo, Ice Peak, Nido and Raspberry formations, all of which are older stratigraphic units of the Mount Edziza volcanic complex.[5][34][35] The Ice Peak Formation is the youngest of the four geological formations, consisting of an upper assemblage of Pleistocene tristanite, trachyte and comenditic trachyte lava flows and a lower assemblage of Pleistocene alkali basalt and hawaiite lava flows with minor tristanite, trachybasalt and mugearite lava flows and pyroclastic breccia. Underlying the Ice Peak Formation are alkali basalt lava flows and flow breccia of the Tenchen Member of the Nido Formation which were erupted from multiple volcanoes during the Pliocene.[5][35]

Miocene alkali basalt and minor sparsely porphyritic hawaiite of the Armadillo Formation underlies the Nido Formation and are in the form of lava flows, flow breccia and agglutinate. The oldest geological formation underlying Tennena Cone is the Raspberry Formation which consists of Miocene alkali basalt and minor hawaiite and mugearite. These volcanic rocks are in the form of lava flows, flow breccia and agglutinate, although pillow lava and tuff breccia occur locally.[5][35] Underlying the Raspberry Formation are sedimentary, volcanic and metamorphic rocks of the Stikinia terrane which are Paleozoic and Mesozoic in age.[5][35][36]

Significance

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Tennena Cone and its eruptive products are of geological significance because they contain an unusually wide range of features characteristic of a small-volume eruption under thick glacial ice.[37] These features include ordinary pillow lavas and vertically-oriented, distended pillow lavas, as well as massive non-pillowed lavas and interbedded gravelly sands and poorly consolidated sandstone.[38] The subglacially emplaced lavas erupted from Tennena Cone are also of geological significance because they can be traced more than 3 kilometres (1.9 miles) away from the vent area.[37] Their well-preserved textures and geomorphological structures can be used to help identify other subglacially-emplaced lava flows on Earth and on other terrestrial bodies such as Mars.[3]

See also

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References

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  1. ^ a b c d Hungerford et al. 2014, p. 41.
  2. ^ a b c d e f g h i j k "Tennena Cone". BC Geographical Names. Archived from the original on 2024-06-08. Retrieved 2024-07-03.
  3. ^ a b c d e f g Hungerford et al. 2014, p. 39.
  4. ^ a b c "Tennena Cone". Catalogue of Canadian volcanoes. Natural Resources Canada. 2009-03-10. Archived from the original on 2010-12-11. Retrieved 2024-07-03.
  5. ^ a b c d e f g h i j k l m n 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.
  6. ^ a b Hungerford et al. 2014, p. 40.
  7. ^ a b Hungerford et al. 2014, pp. 39, 41.
  8. ^ "Acceptance of the 1995 Career Achievement Award by Jack Souther" (PDF). Ash Fall. Geological Association of Canada. 1996. p. 3. Archived from the original (PDF) on 2018-12-05.
  9. ^ "Stikine volcanic belt: Mount Edziza". Catalogue of Canadian volcanoes. Natural Resources Canada. 2009-04-01. Archived from the original on 2009-06-08. Retrieved 2024-07-03.
  10. ^ a b Souther 1992, p. 230.
  11. ^ Field, William O. (1975). "Coast Mountains: Boundary Ranges (Alaska, British Columbia, and Yukon Territory)". Mountain Glaciers of the Northern Hemisphere. Vol. 2. Cold Regions Research and Engineering Laboratory. p. 43. Retrieved 2024-06-19.
  12. ^ Souther 1992, pp. 26, 320.
  13. ^ "Sezill Creek". BC Geographical Names. Archived from the original on 2021-10-01. Retrieved 2024-07-03.
  14. ^ "Taweh Creek". BC Geographical Names. Archived from the original on 2021-10-01. Retrieved 2024-07-03.
  15. ^ 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.
  16. ^ "Edziza: Photo Gallery". Global Volcanism Program. Smithsonian Institution. Archived from the original on 2021-09-21. Retrieved 2024-07-04.
  17. ^ a b "Mount Edziza Provincial Park". BC Parks. Archived from the original on 2023-01-23. Retrieved 2024-07-03.
  18. ^ Edwards & Russell 2000, pp. 1280, 1281, 1283, 1284.
  19. ^ Edwards & Russell 2000, p. 1280.
  20. ^ Hungerford et al. 2014, p. 46.
  21. ^ a b Hungerford et al. 2014, pp. 41, 46.
  22. ^ Hungerford et al. 2014, pp. 43.
  23. ^ Hungerford et al. 2014, pp. 41, 46, 48.
  24. ^ Hungerford et al. 2014, p. 48.
  25. ^ Hungerford et al. 2014, pp. 40, 41, 49.
  26. ^ Hungerford et al. 2014, pp. 40, 49.
  27. ^ Hungerford et al. 2014, pp. 43, 45, 49.
  28. ^ Souther 1992, pp. 26, 267.
  29. ^ a b c d Souther 1992, p. 26.
  30. ^ a b Hungerford et al. 2014, p. 55.
  31. ^ Hungerford et al. 2014, pp. 40, 41, 51.
  32. ^ Hungerford et al. 2014, p. 51.
  33. ^ Hungerford et al. 2014, p. 52.
  34. ^ Hungerford et al. 2014, p. 53.
  35. ^ a b c d Souther, J. G. (1988). Diagrammatic cross-sections A-B-C, D-E, F-G-H-I, J-K-L, M-N-O, P-Q-R to accompany Map 1623A, Mount Edziza Volcanic Complex (PDF) (Diagrammatic cross sections). 1:50,000. Cartography by M. Sigouin, Geological Survey of Canada. Energy, Mines and Resources Canada. Retrieved 2024-07-05.
  36. ^ Souther 1992, pp. 2, 39.
  37. ^ a b Smellie, John L.; Edwards, Benjamin R. (2016). Glaciovolcanism on Earth and Mars: Products, Processes and Palaeoenvironmental Significance. Cambridge University Press. p. 45. ISBN 978-1-107-03739-7.
  38. ^ Hungerford et al. 2014, pp. 40, 41.

Sources

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