Big Raven Formation
This article contains close paraphrasing of a non-free copyrighted source, Souther 1992. (April 2024) |
Big Raven Formation | |
---|---|
Ma | |
Type | Geological formation[1] |
Unit of | Mount Edziza volcanic complex[2] |
Sub-units | Sheep Track Member[1] |
Overlies | Nido Formation, Spectrum Formation, Raspberry Formation, Armadillo Formation, Klastline Formation, Ice Peak Formation, Edziza Formation[3][4] |
Lithology | |
Primary | Alkali basalt, hawaiite[1] |
Other | Trachyte[1] |
Location | |
Coordinates | Big Raven Plateau[5] 57°42′59″N 130°45′06″W / 57.71639°N 130.75167°W[6] Arctic Lake Plateau[5] 57°27′59″N 130°45′06″W / 57.46639°N 130.75167°W[9] |
Region | British Columbia[10] |
Country | Canada[10] |
Type section | |
Named by | Souther et al., 1984[11] |
Location in Mount Edziza Provincial Park |
The Big Raven Formation is a stratigraphic unit of Holocene 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 12,000 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 (15 square miles).
The Big Raven Formation is widespread throughout the MEVC, occurring on or adjacent to the Arctic Lake, Big Raven and Kitsu plateaus. Two lava fields of the Big Raven Formation occur on the Big Raven Plateau which in total contain at least 22 separate vents that issued lava flows. At least four isolated Big Raven vents occur on the eastern flank of Mount Edziza and on the extreme northern slope of the Big Raven Plateau. The Kitsu Plateau contains a much smaller Big Raven lava field near the edge of an escarpment; at least three separate vents are in this lava field. Two isolated Big Raven vents on and adjacent to the Arctic Lake Plateau produced lava flows, as did two isolated Big Raven vents in Walkout Creek valley. Most Big Raven vents are marked by a cone of pyroclastic rocks.
Stratigraphy
The Big Raven Formation overlies the
Age and lithology
The Big Raven Formation is of Holocene age and was deposited during the latest magmatic cycle of the MEVC.
Alkali basalt and hawaiite are the main volcanic rocks comprising the Big Raven Formation, having erupted from at least 30 vents along the entire north–south trending axis of the MEVC.[20] They are in the form of lava flows and pyroclastic cones which largely comprise two lava fields on the northern and western flanks of Mount Edziza and Ice Peak, respectively.[21] Isolated pyroclastic cones and lava flows occur at the northern and southern extremities of the Big Raven Formation, as well as on the eastern flank of Mount Edziza and along Walkout Creek.[22] Trachyte represents a small volume of the Big Raven Formation and mainly comprises air-fall pumice of the Sheep Track Member.[1]
Locations
The Big Raven Formation is widespread throughout the MEVC, occurring on or adjacent to the Kitsu, Arctic Lake and Big Raven plateaus.
Big Raven Plateau
The Big Raven Plateau contains the Desolation Lava Field on the northern flank of Mount Edziza which consists of several lava flows that issued from at least 10 separate Big Raven vents.[27] Another area of Big Raven lava flows called the Snowshoe Lava Field occurs on the western flank of Ice Peak; it issued from at least 12 separate vents.[28] The Sheep Track Member overlies much of the southern end of the Big Raven Plateau, including the Snowshoe Lava Field.[29] At least three Big Raven vents occur on the eastern flank of Mount Edziza and comprise another volcanic zone called the east slope centres.[22] An isolated Big Raven vent called Kana Cone occurs on the extreme northern slope of the plateau while two cinder cones occur on the southern slope of the plateau in Walkout Creek valley.[4][30]
Desolation Lava Field
Blocky
Some of the lava flows comprising the Desolation Lava Field issued from vents adjacent to the northern
Snowshoe Lava Field
The Snowshoe Lava Field is a group of volcanic cones and blocky basalt flows similar in age to the Desolation Lava Field. It covers an area of about 40 square kilometres (15 square miles) and is mostly covered over by air-fall pumice of the Sheep Track Member. As a result, the surface details of most of the upper lava flows in this lava field remain obscured and the cones are mantled with Sheep Track pumice.
The Snowshoe Lava Field contains five transitional cones,[a] one of which is named.[40] Two unnamed transitional cones are on the southwestern edge of Mount Edziza's summit ice cap inside the alpine trim lines, both of which have been reduced to low, drumlin-like ridges as a result of glacial ice overridding them.[41] The three other transitional cones are unglaciated, having formed at lower elevations just below the terminal alpine moraine.[43] Their inner structures have been exposed by sufficient erosion but they still retain their central craters and original conical form. One of these cones, Coffee Crater, was the source of a lava flow that extended to the southwest; the northern edge of the terminal lobe of this lava flow forms a prominent, 18-metre-high (59-foot) escarpment.[41]
Three subaerial cones exist in the Snowshoe Lava Field, two of which are named. The largest subaerial cone, Cocoa Crater, produced a 2-kilometre-wide (1.2-mile) lava flow that travelled into upper Sezill Creek canyon.[44] Keda Cone[b] and an unnamed subaerial cone to the northeast issued the most voluminous lava in the Snowshoe Lava Field, having flowed westward where it engulfed an area more than 3 kilometres (1.9 miles) wide and 8 kilometres (5.0 miles) long.[47] This lava then continued to flow westward into upper Taweh Valley where it transformed into a relatively narrow flow that formerly extended to near Mess Creek. A subaerial vent referred to as The Saucer produced the youngest lava flow in the Snowshoe Lava Field from near the southern edge of Mount Edziza's summit ice cap. Unlike the other three subaerial centres, The Saucer flow appears to have issued without any accompanying lava fountaining, resulting in no cinder cone development.[48]
Sheep Track Member
The southwestern flank of Ice Peak and the surrounding Big Raven Plateau are blanketed with loose, air-fall
Walkout Creek valley
Two small Big Raven cones called the
East slope centres
The heavily eroded eastern flank of Mount Edziza contains at least three satellitic centres of the Big Raven Formation.
Kana Cone
The northernmost Big Raven vent and the northernmost vent of the entire MEVC is marked by the nested Kana Cone which rises about 60 metres (200 feet) above the surrounding terrain.[56] Its summit contains a roughly 20-metre-deep (66-foot) crater that is breached to the north, exposing oxidated bombs and spatter. Lava from the crater breach extends downslope into Klastline Valley where it temporarily dammed the Klastline River; the river has since etched a new channel along the northern valley wall. The lava continued to flow downstream through Klastline Valley and possibly reached the Stikine River where Big Raven lava flows overlie about 100 metres (330 feet) of sediment at the mouths of the Klastline and Tahltan rivers.[57][58]
Arctic Lake Plateau
Two isolated occurrences of the Big Raven Formation occur on the Arctic Lake Plateau,
Northeast of Nahta Cone on the south flank of Kuno Peak in the Spectrum Range are the remains of a Big Raven pyroclastic cone.[62] The remains consist of steeply dipping beds of coarse agglutinated pyroclastic rocks and basaltic lava flows that overlie thick felsenmeer and talus deposits. Much of this cone has been destroyed by repeated landslides and solifluction on Kuno Peak, the former of which also buried lava flows on the Arctic Lake Plateau that originated from this cone.[52]
Kitsu Plateau
The Mess Lake Lava Field is an area of lava flows and tephra deposits between Raspberry Creek in the north, Nagha Creek in the south and Mess Lake in the east.[5][63] It covers an area of about 18 square kilometres (6.9 square miles) and contains three separate vents of Big Raven age. The two oldest vents are marked by slightly eroded pyroclastic cones whose craters and cone-shaped structures are still apparent despite being somewhat rounded. Lava flows from both cones travelled to the west towards the Mess Creek Escarpment where they most likely cascaded into Mess Creek valley. However, any remnants of this lava on the escarpment or in Mess Creek valley have been removed by erosion.[5]
At the southern end of the Mess Lake Lava Field on the steep, south-facing side of Nagha Creek is the third separate vent called
Erosion and vegetation
Varying degrees of erosion have affected the lava flows and pyroclastic cones of the Big Raven Formation. The oldest lava flows are partially obscured by a thin layer of soil while the oldest pyroclastic cones have been deeply eroded or reduced to mounds of red rubble. Lava flows and pyroclastic cones of intermediate age retain most of their original forms, although fine tephra mantling the pyroclastic cones has eroded away to expose larger bombs and agglutinated spatter. The youngest lava flows have remained virtually unchanged since they cooled, containing rough, blocky surfaces and Pele's hair under slabs of basalt and in protected depressions. Intermittent meltwater streams have cut small meandering channels into the youngest pyroclastic cones, although a few of them are still mantled with fine tephra.[1]
Vegetation varies with both age and elevation of the Big Raven Formation. The older lava flows are covered with forest where they entered valleys and travelled down lower slopes; this forest cover is almost as dense as that on
See also
Notes
- ^ Transitional cones are volcanic cones that initially interacted with water during eruption and then later transitioned into normal subaerial volcanic piles as the progressing eruptions displaced ice and meltwater.[42]
- ^ Keda Cone is referred to by the numeronym SLF-9 and is erroneously called Kena Cone in the Catalogue of Canadian volcanoes.[45] According to BC Geographical Names, Keda Cone is the proper name.[46]
References
- ^ a b c d e f g h i j Souther 1992, p. 213.
- ^ ISBN 0-612-25005-9.
- ^ a b c Souther 1992, p. 246.
- ^ doi:10.4095/133498.
- ^ a b c d e f g h i Souther 1992, p. 235.
- ^ "Big Raven Plateau". BC Geographical Names. Archived from the original on 2021-09-30. Retrieved 2024-04-03.
- ^ "Arctic Lake Plateau". BC Geographical Names. Archived from the original on 2021-09-25. Retrieved 2024-04-03.
- ^ Souther 1992, p. 234.
- ^ "Kitsu Plateau". BC Geographical Names. Archived from the original on 2021-10-01. Retrieved 2024-04-03.
- ^ a b c d "Edziza: General Information". Global Volcanism Program. Smithsonian Institution. Archived from the original on 2021-08-10. Retrieved 2021-09-25.
- ^ a b "Big Raven Formation". Lexicon of Canadian Geologic Units. Government of Canada. Retrieved 2023-09-06.
- ISSN 0016-7606.
- ^ a b "Sheep Track Formation". Lexicon of Canadian Geologic Units. Government of Canada. Archived from the original on 2023-12-15. Retrieved 2024-03-06.
- ^ Souther 1992, pp. 246, 267.
- ^ Souther 1992, p. 216.
- ^ Souther 1992, pp. 236, 246.
- ^ Souther 1992, p. 267.
- ^ doi:10.4095/328950.
- ^ a b c "Edziza: Eruptive History". Global Volcanism Program. Smithsonian Institution. Archived from the original on 2023-05-20. Retrieved 2023-06-01.
- ^ Souther 1992, pp. 32, 213, 214.
- ^ Souther 1992, pp. 27, 213, 214.
- ^ a b Souther 1992, pp. 214, 226.
- ^ Souther 1992, pp. 32, 214, 234.
- ^ a b Souther 1992, p. 32.
- ^ "Mount Edziza". BC Geographical Names. Archived from the original on 2018-05-15. Retrieved 2024-03-06.
- ^ Souther 1992, pp. 22, 32.
- ^ a b Souther 1992, p. 26.
- ^ a b Souther 1992, p. 27.
- ^ a b c Souther 1992, p. 228.
- ^ a b Souther 1992, pp. 214, 234.
- ^ Souther 1992, pp. 213, 214.
- ^ Souther 1992, pp. 216, 218.
- ^ Souther 1992, p. 219.
- ^ a b Souther 1992, p. 222.
- ^ Souther 1992, pp. 217, 219.
- ^ Souther 1992, p. 224.
- ^ Souther 1992, p. 229.
- ^ Souther 1992, pp. 26, 230.
- ^ Souther 1992, p. 230.
- ^ a b Souther 1992, pp. 229, 231.
- ^ a b c Souther 1992, p. 231.
- ^ Souther 1992, pp. 26, 182.
- ^ Souther 1992, pp. 214, 231.
- ^ Souther 1992, p. 232.
- ^ "Kena Cone (SLF-9)". Catalogue of Canadian volcanoes. Natural Resources Canada. 2009-03-10. Archived from the original on 2011-07-06. Retrieved 2023-02-19.
- ^ "Keda Cone". BC Geographical Names. Archived from the original on 2021-10-20. Retrieved 2023-08-19.
- ^ Souther 1992, pp. 214, 233.
- ^ Souther 1992, p. 233.
- ^ Souther 1992, pp. 28, 32, 236.
- ^ Souther 1992, pp. 27, 28, 236.
- ^ Souther 1992, pp. 28, 236.
- ^ a b Souther 1992, p. 236.
- ^ Souther 1992, p. 237.
- ^ a b Souther 1992, pp. 234, 235.
- ^ Souther 1992, p. 226.
- ^ Souther 1992, pp. 214, 224, 225.
- ^ Souther 1992, pp. 224, 225.
- NRC Research Press: 1429. Retrieved 2024-03-08.
- ^ Souther 1992, pp. 214, 235.
- ^ Souther 1992, pp. 26, 235.
- ^ a b Logan, J. M.; Drobe, J. R. (1993). Geology and Mineral Occurrences of the Mess Lake Area (104G/7W) (PDF) (Report). Geological Fieldwork 1992, Paper 1993-1. British Columbia Geological Survey. p. 141. Archived from the original (PDF) on 2022-03-22. Retrieved 2024-03-03.
- ^ Souther 1992, pp. 214, 236.
- Department of Energy, Mines and Resources. 1989. Archived from the originalon 2021-05-02. Retrieved 2024-03-07.
Sources
- ISBN 0-660-14407-7.
Further reading
- Smellie, John L.; Edwards, Benjamin R. (2016). Glaciovolcanism on Earth and Mars: Products, Processes and Palaeoenvironmental Significance. ISBN 978-1-107-03739-7.