Anahim hotspot

The Anahim hotspot is a volcanic hotspot located in the West-Central Interior of British Columbia, Canada. One of the few hotspots in North America, the Anahim plume is responsible for the creation of the Anahim Volcanic Belt. This is a 300 km (190 mi) long chain of volcanoes and other magmatic features that have undergone erosion. The chain extends from the community of Bella Bella in the west to near the small city of Quesnel in the east. While most volcanoes are created by geological activity at tectonic plate boundaries, the Anahim hotspot is located hundreds of kilometres away from the nearest plate boundary.

This hotspot's existence was first proposed in the 1970s by three scientists who used John Tuzo Wilson's classic hotspot theory. This theory proposes that a single, fixed mantle plume builds volcanoes that then, cut off from their source by the movement of the North American Plate, become increasingly inactive and eventually erode over millions of years. A more recent theory, published in 2001 by the Geological Society of America, suggests that the Anahim hotspot might be supplied by a mantle plume from the upper mantle rather than a deep-seated plume proposed by Wilson. The plume has since been tomographically imaged, showing it to be roughly 400 km (250 mi) deep. This measurement, however, could be an underestimate as the plume might originate deeper within Earth.

Volcanism as early as 14.5 million years ago has been linked to the Anahim hotspot, with the latest eruption having taken place in the last 8,000 years. This volcanic activity has produced rocks that show a bimodal distribution in composition. While these rocks were being deposited, the hotspot coincided with periods of crustal extension and uplift. Activity in modern times has been limited to earthquakes and volcanic gas emissions.

Anahim hotspot
Anahim hotspot is located in British Columbia
Anahim hotspot
Anahim hotspot (British Columbia)
Location of the Anahim hotspot in British Columbia
CountryCanada
ProvinceBritish Columbia
RegionInterior Plateau
Coordinates52°56′N 123°44′W / 52.93°N 123.73°WCoordinates: 52°56′N 123°44′W / 52.93°N 123.73°WNazko Cone
Last eruption7,200 years ago

Theories

Lower Mantle Superplume
Sketch showing the multi-scale nature of mantle plumes, which involves the creation of the lower-mantle superplume from the D layer and generation of the upper-mantle plumes from the low-viscosity layer below 670 km (420 mi).

Tectonic plates generally focus deformation and volcanism at plate boundaries. However, the Anahim hotspot is about 500 km (310 mi) from the nearest plate boundary. While studying the Anahim Volcanic Belt in 1979, Canadian geologists Mary Bevier, Richard Armstrong and Jack Souther used the hotspot theory to explain this zone of volcanism so far from regular conditions. The theory was first invented by Canadian geophysicist John Tuzo Wilson in 1963 to explain the formation of the Hawaiian Islands.[1]

Wilson's stationary hotspot theory

In 1963, Wilson proposed that small, long lasting, exceptionally hot areas of magma exist under Earth's surface; these heat centres create thermally active mantle plumes, which in turn sustain long-lasting volcanic activity. This "intra-plate" volcanism builds peaks that rise above the surrounding landscape. Plate tectonics cause the local tectonic plate (in the case of the Anahim hotspot, the North American Plate) to slowly slide over the hotspot, carrying its volcanoes with it without affecting the plume. Over hundreds of thousands of years, the magma supply for the volcano is slowly cut off, eventually going extinct. No longer active enough to overpower erosion, the volcano slowly erodes away. As the cycle continues, a new volcanic centre manifests and a volcanic peak arises anew. The process continues until the mantle plume itself collapses.[2]

This cycle of growth and dormancy strings together volcanoes over millions of years, leaving a trail of volcanic mountains and intrusions extending from coastal British Columbia across the Coast Mountains into the Interior Plateau.[3] According to Wilson's theory, the Anahim volcanoes should be progressively older and increasingly eroded the further they are from the hotspot and this is easily observable; the oldest rock on coastal British Columbia, that of the Gale Passage dike swarm, is about 14.5 million years old and deeply eroded, while the rock at Nazko Cone, the hotspot's present centre, is a comparatively young 0.34 million years of age or less.[3][4] Radiocarbon dating of peat directly above and below a tephra layer extending 4 km (2.5 mi) from Nazko Cone suggest that the latest eruption occurred approximately 7,200 years ago.[3]

Anahim Volcanic Belt-en
Path of the Anahim hotspot over the last 14.5 million years

Geophysicists believe that hotspots originate at one or two major boundaries deep in the Earth, either a shallow interface in the lower mantle between an upper convecting layer and a lower non-convecting layer, or a deeper D″ ("D double-prime") layer, approximately 200 km (120 mi) thick and immediately above the core-mantle boundary. A mantle plume would initiate at the interface when the warmer lower layer heats a portion of the cooler upper layer. This heated, buoyant and less-viscous portion of the upper layer would become less dense due to thermal expansion and rise towards the surface as a Rayleigh-Taylor instability.[5] When the mantle plume reaches the base of the lithosphere, the plume heats it and produces melt. This magma then makes its way to the surface, where it is erupted as lava.[6]

Arguments for the validity of the hotspot theory generally centre on the steady age progression of Anahim volcanoes and nearby features: a similar spatiotemporal trend exists for the Yellowstone hotspot track 1,400 km (870 mi) to the southeast. The presence of two hotspot tracks on the same continent and their general agreement between each other provides a unique tool in assessing and testing the motion of North America.[7]

Shallow hotspot theory

Another hypothesis is that the Anahim hotspot is supplied by a miniplume.[8] These mantle plumes have their roots in the upper mantle but they may later originate from the lower mantle.[9] Arguments for an Anahim miniplume are centred on the existence of two small dike swarms at the western (hence oldest) end of the Anahim Volcanic Belt. This assumption is in turn based on the notion that giant dike swarms mark the arrival of deep-seated mantle plumes.[8]

History of study

In 1977, Jack Souther produced a synthesis of volcanism in the Canadian Cordillera and delineated several Neogene-to-Quaternary volcanic belts throughout British Columbia. One of these was the linear Anahim Volcanic Belt, which included the Wells Gray-Clearwater volcanic field at its eastern end.[10] However, its origin had not yet been understood.[11] In 1979, two volcano tectonic models had been proposed by Jack Souther, Mary Bevier and Richard Armstrong. This included a hotspot and a propagating crack controlled by stress fields related to large-scale plate tectonics of western North America.[7]

Earth cutaway schematic-en
Cutaway diagram of Earth's internal structure

Garry C. Rogers of the Geological Survey of Canada speculated in his 1981 NRC Research Press article McNaughton Lake seismicity—more evidence for an Anahim hotspot? that earthquake swarms at McNaughton Lake (now called Kinbasket Lake) may be related to the Anahim hotspot. Rogers noted that if the seismicity is related to a hotspot the surface expression must be lagging 100 km (62 mi) behind the passage of the hotspot. An alternative theory proposed by Rogers is that if the Anahim hotspot is located under the Wells Gray-Clearwater area, the stress field surrounding the hotspot must precede it by approximately 100 km (62 mi).[12]

In 1987, Canadian volcanologist Catherine Hickson revealed that the Wells Gray-Clearwater volcanic field is not part of the Anahim Volcanic Belt, but rather a separate centre that most likely represents an area of lithospheric decompression melting caused by rifting along pre-existing crustal fractures. The Wells Gray-Clearwater volcanic field has since not been considered part of the Anahim Volcanic Belt and the Anahim hotspot is now believed to be in the area of Nazko Cone.[10]

The existence of an Anahim hotspot was supported in a detailed Bulletin of Volcanology report by Kuehn et al. (2015). This included new geochemical and geochronometric data for the Baldface Mountain and Satah Mountain volcanic fields, as well as for Nazko Cone. The data obtained indicated that volcanism in the two volcanic fields were contemporaneous with the Itcha Range shield volcano and that both fields agree with the vector of the North American Plate motion over a hotspot in the British Columbia Interior. It was also noted that the trace and rare-earth element patterns of mafic lavas in the Anahim Volcanic Belt are similar to ocean island basalts, providing more evidence for a hotspot.[7]

Characteristics

Position

The Anahim hotspot has been imaged through seismic tomography and is estimated to be 50–100 km (31–62 mi) wide. Recent high-resolution local tomography indicates a possible lower-mantle plume and a pond of plume material is evidenced by a large low-velocity zone in the upper mantle. These low seismic velocity zones often indicate hotter and more buoyant mantle material. The low-velocity zone is flanked on both sides by high-velocity anomalies of variable amplitude. In the north, high-velocities may reflect the remains of batholithic roots that formed as a result of continuous subduction along the northern continental margin 150 to 50 million years ago. High velocities in the south represent the subducting Juan de Fuca slab. Centered near Nazko Cone, the low-velocity zone extends to a depth of approximately 400 km (250 mi). However, it may extend deeper southward beneath the Juan de Fuca Plate through the transition zone into the lower mantle. This has led to the conclusion that the Anahim hotspot is supplied by a mantle plume over slab edge flow.[13]

Movement

Individual volcanoes drift southwest from the hotspot at a rate of about 2–3 cm (0.79–1.18 in) per year with each successive volcanic centre spending about two million years actively attached to the plume.[7] The oldest Anahim volcano, situated on the Central Coast of British Columbia, formed 14.5 million years ago.[4] If any prior record in the form of seamounts existed off the British Columbia Coast, this record would presumably have been subducted under North America with the Farallon/Juan de Fuca plates and lost. Thus it is unknown if the hotspot existed in the Pacific Ocean prior to being located on the North American continent from ongoing plate motion.[7] However, past geologic field mapping and geochemical studies suggest massive plutons could be present in the offshore continental shelf. These suspected bodies are aligned with the northeast-trending Anahim Volcanic Belt, whose age progression suggests these suspected offshore plutons could be of Miocene age. An earlier displaced portion of the hotspot track might exist on Haida Gwaii as part of the Masset Formation. However, further analyses of Masset volcanic rocks are still required to determine if they are compositionally and istopically similar to alkalic lavas found on the mainland.[14]

Magma

Itcha Range
The Itcha Range as seen from the south with a forested volcanic cone in the foreground

The composition of the volcanoes' magma has changed significantly with time as they grow over the hotspot and migrate away. Volcanic activity 14.5 to 3.0 million years ago was predominately felsic, producing large volumes of rhyolite and trachyte lava.[3][4] This can be explained by the presence of thick granitic structures under these volcanoes, which have been tectonically compressed from being near the North American Plate margin. A unique characteristic of the felsic lava flows is that although they were high in silica content, the flows were overly fluid in nature. This is because the peralkaline content of these felsic lavas decreased the viscosity of the flows a minimum of 10–30 times over that of calc-alkaline felsic flows.[3] Evidence for explosive volcanism exists in the form of pumice flows, bedded tuffs, intensely shattered basement rocks and the high content of coarse basement clasts in rhyolite breccias.[4][15]

Magma production of the Anahim hotspot has shifted from more felsic to more mafic compositions in the last 3.0 million years. For instance, much of the magma created between 3.0 and 0.33 million years ago was igneous phonolite, trachyte, trachyandesite, basalt and basanite; the volcanoes built during this period are almost entirely made of these rock types. Other igneous rocks such as phonotephrite are present in smaller quantities; these occur in the Satah Mountain volcanic field. Volcanic eruptions in the last 0.33 million years have been mainly basanitic and have occurred at the youngest eruptive centre, Nazko Cone.[7] Basanites produced by these eruptions are significantly more undersaturated than basalts from older Anahim volcanoes in the west and may indicate an eastward shift toward a deeper or less depleted mantle source. It is also possible that as the North American Plate moves over the Anahim hotspot, it underlies thinner continental crust.[16] The overall chemistry and mineralogy of the Anahim magmas are analogous to regions of incipient continental rifting above a mantle plume.[4]

Volcanoes

Over the last 14.5 million years, the Anahim hotspot has created at least 40 volcanoes.[4][8] They can be organized into three groupings: the eastern section, which comprises several small cinder cones and is the location of all modern volcanic activity; the central section, which consists of predominantly shield volcanoes; and the western section, all of which have since been reduced to remnants of eruptive breccia and high-level plutons and dike swarms.[4][15] These form one of the six Neogene-Quaternary volcanic provinces in British Columbia.[7]

Volcanic characteristics

Anahim Belt geology
Depth relationships and compositional correlation of plutonic, hypabyssal and volcanic rocks exposed in the western Anahim Belt

The Anahim volcanoes are grouped into three types: volcanic cones, shield volcanoes and lava domes.[7] The shields are characterized by their large size (hundreds of kilometres in volume) and their symmetrical shape. They are the most prominent of the three volcano types, with the Rainbow Range being the highest at around 2,500 m (8,200 ft) above sea level. Their outer slopes merge with older flat-lying basalt flows of the Chilcotin Group, which covers a large percentage of the Interior Plateau.[3] The more abundant lava domes and volcanic cones are much smaller in size (less than one kilometre in volume). These comprise two extensive volcanic fields in the vicinity of the Itcha Range.[7]

Although many Anahim volcanoes are surrounded by Chilcotin Group basalt flows, the exact nature of their relationship is unknown.[3] It is unlikely that the Anahim volcanoes ever were a source area for the Chilcotin basalts as they have distinct transitional geochemistries. The Chilcotin Group is interpreted to be related to back-arc extension behind the Cascadia subduction zone.[7]

Evolution and construction

Each volcano type produced by the Anahim hotspot has its own unique life cycle of growth and erosion. Volcanic cones have their origins from tephra accumulating around vents during Strombolian eruptions. They are composed of trachyte, trachyandesite, basalt, phonolite, basanite and to a lesser extent phonotephrite. In contrast, lava domes are formed mainly by viscous trachytic magma that erupted effusively onto the surface and then piled up thick around vents. Most of these features were formed by a single volcanic eruption and are therefore monogenetic. However, in some cases several eruptions occurred at a single locus to create larger, polygenetic centres (e.g. Satah Mountain, Baldface Mountain, Nazko Cone). Once activity has declined, erosion reduces them into volcanic remnants such as lava plugs.[7]

Shield volcanoes undergo at least two stages of volcanic activity. The initial shield stage is the most productive volcanically and features repeated eruptions of large volumes of predominately fluid peralkaline felsic magmas that become progressively more evolved.[7] During this stage, a small summit caldera may form, as is the case for the Ilgachuz Range.[3] After the shield stage has been completed, the post-shield stage succeeds. This stage of activity is characterized by small volumes of more mafic lavas expressed as small cinder cones and capping flows.[7] Dissection of the shield by stream erosion is also apparent, resulting in the creation of deeply incised radial valleys.[17]

Prolonged erosion eventually removes most if not all traces of the volcanoes to expose their underlying solidified magma systems. Such systems can be 1 to 4 km (0.62 to 2.49 mi) below the surface with rocks ranging from hypabyssal to plutonic. Exposure of the King Island Pluton and the Bella Bella and Gale Passage dike swarms are prime examples of this phase of erosion.[4]

Tectonic history

Extensional tectonics

Locmap-QCS-Hecate-Dixon
Queen Charlotte Sound as delineated by BC Geographical Names, along with Hecate Strait and Dixon Entrance.

Rifting and crustal extension in Queen Charlotte Sound up to about 17 million years ago has been linked to the Early Miocene passage of the Anahim hotspot. Yorath and Chase (1981) proposed that subcrustal melting above the Anahim plume resulted in weakening of the regional crust, setting the stage for rift development. Later, widespread volcanism produced subearial basalt and rhyolite flows in the region of the rift and along transcurrent faults that extend towards the northwest. Haida Gwaii was displaced approximately 70 km (43 mi) to the north along a series of faults extending through Sandspit and Louscoone Islet. This period of rifting and crustal extension contributed to the formation of the Queen Charlotte Basin.[18]

While the rift was in development, a conservative plate boundary would have extended northwards from the landward end of the rift. Such a plate boundary might have been similar to the Gulf of California – San Andreas fault system in the U.S. state of California. This type of configuration need have existed for only a few million years to have generated the 70 km (43 mi) of opening in the rift. Alternatively, the Haida Gwaii block may have been only partially coupled to the offshore plate during a longer period of oblique convergence.[18] Bathyal sediments, perhaps as young as 15 million years, were deposited within the rift zone during and after the rifting took place as the Anahim hotspot passed by.[18][19]

Uplift

Starting about 10 million years ago, the Anahim hotspot began to pass under the Bella CoolaOcean Falls region.[20] This coincided with increased regional uplift of the south-central Coast Mountains.[7] After the hotspot reached the Chilcotin Plateau 8 million years ago, uplift had decreased.[20] This suggests that the uplift could have been thermally driven by the Anahim hotspot, which thinned the lithosphere and caused changes in sub-crustal and surface heat flux.[7][21] About 1 km (0.62 mi) of uplift was achieved during the hotspot's time in the south-central Coast Mountains over a period of a few million years.[20]

Hotspot–fault interactions

The Anahim hotspot was stationed in a tectonically complex region of the Chilcotin Plateau between 3.9 and 1.4 million years ago. This complexity may have given rise to interactions of the hotspot with pre-existing fracture systems, such that magma rose along normal faults to create a 50 km (31 mi) long north–south chain of volcanoes. The Itcha Range developed directly over the intersection whereas the Satah Mountain volcanic field developed along the more distal portions of the fracture system and away from the Itcha Range. A lack of extensive volcanic fields adjacent to the neighbouring Ilgachuz and Rainbow ranges might indicate an absence of fracture systems associated with those volcanoes.[7]

Historical activity

Volcanic eruptions are not known to have occurred from the Anahim hotspot in historical times. However, since 2007 there have been recorded volcano tectonic earthquakes and carbon dioxide emissions in the vicinity of Nazko Cone.[7] The lack of evidence for historic seismicity prior to 2007 suggests that the area is tectonically stable, making the Nechako Basin one of the most seismically inactive areas of British Columbia.[7][22]

Seismicity

Hotspots
World distribution of proposed hotspots, with the Anahim hotspot numbered 45.

From October 9, 2007 to May 15, 2008, a series of earthquakes measuring up to 2.9 magnitude occurred in the Nechako Basin some 20 km (12 mi) west of Nazko Cone. Most of these tremors occurred 25 to 31 km (16 to 19 mi) below the surface, indicating they originated within the lowermost crust. Analysis of seismic waves suggest that the earthquake swarm was caused by brittle failure and fracturing of rock at depth from magma intrusion. No volcanic eruption was likely as the number and size of the seismic events were too small.[22] Nevertheless, this suggests that the Anahim hotspot is seismically active and that small magma movements are still possible.[23] Although these earthquakes were too small to be felt, they generated substantial local interest as they represented a significant concentration of seismic activity within the Anahim Volcanic Belt.[22]

Carbon dioxide emissions

Vigorous degassing of carbon dioxide occurs from several vents in two bogs near Nazko Cone.[24] These vents are in the form of small isolated travertine mounds on the bog surface. A mound with a partially submerged vent had been identified in 2013 with a steady flow of carbon dioxide. Several new vents with no travertine mound were actively releasing carbon dioxide gas in 2015.[25] Analysis of the carbon-13 isotope in the carbon dioxide gas emissions suggest a magmatic origin.[24] This has led to the possibility of a volcanic geothermal system, the existence of which has been investigated by Geoscience BC as part of their Targeting Resources for Exploration and Knowledge project.[26][27] The lack of hot springs and geothermal evidence on the surface suggest that the heat source of such a system would be very deep underground.[27]

Volcanic hazards

The Anahim hotspot is set in a remote location accessed by a network of logging roads from Quesnel on Highway 97.[3] Because of this, the most immediate hazard relating to future eruptions is of local concern only.[28] Although not heavily populated, the area is home to forestry operations and the small community of Nazko.[22] The presence of burned wood within Nazko tephra suggests that this area is prone to forest fires caused by volcanic eruptions. Also, if an eruption column were to be produced, it would disrupt local air traffic.[28] Volcanic ash reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems.[29] Renewed volcanism is likely to result in the creation of mafic cinder cones.[2] The latest such event occurred with the eruption of Nazko Cone 7,200 years ago.[16] However, eruptions of less mafic magma, typical of earlier activity of the Anahim hotspot, cannot be ruled out.[2]

See also

References

  1. ^ W. J. Kious; R. I. Tilling (1999) [1996]. This Dynamic Earth: the Story of Plate Tectonics (1.14 ed.). United States Geological Survey. ISBN 0-16-048220-8.
  2. ^ a b c Casadevall, Thomas J. (2000). Volcanic Ash and Aviation Safety: Proceedings of the First International Symposium on Volcanic Ash and Aviation Safety. United States Geological Survey. p. 50. ISBN 978-0607660661.
  3. ^ a b c d e f g h i Wood, Charles A.; Kienle, Jürgen (2001). Volcanoes of North America: United States and Canada. Cambridge, England: Cambridge University Press. pp. 114, 131, 132, 133, 134, 135, 136. ISBN 0-521-43811-X.
  4. ^ a b c d e f g h Souther, J. G. (1986). "The western Anahim Belt: root zone of a peralkaline magma system". Canadian Journal of Earth Sciences. NRC Research Press. 23: 896, 897, 900, 907. doi:10.1139/e86-091. ISSN 1480-3313.
  5. ^ D. L. Turcotte; G. Schubert (2001). "1". Geodynamics (2 ed.). Cambridge University Press. pp. 17, 324. ISBN 0-521-66624-4.
  6. ^ "Heat is deep and magma is shallow in a hot-spot system". Hawaii Volcano ObservatoryUnited States Geological Survey. 2001-06-18. Retrieved 2016-09-23.
  7. ^ a b c d e f g h i j k l m n o p q r Kuehn, Christian; Guest, Bernard; K. Russell, James; A. Benowitz, Jeff (2015). "The Satah Mountain and Baldface Mountain volcanic fields: Pleistocene hot spot volcanism in the Anahim Volcanic Belt, west-central British Columbia, Canada". Bulletin of Volcanology. Springer: 1, 2, 4, 5, 8, 9, 18, 19, 20, 22, 24, 25. ISSN 0258-8900.
  8. ^ a b c Ernst, Richard E.; Buchan, Kenneth L. (2001). Mantle Plumes: Their Identification Through Time. Geological Society of America. p. 261. ISBN 978-0-8137-2352-5.
  9. ^ Ernst, Richard E.; Buchan, Kenneth L. (2003). "Recognizing Mantle Plumes in the Geological Record". Annual Review of Earth and Planetary Sciences. Annual Reviews: 508. ISSN 1545-4495.
  10. ^ a b Dashtgard, Shahin; Ward, Brent (2014). Trials and Tribulations of Life on an Active Subduction Zone: Field Trips In and Around Vancouver, Canada. Boulder, Colorado: Geological Society of America. pp. 171, 172. ISBN 978-0-8137-0038-0.
  11. ^ "Newsletter of the Volcanology and Igneous Petrology Division". Ash Fall. Geological Association of Canada. 1996. p. 4.
  12. ^ Rogers, Garry C. (1981). "McNaughton Lake seismicity—more evidence for an Anahim hotspot?". Canadian Journal of Earth Sciences. NRC Research Press. 18: 826, 827. doi:10.1139/e81-078. ISSN 1480-3313.
  13. ^ Mercier, J. P.; Bostock, M. G.; Cassidy, J. F.; Dueker, K.; Gaherty, J. B.; Garnero, E. J.; Revenaugh, J.; Zandt, G. (2009). "Body-wave tomography of western Canada". Elsevier: 11 12. ISSN 0040-1951. Cite journal requires |journal= (help)
  14. ^ Young, Ian Fairley (1981). "Structure of the western margin of the Queen Charlotte Basin, British Columbia". University of British Columbia: 67, 69. Cite journal requires |journal= (help)
  15. ^ a b Charland, Anne; Francis, Don; Ludden, John (1992). "Stratigraphy and geochemistry of the Itcha Volcanic Complex, central British Columbia". Canadian Journal of Earth Sciences. NRC Research Press. 30: 132, 135. doi:10.1139/e93-013. ISSN 0008-4077.
  16. ^ a b Souther, J. G.; Clague, J. J.; Mathews, R. W. (1987). "Nazko cone: a Quaternary volcano in the eastern Anahim Belt". Canadian Journal of Earth Sciences. NRC Research Press. 24: 2477, 2479, 2481. doi:10.1139/e87-232.
  17. ^ S. Holland, Stuart (1976). "Landforms of British Columbia: A Physiographic Outline". Government of British Columbia: 70. Cite journal requires |journal= (help)
  18. ^ a b c Yorath, C. J.; Hyndman, Hyndman (1983). "Subsidence and thermal history of Queen Charlotte Basin". Canadian Journal of Earth Sciences. NRC Research Press. 20: 135, 136, 138. doi:10.1139/e83-013. ISSN 0008-4077.
  19. ^ Rohr, K. M. M.; Spence, G.; Asudeh, I.; Ellis, R.; Clowes, R. (1989). "Current Research, Part H". Seismic reflection and refraction experiment in the Queen Charlotte Basin, British Columbia. Geological Survey of Canada: 4. ISBN 0-660-54781-3.
  20. ^ a b c Parrish, Randall Richardson (1982). "Cenozoic Thermal and Tectonic History of the Coast Mountains of British Columbia as Revealed by Fission Track and Geological Data and Quantitative Thermal Models". University of British Columbia: 83, 120, 121. Cite journal requires |journal= (help)
  21. ^ Farley, K. A.; Rusmore, M. E.; Bogue, S. W. (2000). "Exhumation and Uplift History of the Central Coast Mountains, British Columbia, from Apatite (U-Th)/He Thermochronometry". University of California, Davis: 2. Cite journal requires |journal= (help)
  22. ^ a b c d Cassidy, J. F.; Balfour, N.; Hickson, C.; Kao, H.; White, R.; Caplan-Auerbach, J.; Mazzotti, S.; Rogers, G. C.; Al-Khoubbi, I.; Bird, A. L.; Esteban, L.; Kelman, M. (2011). "The 2007 Nazko, British Columbia, Earthquake Sequence: Injection of Magma Deep in the Crust beneath the Anahim Volcanic Belt". Bulletin of the Seismological Society of America. Seismological Society of America. 101: 1732, 1734, 1738. doi:10.1785/0120100013. ISSN 1943-3573.
  23. ^ Jessop, A. (2008). "Geological Survey of Canada, Open File 5906". Natural Resources Canada: 18. Cite journal requires |journal= (help)
  24. ^ a b Dewit, Megan (2014). "The geothermal potential of Nazko Cone, British Columbia". Simon Fraser University: 34. Cite journal requires |journal= (help)
  25. ^ Lett, Ray; Jackaman, Wayne (2015). "Tracing the source of anomalous geochemical patterns in soil, water and seepage gas near the Nazko volcanic cone, BC, NTS 93B/13". Geoscience BC: 11. Cite journal requires |journal= (help)
  26. ^ "The Geothermal Potential of Nazko Cone, British Columbia". Geological Society of America. 2014. Retrieved 2017-03-21.
  27. ^ a b "Geothermal potential of the Nazko area, central British Columbia". Geoscience BC. 2015. Retrieved 2017-03-21.
  28. ^ a b "Nazko Cone". Catalogue of Canadian volcanoes. Natural Resources Canada. 2005-08-19. Archived from the original on June 15, 2008. Retrieved 2016-04-03.
  29. ^ Neal, Christina A.; Casadevall, Thomas J.; Miller, Thomas P.; Hendley II, James W.; Stauffer, Peter H. (2004-10-14). "Volcanic Ash–Danger to Aircraft in the North Pacific". United States Geological Survey.
2007–2008 Nazko earthquakes

The 2007–2008 Nazko earthquakes were a series of small volcanic earthquakes measuring less than 4.0 on the Richter magnitude scale. They took place in the sparsely populated Nazko area of the Central Interior of British Columbia, Canada starting on October 9, 2007 and ending on June 12, 2008. They occurred just west of Nazko Cone, a small tree-covered cinder cone that last erupted about 7,200 years ago.

No damage or casualties resulted from the Nazko earthquakes, which were too small to be felt by people, but local seismographs recorded them. The earthquake swarm occurred at the eastern end of a known volcanic zone called the Anahim Volcanic Belt. This is an east-west trending line of volcanic formations extending from the Central Coast to the Central Interior of British Columbia.

Anahim

Anahim is a name used for several features in British Columbia, Canada, derived from the name of Chief Anahim, a leader of the Tsilhqot'in people in the mid-19th Century:

Anahim Lake, British Columbia, a community in the west-central part of the province

Anahim Lake Airport, the airport of the community of Anahim Lake

Anahim Peak, a volcano in the Anahim Volcanic Belt

Anahim hotspot, an inferred mantle plume feeding the Anahim Volcanic Belt

Anahim Volcanic Belt, a linear belt of volcanoesVarious Indian Reserves of the Tl'etinqox-t'in Government are named Anahim No. 10, Anahim No. 11 etc. Their main reserve community is known by a variant name, Anaham.

Anahim Lake

The subject of this article should not be confused with Anaham, which is a different community located nine kilometres east of Alexis Creek, British Columbia, which is in the same area.Anahim Lake is a small community in British Columbia. The village and surrounding areas (including nearby Nimpo Lake) have a population of approximately 1500. The Ulkatcho First Nation has 729 people living on nearby reserves. Every July, the Anahim Lake Stampede showcases local talent and is the area's major social event. Anahim Lake supports three general stores, one motel, a restaurant, and an RCMP detachment. It is situated on Highway 20, 320 km. west of Williams Lake, 140 km east of Bella Coola.

One major industry of Anahim Lake is forestry. This industry has been hurt by the pine beetle epidemic sweeping through Western Canada. In the summer of 2006, the lumber mill of Anahim Lake closed down and laid off dozens of mill workers. However, the mill has recently re-opened at half capacity. Other local industries include cattle farming, sport fishing, and mushroom picking. The area is famous for its numerous world class fresh water fishing lodges and resorts that bring in enthusiasts from around the world.

Anahim Lake is home to National Hockey League Vezina Trophy winner and Olympic gold medalist Carey Price of the Montreal Canadiens.

Anahim Lake Elementary Jr. Secondary is a public school that is part of School District #27 that serves students from Kindergarten to Grade 10. The school has been in use since it was built in 2006. The current Principal of the school is Mr. Mikal Brogan.

Anahim Lake is the namesake for the Anahim Volcanic Belt, Anahim hotspot and Anahim Peak.

Anahim Peak

Anahim Peak, sometimes mistakenly called Anaheim, is a volcanic cone in the Anahim Volcanic Belt in British Columbia, Canada, located 39 km (24 mi) northwest of Anahim Lake and 11 km (7 mi) east of Tsitsutl Peak. It was formed when the North American Plate moved over a hotspot, similar to the one feeding the Hawaiian Islands, called the Anahim hotspot. It is one of the several volcanoes in the Anahim Volcanic Belt that stands out all by itself, rising from the Chilcotin Plateau, between the Rainbow Range and the Ilgachuz Range and near the headwaters of the Dean River.

Anahim Volcanic Belt

The Anahim Volcanic Belt is a 600 km (373 mi) long volcanic belt, stretching from just north of Vancouver Island to near Quesnel, British Columbia, Canada. The Anahim Volcanic Belt has had three main magmatic episodes: 15–13 Ma, 9–6 Ma, and 3–1 Ma. The volcanoes generally become younger eastward at a rate of 2 cm (0.8 in) to 3.3 cm (1.3 in) a year. The Nazko Cone, which last erupted only 7,200 years ago, is the youngest Anahim volcano. These volcanoes are thought to have formed as a result of the North American Plate sliding westward over a long-lived center of upwelling magma called the Anahim hotspot. The hotspot is thought to be similar to the one feeding the Hawaiian Islands.

Future volcanism is most likely in the form of basaltic cinder cones, but eruptions of less mafic magma, typical of the eastern portions of the belt, cannot be ruled out. A series of earthquakes began October 9, 2007 in the vicinity of Nazko Cone which was related to intense subterranean volcanic activity in the area.

The volcanic belt is defined by 37 Quaternary basalt centers and three large shield volcanoes called the Rainbow Range, Ilgachuz Range and the Itcha Range. These three large volcanoes have built up dome-like piles of lava and fragmental rocks to a height of 8,130 feet (2,478 m) at Tsitsutl Peak in the Rainbow Range, 7,873 feet (2,400 m) at Far Mountain in the Ilgachuz Range, and 7,760 feet (2,365 m) at Mount Downton in the Itcha Range. The Rainbow Range is a low dome-like cone about 20 miles (32 km) diameter, with Anahim Peak an obsidian plug on its north-east flank. The Ilgachuz Range is 15 miles (24 km) or more in diameter, and the Itcha Range is 10 miles (16 km) wide and about 40 miles (64 km) long. All have been dissected by late Tertiary, pre-Pleistocene stream erosion.

Major volcanoes of the Anahim Volcanic Belt include:

Ilgachuz Range, 2,410 metres (7,907 ft)

Itcha Range, 2,368 metres (7,769 ft)

Rainbow Range, 2,478 metres (8,130 ft)

Basalt Falls

Basalt Falls is a waterfall on the Dean River in the Chilcotin District of the Central Interior of British Columbia, located north of the community of Anahim Lake. It is approximately 12 feet (3.7 m) in height and is composed of columnar basalt of the Chilcotin Group.

Chilcotin Group

The Chilcotin Group, also called the Chilcotin Plateau Basalts, is a large area of basaltic lava that forms a volcanic plateau running parallel with the Garibaldi Volcanic Belt in south-central British Columbia, Canada.

Predominantly, during Miocene and Pliocene times, a medium-sized volcanic field of overlapping vents occurred in British Columbia's Interior Plateau. The distribution is assumed to engulf up to 50,000 km2 of the Pacific Northwest, forming a medium-sized large igneous province, of volume 3300 km3. Volcanism occurred as late as Oligocene time, but continues sporadically up to present. Eruptions were most vigorous 6-10 million years ago and 2-3 million years ago, when most of the basalt was released. Less extensive eruptions continued 0.01 to 1.6 million years ago.These lava flows have been dominantly exposed by erosion resulting from the great floods that flowed in this region throughout the past ice ages, which laid bare many layers of the basalt flows along the Fraser Canyon from Soda Creek south to Canoe Creek elsewhere along the Chilcotin, Chilko, Chilanko and Taseko Rivers, and also to the east of the Fraser River at Chasm Provincial Park and along the Upper Deadman River. Prior to Late Pleistocene glacial erosion these centers formed a series of coalesced, low-profile shield volcanoes of unknown volume and distribution.

The Chilcotin Group were thought to potentially be linked to the partly coeval Columbia River Basalt Group. However, its morphology and geochemistry have been proven much similar to other volcanic plateaus such as the Snake River Plain in Idaho and parts of Iceland (Bevier, 1983).

Coast Range Arc

The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon. The Coast Range Arc lies along the western margin of the North American Plate in the Pacific Northwest of western North America. Although taking its name from the Coast Mountains, this term is a geologic grouping rather than a geographic one, and the Coast Range Arc extended south into the High Cascades of the Cascade Range, past the Fraser River which is the northward limit of the Cascade Range proper.

The Coast Range Arc formed as a result of subduction of the Kula and pre-existing Farallon Plates. It is most famous for being the largest granitic outcropping in North America, which then it is usually referred to as the Coast Plutonic Complex or the Coast Mountains Batholith. It is a coast-parallel continental volcanic arc similar to the Andes of South America and the largest continental volcanic arc fossil in the world.

Far Mountain

Far Mountain is the highest of over 13 peaks in the Ilgachuz Range in the Anahim Volcanic Belt in British Columbia, Canada. The Ilgachuz Range is one of the three major shield volcanoes that formed the Anahim Volcanic Belt when the North American Plate moved over a hotspot (the Anahim hotspot). This is similar to the one which feeds the Hawaiian Islands. The mountain is located in the western part of Itcha Ilgachuz Provincial Park.

Ilgachuz Range

The Ilgachuz Range is a name given to an extinct shield volcano in British Columbia, Canada. It is not a mountain range in the normal sense, because it was formed as a single volcano that has been eroded for the past 5 million years. It lies on the Chilcotin Plateau, located some 350 kilometres (220 mi) north-northwest of Vancouver and 30 km north of Anahim Lake. The highest peak of the range is Far Mountain. The range supports a unique grassland ecosystem. This type of grassland has not been seen anywhere else in central and southern British Columbia. The climate is cool and dry; typical of higher elevations of the Interior Plateau.

The 280 kilometres (174 mi) long West Road River rises in the Ilgachuz Range and flows east to its confluence with the Fraser River between Prince George and Quesnel. It drains an area of approximately 12,000 km2 and loses over 900 m elevation before joining the Fraser.

Itcha Range

The Itcha Range, also known as the Itchas, is a small isolated mountain range in the West-Central Interior of British Columbia, Canada. It is located 40 km (25 mi) northeast of the community of Anahim Lake. With a maximum elevation of 2,375 m (7,792 ft), it is the lowest of three mountain ranges on the Chilcotin Plateau extending east from the Coast Mountains. Two mountains are named in the Itcha Range; Mount Downton and Itcha Mountain. A large provincial park surrounds the Itcha Range and other features in its vicinity. More than 15 animal species are known to exist in the Itcha Range area, as well as a grassland community that is limited only to this location of British Columbia. The Itcha Range is within territory which has been occupied by aboriginal peoples for millennia. This area has a relatively dry environment compared to the Coast Mountains in the west.

In contrast to most mountain ranges in British Columbia, the Itcha Range represents an inactive shield volcano. This highly dissected volcanic edifice consists of a variety of rock types, including basanite, hawaiite, trachyte, rhyolite, phonolite and alkali olivine basalt. They were deposited by different types of volcanic eruptions characterized by passive lava flows and explosivity. Two stages of eruptive activity have been identified at the volcano along with three sub-phases that are limited only to the first stage of development. The main body of the Itcha Range is between 3.8 and 3.0 million years old and thus over two million years ago it passed the most active shield stage of life. A period of dormancy lasting for almost a million years followed, which was interrupted by the post-shield stage of volcanism 2.2 to 0.8 million years ago. More recent volcanic activity in and around the Itcha Range might have occurred in the last 340,000 years to produce cinder cones.

The Itcha Range is part of an east-west trending volcanic zone called the Anahim Volcanic Belt. This consists of large shield volcanoes, small cinder cones, lava domes and lava flows that become progressively younger from west to east. Several explanations have been made regarding the creation of this feature, each citing a different geologic process. If volcanic activity were to resume at the Itcha Range, Canada's Interagency Volcanic Event Notification Plan (IVENP) is prepared to notify people threatened by eruptions.

Milbanke Sound Group

The Milbanke Sound Group, also called the Milbanke Sound Cones, is an enigmatic group of five small basaltic volcanoes in the Kitimat Ranges of the Coast Mountains in British Columbia, Canada. Named for Milbanke Sound, this volcanic group straddles on at least four small islands (three of which are uninhabited), including Swindle, Price, Lady Douglas and Lake Island. Not much is known about this group of volcanoes and they remain undated. However, they all likely formed in the past 10,000 years after the last glacial period as evidenced by a small amount of erosion. The age of the most recent volcanic activity is also unknown. Most of the Milbanke Sound Cones are covered by mature forest. Kitasu Hill and Helmet Peak are the only two cones that are officially named.

This group of volcanoes is unlike many other volcanic groups in Canada as it resides on islands instead of on the mainland. The volcanoes form a northwest-southeast trend along the British Columbia Coast. To the west the Milbanke Sound Group is bounded by the Pacific Ocean and elsewhere it is surrounded by adjacent islands that form an archipelago. Although not related, the Milbanke Sound Group is close to the remains of a much older magmatic feature that was formed during the Tertiary period.

Mount Downton

Mount Downton is the highest summit of the 10 km (6 mi) diameter Itcha Range, located 40 km (25 mi) northeast of Anahim Lake and 33 km (21 mi) east of Far Mountain in the Chilcotin District of the Central Interior of British Columbia, Canada. It lies within Itcha Ilgachuz Provincial Park.

Mount MacKenzie

Mount MacKenzie is a volcanic peak, located 40 km (25 mi) northeast of Hagensborg, British Columbia, Canada. It is one of the volcanic peaks of the Rainbow Range, which is one of the three major shield volcanoes that form the Anahim Volcanic Belt. Mount MacKenzie was formed when the North American Plate moved over a hotspot, similar to the one feeding the Hawaiian Islands, known as the Anahim hotspot.

Nazko Cone

Nazko Cone is a small potentially active basaltic cinder cone in central British Columbia, Canada, located 75 km west of Quesnel and 150 kilometers southwest of Prince George. It is considered the easternmost volcano in the Anahim Volcanic Belt. The small tree-covered cone rises 120 m above the Chilcotin-Nechako Plateau and rests on glacial till. It was formed in three episodes of activity, the first of which took place during the Pleistocene interglacial stage about 340,000 years ago. The second stage produced a large hyaloclastite scoria mound erupted beneath the Cordilleran Ice Sheet during the Pleistocene. Its last eruption produced two small lava flows that traveled 1 km to the west, along with a blanket of volcanic ash that extends several km to the north and east of the cone.

Queen Charlotte Basin

The Queen Charlotte Basin is a structural basin mostly beneath the continental shelf offshore, between the Queen Charlotte Islands, Vancouver Island, and the British Columbia mainland, roughly coincident with the physiographic region named the Hecate Depression.The term Queen Charlotte Basin normally refers to the Cenozoic rocks, but these are underlain by what seems to be a thick Mesozoic succession. The Queen Charlotte Basin was formed by periods of extension, including thinning and volcanism during the mid-Cenozoic era. The large Cenozoic plutons that magnetic data suggest exist in the southeastern part of the Queen Charlotte Basin seem to be related to the Anahim hotspot.

Rainbow Range (Chilcotin Plateau)

The Rainbow Range, formerly known as the Rainbow Mountains, is a mountain range in British Columbia, Canada, located 40 kilometres (25 mi) northwest of Anahim Lake. Located on the western edge of the Chilcotin Plateau, the range adjoins the Coast Mountains Pacific Ranges to the south, and the Kitimat Ranges to the north. In some classification systems it is considered part of the Coast Mountains. It lies north of the Bella Coola and Atnarko Rivers and south and west of the Dean River, which curves around its north flank, and is relatively drier in climate and easier of terrain than more mountainous areas immediately west.

Once called Tsitsutl, meaning "rainbow mountains" in the Ulkatcho dialect of the Carrier language, that name is now the name of the range's highest peak.

Satah Mountain volcanic field

The Satah Mountain volcanic field (SMVF) is an extensive north-south trending volcanic chain in the Central Interior of British Columbia that stretches south of the Itcha Range shield volcano to northeast of Nimpo Lake. The chain is located on the Chilcotin Plateau, a major subdivision of the Interior Plateau that includes other nearby volcanic features. It forms a segment of the east-west trending Anahim Volcanic Belt, whose volcanic activity ranges in age from Miocene-to-Holocene. Volcanic features in the Satah Mountain field include lava domes, cinder cones and lava flows. Its name originates from Satah Mountain, the highest volcano, located 35 km (22 mi) northeast of Nimpo Lake.Lava domes and flows are composed of trachyte and the cinder cones consist of basaltic and trachybasaltic lava. The most recently formed cone is well preserved and might have a similar age to the 7,200‑year‑old Nazko Cone at the easternmost end of the Anahim Volcanic Belt. However, recent (2015) argon-argon dating by Kuehn et al. found that the youngest SMVF feature was a 1.43 million year old plug of basaltic trachyandesite.

Tsitsutl Peak

Tsitsutl Peak is the highest volcanic peak of the Rainbow Range in British Columbia, Canada, located within Tweedsmuir South Provincial Park, 43 km (27 mi) northwest of Anahim Lake and 44 km (27 mi) northeast of Thunder Mountain.

Topics of the Anahim Volcanic Belt
Volcanoes
Other

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.