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EspañolANAHIM HOTSPOT
The 'Anahim hotspot' is a Tertiary-to-Holocene hotspot which is partly responsible for the volcanic activity which forms the volcanoes in central British Columbia, Canada.
The volcanic activity in central British Columbia is not close to any plate boundaries, suggesting that a mantle plume must exist underneath central British Columbia.
A belt of volcanoes called the Anahim Volcanic Belt, stretches from the west coast of British Columbia, to the Interior Plateau near Quesnel. The volcanoes generally get younger as you go from the coast to the Interior.
The plume, of which the Anahim hotspot is thought to be the surface expression, is thought to be similar to the hotspot that feeds the volcanoes of the Hawaiian Islands. It has been erupting basaltic magma to form the basaltic volcanoes within the Anahim Volcanic Belt and is believed to have been active for over 23 million years. During the early to middle Miocene, the Coast Mountains were favored thermally-driven uplift arising from the Miocene passage of the Anahim hotspot beneath the range, and response to convergence in late Miocene-Pliocene time. Each of the volcanoes in the Anahim Volcanic Belt was once over the hotspot, and migration of the North American Plate over the hotspot pulled the volcanoes away from the hotspot's magmatic source. As a result, the volcanoes are progressively older to the west. The supply and composition of magma to the volcanoes changes with time as the volcanoes grow over the hotspot and migrate away.
The origin of the Anahim hotspot plume magmas is the Earth's deep mantle, in contrast to the mid-ocean ridge magmas that come from the shallow mantle. Analysis of the chemical composition of the lavas gives important clues about the source and dynamics of the hotspot plume. The hotspot has fed special kinds of low-viscosity magmas to form the broad shield volcanoes, sush as the Ilgachuz Range, Itcha Range and the Rainbow Range.
The Anahim hotspot has been dormant for the past 7200 years. It was last active at a small tree-covered cinder cone, called Nazko Cone. The cycle of the eruption at Nazko Cone, started with an eruption of two different progressions of runney lava flows and an older, grey basalt overlain by a younger, darker black basaltic lava flow. The passive eruptions were followed by a period of explosive eruptions. This explosive activity built three overlying cinder cones that broke by the two lava flows near the end of the explosive phase of activity. The last phase of explosive activity spread tephra to the north and east of the cones. The deepest deposits near the cones is (>3 m) and thin to less than a few centimetres only a few kilometres away, which suggests that the explosive eruptions at Nazko Cone were fairly small. However, the last eruption from Nazko Cone could have started forest fires, since there is charcoal inside the tephra layer.
★ Plate tectonics
★ List of volcanoes in Canada
★ Anahim Volcanic Belt
★ Volcanoes of Canada
★ Coast Mountains
★ Queen Charlotte Basin
★ Volcanoes of Canada - Map of Canadian volcanoes
★ Exhumation and Uplift History of the Central Coast Mountains, British Columbia
★ National Resources Canada
| Contents |
| Evidence |
| Nature of the hotspot |
| See also |
| References |
| External links |
Evidence
The volcanic activity in central British Columbia is not close to any plate boundaries, suggesting that a mantle plume must exist underneath central British Columbia.
A belt of volcanoes called the Anahim Volcanic Belt, stretches from the west coast of British Columbia, to the Interior Plateau near Quesnel. The volcanoes generally get younger as you go from the coast to the Interior.
Nature of the hotspot
The plume, of which the Anahim hotspot is thought to be the surface expression, is thought to be similar to the hotspot that feeds the volcanoes of the Hawaiian Islands. It has been erupting basaltic magma to form the basaltic volcanoes within the Anahim Volcanic Belt and is believed to have been active for over 23 million years. During the early to middle Miocene, the Coast Mountains were favored thermally-driven uplift arising from the Miocene passage of the Anahim hotspot beneath the range, and response to convergence in late Miocene-Pliocene time. Each of the volcanoes in the Anahim Volcanic Belt was once over the hotspot, and migration of the North American Plate over the hotspot pulled the volcanoes away from the hotspot's magmatic source. As a result, the volcanoes are progressively older to the west. The supply and composition of magma to the volcanoes changes with time as the volcanoes grow over the hotspot and migrate away.
The origin of the Anahim hotspot plume magmas is the Earth's deep mantle, in contrast to the mid-ocean ridge magmas that come from the shallow mantle. Analysis of the chemical composition of the lavas gives important clues about the source and dynamics of the hotspot plume. The hotspot has fed special kinds of low-viscosity magmas to form the broad shield volcanoes, sush as the Ilgachuz Range, Itcha Range and the Rainbow Range.
The Anahim hotspot has been dormant for the past 7200 years. It was last active at a small tree-covered cinder cone, called Nazko Cone. The cycle of the eruption at Nazko Cone, started with an eruption of two different progressions of runney lava flows and an older, grey basalt overlain by a younger, darker black basaltic lava flow. The passive eruptions were followed by a period of explosive eruptions. This explosive activity built three overlying cinder cones that broke by the two lava flows near the end of the explosive phase of activity. The last phase of explosive activity spread tephra to the north and east of the cones. The deepest deposits near the cones is (>3 m) and thin to less than a few centimetres only a few kilometres away, which suggests that the explosive eruptions at Nazko Cone were fairly small. However, the last eruption from Nazko Cone could have started forest fires, since there is charcoal inside the tephra layer.
See also
★ Plate tectonics
★ List of volcanoes in Canada
★ Anahim Volcanic Belt
★ Volcanoes of Canada
★ Coast Mountains
★ Queen Charlotte Basin
References
★ Volcanoes of Canada - Map of Canadian volcanoes
★ Exhumation and Uplift History of the Central Coast Mountains, British Columbia
External links
★ National Resources Canada
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