The Northern Cordilleran Volcanic Province (NCVP), formerly known as the Stikine Volcanic Belt, is a geologic province defined by the occurrence of Miocene to Holocene volcanoes in the Pacific Northwest of North America. This belt of volcanoes extends roughly north-northwest from northwestern British Columbia and the Alaska Panhandle through Yukon to the Southeast Fairbanks Census Area of far eastern Alaska, in a corridor hundreds of kilometres wide. It is the most recently defined volcanic province in the Western Cordillera. It has formed due to extensional cracking of the North American continent—similar to other on-land extensional volcanic zones, including the Basin and Range Province and the East African Rift. Although taking its name from the Western Cordillera, this term is a geologic grouping rather than a geographic one. The southmost part of the NCVP has more, and larger, volcanoes than does the rest of the NCVP; further north it is less clearly delineated, describing a large arch that sways westward through central Yukon. At least four large volcanoes are grouped with the Northern Cordilleran Volcanic Province, including Hoodoo Mountain in the Boundary Ranges, the Mount Edziza volcanic complex on the Tahltan Highland, and Level Mountain and Heart Peaks on the Nahlin Plateau. These four volcanoes have volumes of more than 15 km3 (3.6 mi3), the largest and oldest which is Level Mountain with an area of 1,800 km2 (690 mi2) and a volume of more than 860 km3 (210 mi3). Apart from the large volcanoes, several smaller volcanoes exist throughout the Northern Cordilleran Volcanic Province, including cinder cones which are widespread throughout the volcanic zone. Most of these small cones have been sites of only one volcanic eruption; this is in contrast to the larger volcanoes throughout the volcanic zone, which have had more than one volcanic eruption throughout their history. The Northern Cordilleran Volcanic Province is part of an area of intensive earthquake and volcanic activity around the Pacific Ocean called the Pacific Ring of Fire. However, the Northern Cordilleran Volcanic Province is commonly interpreted to be part of a gap in the Pacific Ring of Fire between the Cascade Volcanic Arc further south and the Aleutian Arc further north. But the Northern Cordilleran Volcanic Province is recognized to include over 100 independent volcanoes that have been active in the past 1.8 million years. At least three of them have erupted in the past 360 years, making it the most active volcanic area in Canada. Nevertheless, the dispersed population within the volcanic zone has witnessed few eruptions due to remoteness and the infrequent volcanic activity.
Geology
Origins and chemistry
The Northern Cordilleran Volcanic Province has been a zone of active volcanism since it began to form 20 million years ago. Unlike other parts of the Pacific Ring of Fire, the Northern Cordilleran Volcanic Province has its origins in continental rifting—an area where the Earth's crust and lithosphere is being pulled apart. This differs from other portions of the Pacific Ring of Fire as it consists largely of volcanic arcs formed by subducting oceanic crust at oceanic trenches along continental margins circling the Pacific Ocean. The continental crust at the Northern Cordilleran Volcanic Province is being stretched at a rate of about 2 cm (1 in) per year. This incipient rifting formed as a result of the Pacific Plate sliding northward along the Queen Charlotte Fault, on its way to the Aleutian Trench, which extends along the southern coastline of Alaska and the adjacent waters off the southern coast of the Kamchatka Peninsula. As a result, volcanism in the Northern Cordilleran Volcanic Province is also not related to back-arc basin volcanism. When the stored energy is suddenly released by slippage across the fault at irregular intervals, it can create very large earthquakes, such as the magnitude 8.1 Queen Charlotte Islands earthquake of 1949. As these far-field forces stretch the North American crust, the near surface rocks fracture along steeply dipping faults parallel to the rift zone. Hot magma rises between these fractures to create passive or effusive eruptions. Volcanoes within the Northern Cordilleran Volcanic Province are located along short northerly trending segments which in the northern part of the volcanic province are unmistakenably involved with north-trending rift structures, including synvolcanic grabens and grabens with one major fault line along only one of the boundaries (half-grabens). Grabens are indicative of tensional forces and crustal stretching. Two major north-trending faults hundreds of kilometres long extend along the Northern Cordilleran Volcanic Province. These two rock fractures, known as the Tintina and Denali fault systems, have been tectonically active since the Cretaceous period as strike-slip faults. The Denali fault to the west and the Tintina fault to the east are nearly 2,000 km (1,200 mi) long, extending from northern British Columbia to central Alaska. Other mechanisms suggested for triggering volcanism in the Northern Cordilleran Volcanic Province include mantle plumes, deglaciation and slab windows, although continental rifting is the most accurate mechanism for activating volcanism in the volcanic zone. Further evidence for continental rifting in the Northern Cordilleran Volcanic Province is magmas are mainly alkaline, it includes highly alkaline and peralkaline rock types, the main spatial-temporal pattern of volcanism is in the middle of the volcanic province followed by movement to the south, north and possibly northeast, heat flow in the Northern Cordilleran Volcanic Province is high, seismic activity is largely absent in the volcanic province and the largest period of volcanism correlates with an interval of net extension between the Pacific and North American plates.
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