page_title: Volcanic history of the Northern Cordilleran Volcanic Province
section_title: Volcanism 1.6 million to 10,000 years ago
hierarchical_section_title: Volcanic history of the Northern Cordilleran Volcanic Province / Volcanism 1.6 million to 10,000 years ago
caption_attribution_description: English: Satellite image of Heart Peaks (upper-left corner) and Level Mountain (middle).
context_page_description: The volcanic history of the Northern Cordilleran Volcanic Province presents a record of volcanic activity in northwestern British Columbia, central Yukon and the U.S. state of easternmost Alaska. The volcanic activity lies in the northern part of the Western Cordillera of the Pacific Northwest region of North America. Extensional cracking of the North American Plate in this part of North America has existed for millions of years. Continuation of this continental rifting has fed scores of volcanoes throughout the Northern Cordilleran Volcanic Province over at least the past 20 million years and occasionally continued into geologically recent times.
  Eruptive activity in the Northern Cordilleran Volcanic Province throughout its 20 million year history has been mainly the production of alkaline lavas, including alkaline basalts. A range of alkaline rock types not commonly found in the Western Cordillera are regionally widespread in the Northern Cordilleran Volcanic Province. These include nephelinite, basanite and peralkaline phonolite, trachyte and comendite lavas.
context_section_description: Throughout the Pleistocene epoch 1.6 million to 10,000 years ago, volcanism in the Northern Cordilleran Volcanic Province was broadly associated with glacial ice and ice sheets during glacial periods, including the large Cordilleran Ice Sheet. This volcano-ice association can be recognized in three different physiographic settings, each displaying unique relationships between topography, volcanism and glacial ice. The first volcano-ice interaction is displayed as tuyas, including Tuya Butte, on the Tanzilla Plateau in the Northern Interior of British Columbia. This sub-section of the Stikine Plateau consists of large flatlands with hills of low relief, and might have been one of the areas of ice accumulation for the Cordilleran Ice Sheet. Tanzilla Plateau volcanism throughout the Pleistocene epoch was basaltic subglacial eruptions. The most generally known subglacial volcanoes are distinctive tuyas, which commonly reach more than 100 m (330 ft) in elevation. Other volcanic forms also exist, some of which are basic and others that are probably the products of weathering. The subdued relief on the Tanzilla Plateau strongly influenced edifice morphologies, favoring broad-based tuyas. The hydrological conditions in these areas likely were controlled by relatively uniform ice thickness and gentle topography.
  The seconed type of volcano-ice interaction is located only to the east, south and southwest of the Tanzilla Plateau, in the Cassiar Mountains, Skeena Mountains and in the Boundary Ranges. Volcanic activity in these locations is also largely mafic in composition, but the extensive elevations of these areas had a much more impressive influence on glaciation and subglacial volcanism. High altitude glaciation took over when the Cordilleran Ice Sheet was not present and even when buried by the Cordilleran Ice Sheet, basal ice movement was strongly influenced by the deep, pre-glacial drainages. Accordingly, the erosional remnants of subglacial volcanoes are minor and intermittent. In the Skeena Mountains, separated outcrops of pillow lava and volcanic breccia are generally found side by side on the summits of sharp rugged mountain ridges, with presumably temporally-associated pyroclastic rocks having collected downslope.
  The third type of volcano-ice interaction is geographically restricted to three volcanoes, including Level Mountain, the Mount Edziza volcanic complex and Hoodoo Mountain. All three volcanoes are broad enough to hold ice caps that likely altered regional ice flow while still being altered by the Cordilleran Ice Sheet at individual periods. The Mount Edziza and Level Mountain complexes have shelves of older lava with elevations more than 1 km (0.62 mi) and have been zones of volcanic activity long enough that their geothermal activities might have had effects on movements of the Cordilleran Ice Sheet much like the Grímsvötn caldera in Iceland, which has been a significant heat source beneath the vast Vatnajökull icecap. At the Edziza complex, most of the subglacial products were formed on top of the main lava plateau, which now rises at least 1,000 m (3,300 ft) in elevation above adjacent stream valleys. The Edziza complex consists of a collection of mafic subglacial products, but more unusually, including Hoodoo Mountain and Level Mountain, comprises some of the largest deposits of peralkaline felsic subglacial volcanics known. At the Edziza and Level Mountain complexes, glacier hydrology of the Cordilleran Ice Sheet was possibly dominated by a complicated interaction between drainage on the flat plateaus under relatively thinner ice and drainage within nearby steep valleys filled with much thicker ice.
  Just northwest of Level Mountain, the Heart Peaks shield volcano rises with a topographic prominence of 1,025 m (3,363 ft) above the Nahlin Plateau with rhyolitic lava domes capping its summit. Heart Peaks is made of flat-lying basaltic and trachybasaltic lava flows and pyroclastic rocks. The most recent eruption at the shield is of dominantly Pleistocene age and late-stage Holocene activity is uncertain.
  On th
caption: Heart Peaks in the upper-left corner and the central and largest, is the treeless plateau of the Level Mountain shield volcano whose stratovolcano and domes are etched out by a light snowfall. Intermontane lowland lakes are shown as irregular dark blue patches.
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