Figure A23. Mount Edziza Mount Edziza is the remnant of a large shield volcano, now heavily eroded by overriding glaciers. The peak is 2590 m high. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 27.9 kb, 400 X 258, notice]

Mount Edziza, the second largest volcanic complex in Canada, is in northwestern British Columbia. Its glacier covered peaks are visible from the Stewart-Cassiar highway, 40 km to the west. This area of long-lived volcanic activity was studied in detail for many years by Dr. Jack Souther of the Geological Survey of Canada. Souther's (1992) on Mount Edziza and the surrounding volcanoes highlighted the importance and size of the region, one of the largest areas of young volcanic activity in Canada. The complex comprises a large plateau of predominantly basaltic lava flows; four large stratovolcanoes built on top of the plateau. The plateau is about 65 km long and a maximum of 20 km wide. The higher peaks of the complex were built upon a base of fluid basalt lava flows and are now glacier covered (Figure A23). Throughout the length of the volcanic complex, numerous eruptions have occurred within the last 10 000 years (or since the end of the last ice age). The most recent activity formed two large lava fields and several smaller, isolated cinder cones surrounded by lava flows (Figure A24, Figure A25). Desolation lava field, covering 150 km² on the northern end of the volcanic plateau, is the largest area of young lava flows. The longest lava flow from the Desolation field, and the youngest in the volcanic complex, is 12 km long. Eve cone, in the middle of the Desolation lava field, is one of the most symmetrical and best preserved cinder cones in Canada. Other young lava flows and cinder cones at Mount Edziza include Kana cone, Cinder cliff, Icefall cone, Ridge cone, Walkout Creek, the Mess Lake and Snowshoe lava fields, and two isolated cones at the southern end of the volcanic plateau. Many of the young cinder cones and lava flows at Mount Edziza are covered by light yellow pumice, referred to as the 'Sheep Track Member' by Souther (1992). The volcano that produced the pumice has not been discovered, but probably has been covered by glacier ice.

Figure A24. Pyramid Dome Pyramid Dome is a relatively young dome on the northwest flank of Mount Edziza. The dome represents just one of the several different styles of volcanism found in the Mount Edziza volcanic complex. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 20.1 kb, 400 X 264, notice]

Figure A25. Williams Cone Williams cone is one of numerous postglacial cinder cones dotting the landscape around Mount Edziza. The most recent of these has been dated at 1350 radiocarbon years ago. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 15.8 kb, 400 X 261, notice]

Active or recently active warm springs are found in several areas along the western flank of the volcanic plateau, including Elwyn springs (36°C), Taweh springs (46°C), and inactive springs near Mess Lake. All three hydrothermal areas are near the youngest lava fields on the plateau and are probably associated with the most recent volcanic activity at Mount Edziza. The vast plateau has also been an important cultural resource. The Tahltan people, who now live largely near Telegraph Creek, British Columbia, used volcanic glass (obsidian) from Mount Edziza to make tools and for trading material. More recently, most of the plateau has been made into a provincial park to preserve the volcanic and culture treasures unique to the northern British Columbia area.

Track Bench pumice deposit highlights one of the important volcanic hazards associated with the Mount Edziza volcanic complex - the possibility of a large, explosive volcanic eruption. Mount Edziza has a history of producing not only fluid and relatively passive basaltic lava flows, but also more silica-rich trachytic and rhyolitic lava flows and explosive eruptions. The silica-rich compositions are similar to those associated with the most violent eruptions on Earth, and scientists believe that the ice cap on top of Mount Edziza might be covering at least one volcanic caldera or crater. An explosive eruption could produce an ash cloud that would affect parts of northwestern Canada. As well, in the past, lava flows from Mount Edziza and closely related volcanoes to the north have dammed the Stikine River, which now has a major salmon fishery. Forest fires started by volcanic eruptions are also a possibility in this part of the world.