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Mount Edziza ( ; ) is a volcanic mountain in Cassiar Land District of northwestern British Columbia, Canada. It is located on the Big Raven Plateau of the Tahltan Highland which extends along the western side of the Stikine Plateau. Mount Edziza has an elevation of , making it the highest point of the Mount Edziza volcanic complex and one of the highest in Canada. However, it had an elevation of at least before its formerly cone-shaped summit was likely destroyed by a violent eruption in the geologic past; its current flat summit contains an ice-filled, volcanic crater. The mountain contains several , and on its flanks, as well as an ice cap containing several outlet glaciers which extend to lower elevations. All sides of Mount Edziza are drained by tributaries of Mess Creek and Kakiddi Creek which are situated within the Stikine River watershed.
Mount Edziza consists of several types of and at least six geological formations that formed during six distinct stages of volcanic activity. The first stage 1.1 million years ago produced basalt flows and a series of rhyolite and trachyte domes. Basalt flows and smaller amounts of trachyte, tristanite, trachybasalt, benmoreite and mugearite produced during the second stage about 1 million years ago comprise Ice Peak, a glacially eroded stratovolcano forming the south peak of Mount Edziza. The third and fourth stages 0.9 million years ago created basalt and the central trachyte stratovolcano of Mount Edziza, respectively. Thick trachyte flows were issued during the fifth stage 0.3 million years ago, most of which have since eroded away. The sixth stage began in the last 20,000 years with the eruption of cinder cones, basalt flows and minor trachyte ejecta. Renewed volcanism could block local streams with lava flows, disrupt air traffic with volcanic ash and produce floods or from melting glacial ice.
Indigenous peoples have lived adjacent to Mount Edziza for thousands of years. It is a sacred mountain to the Tahltan people, who historically used volcanic glass from it to make tools and weaponry. Mineral exploration just southeast of Mount Edziza had commenced by the 1950s where gold, silver and other metals were discovered. This mineral exploration was conducted by several mining companies into the early 1990s. Mount Edziza and the surrounding area were made into a large provincial park in the early 1970s to showcase the volcanic landscape. The mountain and provincial park can only be accessed by aircraft or by a network of from surrounding roads.
A number of explanations have been made regarding the origin of the name Edziza. A 1927 report by J. Davidson of the British Columbia Land Surveyors claims that Edziza means in the Tahltan language, referring to the deep volcanic ash deposits or pumice-like sand covering large portions of the Big Raven Plateau around Mount Edziza. According to David Stevenson of University of Victoria's Anthropology Department, or is instead translated as kutlves in Tahltan. An explanation listed in the BC Parks brochure is that Edziza means in the Tahltan language. Another explanation proposed by Canadian volcanologist Jack Souther is that Edziza is a corruption of Edzerza, the name of a local Tahltan family. Obsolete spellings of Edziza include Eddziza, Eddiza, Edidza, Edzia and Etseza.
Mount Edziza is in the Southern Boreal Plateau Ecosection which consists of several upland summits, wide river valleys and deeply incised plateaus. It is one of seven ecosections comprising the Boreal Mountains and Plateaus Ecoregion, a large ecoregion of northwestern British Columbia encompassing high plateaus and rugged mountains with intervening . of Picea mariana and Picea glauca spruce occur in the lowlands and valley bottoms of this ecoregion whereas birch, spruce and willow form forests on the mid-slopes. Extensive Alpine plant altai fescue covers the upper slopes, but barren rock is abundant at higher .
The region is characterized by warm summers and cold, snowy winters; temperatures are warmest in mid-summer during the day when they may hit the range. However, temperatures can drop below freezing during summer nights, making snow or freezing rain a possibility at any time of the year. The closest to Mount Edziza are located at Telegraph Creek and Dease Lake, which lie about to the northwest and to the northeast, respectively.
Four outlet glaciers of the ice cap are named, and all have names of Tahltan origin. Idiji Glacier descends from the eastern side of the ice cap near the river source of Tennaya Creek. At the head of Tenchen Creek is Tenchen Glacier, a debris-covered glacier on the eastern side of the ice cap. Tencho Glacier at the southern end of the ice cap is the largest outlet glacier. At the head of Tennaya Creek on the eastern side of the ice cap is Tennaya Glacier.
As a part of the Mount Edziza volcanic complex, Mount Edziza was covered by a regional ice sheet during the Pleistocene which receded and advanced periodically until about 11,000 years ago when deglaciation was essentially complete in a steadily warming climate. This warming trend ceased about 2,600 years ago, causing glaciers to advance from Mount Edziza and elsewhere along the volcanic complex as a part of the neoglaciation. The present trend towards a more moderate climate put an end to the neoglacial period in the 19th century. This has resulted in rapid glacial recession throughout the Mount Edziza volcanic complex. This rapid glacial recession is apparent from the lack of vegetation on the barren, rocky ground between the glaciers and their which are up to apart.
The central, high edifice of Mount Edziza is a nearly symmetrical stratovolcano, its symmetry having been broken by several steep-sided lava domes. Its eastern flank has been eroded by a narrow cirque which is bounded by near-vertical that breach the eastern summit crater rim. A system of radial meltwater channels has moderately eroded the upper flanks and summit crater rim elsewhere. Lesser modification by erosion has taken place on the southern and northwestern flanks of the stratovolcano. Along the north side of Tenchen Valley on the eastern flank of the stratovolcano are high cliffs exposing explosion , trachyte lavas and landslide or lahar deposits. Although Mount Edziza is surrounded by relatively flat terrain of the Big Raven Plateau to the north, west and south, the terrain east of the mountain is characterized by a series of ridges with intervening valleys. Among these ridges are Idiji Ridge and Sorcery Ridge which are the namesakes of Idiji Glacier and Sorcery Creek.
About south of the summit is Ice Peak, the south peak of Mount Edziza. This prominent pyramidal peak has an elevation of and is the glacial erosion remains of an older stratovolcano whose northern flank is buried under the younger edifice of Mount Edziza. The southern and western flanks are approximal to those of the original stratovolcano whereas the eastern flank has been almost completely destroyed by headward erosion of glacial valleys. At its climax, the stratovolcano had a symmetrical profile and contained a small crater at its summit; the current peak is an erosional remnant etched from the eastern crater rim.
A circular lava dome on the southeastern crater rim of Mount Edziza called Nanook Dome has an elevation of . Sphinx Dome, in elevation, is a partially buried lava dome on the northeastern flank of Mount Edziza. Remnants of a volcanic pile called Pharaoh Dome occur along the eastern flank of Mount Edziza. They lie at an elevation of between Tennaya Creek and Cartoona Ridge. Cinder Cliff is a high barrier of on the eastern side of Mount Edziza at an elevation of in the north fork of Tenchen Creek. The Neck, in elevation, is a circular volcanic plug on the southeastern flank of Ice Peak.
The Snowshoe Lava Field on the west flank of lce Peak contains at least 12 volcanic cones, a handful of which are named. Tennena Cone is a symmetrical volcanic cone high on the west side of Ice Peak. It has an elevation of and is almost completely surrounded by ice. Cocoa Crater is the largest cone in the Snowshoe Lava Field and is in elevation. To the southeast is Coffee Crater which has an elevation of . Keda Cone, in elevation, lies just south of Coffee Crater on the south side of upper Taweh Creek. A saucer-shaped mound of lava called The Saucer is in elevation and has a diameter of about .
The Desolation Lava Field on the northern flank of Mount Edziza contains at least 10 cinder cones, most of which are clustered near the northern trim line of Mount Edziza's ice cap. Sleet Cone and Storm Cone are rounded, mostly soil-covered, conical mounds that reach elevations of and , respectively. North of Storm Cone are the Triplex Cones, a group of three eroded circular mounds reaching an elevation of . Twin Cone, in elevation, is a pyroclastic cone whose southeastern side has been breached. Moraine Cone has an elevation of nearly and has been nearly destroyed by alpine glaciation. The northeastern side of Mount Edziza contains Williams Cone, a prominent cinder cone in elevation. Eve Cone, in elevation, is a symmetrical cone between Buckley Lake and Mount Edziza. The northernmost cinder cone in the Desolation Lava Field is Sidas Cone which consists of two symmetrical halves and reaches an elevation of .
Tsecha Creek is a northeast-flowing stream originating from the northern flank of Mount Edziza. Nido Creek flows northeastward from the eastern side of Mount Edziza into Nuttlude Lake. Flowing from the eastern flank of Mount Edziza just southeast of The Pyramid is Tenchen Creek. Shaman Creek flows east and north into Kakiddi Lake from the southern flank of Mount Edziza. Tennaya Creek flows northeastward from the eastern side of Mount Edziza into Nuttlude Lake. All five streams are tributaries of Kakiddi Creek, a north-flowing tributary of the Klastline River which flows north into the Stikine River.
The Pyramid Formation includes Sphinx Dome, Pharaoh Dome and The Pyramid which were the main sources of the rhyolites and trachytes of this geological formation. The Pyramid is a prominent trachyte dome whose structure has not been greatly modified by erosion, nor has it been buried under younger lavas. In contrast, much of the southern edge of Sphinx Dome has been destroyed by headward erosion of Cook Creek; the western half of this rhyolite dome is also buried under trachyte of the Edziza Formation. From Cartoona Ridge north to Tennaya Creek are isolated remnants of Pharaoh Dome, the main mass of which comprises flow-layered rhyolite and is buried under basalt of the Ice Peak Formation.
The Ice Peak Formation also includes the Koosick and Ornostay bluffs, both of which are thick lobes of trachyte that originated under the summit ice cap. Both bluffs are similar in geomorphology and composition, consisting of several lava flows up to thick. The Neck, which forms a prominent high on Sorcery Ridge, is also part of the Ice Peak Formation. Potassium–argon dating of pantelleritic trachyte from the Ice Peak Formation has yielded ages of 1.6 ± 0.2 million years, 1.5 ± 0.4 million years and 1.5 ± 0.1 million years. These dates being older than those of the Pyramid Formation may be due to excess argon in the Ice Peak Formation; therefore the dates are considered unreliable.
Ice Peak Formation basalt flows on the northwestern flank of Mount Edziza are interbedded with recording a regional glaciation that occurred during the Early Pleistocene. The lowermost basalt flow contains basal pillow lava, directly overlies and is brecciated and deformed, suggesting it may have been extruded onto a glacier or an ice sheet. Its extrusion onto glacial ice is also evident due to the lack of fluvial and lacustrine sediments at the base of the basalt flow which suggests it did not extrude into lakes or streams. The steep sides and unusually large thicknesses of the trachyte flows comprising Koosick and Ornostay bluffs is attributed to them having been extruded through glacial ice.
Fission track dating of apatite from partially fused granitic in contaminated Pillow Ridge Formation basalt has yielded ages of 0.9 ± 0.3 million years and 0.8 ± 0.25 million years. In contrast, potassium–argon dating has yielded an anomalously old age of 5.9 ± 0.9 million years which is inconsistent with the ages of the underlying and overlying formations. This date being much older than the fission track dates most likely results from contamination and introduction of excess argon from the partially fused granitic and gneissic xenoliths in Pillow Ridge Formation basalt.
Eruptions on the heavily eroded eastern flank of Mount Edziza created Icefall Cone, Ridge Cone and Cinder Cliff which comprise a separate volcanic zone called the east slope centres. The Sheep Track Member is the product of an explosive eruption that originated from the southwestern flank of Ice Peak. It was deposited on all lava flows and cinder cones in the Snowshoe Lava Field with the exception of The Saucer which likely postdates the Sheep Track eruption. The source of the Sheep Track pumice is unknown, but it probably originated from a vent hidden under Tencho Glacier. Holocene in age, the Big Raven Formation has yielded dates of 6520 BCE ± 200 years, 750 BCE ± 100 years, 610 CE ± 150 years and 950 CE ± 6000 years.
Mount Edziza trachyte and rhyolite have silica-rich compositions that are comparable to those associated with the most powerful eruptions around the world; parts of northwestern Canada could be affected by an ash column if an explosive eruption were to happen from the volcano. Ash columns can drift for thousands of kilometres downwind and often become increasingly spread out over a larger area with increasing distance from an erupting vent. Mount Edziza lies under a major air route from Vancouver, British Columbia to Whitehorse, Yukon, suggesting the volcano poses a potential threat to air traffic. Volcanic ash reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems.
Like other volcanoes in Canada, Mount Edziza is not monitored closely enough by the Geological Survey of Canada to ascertain its activity level. The Canadian National Seismograph Network has been established to monitor earthquakes throughout Canada, but it is too far away to provide an accurate indication of activity under the mountain. It may sense an increase in seismic activity if Mount Edziza becomes highly restless, but this may only provide a warning for a large eruption; the system might detect activity only once the volcano has started erupting. If Mount Edziza were to erupt, mechanisms exist to orchestrate relief efforts. The Interagency Volcanic Event Notification Plan was created to outline the notification procedure of some of the main agencies that would respond to an erupting volcano in Canada, an eruption close to the Canada–United States border or any eruption that would affect Canada.
Two obsidian flows of the Pyramid Formation occur on The Pyramid and are exposed as two outcrops; they were quarried as evidenced by the occurrence of this obsidian in at least five archaeological sites outside of Tahltan territory. The Ice Peak Formation contains two obsidian flows on Sorcery Ridge that were also exploited as an obsidian source. Sorcery Ridge obsidian occurs in at least two archaeological sites outside of Tahltan territory.
In or before 1974, two Tahltan men named Johnny Edzerza and Hank Williams were killed in an avalanche while they were crossing the mountain. Edzerza was buried on Mount Edziza, but his surname was erroneously spelled "Edzertza" on his grave marker. Williams Cone on the northeastern side of Mount Edziza was named in honour of Hank Williams whereas Eve Cone between Mount Edziza and Buckley Lake was named in honour of Johnny Edzerza's wife, Eve Brown Edzerza.
Mount Edziza continues to be an important cultural resource for the Tahltan people. In 2021, Chad Norman Day, president of the Tahltan Central Government, said "Mount Edziza and the surrounding area has always been sacred to the Tahltan Nation. The obsidian from this portion of our territory provided us with weaponry, tools and trading goods that ensured our Tahltan people could thrive for thousands of years."
Between 1976 and 1981, geochemical and geological surveys were conducted on the Spectrum property by Consolidated Silver Ridge Mines and Newhawk Mines. Consolidated Silver Ridge Mines built an airstrip and carried out of drilling in 28 holes during this time. Newhawk Mines constructed an access road and of underground development on the Hawk vein. Further geochemical and geological surveying was performed by Moongold Resources from 1987 to 1989. Mineral exploration conducted by Columbia Gold Mines from 1990 to 1992 consisted of rock sampling, trenching and of drilling in 50 holes.
In 2021, an approximately conservation area called the Mount Edziza Conservancy was established east of Mount Edziza along the eastern border of Mount Edziza Provincial Park. It was established in collaboration with Skeena Resources, BC Parks, the Tahltan Central Government and the Nature Conservancy of Canada after Skeena Resources returned their mineral tenures on the Spectrum property. The name of this conservation area was changed to the Tenh Dẕetle Conservancy in 2022 to better reflect the culture, history and tradition of the Tahltan First Nation.
To the east, the roughly long Klastline River Trail begins at the community of Iskut on the Stewart–Cassiar Highway. It extends northwest and west along the Klastline River for much of its length. The trail enters Mount Edziza Provincial Park at about where Kakiddi Creek drains into the Klastline River. After entering Mount Edziza Provincial Park, the Klastline River Trail traverses northwest along the Klastline River for about and then crosses the river north of Mount Edziza. From there, the Klastline River Trail traverses west for about to the northeastern end of Buckley Lake where it meets with the Buckley Lake Trail and the Buckley Lake to Mowdade Lake Route.
The Buckley Lake to Mowdade Lake Route traverses south from Buckley Lake along Buckley Creek and gradually climbs onto the northern end of the Big Raven Plateau where Eve Cone, Sidas Cone and Tsekone Ridge are visible along the route. Most of the Buckley Lake to Mowdade Lake Route is marked by a series of rock from Tsekone Ridge onwards. The distance between Buckley Lake and Mowdade Lake is about , but the hiking length between these two lakes varies depending on the route taken; it can take a minimum of 7 days to hike the Buckley Lake to Mowdade Lake Route. The weather can change extremely fast along this hiking trail.
Mount Edziza can also be accessed by float plane or helicopter, both of which are available for charter at the communities of Iskut and Dease Lake. Kakiddi Lake, Nuttlude Lake, Mowdade Lake, Mowchilla Lake and Buckley Lake are large enough to be used by float-equipped aircraft. Landing on the latter two lakes with a private aircraft requires a letter of authorization from the BC Parks Stikine Senior Park Ranger.
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