Mount Edziza
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 volcanoes 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, crater. The mountain contains several lava domes, cinder cones and lava fields 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 volcanic rocks 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 ridges 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 lahars 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 preserve the volcanic landscape. The mountain and provincial park can only be accessed by aircraft or by a network of horse trails from surrounding roads.
Name and etymology
The mountain was labelled Edziza Peak on Geological Survey of Canada maps as early as 1926. This name for the mountain was adopted by the Geographical Names Board of Canada on September 24, 1945, as identified on the 1926 Geological Survey of Canada map sheet 309A. Edziza Mountain appeared in the 1930 BC Gazetteer, in which the name was erroneously spelled Edzia. On December 3, 1974, the form of name was changed from Edziza Peak to Mount Edziza in accordance with a 1927 British Columbia Land Surveyors report, two world aeronautical charts published in 1950, and three British Columbia maps published in 1931, 1933 and 1943. The form of the name was also changed to reflect entrenched local usage and in conformation with Mount Edziza Provincial Park, which was established in 1972. To the local Tahltan people, Mount Edziza is called Tenh Dẕetle, which translates to.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.
Geography and geomorphology
Location and climate
Mount Edziza rises from within the middle of the Big Raven Plateau, a barren plateau in Cassiar Land District bounded on the west by Mess Valley, on the north by Klastline Valley, on the east by Kakiddi Valley and on the south by Chakima and Walkout valleys. It lies at the northern end of the Mount Edziza volcanic complex which also includes the smaller Arctic Lake and Kitsu plateaus to the south. This complex of shield volcanoes, stratovolcanoes, lava domes, calderas and cinder cones forms a broad, intermontane plateau at the eastern edge of the Tahltan Highland, a southeast-trending upland area extending along the western side of the Stikine Plateau.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 ecological region of northwestern British Columbia encompassing high plateaus and rugged mountains with intervening lowlands. Boreal forests of black and white spruce occur in the lowlands and valley bottoms of this ecoregion whereas birch, spruce and willow form forests on the mid-slopes. Extensive alpine altai fescue covers the upper slopes, but barren rock is abundant at higher elevations.
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 weather stations to Mount Edziza are located at Telegraph Creek and Dease Lake, which lie about to the northwest and to the northeast, respectively.
Glaciation
Mount Edziza is covered with snow year-round, containing a long and wide ice cap which covers an area of. Several small outlet glaciers extending down to elevations of drain the ice cap. Outlet glaciers on the western side of the ice cap spread in broad lobes onto the Big Raven Plateau whereas distributary glaciers on the eastern side drape down steep slopes to form discontinuous icefalls. The Mount Edziza glacier complex is the only one worthy of note on the Stikine Plateau.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 head 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 trim lines which are up to apart.
Structure
Mount Edziza has an elevation of, making it the highest point of the Mount Edziza volcanic complex. It has been considered by some to be the highest or tallest volcano in Canada, but others have given higher elevations of for the Silverthrone volcanic complex in southwestern British Columbia. The nearly flat summit of Mount Edziza contains a circular ridge that surrounds an ice-filled, in diameter crater. This ridge is partially exposed above the ice cap as a discontinuous series of spires and serrated nunataks. Spires forming the southern end of the ridge are the highest and consist of greenish grey, sparsely porphyritic trachyte. They comprise well-formed, small diameter rock columns that rise nearly vertically more than above the ice cap. Nunataks elsewhere on the summit ridge are more subdued, consisting of pyroclastic debris that has been glacially reworked. The eastern side of the ridge has been breached by active cirques where remnants of several lava lakes are exposed inside the crater. Formation of the summit crater was likely caused by a violent eruption at the zenith of the mountain's growth, although it may have also formed during the eruption of the Kakiddi Formation lava flows or the effusion of voluminous lava during dome construction. Prior to its formation, the summit of the mountain was at least higher than it is today, having possibly risen as a narrower summit cone truncated with a smaller crater.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 headwalls 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 breccias, 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 pyramid-shaped horn has an elevation of and is the glacially eroded 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.