| Mount Edziza | |
|---|---|
| Edziza Peak Edziza Mountain | |
 The ice-filled summit crater of Mount Edziza | |
| Highest point | |
| Elevation | 2,786 m (9,140 ft)[1] |
| Coordinates | 57°42′55″N130°38′04″W / 57.71528°N 130.63444°W /57.71528; -130.63444[2] |
| Naming | |
| Etymology | Unclear |
| Native name | Tenh Dẕetle (Tahltan)[3] |
| English translation | 'Ice Mountain'[3] |
| Geography | |
  Mount Edziza Location in British Columbia | |
 | |
| Location inMount Edziza Provincial Park | |
| Country | Canada[1] |
| Province | British Columbia[1] |
| District | Cassiar Land District[2] |
| Protected area | Mount Edziza Provincial Park[4] |
| Parent range | Tahltan Highland[5] |
| Topo map | NTS 104G10 Mount Edziza[2] |
| Geology | |
| Formed by | Volcanism[6] |
| Rock age | 1.1Ma to less than 20ka[7][8] |
| Rock type(s) | Basalt,trachybasalt,tristanite,mugearite,benmoreite,trachyte,rhyolite[1][9] |
| Volcanic region | Northern Cordilleran Province[10] |
| Last eruption | Holocene age[8][11] |
Mount Edziza (/ədˈzaɪzə/əd-ZY-zə;Tahltan:Tenh Dẕetle[ten̥ˈdðetle]) is avolcanic mountain inCassiar Land District of northwesternBritish Columbia, Canada. It is located on theBig Raven Plateau of theTahltan Highland which extends along the western side of theStikine Plateau. Mount Edziza has an elevation of 2,786 metres (9,140 feet), making it the highest point of theMount Edziza volcanic complex and one of the highestvolcanoes in Canada. However, it had an elevation of at least 3,396 m (11,142 ft) 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, 2-kilometre-in diameter (1.2-mile)crater. The mountain contains severallava domes,cinder cones andlava fields on its flanks, as well as anice cap containing severaloutlet glaciers which extend to lower elevations. All sides of Mount Edziza are drained bytributaries ofMess Creek andKakiddi Creek which are situated within theStikine River watershed.
Mount Edziza consists of several types ofvolcanic rocks and at least sixgeological formations that formed during six distinct stages ofvolcanic activity. The first stage 1.1 million years ago producedbasalt flows and a series ofrhyolite andtrachyte domes. Basalt flows and smaller amounts of trachyte,tristanite,trachybasalt,benmoreite andmugearite produced during the second stage about 1 million years ago compriseIce Peak, a glacially erodedstratovolcano forming the south peak of Mount Edziza. The third and fourth stages 0.9 million years ago created basaltridges 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 trachyteejecta. Renewedvolcanism could block local streams with lava flows, disrupt air traffic withvolcanic ash and produce floods orlahars from melting glacial ice.
Indigenous peoples have lived adjacent to Mount Edziza for thousands of years and it is asacred mountain to theTahltan people who historically usedvolcanic glass from it to make tools and weaponry.Mineral exploration just southeast of Mount Edziza had commenced by the 1950s wheregold,silver and other metals were discovered. This mineral exploration was conducted by severalmining companies into the early 1990s. Mount Edziza and the surrounding area was made into alarge provincial park in the early 1970s to showcase the volcanic landscape. The mountain andprovincial park can only be accessed by aircraft or by a network offootpaths from surrounding roads.
The mountain was labelledEdziza Peak onGeological Survey of Canada maps as early as 1926. This name for the mountain was adopted by theGeographical 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 spelledEdzia. On December 3, 1974, the form of name was changed fromEdziza Peak toMount Edziza in accordance with a 1927British Columbia Land Surveyors report, twoworld 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 withMount Edziza Provincial Park, which was established in 1972.[2] To the localTahltan people, Mount Edziza is calledTenh Dẕetle, which translates to'Ice Mountain'.[2][3]
A number of explanations have been made regarding the origin of the nameEdziza. A 1927 report by J. Davidson of the British Columbia Land Surveyors claims thatEdziza means'sand' in theTahltan language, referring to the deepvolcanic ash deposits orpumice-like sand covering large portions of theBig Raven Plateau around Mount Edziza. According to David Stevenson ofUniversity of Victoria's Anthropology Department,'sand' or'dust' is instead translated askutlves in Tahltan. An explanation listed in theBC Parks brochure is thatEdziza means'cinders' in the Tahltan language. Another explanation proposed by CanadianvolcanologistJack Souther is thatEdziza is acorruption ofEdzerza, the name of a local Tahltan family. Obsolete spellings ofEdziza includeEddziza,Eddiza,Edidza,Edzia andEtseza.[2]
Mount Edziza rises from within the middle of the Big Raven Plateau, abarren plateau inCassiar Land District bounded on the west by Mess Valley, on the north byKlastline Valley, on the east by Kakiddi Valley and on the south byChakima andWalkout valleys.[2][5][12] It lies at the northern end of theMount Edziza volcanic complex which also includes the smallerArctic Lake andKitsu plateaus to the south.[13] This complex ofshield volcanoes,stratovolcanoes,lava domes,calderas andcinder cones forms a broad,intermontane plateau at the eastern edge of theTahltan Highland, a southeast-trendingupland area extending along the western side of theStikine Plateau.[14][15]
Mount Edziza is in theSouthern Boreal Plateau Ecosection which consists of several upland summits, wide river valleys and deeply incised plateaus.[16] It is one of seven ecosections comprising theBoreal Mountains and Plateaus Ecoregion, a largeecological region of northwesternBritish Columbia encompassing high plateaus and rugged mountains with interveninglowlands.[17]Boreal forests ofblack andwhitespruce occur in the lowlands and valley bottoms of this ecoregion whereasbirch, spruce andwillow form forests on the mid-slopes. Extensivealpinealtai fescue covers the upper slopes, but barren rock is abundant at higher elevations.[18]
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 30 degrees Celsius (86 degrees Fahrenheit) range. However, temperatures can drop below freezing during summer nights, making snow or freezing rain a possibility at any time of the year.[4] The closestweather stations to Mount Edziza are located atTelegraph Creek andDease Lake, which lie about 40 km (25 mi) to the northwest and 85 km (53 mi) to the northeast, respectively.[19]
Mount Edziza is covered with snow year-round, containing a 15 km (9.3 mi) long and 9 km (5.6 mi) wideice cap which covers an area of 70 km2 (27 sq mi).[4][20][21] Several smalloutlet glaciers extending down to elevations of 1,700 to 2,000 m (5,600 to 6,600 ft) 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 discontinuousicefalls.[20][21] The Mount Edziza glacier complex is the only one worthy of note on the Stikine Plateau.[22]
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 thehead ofTennaya Creek.[5] At the head ofTenchen Creek isTenchen Glacier, a debris-covered glacier on the eastern side of the ice cap.[5][23]Tencho Glacier at the southern end of the ice cap is the largest outlet glacier.[5][24] At the head of Tennaya Creek on the eastern side of the ice cap isTennaya Glacier.[5][25]
As a part of the Mount Edziza volcanic complex, Mount Edziza was covered by aregional ice sheet during thePleistocene which receded and advanced periodically until about 11,000 years ago whendeglaciation was essentially complete in a steadily warming climate.[26][27] 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 theneoglaciation. 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 theirtrim lines which are up to 2 km (1.2 mi) apart.[28]
Mount Edziza has an elevation of 2,786 m (9,140 ft), making it the highest point of the Mount Edziza volcanic complex.[1][14] It has been considered by some to be the highest or tallest volcano in Canada, but others have given higher elevations of 2,860 and 3,160 m (9,380 and 10,370 ft) for theSilverthrone volcanic complex in southwestern British Columbia.[29][30][31][32] The nearly flat summit of Mount Edziza contains a circularridge that surrounds an ice-filled, 2 km (1.2 mi) in diametercrater.[33][34] This ridge is partially exposed above the ice cap as a discontinuous series of spires and serratednunataks. Spires forming the southern end of the ridge are the highest and consist of greenish grey, sparselyporphyritic[a]trachyte. They comprise well-formed, small diameter rock columns that rise nearly vertically more than 90 m (300 ft) above the ice cap. Nunataks elsewhere on the summit ridge are more subdued, consisting ofpyroclastic debris that has been glacially reworked.[36] The eastern side of the ridge has been breached by activecirques where remnants of severallava lakes are exposed inside the crater.[37] 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 theKakiddi Formation lava flows or the effusion of voluminous lava during dome construction. Prior to its formation, the summit of the mountain was at least 610 m (2,000 ft) higher than it is today, having possibly risen as a narrower summit cone truncated with a smaller crater.[38]
The central, 2,786 m (9,140 ft) high edifice of Mount Edziza is a nearly symmetrical stratovolcano, its symmetry having been broken by several steep-sided lava domes.[1][36] Its eastern flank has been eroded by a narrow cirque which is bounded by near-verticalheadwalls that breach the eastern summit crater rim.[39] A system of radial meltwaterchannels has moderately eroded the upper flanks and summit crater rim elsewhere.[39] Lesser modification by erosion has taken place on the southern and northwestern flanks of the stratovolcano.[36] Along the north side of Tenchen Valley on the eastern flank of the stratovolcano are 850 m (2,790 ft) high cliffs exposing explosionbreccias, trachyte lavas andlandslide orlahar deposits.[40] 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 areIdiji Ridge andSorcery Ridge which are the namesakes of Idiji Glacier andSorcery Creek.[8]
About 3 km (1.9 mi) south of the summit isIce Peak, the south peak of Mount Edziza.[8][41] This prominentpyramid-shaped horn has an elevation of 2,500 m (8,200 ft) and is theglacially eroded remains of an older stratovolcano whose northern flank is buried under the younger edifice of Mount Edziza.[33][41][42] 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.[39] 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.[33][43]
High on the eastern rim of Ice Peak are two glaciatedvolcanic cones calledIcefall Cone andRidge Cone, both with elevations of about 2,285 m (7,497 ft).[44] Punch Cone on the western flank of Ice Peak protrudes through Mount Edziza's ice cap whereasKoosick Bluff andOrnostay Bluff, also on the western flank of Ice Peak, extend westward onto the surrounding Big Raven Plateau.[8][45] The northeastern side of Mount Edziza containsThe Pyramid, a pyramid-shaped lava dome 2,199 m (7,215 ft) in elevation.[46][47]Pillow Ridge on the northern side of Mount Edziza has an elevation of 2,400 m (7,900 ft) whereasTsekone Ridge northwest of Mount Edziza has an elevation of 1,920 m (6,300 ft).[5][47][48] High on the western side of Mount Edziza isTriangle Dome, an elliptical lava dome 2,680 m (8,790 ft) in elevation.Glacier Dome reaches an elevation of 2,225 m (7,300 ft) on Mount Edziza's lower northeastern flank.[47][49]
A circular lava dome on the southeastern crater rim of Mount Edziza calledNanook Dome has an elevation of 2,710 m (8,890 ft).[50][47]Sphinx Dome, 2,380 m (7,810 ft) in elevation, is a partially buried lava dome on the northeastern flank of Mount Edziza.[47][51] Remnants of a volcanic pile calledPharaoh Dome occur along the eastern flank of Mount Edziza.[52] They lie at an elevation of 2,200 m (7,200 ft) between Tennaya Creek and Cartoona Ridge.[47][52]Cinder Cliff is a 210 m (690 ft) high barrier ofvolcanic rocks on the eastern side of Mount Edziza at an elevation of 1,800 m (5,900 ft) in the north fork of Tenchen Creek.[47][53]The Neck, 1,830 m (6,000 ft) in elevation, is a circularvolcanic plug on the southeastern flank of Ice Peak.[47][54]
TheSnowshoe Lava Field on the west flank of lce Peak contains at least 12 volcanic cones, a handful of which are named.[55]Tennena Cone is a symmetrical volcanic cone high on the west side of Ice Peak.[56][57] It has an elevation of 2,350 m (7,710 ft) and is almost completely surrounded by ice.[47][57]Cocoa Crater is the largest cone in the Snowshoe Lava Field and is 2,117 m (6,946 ft) in elevation.[47][58] To the southeast isCoffee Crater which has an elevation of 2,000 m (6,600 ft).[47][59]Keda Cone, 1,980 m (6,500 ft) in elevation, lies just south of Coffee Crater on the south side of upperTaweh Creek.[47][60] Asaucer-shaped mound of lava calledThe Saucer is 1,920 m (6,300 ft) in elevation and has a diameter of about 0.5 km2 (0.19 sq mi).[47][61]
TheDesolation Lava Field contains at least 10 cinder cones, most of which are clustered near the northerntrim line of Mount Edziza's ice cap.[62]Sleet Cone andStorm Cone are rounded, mostly soil-covered, conical mounds that reach elevations of 1,783 m (5,850 ft) and 2,135 m (7,005 ft), respectively.[63] North of Storm Cone are theTriplex Cones, a group of three eroded circular mounds reaching an elevation of 1,785 m (5,856 ft).Twin Cone, 1,430 m (4,690 ft) in elevation, is apyroclastic cone whose southeastern side has been breached.[47][64]Moraine Cone has an elevation of nearly 2,135 m (7,005 ft) and has been nearly destroyed by alpine glaciation.[65] The northeastern side of Mount Edziza containsWilliams Cone, a prominent cinder cone 2,100 m (6,900 ft) in elevation.[47][66]Eve Cone, 1,740 m (5,710 ft) in elevation, is a symmetrical cone betweenBuckley Lake and Mount Edziza.[47][67][68][68] The northernmost cinder cone in the Desolation Lava Field isSidas Cone which consists of two symmetrical halves and reaches an elevation of 1,540 m (5,050 ft).[47][55][69]
Mount Edziza is drained on all sides by streams within theStikine River watershed.[5][39]Elwyn Creek is a westward-flowing stream originating from the northwestern flank of Mount Edziza.[5][70] It contains one namedtributary,Kadeya Creek, which flows northwest from Mount Edziza.[5][71]Sezill Creek is a westward-flowing stream originating from the western flank of Mount Edziza.[5][72] It is a tributary of Taweh Creek which flows northwest from just south of Mount Edziza.[5][73] Elwyn Creek and Taweh Creek are tributaries ofMess Creek which flows northwestward into the Stikine River.[5][74]
Tsecha Creek is a northeast-flowing stream originating from the northern flank of Mount Edziza.[5]Nido Creek flows northeastward from the eastern side of Mount Edziza intoNuttlude Lake.[5][75] Flowing from the eastern flank of Mount Edziza just southeast of The Pyramid is Tenchen Creek.[5]Shaman Creek flows east and north intoKakiddi Lake from the southern flank of Mount Edziza.[5][76] Tennaya Creek flows northeastward from the eastern side of Mount Edziza into Nuttlude Lake.[5][77] All five streams are tributaries ofKakiddi Creek, a north-flowing tributary of theKlastline River which flows north into the Stikine River.[5][78]
Mount Edziza is part of theNorthern Cordilleran Volcanic Province, a broad area of shield volcanoes, lava domes, cinder cones and stratovolcanoes extending from northwestern British Columbia northwards throughYukon into easternmostAlaska.[79] The dominant rocks comprising these volcanoes arealkali basalts andhawaiites, butnephelinite,basanite andperalkaline[b]phonolite, trachyte andcomendite are locally abundant. These rocks were deposited by volcanic eruptions from 20 million years ago to as recently as a few hundred years ago. The cause ofvolcanic activity in the Northern Cordilleran Volcanic Province is thought to be due torifting of theNorth American Cordillera driven by changes in relativeplate motion between theNorth American andPacific plates.[81]
A wide variety of volcanic rocks comprise Mount Edziza, the mainmafic[c] rock beingbasalt which comprises lava flows, cinder cones and ashbeds on the flanks of the mountain.[1][83] Basalt at Mount Edziza is in the form of alkali basalt and hawaiite; the latter is thought to be the product of partialfractional crystallization[d] in subterraneanmagma chambers.[85][86] Volcanic rocks ofintermediate composition such astrachybasalt,tristanite,mugearite andbenmoreite are restricted to Ice Peak where they form the upper part of this subsidiary peak.[87] Ice Peak is the only location where mugearites and benmoreites are found in the Mount Edziza volcanic complex.[7]Felsic[e] volcanic rocks such as trachyte andrhyolite form the central stratovolcano of Mount Edziza, the upper part of Ice Peak and several lava domes and flows, as well as pyroclastic rocks.[88]
Mount Edziza is subdivided into at least sixgeological formations, each the product of a distinct stage of volcanic activity.[8][89] These periods of volcanic activity occurred during four magmatic cycles of the Mount Edziza volcanic complex; each cycle began with the effusion of alkali basalt and culminated with the eruption of lesser volumes of felsic magma.[90] The oldest geological formation comprising Mount Edziza is thePyramid Formation, which formed during a period of volcanic activity 1.1 million years ago at the end of thesecond magmatic cycle.[8][7] Another period of volcanic activity about 1 million years ago during the start of thethird magmatic cycle deposited the Ice Peak Formation on the southern part of the Pyramid Formation.[91] The third and fourth oldest geological formations comprising Mount Edziza are the Pillow Ridge andEdziza formations, which were deposited by volcanic eruptions 0.9 million years ago during the later stages of the third magmatic cycle; they both overlie the Ice Peak Formation.[8][92] A period of volcanic activity at the end of thefourth magmatic cycle 0.3 million years ago deposited the Kakiddi Formation, the fifth oldest geological formation comprising Mount Edziza which also overlies the Ice Peak Formation.[8][93] The youngest geological formation is theBig Raven Formation, which was formed by a period of volcanic activity during thefifth magmatic cycle in the last 20,000 years.[8][94]
The Pyramid Formation is exposed along the deeply eroded eastern flank of Mount Edziza where rhyolite and trachyte flows, domes and pyroclastic rocks of this formation comprise ridges and prominent cliffs. A basaltic lava flow sequence up to 65 m (213 ft) thick overlies the basal trachyticsurge deposit of the Pyramid Formation; it is included as a part of this formation due to it being coeval with the early stages of Pyramid felsic volcanism.[95]Potassium–argon dating of the Pyramid Formation has yielded ages of 1.2 ± 0.4 million years and 1.2 ± 0.03 million years from comenditicglass, as well as 0.94 ± 0.12 million years and 0.94 ± 0.05 million years from trachyte.[96]
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.[95] The Pyramid is a prominent trachyte dome whose structure has not been greatly modified by erosion, nor has it been buried under younger lavas.[97] 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.[51] 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.[98]
The Ice Peak Formation consists of lava and pyroclastic rocks that originated mainly from Ice Peak about 5 km (3.1 mi) south of the summit of Mount Edziza.[99] Twostratigraphic units comprise this once symmetrical stratovolcano, both of which arelithologically distinct.[100] The lower stratigraphic unit, which forms much of the volcanic pile, is an assemblage of mostly thin basalt flows. Lavas of intermediate composition such as tristanite, trachybasalt and mugearite are very limited in extent.[101] The upper stratigraphic unit is a highly varied succession of lavas and pyroclastic rocks forming the high, central edifice of Ice Peak.[99] It consists of basalt, trachyte and a variety of intermediate rocks such as tristanite, trachybasalt, benmoreite and mugearite.[9]
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 ingeomorphology and composition, consisting of several lava flows up to 75 m (246 ft) thick.[102][103] The Neck, which forms a prominent 215 m (705 ft) highbuttress on Sorcery Ridge, is also part of the Ice Peak Formation. Potassium–argon dating ofpantelleritic 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.[54] These dates being older than those of the Pyramid Formation may be due to excessargon in the Ice Peak Formation and are therefore considered unreliable.[104][105]
Ice Peak Formation basalt flows on the northwestern flank of Mount Edziza areinterbedded withdiamictites recording a regional glaciation that occurred during theEarly Pleistocene.[106] The lowermost basalt flow contains basalpillows, directly overlieshyaloclastites and is brecciated and deformed, suggesting it may have been extruded onto a glacier or anice sheet.[43][106] Its extrusion onto glacial ice is also evident due to the lack offluvial andlacustrine sediments at the base of the basalt flow which suggests it did not extrude into lakes or streams.[106] 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.[107]
The Pillow Ridge Formation is restricted to Pillow Ridge and Tsekone Ridge on Mount Edziza's northwestern flank, both of which areglaciovolcanic in origin.[48][108] Pillow Ridge is a nearly 4 km (2.5 mi) long, northwesterly-trending ridge of basaltic pillow lava, pillow breccia,tuff breccia anddikes.[48] Its upper surface is sparsely covered by trachyte of the Edziza Formation whereas the western edge of the ridge overlaps with a large flow of Edziza trachyte.[109] Tsekone Ridge is an isolated volcanic pile adjacent to Pillow Ridge consisting of basaltic pillow lava and tuff breccia that has been cut by vertical north-trendingfeeder dikes.[110] This ridge is elliptical in structure, containing a nearly 2 km (1.2 mi) long, north–south trending axis.[48] Nearly surrounding Tsekone Ridge are trachyte flows of the Edziza Formation which is slightly younger than the Pillow Ridge Formation.[111]
Fission track dating ofapatite from partially fusedgraniticxenoliths[f] in contaminated Pillow Ridge Formation basalt has yielded ages of 0.9 ± 0.3 million years and 0.8 ± 0.25 million years.[113] 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 andgneissic xenoliths in Pillow Ridge Formation basalt.[114]
The Edziza Formation consists mainly of trachyte that straddles the pantelleritic trachyte and comenditic trachyte boundary.[115] It includes the central stratovolcano of Mount Edziza, as well as several satellitic features on its summit and flanks.[116] Inside the summit crater of the stratovolcano is a succession of at least four lava lakes exposed in the breached eastern crater rim.[37][117] They are represented by at least four cooling units, the lower two of which are about 30 m (98 ft) thick.[117] The two upper cooling units reach thicknesses of about 90 m (300 ft) and may have originated from Nanook Dome, the largest of three lava domes consisting of Edziza Formation trachyte.[118] Nanook Dome is about 750 m (2,460 ft) in diameter whose structure appears to be nearly identical to its original form.[119] The other two Edziza Formation trachyte domes, Glacier Dome and Triangle Dome, are elliptical in structure and contain concentric flow layering.[49] Potassium–argon dating of pantelleritic trachyte or comenditic trachyte from the Edziza Formation has yielded an age of 0.9 ± 0.3 million years.[115][120]
The Kakiddi Formation consists of the remains of thick trachyte flows and associated pyroclastic rocks. They are lithologically and geomorphologically similar to Edziza Formation trachytes, but occur south of the central stratovolcano of Mount Edziza. The remains of a nearly 1 km (0.62 mi) wide, rubble-covered trachyte flow are present on the eastern flank of Ice Peak in Sorcery Valley and in the south fork of Tennaya Valley where it is divided into two tributary branches. In Kakiddi Valley, the lava flow appears to have spread out to form a once continuous, terminal lobe at least 5 km (3.1 mi) wide. Remnants of this terminal lobe are present in the form of isolatedoutcrops adjacent to Kakiddi Lake and Nuttlude Lake.[121] The source of this Kakiddi flow remains unknown, but the tributary branch that descended Tennaya Valley probably originated from a vent near the summit of Ice Peak that is now covered by glaciers.[122] Another plausible source is Nanook Dome on the southeastern crater rim of Mount Edziza.[123] A relatively small trachyte flow descended from Punch Cone on the western flank of Ice Peak and spread onto the Big Raven Plateau.[124] Potassium–argon dating of the Kakiddi Formation has yielded ages of 0.31 ± 0.07 million years from mugearite, as well as 0.30 ± 0.02 million years, 0.29 ± 0.02 million years and 0.28 ± 0.02 million years from trachyte.[125]
The Big Raven Formation includes the Desolation Lava Field, the Snowshoe Lava Field, Icefall Cone, Ridge Cone, Cinder Cliff and theSheep Track Member.[126] All of these features consist of alkali basalt and hawaiite with the exception of the Sheep Track Member which comprises a small volume of trachyte pumice.[85] Some of the lava flows comprising the Desolation Lava Field issued from vents adjacent to the northern trim line of the summit ice cap where meltwater interacted with the erupting lava to formtuff rings. These tuff rings, composed of quenched breccia, later transitioned into normalsubaerial cinder cones as the progressing eruptions displaced ice and meltwater.[56] The Snowshoe Lava Field containssubglacial and subaerial cones, as well as transitional cones which consist of bothsubaqueous and subaerialejecta.[127]
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.[128] The Sheep Track Member is the product of anexplosive eruption that originated from the southwestern flank of Ice Peak.[129] 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.[130]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.[131]
Underlying the aforementioned geological formations is the Tenchen Member of theNido Formation, one of many stratigraphic units forming the Big Raven Plateau. Basalt flows and pyroclastic rocks of thisPliocenegeological member are exposed north ofRaspberry Pass on the eastern and western flanks of Mount Edziza.[8][132] Much of the Tenchen Member as well as the southern edge of the Ice Peak volcanic pile are underlain by theArmadillo Formation which consists ofMiocene comendite, trachyte and alkali basalt.[8][91] Most of Mount Edziza is also underlain by Miocene basalt flows of theRaspberry Formation which form the base of prominentescarpments east and west of the mountain.[8][133] These geological formations are underlain by theStikiniaterrane, aPaleozoic andMesozoicsuite of volcanic andsedimentary rocks thataccreted to thecontinental margin of North America during theJurassic.[134][135]
ANatural Resources Canada report published in 2021 considers Mount Edziza a high threat volcano because it has had the highest eruption rate in Canada throughout the Holocene. However, its extremely remote location makes it lesshazardous thanMount Garibaldi,Mount Price,Mount Cayley andMount Meager in southwestern British Columbia.[136] The hazard rating of Mount Edziza is similar to that ofMount Churchill in the U.S. state of Alaska which deposited theWhite River Ash across northwestern Canada in the last 2,000 years.[137][138] Lava flows are a potential hazard at Mount Edziza as they have formerlydammed local streams.[139] Another potential hazard is the ignition of wildfires by eruptions since the surrounding area contains vegetation.[4][139] An eruption under the ice cap could produce floods or lahars that may flow into the Stikine orIskut rivers, potentially destroyingsalmon runs and threateningriver bank villages.[140][141]
Mount Edziza trachyte and rhyolite havesilica-rich compositions that are comparable to those associated with the most powerful eruptions around the world; parts of northwestern Canada could be affected by anash column if an explosive eruption were to happen from the volcano.[139] 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.[142] Mount Edziza lies under a majorair route fromVancouver, British Columbia toWhitehorse, Yukon, suggesting the volcano poses a potential threat to air traffic.[140] Volcanic ash reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems.[143]
Like other volcanoes in Canada, Mount Edziza is notmonitored closely enough by the Geological Survey of Canada to ascertain its activity level. TheCanadian National Seismograph Network has been established tomonitor 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.[144] If Mount Edziza were to erupt, mechanisms exist to orchestrate relief efforts. TheInteragency 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 theCanada–United States border or any eruption that would affect Canada.[145]
Mount Edziza lies within the traditional territory of the Tahltan people which covers an area of more than 93,500 km2 (36,100 sq mi).[146] Historically, Mount Edziza and other volcanoes of the Mount Edziza volcanic complex were sources ofobsidian for the Tahltan people.[147] This volcanic glass was used in the manufacturing of projectile points and cutting blades which were widely traded throughout thePacific Northwest.[4] Artifacts made ofEdziza obsidian have been recovered fromarchaeological sites over an area of more than 2,200,000 km2 (850,000 sq mi) across Alaska,Alberta, Yukon and theBritish Columbia Coast, making it the most widely distributed obsidian in western North America. TheHidden Falls archaeological site in Alaska has yielded ahydration date of 10,000 years for Edziza obsidian, suggesting the area was being exploited as an obsidian source soon after ice sheets of theLast Glacial Period retreated.[148]
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 fivearchaeological sites outside of Tahltan territory. The Ice Peak Formation contains two obsidian flows on Sorcery Ridge that were also exploited as an obsidian source.[149] Sorcery Ridge obsidian occurs in at least two archaeological sites outside of Tahltan territory.[150]
In or before 1974, two Tahltan men named Johnny Edzerza and Hank Williams were killed in anavalanche while they were crossing the mountain. Edzerza was buried on Mount Edziza, but his surname was erroneously spelled "Edzertza" on his grave marker.[2] 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.[66][68]
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."[151]
Just southeast of Mount Edziza was an area once known as the Spectrum property, a block ofmineral claims that coveredquartz,pyrite andchalcopyritemineralization in fractured sedimentary and volcanic rocks ofLate Triassic age.[152][153] Commodities on the property includedcopper,gold,lead,silver andzinc.[153]Mineral exploration on the Spectrum property began as early as 1957 when Torbit Silver Mines performed surface work on the gold-bearing Hawkvein. This was followed by drilling of the Hawk vein by Shawnigan Mining and Smelting in 1967. Exploration by Mitsui Mining and Smelting in 1970 involvedgeophysical and geochemical surveying. From 1971 to 1973,Imperial Oil conducted geophysical,geological and geochemical surveying, as well as 463 m (1,519 ft) of drilling in four holes.[152]
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 anairstrip and carried out 3,232 m (10,604 ft) of drilling in 28 holes during this time. Newhawk Mines constructed an access road and 313 m (1,027 ft) ofunderground 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 7,066 m (23,182 ft) of drilling in 50 holes.[152]
Mount Edziza and the surrounding area was designated as aprovincial park in 1972 to showcase the volcanic landscape; a 101,171 hectares (250,000 acres)recreation area surrounding the 132,000 ha (330,000 acres) park was also established in 1972.[4][154][155] In 1989, Mount Edziza Provincial Park roughly doubled in size when 96,770 ha (239,100 acres) was annexed from theMount Edziza Recreation Area.[155] With this annexation, the recreation area was greatly reduced in size to around 4,000 ha (9,900 acres).[154] This remnant of the recreation area was east of Mount Edziza until 2003 when it was disestablished.[5][154] Mount Edziza Provincial Park now covers an area of 266,180 ha (657,700 acres), making it one of the largestprovincial parks in British Columbia.[156]
In 2021, an approximately 3,528 ha (8,720-acre)conservation area called theMount Edziza Conservancy was established east of Mount Edziza along the eastern border of Mount Edziza Provincial Park.[157] It was established in collaboration with Skeena Resources,BC Parks, the Tahltan Central Government and theNature Conservancy of Canada after Skeena Resources returned their mineral tenures on the Spectrum property.[158] The name of this conservation area was changed to the Tenh Dẕetle Conservancy in 2022 to better reflect the culture, history and tradition of theTahltan First Nation.[3][157]
Mount Edziza lies in a remote location that is accessible only during summer and early autumn.[159] There is no established road access to the mountain, although theStewart–Cassiar Highway to the east and the Telegraph Creek Road to the northwest both extend within 40 km (25 mi) of Mount Edziza.[160][161] Extending from these roads arehorse trails that provide access to the mountain.[162] From Telegraph Creek, the Buckley Lake Trail extends about 15 km (9.3 mi) southeast along Mess Creek and Three Mile Lake. It then traverses about 15 km (9.3 mi) northeast along Dagaichess Creek and Stinking Lake to the northeastern end of Buckley Lake where it meets with the Klastline River Trail and the Buckley Lake to Mowdade Lake Route.[30]
To the east, the roughly 50 km (31 mi) long Klastline River Trail begins at the community ofIskut on the Stewart–Cassiar Highway.[163] It extends northwest and west along the Klastline River for much of its length.[160] The trail enters Mount Edziza Provincial Park at about 25 km (16 mi) where Kakiddi Creek drains into the Klastline River.[163] After entering Mount Edziza Provincial Park, the Klastline River Trail traverses northwest along the Klastline River for about 10 km (6.2 mi) and then crosses the river north of Mount Edziza.[160] From there, the Klastline River Trail traverses west for about 5 km (3.1 mi) to the northeastern end of Buckley Lake where it meets with the Buckley Lake Trail and the Buckley Lake to Mowdade Lake Route.[30]
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.[5][30][164] Most of the Buckley Lake to Mowdade Lake Route is marked by a series of rockcairns from Tsekone Ridge onwards. The distance between Buckley Lake and Mowdade Lake is about 70 km (43 mi), 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.[164]
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.[159][162] Kakiddi Lake, Nuttlude Lake, Mowdade Lake, Mowchilla Lake and Buckley Lake are large enough to be used by float-equipped aircraft.[4][162] Landing on the latter two lakes with a private aircraft requires a letter of authorization from the BC Parks Stikine Senior Park Ranger.[4]
