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54-548: The Spectrum Range is the eroded remains of a large lava dome whose original surface is only preserved as a few small remnants on the summits of the higher peaks. This dome formed between 3.5 and 2.5 million years ago during the second magmatic cycle of the Mount Edziza volcanic complex and was originally more than 25 kilometres (16 miles) wide. Much of the dome consists of massive rhyolite and trachyte lava flows but relatively minor basalt lava flows erupted later during

108-479: A caldera or an irregular collapse structure. It occurs within a roughly circular area about 10 kilometres (6.2 miles) in diameter and likely formed by collapse of a shallow magma chamber during eruption of the Spectrum Formation lavas. At least 1 kilometre (0.62 miles) of vertical caldera collapse may have resulted if the magma chamber was similar in diameter to this circular area, but poor exposure of

162-554: A geological formation of the Mount Edziza volcanic complex. The base of Kounugu Mountain consists of basaltic lava flows of the Kounugu Member which erupted from multiple volcanoes during the Pliocene epoch. These lava flows are overlain directly by rhyolite of the Spectrum Formation which comprises the bulk of Kounugu Mountain. The Spectrum Formation is the eroded remains of a large Pliocene lava dome that forms

216-553: A basaltic lava flow but it was later buried under debris from the landsliding. Although volcanic activity at the Spectrum Range continued into the current Holocene epoch , the last eruption is unknown. Alteration of Spectrum Formation rocks caused by fumarolic activity during the formation of the Spectrum Dome occurs at Yeda Peak and elsewhere throughout the Spectrum Range. Fumarolic alteration at Yeda Peak occurs in

270-429: A broad area of volcanoes and lava flows extending from northwestern British Columbia northwards through Yukon into easternmost Alaska . The dominant rocks comprising these volcanoes are alkali basalts and hawaiites , but nephelinite , basanite and peralkaline phonolite , trachyte and comendite are locally abundant. These rocks were deposited by volcanic eruptions from 20 million years ago to as recently as

324-453: A cryptodome was in the May 1980 eruption of Mount St. Helens , where the explosive eruption began after a landslide caused the side of the volcano to collapse, leading to explosive decompression of the subterranean cryptodome. A lava spine or lava spire is a growth that can form on the top of a lava dome. A lava spine can increase the instability of the underlying lava dome. A recent example of

378-406: A deeper, hotter and longer lived hydrothermal system than elsewhere in the Spectrum Range, the lava flow fumaroles were small and relatively short-lived. The multi-coloured rocks which give the Spectrum Range its name are partially the result of fumarolic alteration. At the head of Ball Creek valley is a subvolcanic mass of granite with abnormally high soda content that probably intruded into

432-704: A few hundred years ago. The cause of volcanic activity in the Northern Cordilleran Volcanic Province is thought to be due to rifting of the North American Cordillera driven by changes in relative plate motion between the North American and Pacific plates. Underlying nearly all of the Spectrum Range is the Kounugu Member of the Nido Formation , one of many stratigraphic units comprising

486-703: A flow front 400 metres (1,300 ft) tall (the dark scalloped line at lower left). There is another prominent coulée flow on the flank of Llullaillaco volcano, in Argentina , and other examples in the Andes . Kounugu Mountain Kounugu Mountain is a mountain in the Spectrum Range at the southern end of the Mount Edziza volcanic complex in northwestern British Columbia , Canada. It

540-617: A lava spine is the spine formed in 1997 at the Soufrière Hills Volcano on Montserrat. Coulées (or coulees) are lava domes that have experienced some flow away from their original position, thus resembling both lava domes and lava flows . The world's largest known dacite flow is the Chao dacite dome complex , a huge coulée flow-dome between two volcanoes in northern Chile . This flow is over 14 kilometres (8.7 mi) long, has obvious flow features like pressure ridges, and

594-467: A part of the Mount Edziza volcanic complex, the Spectrum Range is drained on all sides by streams within the Stikine River watershed . Kitsu Creek is a northwest-flowing stream originating from the northern side of Kitsu Peak. It contains one named tributary, Nagha Creek , which also flows northwest from the Spectrum Range. Tadekho Creek originates from between Kuno and Yeda peaks and flows to

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648-452: A rough indicator of magma supply , but it shows no systematic relationship to the timing or characteristics of lava dome explosions. Gravitational collapse of a lava dome can produce a block and ash flow . A cryptodome (from the Greek κρυπτός , kryptos , "hidden, secret") is a dome-shaped structure created by accumulation of viscous magma at a shallow depth. One example of

702-659: A valley between Artifact and Obsidian ridges. Ball and More creeks both flow south from the southern end of the Spectrum Range near Yeda Peak, the former of which contains an east-flowing tributary called Chachani Creek. The Little Iskut River and Ball and More creeks are tributaries of the Iskut River which flows south and then west into the Stikine River. The Spectrum Range is part of the Northern Cordilleran Volcanic Province ,

756-429: 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. The Spectrum Range can be accessed by float plane or helicopter, both of which are available for charter at

810-532: Is locally covered with iron and manganese oxides . The Spectrum Range lies at the southern end of Mount Edziza Provincial Park , a protected area founded in 1972 to showcase the volcanic landscape. This remote wilderness area of northwestern British Columbia is not accessible by motorized vehicles to help protect the very sensitive environment. Instead, access is mainly via aircraft or unmaintained hiking trails that cross creeks. Mount Edziza Provincial Park covers 266,180 hectares (657,700 acres), making it one of

864-475: Is southeast of Yeda Peak , west and northwest of the Little Iskut River , south of Stewbomb Creek valley and just north of Little Ball Lake . It has an elevation of 2,267 metres (7,438 feet) and lies at the southeastern end of the Spectrum Range. The mountain is also at the southeastern end of Mount Edziza Provincial Park which is southeast of the community of Telegraph Creek . The name of

918-528: The Mount Edziza volcanic complex which includes the adjacent Arctic Lake and Kitsu plateaus, as well as Mount Edziza and the Big Raven Plateau to the north. This volcanic complex consists of a group of overlapping shield volcanoes , stratovolcanoes , lava domes and cinder cones that have formed over the last 7.5 million years. It contains an intermontane plateau that is overlain by four central volcanoes along its north–south trending axis;

972-543: The Raspberry Formation , the oldest unit of the Mount Edziza volcanic complex. This geological formation is of late Miocene age and originated as a composite shield volcano that erupted lava from at least three locations near Raspberry Pass. The Nido and Raspberry formations are underlain by the Stikinia terrane , a Paleozoic and Mesozoic suite of volcanic and sedimentary rocks that accreted to

1026-461: The continental margin of North America during the Jurassic . The Spectrum Range consists mainly of trachyte, comendite and pantelleritic trachyte and rhyolite of the Spectrum Formation, the fifth oldest stratigraphic unit of the Mount Edziza volcanic complex. More than 90% of these volcanic rocks were erupted as lava while less than 10% of them were erupted as pumice and pyroclastic flows ;

1080-598: The Arctic Lake Formation which formed during a period of volcanic activity 0.71 million years ago. Volcanism during the Holocene created subaerial cinder cones and lava flows on the northwestern and southwestern sides of the Spectrum Range, all of which are part of the Big Raven Formation . The basaltic Mess Lake Lava Field on the northwestern flank issued from three cinder cones adjacent to

1134-545: The Kitsu Member which likely issued from multiple eruptive centres on the dome's summit that have since been removed by erosion. These lava flows travelled over a layer of polymict gravel that overlies older volcanic rocks of the Spectrum Formation. Following construction of the Spectrum Dome, lesser activity continued into the Quaternary from parasitic vents in and adjacent to the Spectrum Range. Volcanism during

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1188-447: The Mount Edziza volcanic complex. Basaltic lava flows of this Pliocene geological member are exposed around the perimeter of the Spectrum Range and are limited only to the area south of the broad east–west valley of Raspberry Pass . They issued from at least four separate eruptive centres that have been either deeply eroded or have been completely destroyed by erosion. Also underlying the Spectrum Range are flat-lying basalt flows of

1242-451: The Mount Edziza volcanic complex. A relatively small initial eruption of pumice and ash was followed by the effusion of massive rhyolite flows that reached 13 kilometres (8.1 miles) long. These rhyolite flows accumulated in rapid succession to form the broad Spectrum Dome which reached a thickness of at least 750 metres (2,460 feet) and a width of more than 25 kilometres (16 miles). The predominantly rhyolitic eruptions were later replaced by

1296-596: The Pleistocene created a number of small volcanoes on the southwestern flank of the mountain range that formed in subaerial and subglacial environments. Subaerial lava fountaining at the extreme northern end of the Arctic Lake Plateau created the Outcast Hill cinder cone which blocked westerly flowing streams to create a temporary lake against its eastern side. About 4 kilometres (2.5 miles) to

1350-560: The Spectrum Dome is estimated to have been 101 cubic kilometres (24 cubic miles) based on restoration calculations of the original surface. As a part of the Mount Edziza volcanic complex, the Spectrum Range 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

1404-577: The Spectrum Range 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 which 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 2 kilometres (1.2 miles) apart. Unlike Mount Edziza which has an approximately 70-square-kilometre (27-square-mile) ice cap ,

1458-499: The Spectrum Range is covered with relatively small separate glaciers that occupy cirques on most peaks greater than 2,130 metres (6,990 feet) in elevation. The largest glacier is Nagha Glacier which initiates just northwest of Yeda Peak and terminates at the head of the valley between Yagi Ridge and the Kitsu Plateau. Yeda Glacier, an informally named glacier at the head of Ball Creek , existed south of Yeda Peak in 1988. As

1512-439: The Spectrum Range is the southernmost and third oldest central volcano. Extending outward from the central portion of this nearly circular group of pyramidal peaks and long, narrow-creasted ridges is a crudely radial drainage system characterized by deeply incised valleys. Talus and felsenmeer deposits cover large portions of the valley slopes which rise to broad, rounded crests of the interfluvial ridges. These ridges are

1566-415: The Spectrum Range originally had a width of more than 25 kilometres (16 miles) as indicated by the existence of erosional remnants around its northern and southwestern edges. It was also originally higher than its current elevation of 2,430 metres (7,970 feet) as evidenced by the thick, gently dipping lava flows comprising the summit of Kitsu Peak, the highest point of the Spectrum Range. The original volume of

1620-482: The Spectrum Range to the northwest and includes the Mess Lake Lava Field which consists of geologically recent lava flows and tephra from three pyroclastic cones . To the north and northeast, the Spectrum Range is bounded by Raspberry Pass and Artifact Creek valley, respectively, the latter of which separates Artifact Ridge from the mountain range. The Spectrum Range lies at the southern end of

1674-406: The base of the Spectrum Dome during the explosive Yeda Peak breccia pipe eruption. It lies along the edge of the hypothetical caldera or irregular collapse structure and comprises a series of glacially rounded bluffs along the southwestern side of Ball Creek valley. The soda granite forming this subvolcanic intrusion is lustrous brown and medium to coarse-grained, consisting mostly of feldspar that

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1728-467: The breccia pipe comprising this peak and along adjacent fractures; it likely resulted from fumarolic activity after the explosive eruption that formed the Yeda Peak crater. Alteration elsewhere in the Spectrum Range was caused by fumarolic activity during the cooling and degassing of lava flows comprising the Spectrum Formation. In contrast to the fumarolic activity at Yeda Peak which was likely sourced by

1782-441: The communities of Iskut and Dease Lake . Private aircraft are prohibited from landing on the Kitsu Plateau lava flows. Mess Lake northwest of the Spectrum Range, 180 Lake southeast of the Spectrum Range, Arctic Lake and Little Arctic Lake southwest of the Spectrum Range and Little Ball Lake just south of Kounugu Mountain at the southwestern end of the Spectrum Range are large enough to be used by float-equipped aircraft. Landing on

1836-422: The depression and of the bounding vertical faults has given fragmentary evidence. The southwestern side of a northwesterly-trending, nearly vertical fault adjacent to Stewbomb Creek has dropped at least 90 metres (300 feet) and is cut by parallel rhyolite dikes . The rocks comprising the Spectrum Range were deposited by volcanic eruptions between 3.5 and 2.5 million years ago during the second magmatic cycle of

1890-400: The dome's conduit . Domes undergo various processes such as growth, collapse, solidification and erosion . Lava domes grow by endogenic dome growth or exogenic dome growth. The former implies the enlargement of a lava dome due to the influx of magma into the dome interior, and the latter refers to discrete lobes of lava emplaced upon the surface of the dome. It is the high viscosity of

1944-404: The dome's formation. These lava flows form the nearly circular group of pyramidal peaks and long, narrow-crested ridges comprising the Spectrum Range; the basalt flows mainly cap the higher peaks. Volcanism in the last 2.5 million years has mainly occurred on the northwestern and southwestern sides of the Spectrum Range but the precise age of the latest eruption is unknown. The Spectrum Range

1998-548: The edge of the Mess Creek Escarpment. Lava from the two oldest cones flowed to the west and probably cascaded over the escarpment into Mess Creek valley. The youngest cinder cone, The Ash Pit , formed at the south end of the Mess Lake Lava Field and was the source of a northeasterly-trending tephra deposit on the Kitsu Plateau. An eruption near the northern edge of the Arctic Lake Plateau created

2052-434: The effusion of trachyte lava as deeper parts of the underlying magma chamber were tapped. Formation of the Spectrum Dome was followed by evacuation of the magma chamber, resulting in the creation of the caldera which was eventually buried by lava from subsequent eruptions. Yeda Peak, a 2,240-metre-high (7,350-foot) pinnacle in the middle of the Spectrum Range, was the site of a subsequent explosive eruption that resulted in

2106-447: The eroded remains of a once continuous lava dome whose original surface is only preserved as a few small remnants on the summits of the higher peaks. The ridges and peaks decrease in elevation away from the central portion of the mountain range. Among these peaks and ridges are Kitsu Peak , Yeda Peak , Kuno Peak , Kounugu Mountain , Obsidian Ridge and Yagi Ridge . The current, approximately 19-kilometre-wide (12-mile) dome comprising

2160-489: The formation of a crater . Some of the ejecta accumulated around the vent to form a low volcanic cone while the more volatile, pumice-rich phases of the eruption sent ash flows down the slopes of the Spectrum Dome. Renewed volcanism at Exile Hill 8 kilometres (5.0 miles) to the west on the Arctic Lake Plateau produced a similar but much smaller eruption that created a roughly 200-metre-wide (660-foot) breccia pipe . Late-stage volcanism also deposited alkali basalt flows of

2214-425: The intermittent buildup of gas pressure , erupting domes can often experience episodes of explosive eruption over time. If part of a lava dome collapses and exposes pressurized magma, pyroclastic flows can be produced. Other hazards associated with lava domes are the destruction of property from lava flows , forest fires , and lahars triggered from re-mobilization of loose ash and debris. Lava domes are one of

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2268-420: The isolated Nahta Cone on the southwestern flank of the Spectrum Range which was the source of a narrow, 3-kilometre-long (1.9-mile) basaltic lava flow that travelled northward into the head of Nahta Creek. Volcanic activity on the southern flank of Kuno Peak at the southwestern end of the Spectrum Range created a cinder cone that was subsequently destroyed by landsliding on Kuno Peak. This cinder cone also produced

2322-552: The largest provincial parks in British Columbia. Hunting, camping, fishing, hiking, wildlife viewing and nature studying are some of the activities available in Mount Edziza Provincial Park. Wildlife in the area includes moose , caribou , mountain goats , stone sheep , wolves , bears , squirrels , owls , ptarmigans , ravens , gyrfalcons , grouse and migratory songbirds . The climate

2376-650: The latter two lakes with a private aircraft requires a letter of authorization from the BC Parks Stikine Senior Park Ranger. Lava dome In volcanology , a lava dome is a circular, mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano . Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on Earth form lava domes. The geochemistry of lava domes can vary from basalt (e.g. Semeru , 1946) to rhyolite (e.g. Chaiten , 2010) although

2430-427: The lava is in the form of flows that individually reach thicknesses of up to 200 metres (660 feet). These volcanic rocks are overlain locally by eroded remnants of Kitsu Member basaltic lava flows which preserve the unmodified upper surface of the original Spectrum Dome and cap the higher peaks of the Spectrum Range. In the middle of the Spectrum Range at the base of the volcanic pile is a buried depression that may be

2484-510: The lava that prevents it from flowing far from the vent from which it extrudes, creating a dome-like shape of sticky lava that then cools slowly in-situ. Spines and lava flows are common extrusive products of lava domes. Domes may reach heights of several hundred meters, and can grow slowly and steadily for months (e.g. Unzen volcano), years (e.g. Soufrière Hills volcano), or even centuries (e.g. Mount Merapi volcano). The sides of these structures are composed of unstable rock debris. Due to

2538-464: The majority are of intermediate composition (such as Santiaguito , dacite - andesite , present day) The characteristic dome shape is attributed to high viscosity that prevents the lava from flowing very far. This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma . Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of

2592-592: The mountain became official on January 2, 1980, after being submitted to the BC Geographical Names office by the Geological Survey of Canada . Kounugu was the guardian of fresh water in Tahltan folklore "who slept throughout the day on top of the well that contained his treasure". Kounugu Mountain is the namesake of the Kounugu Member, a geological member of the Nido Formation which is

2646-442: The northwest. Kitsu and Tadekho creeks both flow into Mess Creek which is a northwest-flowing tributary of the Stikine River. The Little Iskut River originates from Little Ball Lake just south of Kounugu Mountain and flows to the northeast where it collects Stewbomb Creek flowing east from the Spectrum Range. Stewbomb Creek contains one named tributary, Artifact Creek, which originates adjacent to Kitsu Peak and flows through

2700-592: The preserved domes have high silica content and consist of rhyolite or dacite . Existence of lava domes has been suggested for some domed structures on the Moon , Venus , and Mars , e.g. the Martian surface in the western part of Arcadia Planitia and within Terra Sirenum . Lava domes evolve unpredictably, due to non-linear dynamics caused by crystallization and outgassing of the highly viscous lava in

2754-567: The principal structural features of many stratovolcanoes worldwide. Lava domes are prone to unusually dangerous explosions since they can contain rhyolitic silica -rich lava. Characteristics of lava dome eruptions include shallow, long-period and hybrid seismicity , which is attributed to excess fluid pressures in the contributing vent chamber. Other characteristics of lava domes include their hemispherical dome shape, cycles of dome growth over long periods, and sudden onsets of violent explosive activity. The average rate of dome growth may be used as

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2808-415: The south, Tadekho Hill formed on top of a 180-metre-high (590-foot) remnant of Spectrum Formation trachyte. Lava from this volcano spread onto the surrounding plateau surface to form a small shield volcano. Subsequent subglacial volcanism near the central portion of the Arctic Lake Plateau formed the subglacial mound of Wetalth Ridge. All three Pleistocene volcanoes are basaltic in composition and are part of

2862-802: The southern end of the Tahltan Highland east of the Boundary Ranges of the Coast Mountains and west of the Skeena Mountains in Cassiar Land District . To the southwest, the Spectrum Range is surrounded by the Arctic Lake Plateau which includes adjacent volcanic features such as Outcast Hill , Wetalth Ridge , Exile Hill , Nahta Cone and Tadekho Hill . The Kitsu Plateau surrounds

2916-629: Was labelled as the Rainbow Mountains on a BC Lands map published in 1929 which was followed by renaming of the mountain range to the Spectrum Mountains in 1945. In 1954, the form of name was changed to the Spectrum Range in accordance to the Geological Survey of Canada memoir 247 published in 1948. These names for the mountain range refer to its multi-coloured rocks; pale green, light grey and white rocks weather to bright hues of orange, yellow and red. The Spectrum Range lies at

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