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Silverthrone Caldera

Coordinates: 51°31′03″N 126°06′47″W / 51.51750°N 126.11306°W / 51.51750; -126.11306
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Silverthrone Caldera
Silverthrone Caldera Complex
Satellite imagery of mountainous terrain with an oval-shaped outline depicting the approximate boundaries of a geological feature
Approximate outline of the Silverthrone Caldera
Highest point
PeakSilverthrone Mountain[1][2]
Elevation2,860 m (9,380 ft)[3]
Coordinates51°31′03″N 126°06′47″W / 51.51750°N 126.11306°W / 51.51750; -126.11306[4]
Dimensions
Width20 km (12 mi)[5]
Geography
Relief map of British Columbia pinpointing the location of the Silverthrone Caldera
Relief map of British Columbia pinpointing the location of the Silverthrone Caldera
Silverthrone Caldera
Location in British Columbia
Map
Interactive map of the Silverthrone area
CountryCanada[3]
ProvinceBritish Columbia[3]
DistrictRange 2 Coast Land District[6]
Parent rangePacific Ranges[7]
Topo map(s)NTS 92M9 Machmell River[4]
NTS 92M8 Catto Creek[6]
Geology
Formed bySubduction zone volcanism[3]
Rock age(s)750,000 years and younger[5]
Volcanic arcCascade Volcanic Arc[8]
Volcanic belt
Last eruptionUnknown[3]
Climbing
AccessHelicopter or trekking on foot[1]

The Silverthrone Caldera is a potentially active volcano in Range 2 Coast Land District of southwestern British Columbia, Canada. It lies within the Pacific Ranges of the Coast Mountains and reaches an elevation of 2,860 metres (9,380 feet), although some sources give the elevation as high as 3,160 m (10,370 ft). The caldera is about 20 kilometres (12 miles) wide and has been deeply eroded, resulting in the formation of rugged topography. Several glacial meltwater streams originating from the caldera flow through valleys in the Pacific Ranges; among these streams are the Pashleth, Selman and Catto creeks and the Kingcome and Wakeman rivers.

Volcanic rocks deposited by eruptions of the Silverthrone Caldera and associated vents include rhyolites, dacites, andesites and basaltic andesites. They are exposed in valleys, but at higher elevations, they are largely buried under glacial ice of the 3,600 km2 (1,400 sq mi) Ha-Iltzuk Icefield. These rocks comprise three units; a 750,000-year-old basal breccia unit, a 400,000-year-old unit of overlying lava flows and domes, and a less than 13,000-year-old series of lava flows and pyroclastic cones. The caldera mainly poses a threat to air traffic from renewed explosive eruptions, but lahars or debris flows could also be produced from the melting of glacial ice.

The Silverthrone Caldera was a source of obsidian for indigenous peoples during the pre-contact era and was studied in the 1970s as a potential source of geothermal energy. Geological studies have been conducted at the volcano since at least the 1960s, but its very remote location has impeded detailed fieldwork. As a result, the eruptive history of the caldera is poorly known and its affinity to the Garibaldi Volcanic Belt remains unclear. The volcano can only be reached by helicopter or, with great difficulty, by trekking on foot through valleys of the Pacific Ranges.

Names and etymology

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The Silverthrone Caldera has also been described as the Silverthrone Caldera Complex and the Silverthrone Depression.[11][12] Other terms, such as the Silverthrone volcanic complex and the Silverthrone volcanic field, refer to the caldera and associated volcanic rocks.[13][14] Such terms are derived from Silverthrone Mountain, a volcanic feature associated with the caldera whose name has been identified in Canadian Alpine Journal articles as early as 1933.[4][14] In a 1968 Geological Survey of Canada report, the eruptive products of the caldera were referred to as the Mount Silverthrone volcanic complex by Jack Souther, Canada's first volcanologist.[15][16]

In addition to Silverthrone Mountain, the Silverthrone Caldera also shares its name with Silverthrone Glacier, an outlet glacier of the local Ha-Iltzuk Icefield which covers approximately 3,600 km2 (1,400 sq mi) of the southern Coast Mountains.[17] Silverthrone is descriptive of the icy landscape; it was probably coined by Don Munday who carried out the first ascent of Silverthrone Mountain along with his wife Phyllis Munday in 1936.[4][9][18]

Geography

[edit]

Location and climate

[edit]
Satellite imagery of a glacier in a valley surrounded by rock and ice
Pashleth Glacier is the source of Pashleth Creek which drains part of the Silverthrone Caldera

The volcano is 55 km (34 mi) north of Kingcome Inlet and 60 km (37 mi) northwest of Knight Inlet in southwestern British Columbia, Canada.[3] It lies in a rugged, ice-dominated portion of the Pacific Ranges which are the southernmost subdivision of the Coast Mountains.[7] The surrounding mountains are the highest in British Columbia south of the Saint Elias Mountains; Mount Waddington northeast of the head of Knight Inlet has an elevation of 4,016 m (13,176 ft) and is the highest mountain entirely within British Columbia.[7][19] Characterizing the landscape at higher elevations are glaciers and massive icefields, although bedrock composed of granitoids is greatly exposed. The area is part of the Central Pacific Ranges Ecosection which is one of the seven ecosections comprising the Pacific Ranges Ecoregion.[7]

Moist air originating from the Pacific Ocean ascends over Queen Charlotte Sound, Queen Charlotte Strait or the Vancouver Island Ranges before reaching the Pacific Ranges. While ascending the Pacific Ranges, this air comes in contact with cold air from the British Columbia Interior and drops significant precipitation in the form of heavy rains or snow. The heavy rains are absorbed by wet mountain hemlock subalpine forests on mid-elevation slopes and wet western hemlock forests in valleys and lower elevation slopes. Alpine vegetation is restricted to a narrow band between the subalpine forests and the higher icefields. There are no settlements near the Silverthrone Caldera, although summer sport fishing recreation camps and logging operations have been in the area.[20]

Drainage

[edit]

From Kingcome Glacier in the southern part of the caldera, the Kingcome River flows south into the head of Kingcome Inlet northeast of Broughton Island.[21][22][23] Trudel Creek, a tributary of the Kingcome River, originates from the head of Trudel Glacier and flows southwest along the inferred southeastern boundary of the Silverthrone Caldera.[21][24][25] Charnaud Creek originates from a valley-filling lava flow adjacent to the southeastern boundary of the caldera and flows southwest into the Kingcome River.[21][24][26] At the terminus of Pashleth Glacier in the northern part of the caldera is Pashleth Creek; it flows northwest into the Machmell River which flows west into Owikeno Lake at the head of Rivers Inlet.[21][27][28][29] Selman Creek, a tributary of Pashleth Creek, flows to the northeast from Selman Lake at the northern end of the Silverthrone Caldera.[21][27][30][31] From an unnamed glacier just south of Selman Lake at the western end of the central volcanic ridge, the Wakeman River flows south into Wakeman Sound of Kingcome Inlet.[21][24][32] Catto Creek originates from an unnamed glacier on the central volcanic ridge and flows southwest across the inferred southwestern boundary of the caldera before it empties into the Wakeman River.[21][24][33]

Geology

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Tectonic setting

[edit]

The relationship of the Silverthrone Caldera to other volcanoes in southwestern British Columbia remains unclear due to there having been very little geological studies conducted at the caldera.[13][34] It has been considered to be part of the Garibaldi Volcanic Belt, but it lies 190 km (120 mi) north of the main portion of this volcanic zone, making its connection to the Garibaldi Volcanic Belt questionable.[13][35][36] The volcano has also been included as part of the much older Pemberton Volcanic Belt, which overlaps with the trend of the Garibaldi Volcanic Belt near Meager Creek to the southeast.[10][37] Both volcanic belts were formed by subduction zone volcanism along the continental margin of western North America in the last 29 million years and are part of the Cascade Volcanic Arc.[38][39][40] The types of volcanic rocks at the Silverthrone Caldera are comparable to those found in continental arcs; they belong to the calc-alkaline magma series.[38][41] Likewise, the lifespan of the caldera is comparable to most of the large evolved eruptive centres in the Cascade Volcanic Arc, which have lifespans ranging from 100,000 to 1,000,000 years.[42][43]

Silverthrone and its closest prominent neighbour, the Franklin Glacier Complex about 55 km (34 mi) to the east-southeast, are sometimes excluded from the Garibaldi Volcanic Belt due to their ambiguous affinity.[13][36] When included, Silverthrone is the northernmost major eruptive centre of both the Garibaldi Volcanic Belt and the Cascade Volcanic Arc.[44] However, the relationship of the minor Milbanke Sound Cones further to the northwest with volcanoes of the Garibaldi Volcanic Belt also remains unclear.[45][46] This is because little is known about these volcanic cones; they may reflect a northern extension of the Garibaldi Volcanic Belt or they may have formed as a result of a different geological process.[46] Further studies of the magmatic products of the Silverthrone and Franklin Glacier complexes are required to provide additional insights on mantle and slab processes.[36] The Smithsonian Institution's Global Volcanism Program lists the tectonic setting of the Silverthrone Caldera as a subduction zone and the underlying continental crust more than 25 km (16 mi) thick.[3]

The tectonic settings of the Silverthrone and Franklin Glacier complexes appear to differ from other volcanoes in the Garibaldi Volcanic Belt.[37] The main portion of this volcanic belt, which extends from the Salal Glacier volcanic complex in the north to the Watts Point volcanic centre in the south, is the result of subduction of the Juan de Fuca Plate beneath the North American Plate.[37][38] Immediately north of the Juan de Fuca Plate is the Explorer Plate, both of which are separated by the Nootka Fault.[37] The Silverthrone and Franklin Glacier complexes lie inboard of the Explorer Plate which is subducting under the North American Plate at a rate of about 2 centimetres (0.79 inches) per year.[37][47] However, both tectonic plates are currently locked to some degree in the Cascadia subduction zone.[47]

Structure

[edit]
A drawing of a volcano erupting ash and pumice into the sky
A drawing of a volcano collapsing into the underlying magma chamber
A drawing of a large crater formed by collapse of a volcano into the underlying magma chamber
A cataclysmic eruption resulting in the formation of a caldera

The Silverthrone Caldera is a roughly circular subsidence structure about 20 km (12 mi) wide in the central part of the Coast Crystalline Complex.[14][15] Such structures form when magma chambers are partially emptied during eruptions, resulting in the land surface subsiding and the area above the shallow magma chamber collapsing.[48] Subsidence of the area above the magma chamber results in the formation of steep-sided ring faults which are cylindrical fractures around the edges of calderas.[49][50] Calderas as large as Silverthrone form as a result of massive Plinian eruptions which send ash columns high into the stratosphere and create large-scale pyroclastic flows.[48][51] These caldera-forming eruptions are orders of magnitude larger than the 1980 eruption of Mount St. Helens and range from 6 to 8 on the Volcanic Explosivity Index. Their extreme explosivity is caused by silica-rich magma which cools on the land surface in the form of volcanic rocks such as dacite and rhyolite.[48] Reconnaissance mapping of volcanic rocks associated with the caldera prior to 1980 indicates Silverthrone is one of the largest centres of Quaternary felsic[a] volcanism in British Columbia.[53]

The inferred boundaries of the Silverthrone Caldera are exposed to the south and west whereas the northern and eastern boundaries are buried under volcanic deposits and glacial ice, respectively.[21] Unlike the neighbouring Franklin Glacier Complex whose volcanic rocks have been mostly eroded away to expose underlying subvolcanic intrusions, the Silverthrone Caldera still possesses mainly volcanic rocks.[14][54] The main volcanic rocks at the caldera are rhyolites, dacites, andesites and basaltic andesites which comprise breccias, lava domes, lava flows and volcanic cones.[14] Deep dissection of these volcanic deposits by erosion has created the current rugged topography, although some of them remain hidden at higher elevations under glacial ice of the Ha-Iltzuk Icefield.[13] The volcanic deposits extend over a distance of more than 25 km (16 mi) and vary in elevation from near sea level to 2,860 m (9,380 ft) or 3,160 m (10,370 ft).[3][5][13] They have a volume of at least twice as much as that of the Mount Meager complex, which consists of 20 km3 (4.8 cu mi) of volcanic rocks.[55][56]

Underlying the eruptive products of the Silverthrone Caldera are older rocks of the Coast Plutonic Complex.[14][57] This 1,700 km (1,100 mi) long and 50–175 km (31–109 mi) wide geological feature is the largest magmatic arc of the North American Cordillera and one of the largest subduction-related plutonic rock assemblages on Earth.[58][59] Dominated by tonalite, diorite and quartz diorite, the Coast Plutonic Complex is also one of the least felsic batholith-like belts encircling the Pacific Ocean. It is Early Jurassic to Paleogene in age and formed during a time when large-scale terrane and magmatic accretion led to significant continental growth in the North American Cordillera.[59]

Geothermal potential

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Silverthrone was studied for producing geothermal energy in the 1970s due to its potential similarity to the Mount Meager complex which is the most advanced, volcano-hosted, high temperature geothermal energy project in Canada.[60][61] Evidence for a geothermal system at Silverthrone includes hot springs, geologically recent volcanism and extensive hydrothermal alteration. There is limited heat flow data available for the volcano, but if a geothermal system is present, it would potentially be hosted in the local crystalline basement rocks. No flow rates for the local springs have been reported and the heat exchange potential remains unknown.[62] At least one spring with a recorded temperature of 50 °C (122 °F) possibly occurs along a ring fault associated with the collapse of the Silverthrone Caldera.[63] As of 2016, the only geothermal exploration conducted at Silverthrone has been geological mapping.[62]

The lack of detailed geothermal analysis for the Silverthrone Caldera is due to its very remote location and the lack of electrical development at the volcano.[64][65] As a result, geothermal exploration at the volcano is less favourable than elsewhere in British Columbia such as at Mount Cayley, Mount Garibaldi and Mount Meager.[66] Based on the volume of the silicious volcanic rocks found at Silverthrone, its geothermal power potential is 2,000 megawatts, which is comparable to that for the Mount Edziza region but greater than those for Mount Cayley and Meager Creek combined. Unlike the Meager Creek–Mount Cayley complex and Mount Edziza region which have high and medium surface thermal manifestations, respectively, the surface thermal manifestation at Silverthrone is low.[67] Nevertheless, there is a good possibility of finding a geothermal resource that is less than 80 °C (176 °F).[62]

Eruptive history

[edit]

The eruptive history of the Silverthrone Caldera is poorly known due to limited geological studies but it is probably similar in age to those of other volcanoes in the Garibaldi Volcanic Belt.[13] Three stages of volcanic activity have been identified at the caldera, each of which have been radiometrically dated. Most of the volcanic deposits inside the Silverthrone Caldera appear to have been erupted between 100,000 and 900,000 years ago during the Pleistocene epoch.[68][69] According to the Global Volcanism Program, the last eruption of the Silverthrone Caldera is unknown, but there is credible evidence for the caldera having been active during the current Holocene epoch, which began about 11,700 years ago.[3][70][71] Radiocarbon dating indicates the latest volcanic eruptions occurred in the last 13,000 years and the volcanic deposits from these eruptions postdate the current topography.[3][68] The Silverthrone Caldera has been much more recently active than the neighbouring Franklin Glacier Complex, which has yielded dates no younger than 2.2 ± 0.1 million years.[13][72]

First stage

[edit]
A map of volcanic deposits in and around a subsidence structure
Geological map of the Silverthrone volcanic field displaying three volcanic phases and an outline of the caldera

Volcanism during the first stage of activity about 750,000 years ago deposited a 1,200 m (3,900 ft) thick breccia unit at the base of the intracaldera sequence.[73] The breccia is deeply eroded, exposed in valley bottoms and has been locally welded together by volcanic heat.[13][68] Angular to subangular granitic, metamorphic and volcanic fragments up to 3 m (9.8 ft) in diameter, derived from the underlying basement rocks, occur in the breccia which contains a white to light grey matrix.[15][68] Characterizing the welded breccia is an eutaxitic texture, a banded appearance which forms when pumice-rich material is erupted explosively and is then quickly covered and compressed by overlying volcanic rocks while still in a hot, plastic state.[68][74][75]

Evidence for the basal breccia having been deposited during caldera collapse includes the existence of irregular subvolcanic intrusions and a profusion of dikes within the breccia but not in the surrounding country rocks, as well as steep contacts of the breccia with the older country rocks which is indicative of a fault-bounded structure.[1][68] Potassium–argon dating of rhyolite glass about 100 m (330 ft) above the basal breccia has yielded a date of 0.75 ± 0.08 million years.[68]

Second stage

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The second stage of volcanic activity about 400,000 years ago issued a series of lava domes and flows over the basal breccia deposited during the first stage. These eruptive products are rhyolitic, dacitic and andesitic in composition; the lava flows reach a composite thickness of 900 m (3,000 ft). Like the basal breccia, erosion has greatly modified the lava domes and flows of this second stage of volcanic activity.[73] Near the summit of Silverthrone Mountain are overlapping andesite and rhyolite domes which most likely formed during this stage of volcanism.[1] Potassium–argon dating of an andesite flow overlying rhyolite in the south-central part of the caldera has yielded a date of 0.4 ± 0.1 million years.[73]

Third stage

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Volcanism during the third stage of activity was characterized by the eruption of basaltic andesite lava flows and pyroclastic cones.[73] Most of them issued from vents around the parameter of the caldera, the largest of which is continuously exposed for more than 25 km (16 mi) in the Pashleth Creek and Machmell River valleys.[1][13] It has a blocky surface and originated from the northern margin of the caldera; the Machmell River Cone lies at the head of this lava flow at 51°31′N 126°13′W / 51.51°N 126.21°W / 51.51; -126.21 (Machmell River Cone).[1][76] A relatively small basaltic andesite flow at the head of the Kingcome River originated inside the southern part of the caldera and travelled to the southeast just outside the inferred boundary of this collapse structure.[1] The lava flow is considered to be Holocene in age and is in the form of an eroded volcanic outcrop at the mouth of Trudel Creek.[1][24][77] A smaller north–south trending basaltic andesite flow on the southeastern side of the caldera at the head of Charnaud Creek was erupted during the Holocene and is also in the form of an eroded volcanic outcrop.[1][24][78] At higher elevations on the eastern side of the caldera, the eroded remains of pyroclastic cones project through glacial ice of the Ha-Iltzuk Icefield.[73]

Potassium–argon dating of the basaltic andesite flow occupying the Machmell River and Pashleth Creek valleys has yielded ages of 1.0 ± 0.2 million years and 1.1 ± 0.1 million years.[68] These ages are considered to be too old since high-energy streams originating from glaciers have only begun to erode a channel along the edge of the lava flow.[3][68] An explanation for the erroneous ages lies in the presence of xenoliths[b] and other inclusions from the underlying Mesozoic basement, which can negatively influence the ages of rocks in radiometric dating.[68][80] Radiocarbon dating has provided a date of 12,200 ± 140 years for barnacles buried by the lava flow. This radiocarbon date was obtained 8.5 km (5.3 mi) upstream from the mouth of the Machmell River and provides a maximum age for the lava flow, which may have been extruded much more recently.[3] The low degree of erosion of this lava flow by the Machmell River and the presence of loose, unsorted sediments deposited by glacial meltwater streams under the flow suggest it was erupted less than 1,000 years ago.[1]

Volcanic hazards

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Satellite imagery of a roughly oval-shaped area of ice and snow surrounded by valleys in mountainous terrain
Melting of the Ha-Iltzuk Icefield caused by renewed volcanism at the Silverthrone Caldera could cause lahars or debris flows

A review of Canadian volcanoes published in 2024 assessed Silverthrone as the only "moderate" threat volcano in Canada.[81] The review noted that although the volcano scores highly for primary volcanic hazard factors, it has a relatively low exposure score due to its very remote location.[65][82] Therefore, the review gave Silverthrone a lower hazard rating than for Mount Edziza, Mount Price, Mount Cayley, Mount Meager and Mount Garibaldi, which were rated as "high" and "very high" threat volcanoes.[83] Small magnitude, shallow earthquakes have been recorded near Silverthrone since 1980, but because this seismicity is not demonstrably magmatic in origin, the volcano was given a score of 0.5 on a scale of 0 to 1 for observed seismic unrest.[84] Nevertheless, the presence of seismicity suggests the Silverthrone Caldera is potentially active and its volcanic hazards may be significant.[85]

Silverthrone mainly poses a threat to air traffic since there are no communities near the volcano.[82] Volcanic ash reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems.[86] Silverthrone was rated "high" in the 2024 review for volcano knowledge uncertainty and was scored "positive" for sector collapse potential.[87] Sector collapses are one of the most hazardous volcanic events on Earth, involving the structural failure and subsequent collapse of at least 1 km3 (0.24 cu mi) of a volcano.[88][89] Such collapses can result from destabilization by magma intrusion or associated phreatomagmatic eruptions.[89] More than 3 km3 (0.72 cu mi) of snow and ice permanently covers Silverthrone, making it a potential source of lahars or debris flows which typically enter river valleys.[90][91] Eruptions may trigger lahars by melting snow and ice but lahars can also begin as landslides of wet, hydrothermally altered rock on steep slopes.[91]

Monitoring

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Like other volcanoes in Canada, the Silverthrone Caldera 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 the Silverthrone Caldera 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.[92] If the Silverthrone Caldera 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.[93]

Human history

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Kingcome obsidian

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A map showing the locations of obsidian sources in British Columbia
Silverthrone Caldera
Silverthrone Caldera
Mount Edziza
Mount Edziza
Mount Garibaldi
Mount Garibaldi
Anahim Peak
Anahim Peak
Ilgachuz Range
Ilgachuz Range
Mackenzie Pass
Mackenzie Pass
class=notpageimage|
Location of the Silverthrone Caldera in relation to other obsidian sources in British Columbia

Around 2013, Silverthrone was identified as the source of the Kingcome obsidian by cultural resource management archaeologists and the Tsawataineuk First Nation.[94] This makes the caldera one of several volcanoes in British Columbia with known obsidian source material often found at archaeological sites throughout the province; others include Mount Garibaldi, Anahim Peak, the Ilgachuz Range and the Mount Edziza volcanic complex.[95] Artifacts made of Kingcome obsidian have been found at archaeological sites in the Sunshine Coast region, which was the location of trading between indigenous peoples about 5,000–2,000 years ago.[94][96] Obsidian from Mount Garibaldi occurs with the Kingcome obsidian in this part of British Columbia, as does obsidian from Whitewater Ridge and Gregory Creek in the U.S. state of Oregon.[96]

The Kingcome and Mount Garibaldi obsidians are of only moderately good quality because they contain relatively large phenocrysts; these crystals would have made both obsidians more difficult to work with during the crafting of artifacts.[96][97] As a result, artifacts made of Kingcome and Mount Garibaldi obsidian were not traded as widely as artifacts made of other types of volcanic glass. Kingcome obsidian mainly occurs north of Powell River and in Desolation Sound where ancient settlements were established.[97] The Silverthrone Caldera lies in Kwakwakaʼwakw territory which covers the northern end of Vancouver Island and surrounding lands.[97][98]

Geological studies

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In 1967, Silverthrone was one of five eruptive centres visited by Jack Souther as part of a study to investigate geologically young volcanic rocks in the Canadian Cordillera. Specimens of the volcano were collected for chemical and petrographic analyses. Souther also noted the basal breccia, the overlying lava flows, the deep dissection of the volcanic deposits and a possible fault-bounded structure associated with the collapse of the caldera. The youngest lava flows occupying the local valleys were said to be probably no older than Early Pleistocene age.[15] The other eruptive centres visited by Jack Souther in 1967 were the Mount Edziza volcanic complex in the Northern Cordilleran Volcanic Province and the Rainbow, Ilgachuz and Itcha ranges in the Anahim Volcanic Belt.[99][100][101]

Further studies were carried out by Green et al. (1988) who inferred the boundaries of the caldera and obtained the four aforementioned potassium–argon dates from three locations in and adjacent to the caldera.[73] Mejia et al. (2002) sampled basaltic andesite flows from Silverthrone and obtained 16 potassium–argon dates. Most of these dates indicated the lava flows were extruded sometime in the last 120,000 years, but two of the potassium–argon dates gave ages as old as 400,000 years.[102] As of 2023, the remoteness of the Silverthrone Caldera has impeded detailed fieldwork.[11]

Mineral exploration

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A mineralized dacitic breccia pipe was discovered at the Silverthrone Caldera in the 1990s following retreat of the headwall of Kingcome Glacier. It was noted to contain multicoloured clay and silica minerals such as opal, malachite, pyrolusite and celadonite, which were characterized by intense hues of blue and green. The breccia pipe, partially enclaved by dacite pitchstone, was considered to be hydrothermal in origin and was obscured by Kingcome Glacier in 1979 as evidenced by the photos and topographic maps of that time. A report of the British Columbia Prospectors Assistance Program listed copper and gemstones as commodities in the breccia pipe.[103]

Conservation

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Part of Silverthrone lies in the Catto Creek Conservancy, a 7,249-hectare (17,910-acre) conservation area in Range 2 Coast Land District established on August 23, 1973, under the Protected Areas of British Columbia Act.[6][65] This protected area was mainly established to preserve a group of geomorphological features known as “the paint pots”, but it also allows a number of recreational activities, such as camping, hiking, fishing and hunting. Both wilderness and winter camping are permitted in the Catto Creek Conservancy, but no facilities are provided, such that visitors must be fully prepared and self-sufficient to camp in this conservancy.[65]

Accessibility

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Access to the Silverthrone Caldera is difficult due to its very remote location in the Pacific Ranges of the Coast Mountains.[5][7][65] It can be reached by charter helicopter from Tatlayvoko Lake or Campbell River, the latter of which is the nearest town to the volcano.[5][65] The flying times from Tatlayoko Lake and Campbell River are about one and two hours, respectively.[65] A much more difficult way to access Silverthrone is to traverse one of the several intermontane valleys on foot, which can be reached from the British Columbia Coast or the Interior Plateau. The icefields of the Silverthrone area can be trekked on foot from the adjoining valleys.[1]

See also

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Notes

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  1. ^ Felsic pertains to magmatic rocks that are enriched with silicon, oxygen, aluminum, sodium and potassium.[52]
  2. ^ Xenoliths are rock fragments that become enveloped in a larger rock during the latter's development and solidification.[79]

References

[edit]
  1. ^ a b c d e f g h i j k Souther 1990, p. 139.
  2. ^ Whipple 2023, p. 336.
  3. ^ a b c d e f g h i j k l Global Volcanism Program: Silverthrone, General Information.
  4. ^ a b c d BC Geographical Names: Silverthrone Mountain.
  5. ^ a b c d e Souther 1990, p. 138.
  6. ^ a b c BC Geographical Names: Catto Creek Conservancy.
  7. ^ a b c d e Demarchi 2011, p. 37.
  8. ^ Hickson 1994, p. 234.
  9. ^ a b Morison & Hickson 2023, p. 465.
  10. ^ a b Souther 1976, p. 15.
  11. ^ a b Morison & Hickson 2023, p. 468.
  12. ^ Whipple 2023, p. 331.
  13. ^ a b c d e f g h i j Natural Resources Canada: Silverthrone Caldera.
  14. ^ a b c d e f Souther 1990, pp. 138, 139.
  15. ^ a b c d Souther 1968, p. 42.
  16. ^ Barrett 2014.
  17. ^ NASA Earth Observatory.
  18. ^ Bridge 2002, p. 153.
  19. ^ BC Geographical Names: Mount Waddington.
  20. ^ Demarchi 2011, p. 38.
  21. ^ a b c d e f g h Green et al. 1988, p. 577.
  22. ^ BC Geographical Names: Kingcome Glacier.
  23. ^ BC Geographical Names: Kingcome River.
  24. ^ a b c d e f Department of Energy, Mines and Resources 1980, 2nd edition.
  25. ^ BC Geographical Names: Trudel Creek.
  26. ^ BC Geographical Names: Charnaud Creek.
  27. ^ a b Department of Energy, Mines and Resources 1980, 1st edition.
  28. ^ BC Geographical Names: Owikeno Lake.
  29. ^ BC Geographical Names: Machmell River.
  30. ^ BC Geographical Names: Selman Creek.
  31. ^ BC Geographical Names: Selman Lake.
  32. ^ BC Geographical Names: Wakeman River.
  33. ^ BC Geographical Names: Catto Creek.
  34. ^ Green et al. 1988, pp. 563, 564.
  35. ^ Green et al. 1988, p. 563.
  36. ^ a b c Mullen & Weis 2015, p. 105.
  37. ^ a b c d e Green et al. 1988, p. 564.
  38. ^ a b c Souther 1990, pp. 112, 113.
  39. ^ Madson et al. 2006, p. 27.
  40. ^ Manthei et al. 2010, pp. 2, 3.
  41. ^ Hildreth 2007, p. 76.
  42. ^ Souther 1990, p. 112.
  43. ^ Hildreth 2007, p. 64.
  44. ^ Russell et al. 2023, p. 1453.
  45. ^ Souther 1990, p. 110.
  46. ^ a b Natural Resources Canada: Milbanke Sound Cones.
  47. ^ a b Gao et al. 2017, p. 1569.
  48. ^ a b c National Park Service.
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