The Silverthrone Caldera, also referred to as the Silverthrone Caldera Complex, is a volcano in Range 2 Coast Land District of 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 25 by 20 kilometres (16 by 12 miles) in size and has been deeply eroded, resulting in the formation of rugged topography. Several glacial meltwater streams originating from the volcano flow through valleys in the Pacific Ranges. These include the Pashleth, Selman and Catto creeks and the Kingcome and Wakeman rivers. The caldera contains several named mountains, including Mounts Somolenko, Overill, Kinch, Squire, Ardern and Calli, as well as Petrovsky Peak and Silverthrone Mountain. 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 mi2) Ha-Iltzuk Icefield. These rocks comprise three geological 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. Small magnitude, shallow earthquakes have been recorded near the volcano since 1980, but they have not been demonstrated to be magmatic in origin. The main potential hazard posed by future volcanism is to air traffic if explosive eruptions were to occur from the caldera. The Silverthrone Caldera was a source of obsidian for Indigenous peoples during the pre-contact era. 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 not well-known and its affinity to the Garibaldi Volcanic Belt remains unclear. The volcano was studied in the 1970s as a potential source of geothermal energy. It can be reached by helicopter or by trekking on foot through nearby valleys.
Names and etymology The Silverthrone Caldera has been described as the Silverthrone Caldera Complex and the Silverthrone Depression. Other terms, such as the Silverthrone volcanic complex and the Silverthrone volcanic field, refer to the caldera and associated volcanic rocks. Such terms are derived from Silverthrone Mountain, a volcanic feature associated with the caldera whose name has been reported in Canadian Alpine Journal articles as early as 1933. 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. 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 mi2) of the southern Coast Mountains. Silverthrone is descriptive of the icy landscape; it may have been coined by Don Munday who, with his wife Phyllis Munday, carried out the first ascent of Silverthrone Mountain in 1936.
Geography
Location and climate 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. It lies in a rugged, ice-dominated portion of the Pacific Ranges which are the southernmost subdivision of the Coast Mountains. 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. Characterizing the landscape at higher elevations are glaciers and extensive icefields, although bedrock composed of granitoids is greatly exposed. The area is part of the Central Pacific Ranges Ecosection, one of seven ecosections comprising the Pacific Ranges Ecoregion. 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.
Drainage
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. 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. Charnaud Creek originates from a valley-filling lava flow adjacent to the southeastern boundary of the caldera and flows southwest into the Kingcome River. 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. Selman Creek, a tributary of Pashleth Creek, flows to the northeast from Selman Lake at the northwestern end of the Silverthrone Caldera. 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. 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. Silverthrone Glacier flows southeastward from Silverthrone Mountain through a valley to Klinaklini Glacier, which lies at the head of the West Klinaklini River.
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