Mount Cayley

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Mount Cayley
Mount Cayley in April 2004
Elevation	2,385 m (7,825 ft)
Location	Squamish River, British Columbia, Canada
Range	Pacific Ranges
Prominence	674 m (2,211 ft)
Coordinates	50°07′13″N, 123°17′26″WCoordinates: 50°07′13″N, 123°17′26″W
Topo map	NTS 92J/03
Type	Stratovolcano
Volcanic arc/belt	Cascade Volcanic Arc Garibaldi Volcanic Belt
Age of rock	Pleistocene
Last eruption	310,000 BP
First ascent	1928 E. Brooks, T. Fyles, W. Wheatley
Easiest route	rock/ice climb
Listing	List of volcanoes in Canada List of Cascade volcanoes

Mount Cayley is a potentially active^[1] stratovolcano in the Squamish-Lillooet Regional District, British Columbia located 11 kilometres (7 mi) southwest of Callaghan Lake and 24 kilometres (15 mi) west of Whistler, British Columbia, Canada. This heavily eroded multiple plug dome complex is the largest and long-lived center (3.8 to 0.31 million years ago) of the Garibaldi Volcanic Belt which is a segment of the Cascade Volcanic Arc, but it is not within the geographic boundary of the Cascade Range. It is located in the Pacific Ranges complex of the Coast Mountains, rising 2,385 m (7,825 ft) above the Squamish River to the west and 1,844 m (6,050 ft) above the Cheakamus River to the east.

To Sḵwxwú7mesh, the indigenous people from this territory, the name for the mountain is t'ak't'ak mu'yin tl'a in7in'a'xe7en, meaning Landing Place of the Thunderbird. This mountain considered "very sacred" to these people because in their history it was home of the legendary Thunderbird.^[2] Like Black Tusk, the rock was said to have been burnt black by the Thunderbird's lightning.^[3]

Contents 1 Human history 2 Geology 3 Area 3.1 Related features 4 Geological history 5 Volcanic hazards 6 Subsidiary peaks 7 See also 8 References 9 External links

[edit] Human history

The first recorded ascent of Mount Cayley were made by the mountaineers E.C. Brooks, W.G. Whealey, B.Clegg, R.E. Knight, and Tom Fyles in 1928. During this time, the party named the volcano after the late Beverley Cochrane Cayley, who was an ardent mountaineer of the executive committees of the British Columbia Mountaineering Club and the Vancouver section of the Alpine Club for several years.^[4] Beverley Cayley was a friend of those in the climbing party, and died 8 June 1928 at the age of 29 in Vancouver. Photographs of Mount Cayley were published in the Canadian Alpine Journal Vol XX in 1931.^[4]

[edit] Geology

Mount Cayley lies within the Coast Plutonic Complex, which is the single largest contiguous granite outcropping in the world.^[5] The intrusive and metamorphic rocks extend approximately 1,800 km (1,118 mi) along the coast of British Columbia, the Alaska Panhandle and southwestern Yukon. This is a remnant of a Jurassic-to-Eocene volcanic arc called the Coast Range Arc that formed as a result of subduction of the Farallon and Kula Plates.^[6] In addition, Garibaldi, Meager, Cayley and Silverthrone areas are of recent volcanic origin and are associated with the present-day Cascade Volcanic Arc.

There are several hot springs and anomalous geophysical properties around Mount Cayley.^[7] Its hot springs have made it a target for geothermal exploration.^[8] It lies in the central part of the Garibaldi Volcanic Belt of volcanic centers in southwestern British Columbia and contains several complex features which probably represent multiple eruptions under different conditions and are difficult to classify.

Mount Cayley consists of poorly lithified pyroclastic rocks and lavas, which underwent three stages of volcanic activity. Its first phase of activity is characterized by a compound stack of plagioclase, hypersthene, hornblende, phyric dacite flows, tephra, and breccia, which are hydrothermally changed to an unstable degrees. The Vulcan's Thumb phase followed, named for the biggest of a number of slight peaks extend beyond from Pyroclastic Peak. Its creation consist of vent breccia, massive lava flows, and agglutinated breccia of plagioclase, hypersthene, hornblende, biotite, phyric dacite deposited as part of an edifice that raised upon the southwestern edge of the ancestral Mount Cayley. The third phase of activity constructed two minor plagioclase-hypersthene-biotite-phyric dacite lava domes, associated flows and tephra pieces that are uncovered in the Shovelnose Creek valley. There are no noticeable suggestions of volcano-ice contacts at Mount Cayley.

[edit] Area

Mount Cayley is associated with a Miocene-to-Pleistocene volcanic field. The high elevations of the volcanic field, coupled with its cluster of mostly high altitude, non-overlapping vents, has resulted in numerous eruptions under ice more than 800 m (2,625 ft) thick which is relatively rare. Due to the steep underlying topography and vent-ice geometries during eruptions, ice associated with most eruptions is likely to have been permeable, promoting abundant water during eruption (i.e. pillows, hyaloclastite).

The field includes flow-dominated tuyas and subglacial domes. Ice-impounded flows are also present. Subglacial domes are steep-sided, rounded lava masses characterized by fine-scale joints whose orientations suggest cooling against steeply-inclined surfaces that are no longer present, such as ice. These represent subglacial eruptions which never breached the surface. Tuyas are a distinctive, flat-topped, steep-sided lava mass formed when magma intrudes into and melts a vertical pipe in an overlying ice sheet or glacier. The partially molten mass cools as a large block, with gravity flattening its upper surface. Unlike conventional tuyas, tuyas in the volcanic field are flow-dominated tuyas and contain few or no pillow lavas and little or no hyaloclastite. Ice-impounded flows commonly truncate in steep, intensely-jointed, glassy cliffs, and represent subaerial flows which flowed downslope to pond against valley-filled ice. Many of the volcanic features are thought to have originated from a single source because of structural similarities and have similar ages.

[edit] Related features

• Little Ring Peak is a volcano that has not been previously studied. It contains 70% of brown glass, with sparse plagioclase phenocrystals and contains a tuya-like form, but its inner stratigraphy is yet unknown. It is located at the northernmost known extent of the volcanic complex.^[9]
• Cauldron Dome is an almost flat-topped pile of coarsely plagioclase-orthophyroxene-phyric andesite flows and is similar to a tuya.^[9]
• Mount Brew is a partially forested subglacial volcano which lies on a ridge system that separates Roe Creek from Brandywine Creek.^[9]
• The Mount Fee volcanic neck consists of two sharp blades of volcanic rock at the head of Brandywine Creek. It is located 13 km south of Callaghan Lake and 21 km west of Whistler. The south tower of Mount Fee is the highest.
• The Pali Dome subglacial volcano, located north of Mount Cayley, is partially obscured by ice and is dominated by coarsely plagioclase-hypersthene-phyric-andesite flows.^[9]
• The Slag Hill subglacial volcano consists of glassy, augite-phyric basaltic andesite in steep-sided, glassy, finely jointed domes and one small, flat-topped bluff.^[9]
• Ring Mountain is a flow-dominated tuya located on the east side of the upper Squamish River. Its age is unknown, but lack of evidence for glacial overriding and preservation of finely-jointed, glassy lavas suggests that the volcano may have formed about 10,000-12,000 years ago.^[10]
• The Ember Ridge subglacial volcano, located at the southern known extent of the volcanic complex, last erupted during the Pliocene period. It is made of series of steep-sided domes of glassy, complexly jointed, hornblende-phyric basalt.^[9]

[edit] Geological history

In 1968 and 1983, rock avalanches occurred on Cayley's flanks. Signifiant damage was experienced by forest stands and logging roads, however no injuries resulted. In 1984, a small debris flow slid from the western flank of Mount Cayley and dammed the Squamish River.^[11]

[edit] Volcanic hazards

Mount Cayley is one of the top 11 Canadian volcanoes associated with seismic activity since 1985, the others include: Castle Rock, Mount Edziza, Mount Meager, Hoodoo Mountain, Lava Fork Valley, Crow Lagoon, Mount Silverthrone, Wells Gray-Clearwater Volcanic Field and Nazko Cone.^[7] Because of its remote location, the Mount Cayley volcanic complex has not been studied or mapped in detail. To date, most geological studies of the Mount Cayley volcanic complex have focused on landslide hazards and geothermal potential. The hydrothermal and seismic activity at Mount Cayley suggests that the volcanic complex still contains living magma plumbing systems preceding a volcanic eruption, but activity might also die out without an eruption. Although the existing data do not allow a clear conclusion, these observations are further indications that some of Canada's volcanoes are potentially active, and that their associated hazards may be significant. It is noteworthy that the seismic activity correlates with some of Canada's most youthful volcanoes, and with long-lived volcanic centers with a history of significant explosive behavior, such as Mount Cayley and other major volcanic centers in the Garibaldi Volcanic Belt. For this reason the Geological Survey of Canada are planning for developing hazard maps and emergency plains for Mount Cayley and Mount Meager volcanic complexes.^[12]

A scenario of an eruption of Mount Cayley shows how western Canada is vulnerable to an eruption. The scenario is based on past activity in the Garibaldi Volcanic Belt and involves both effusive and explosive eruptions. The scenario impact is largely a result of the concentration of vulnerable infrastructure in valleys.^[13]

In 2003, Catherine Hickson, a scientist with the Geological Survey of Canada, was one of the three scientists to report on the hypothetical eruption at Mount Cayley.^[14] The first signs of activity at the volcano would probably be enlarged seismic activity in and close to the mountain. Hot springs on the mountainside would, by this point, display more "vigour"; in other words, they would get hotter. An eruption at Mount Cayley would be explosive in nature. Ash would probably spread to most of the west coast from Seattle to Anchorage, causing all airports to be closed and all relevant flights to be diverted of cancelled. The ash plume would then sweep eastward and disrupt air traffic across Canada from Alberta to Newfoundland. Flooding would turn out to be a huge issue for the community of Squamish and could eventually overrun parts of Highway 99.

The worst case scenario for an eruption is a caldera event, as happened at Mount Mazama in Oregon. An eruption could produce a large pyroclastic flow, such as what occurred in the 1980 eruption of Mount St. Helens.

[edit] Subsidiary peaks

Mount Cayley contains five named summits. The highest is the main summit of Mount Cayley. The second highest summit is Pyroclastic Peak, 2,349 m (7,707 ft), a steep, rotten volcanic peak immediately south on the ridge from Mount Cayley. The third highest highest summit is Powder Mountain, 2,347 m (7,700 ft) , a gentle volcanic dome north of Mount Cayley. The fourth highest summit is Vulcan's Thumb, 2,290 m (7,500 ft). The lowest of the five summits is Wizard Peak, 2,251 m (7,385 ft), a long eastwest ridge, with a very steep cliff on the north face.

[edit] See also

• Cascade Volcanic Arc
• Garibaldi Volcanic Belt
• Cascade Range
• Volcanism in Canada
• Geology of the Pacific Northwest

[edit] References

[edit] External links

• Mount Cayley in the Canadian Mountain Encyclopedia
• Pyroclastic Peak in the Canadian Mountain Encyclopedia
• Skiing the Cascade Volcanoes
• Catalogue of Canadian volcanoes: Mount Cayley
• The Mount Cayley volcanic field: Mapping glaciovolcanic features at a convergent margin
• Glaciovolcanism in British Columbia's Mount Cayley Volcanic Field

v • d • e Major Cascade Volcanoes British Columbia Mount Silverthrone · Silverthrone Caldera · Plinth Peak · Mount Meager · Mount Cayley · Mount Garibaldi Washington Mount Baker · Glacier Peak · Mount Rainier · Mount St. Helens · Mount Adams Oregon Mount Hood · Mount Jefferson · Three Sisters · Broken Top · Mount Bachelor · Newberry Volcano · Mount Thielsen · Mount Mazama (Crater Lake) · Mount McLoughlin California Medicine Lake Volcano · Mount Shasta · Shastina · Mount Tehama · Lassen Peak