Silverthrone Caldera

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Silverthrone Caldera
Elevation approx. 2,865 m (9,400 ft)
Location British Columbia, Canada
Range Pacific Ranges
Prominence approx. 975 m (3200 ft)
Coordinates 51°31′41.9″N, 126°06′47.9″W
Type Caldera
Volcanic arc/belt Cascade Volcanic Arc
Pemberton Volcanic Belt
Age of rock Holocene
Last eruption Unknown; possibly younger than 1000
Listing List of volcanoes in Canada
List of Cascade volcanoes

The Silverthrone Caldera is a circular 20 km (12 mi) wide, deeply dissected caldera complex in Regional District of Mount Waddington, British Columbia, located over 320 km (199 mi) northwest of the city of Vancouver and about 50 km (31 mi) west of Mount Waddington, British Columbia, Canada. The complex and the surrounding area may be the northernmost section of the Cascade Volcanic Arc, but scientific study has been very limited due to its extremely remote location. Some geological references suggest that it represents the northernmost of the Cascade Volcanic Arc, because the Pemberton Volcanic Belt is usually merged with the Garibaldi Volcanic Belt,[1][2][3] but its relationship to volcanism caused by the Cascadia subduction zone (ie. the Cascade Volcanic Arc) has not been firmly established.

Mount Silverthrone, a lava dome and the highest summit on the northeast edge of the complex, may also be the highest volcano in Canada, but even its elevation is not definitely known. Some references state an elevation as high as 3,160 m (10,367 ft), but the current topographic map shows contours only as high as 2,865 m (9,400 ft), and no spot elevation is given. In addition, it is unclear whether the highest point is of volcanic origin or not, since the summit is covered with permanent snow and ice, and the composition of the underlying rock is unknown.

The Silverthrone Caldera is one of the few calderas buried beneath the ice caps of western Canada, another example is Mount Edziza in far northwestern British Columbia, which is almost 2 km (1 mi) wide.

Contents

[edit] Geology and eruptive history

Map of the Garibaldi Volcanic Belt centers, including the Mount Silverthrone area.
Map of the Garibaldi Volcanic Belt centers, including the Mount Silverthrone area.

The Silverthrone Caldera contains rhyolitic, dacitic and andesitic lava domes, lava flows and breccia.[4] It lies within the Coast Plutonic Complex, which is the single largest contiguous granite outcropping in the world. The plutonic and metamorphic rocks extend approximately 1,800 kilometers on the coast of British Columbia, southwestern Yukon and southeastern Alaska. In addition, Garibaldi, Meager, Cayley and Silverthrone areas are of recent volcanic origin. The volcanic terrain in the Silverthrone area is very similar to the Mount Meager volcanic complex. However, there is much more ice.

Most of the caldera's eruptions occurred during the last ice age[5] and the products have since been heavily eroded. The Silverthrone Caldera was episodically active during both Pemberton and Garibaldi Volcanic Belt stages of volcanism. The bulk of the complex appears to have been erupted between 0.1 and 0.5 million years ago, but postglacial andesitic and basaltic-andesite cones and lava flows are also present.[4] Anomalously old Potassium-argon dates of 1.0 and 1.1 million years were obtained from a lava flow in the postglacial Pashleth Creek and Machmel River valleys. This flow is clearly much younger than the K-Ar date and high-energy glacial streams have only begun to etch a channel along the margin of the flow. A radiocarbon date from barnacles 8.5 kilometres (5 mi) upstream from the mouth of the Machmel River and buried by the flow yielded an age of 12,200 +/- 140 years. This is a maximum age for the lava flow, which could be much younger.[4] The last eruption from the caldera produced a lava flow that ran up against ice in Charnaud Creek. The lava flow was dammed by the ice and made a cliff with a waterfall up against it.[6] This andesitic lava flow represents the very edge of the volcanic complex. The thin columns indicate cooling was comparatively rapid while the long faces indicate that the large slab cooled as a unit. Additionally, the entablature is found on the bottom, the opposite of what can be seen in the more well-known flood basalts in the Chilcotin or in the Washington/Oregon desert. So it cooled from the bottom up rather than the top down.

The Silverthrone Caldera is one of the top 11 Canadian volcanoes with recent seismic activity, the others include: Castle Rock, Mount Edziza, Mount Cayley, Hoodoo Mountain, Lava Fork Valley, Crow Lagoon, Mount Meager, Wells Gray-Clearwater Volcanic Field, Mount Garibaldi and Nazko Cone.

[edit] Mount Silverthrone Volcanic Field

[edit] See also

[edit] References

  1. ^ Canada Volcanoes and Volcanics Retrieved on 2007-11-28
  2. ^ Preliminary petrography and chemistry of the Mount Cayley volcanic field Retrieved on 2007-11-15
  3. ^ Volcanoes of Canada Retrieved on 2007-11-15
  4. ^ a b c Smithsonian Institution Global Volcanism Program: Silverthrone Caldera Retrieved on 2007-11-12
  5. ^ Skiing the Pacific Ring of Fire and Beyond: Silverthrone Mountain Retrieved on 2007-11-12
  6. ^ Charnaud Waterfall Retrieved on 2007-11-13

[edit] External links

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