Wells Gray-Clearwater Volcanic Field
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| Wells Gray-Clearwater Volcanic Field | |
|---|---|
 A view from Green Mountain with Pyramid Mountain in the distance |
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| Elevation | 2,100 metres (6,900 feet) |
| Location | British Columbia, Canada |
| Range | Quesnel Highland/Cariboo Mountains |
| Coordinates | |
| Type | Monogenetic volcanic field |
| Age of rock | Pliocene-to-Holocene |
| Last eruption | 1550? |
The Wells Gray-Clearwater Volcanic Field, also called the Clearwater Cone Group, is a potentially active[1] monogenetic volcanic field located in the Quesnel Highland of east-central British Columbia, Canada. It is the easternmost volcanic center in British Columbia, as well as Canada's largest independent volcanic field.[2] The field consists of a tight cluster of numerous small, basaltic volcanoes and extensive lava flows.
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[edit] Geology
The origin of the volcanism is yet unknown but is probably related to crustal thinning. Many individual volcanoes in the field have been active for the past 3 million years during which time the region was covered by thick glacial ice at least twice, prior to the well known Fraser Glaciation (also known as the Wisconsin Glaciation). During this time, eruptions occurred underneath the thick blankets of glacial ice, forming many tuyas and other subglacial volcanoes that never broke through the overlying glacial ice, such as Pyramid Mountain. Buck Hill Cone was erupted during the latest Pleistocene waning stages of the Fraser glaciation.[3]
The southern part of the volcanic field has experienced continuous volcanic activity since the end of the last ice age, creating explosion craters, pillow lava and cinder cones in the Spanish Creek, Ray Lake and Kostal Lake areas. Dragon Cone is the source of a 15 km (9 mi) long lava flow that dams the southern end of Clearwater Lake at 3 m (10 ft) high. This flow is just one of the examples of volcanic activity that have occurred in the Wells Gray-Clearwater Volcanic Field since the last ice age.[4] Flows from Flourmill and Spanish Lake Cones rest on glaciated bedrock without an intervening paleosol, suggesting an early Holocene age.[3] The most recent eruption was about 400 years ago at a cinder cone called Kostal Cone.[3] Some of the lava flows in the field are similar to those that erupted at Volcano Mountain in the Yukon, where olivine nephelinite occurs. Canada's only maar-like volcano is found in the Wells Gray-Clearwater Volcanic Field.[5]
Perhaps the most distinctive volcano in the field is Whitehorse Bluffs, which has a most unvolcano-like form. Unlike most volcanoes in the field, Whitehorse Bluffs is the eroded remnant that marks the place of a violent explosive eruption.
A viewing platform on Green Mountain in the southern part of the Wells Gray Provincial Park affords views of a number of field's tuyas including McLeod Hill, Mosquito Mound and Pyramid Mountain.[4]
Helmcken Falls on the Murtle River owns its foundation to the deposits of volcanic rock that were placed down in the wide valley of the Murtle River. Numerous effusive eruptions created several layers of lava which created flat areas, over which enormous floods flowed during the last ice age. These floods shaped the upright cliff in the lava flows over which the river now flows.
About half a million years ago, volcanic activity began sending basaltic lava flows into the Spahats Creek area layer by layer which eventually cooled. The layers of these volcanic flows can still be seen today. During the most recent ice age the Clearwater canyon was cut out of the surroundings by the thick glacial ice that covered the region. As the ice age ended Spahats Creek began cutting into the layers of lava and created a canyon which it lies in today forming Spahats Falls.
[edit] Human context
[edit] Usage
Much of the volcanic field's beauty and that of the surrounding area prompted the provincial government to set the area aside as a large wilderness park in 1939 called the Wells Gray Provincial Park. It includes several of the small volcanoes, spectacular lava flows and rugged valleys cut by impressive waterfalls. The 142 m (466 ft) high, free-falling Helmcken Falls is the park's main tourist draw, which is the fourth highest waterfall in Canada.[6]
A single road enters the park, but from it, a number of the field's volcanic features can be viewed. Short hikes lead to several spectacular volcanic features can be viewed. The road terminates at the southern end of Clearwater Lake, where a short hike up the Kosta Lake trail leads to the "Dragon's Tongue" lava flow which was erupted from Dragon Cone during the early Holocene.
[edit] Hazards
The Wells Gray-Clearwater Volcanic Field is one of the top 11 volcanic areas in Canada associated with volcano-seismic activity since 1985, the others include: Castle Rock,[7] Mount Edziza,[7] Mount Cayley,[7] Hoodoo Mountain,[7] Lava Fork Valley,[7] Crow Lagoon,[7] Silverthrone Caldera,[7] Mount Meager,[7] Mount Garibaldi[7] and Nazko Cone.[7] Beneath areas of monogenetic cinder cone activity, such as the Wells Gray-Clearwater Volcanic Field, the seismicity appears to be more dispersed.[1] In a few cases earthquakes are clustered in time and space, suggestive of volcanic earthquake swarms.[1] 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.[1]
Since the field is not extinct, new volcanic events may occur at any time. Based on past volcanic activity, the field has a long history of producing Strombolian eruptions. Such eruptions consist of ejection of incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters. They are small to medium in volume, with sporadic violence. Named after the Italian volcano Stromboli, Strombolian eruptive activity can be very long-lasting because the conduit system is not strongly affected by the eruptive activity, so that the eruptive system can repeatedly reset itself. For example, the Parícutin volcano erupted continuously between 1943-1952, Mount Erebus, Antarctica has produced Strombolian eruptions for at least many decades, and Stromboli itself has been producing Strombolian eruptions for several thousand years. Since the region is mostly forested and lava flows are likely to travel long distances, it is possible that eruptions could start large forest fires, although many more types of eruptions are possible, such as Whitehorse Bluffs, which was formed by repeated subaqueous explosive eruptions.[4]
[edit] List of volcanoes
The volcanoes within the field include:
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[edit] See also
- Volcanism in Canada
- Chilcotin Plateau Basalts
- Anahim Volcanic Belt
- Garibaldi Volcanic Belt
- Northern Cordilleran Volcanic Province
- List of volcanoes in Canada
[edit] Notes
- ^ a b c d An Assessment of Natural Hazards and Disasters in Canada Retrieved on 2008-05-13
- ^ Volcanoes of Canada - Map of Canadian volcanoes
- ^ a b c Smithsonian Institution Global Volcanism Program: Wells Gray-Clearwater Volcanic Field
- ^ a b c Catalogue of Canadian volcanoes - Wells Gray - Clearwater volcano field
- ^ Volcanoes of Canada - Types of volcanoes
- ^ http://www.wellsgray.ca/helmcken.html Wells Gray Park website
- ^ a b c d e f g h i j Volcanoes of Canada
[edit] References
- Goward, Trevor; Hickson, Cathie (1995). Nature Wells Gray: Volcanoes, Waterfalls, Wildlife, Trails & More. Lone Pine Publishing. ISBN 1-55105-065-X.
- Wood, Charles A.; Jürgen Kienle, eds. (1990). Volcanoes of North America. Cambridge University Press. ISBN 0-521-43811-X.
- Mathews, Bill; Monger, Jim (2005). Roadside Geology of Southern British Columbia. Mountain Press Publishing Company. ISBN 0-87842-503-9.
