Garibaldi Volcanic Belt
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The Garibaldi Volcanic Belt is a north-south range of volcanoes in southwestern British Columbia, Canada. It is the northern extension of the Cascade Volcanic Arc, a chain of volcanoes of major andesitic to dacitic stratovolcanoes extending northward from northern California to British Columbia and contains the most explosive young volcanoes in Canada. The Garibaldi Volcanic Belt includes the Bridge River Cones, Mount Cayley, Mount Fee, Mount Garibaldi, Mount Price, Mount Meager and the Squamish Volcanic Field.
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[edit] Geology
Eruption styles in the Garibaldi Volcanic Belt range from effusive to explosive, with compositions from basalt to rhyolite. Morphologically, centers include calderas, cinder cones, stratovolcanoes and small isolated lava masses. Due to repeated continental and alpine glaciations, many of the volcanic deposits in the belt reflect complex interactions between magma composition, topography, and changing ice configurations.
Mount Meager is the most unstable volcanic massif in Canada. It has dumped clay and rock several meters deep into the Pemberton Valley at least three times during the past 7,300 years. Recent drilling into the Pemberton Valley bed encountered remnants of a debris flow that had travelled 50 kilometers from the volcano shortly before it last erupted 2350 years ago. About 1,000,000,000 m³ of rock and sand extended over the width of the valley. Two previous debris flows, about 4,450 and 7,300 years ago, sent debris at least 32 kilometers from the volcano. Recently, the volcano has created smaller landslides about every ten years, including one in 1975 that killed four geologists near Meager Creek. The possibility of Mount Meager covering stable sections of the Pemberton Valley in a debris flow is estimated at about one in 2400 years. There is no sign of volcanic activity with these events. However scientists warn the volcano could release another massive debris flow over populated areas anytime without warning.
Volcanoes of the Garibaldi Volcanic Belt have been sporadically active over a time span of several millions of years. The most recenty documented eruption was the 2350 BP eruption of Mount Meager. This eruption may have been close in size to that of the May 18, 1980 eruption of Mount St. Helens. Ash from this eruption can be traced eastward to western Alberta. Hot springs in the vicinity of Mount Cayley and Mount Meager suggest that magmatic heat is still present. The long history of volcanism in the region, coupled with continued subduction off the coast, suggests that volcanism has not yet ended in the Garibaldi Volcanic Belt. Long repose periods, up to several thousand years, between major explosive events at the major volcanoes (Mounts Meager, Cayley and Garibaldi), appears to typify the Garibaldi Volcanic Belt.
Young dikes in the Squamish-Garibaldi area show a strong north-northwest to north-northeast trend. Ages of these dikes are not well constrained but they are probably mainly Miocene and younger; at least some are related to Garibaldi volcanism.
The Garibaldi Volcanic Belt contains two extra volcanic fields, the Franklin Glacier Volcano and the Silverthrone Caldera, which lie 140 and 190 kilometres northwest of the main volcanic belt. These volcanoes are originally part of the eroded Miocene Pemberton Volcanic Belt.
The Chilcotin Plateau Basalts east of the Garibaldi Volcanic Belt, is thought to have formed as a result of extension of the crust behind the Cascadia subduction zone.
[edit] Cascadia subduction zone
The Garibaldi Volcanic Belt was formed by subduction of the Juan de Fuca Plate and the Explorer plates (remnants of the much larger Farallon Plate) under the North American Plate along the Cascadia subduction zone. This is a 680 mi (1,094 km) long fault, running 50 mi (80 km) off the west-coast of the Pacific Northwest from northern California to Vancouver Island, British Columbia. The plates move at a relative rate of over 0.4 inches (10 mm) per year at a somewhat oblique angle to the subduction zone.
Unlike most subduction zones worldwide, there is no oceanic trench present along the continental margin in Cascadia. Instead, terranes and the accretionary wedge have been uplifted to form a series of coast ranges and exotic mountains. A high rate of sedimentation from the outflow of the three major rivers (Fraser River, Columbia River, and Klamath River) which cross the Cascade Range contributes to further obscuring the presence of a trench. However, in common with most other subduction zones, the outer margin is slowly being compressed, similar to a giant spring. When the stored energy is suddenly released by slippage across the fault at irregular intervals, the Cascadia subduction zone can create very large earthquakes such as the magnitude 9 Cascadia earthquake of 1700.
[edit] History
First Nations people have inhabited the area for thousands of years and developed their own myths and legends concerning the Cascade volcanoes. According to some of these tales, Mount Garibaldi was used as refuge from a great flood.
Hot springs in the Canadian side of the arc, were originally used and revered by First Nations people. The springs located on Meager Creek are called Teiq[1] in the language of the Lillooet River and were the farthest up the Lillooet River the spirit-beings/wizards known as "the Transformers" reached during their journey into the Lillooet Country, and a "training" place for young First Nations men who would privite themselves at the at the springs to acquire power and knowledge. In this area, also, was found the blackstone chief's head pipe that is famous of Lillooet artifacts; found buried in volcanic ash, one supposes from the 2350 BP eruption of Mount Meager.
Volcanics of the Garibaldi Volcanic Belt were first discovered and mapped in 1911.
[edit] Volcanoes
The volcanoes within the belt include (in approximately south-north order):
- Mount Cayley
- Mount Fee
- Brandywine Mountain
- Pyroclastic Peak
- Vulcan's Thumb
- Powder Mountain
- Mount Brew
- Little Ring Peak
- Pali Dome
- Cauldron Dome
- Crucible Dome
- Ring Mountain
- Ember Ridge
- Slag Hill
- Cheakamus Valley Vent
- Bridge River Cones
- Nichols Valley Flows
- Sham Hill
- Tuber Hill
- Tuber Hill East
- Salal Glacier
- Silverthrone Caldera
- Mount Silverthrone
- Machmel River Cone
- Charnaud Creek
- Trudel Creek
[edit] See also
- Cascade Volcanoes
- Anahim Volcanic Belt
- Northern Cordilleran Volcanic Province
- Wrangell Volcanic Field
- Chilcotin Plateau Basalts
- Wells Gray-Clearwater Volcanic Field
- Garibaldi Lake Volcanic Field
- Volcanism in Canada
- List of volcanoes in Canada
- Geology of the Pacific Northwest
[edit] References
- ^ Mount Meager in the Canadaian Mountain Encyclopedia. Retrieved on 2007-10-16
[edit] External links
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