Mount Garibaldi
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| Mount Garibaldi | |
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| Missing image 9497IM002334.JPG | |
| Elevation: | 2,678 metres (8,786 feet) |
| Coordinates: | Template:Coor dm |
| Location: | British Columbia, Canada |
| Topo map: | NTS 92G/14 |
| Range: | Cascade Range |
| First ascent: | |
| Easiest route: | scramble |
Mount Garibaldi is a stratovolcano in the British Columbia part of the Cascade Range. This heavily eroded dome complex is 40 miles (64 km) north of Vancouver and is located in Garibaldi Provincial Park. Garibaldi is the largest volcano in the Garibaldi Belt of volcanic centers (over 18 total) in southern British Columbia and is one of the only High Cascades that is made exclusively of dacite (Glacier Peak is the only other). The mountain has a unique asymmetrical shape due to the fact that its main cone was constructed atop part of a large glacier system that has since melted away.
In modern times, the apron of material from the volcano's main vent extends at least three miles (4.8 km) from its source in places that were covered by ice and in other areas its extent is less and its slope is steeper. After its slow collapse, a series of debris flows carried 2.5 km³ of the mountain into the Squamish Valley where it covers 10 mile² (26 km²) to a thickness of about 300 feet (90 m). 0.8 cubic miles (3.3 km³) of material remains in the volcano.
Garibaldi has three principle peaks;
- The southern peak, Atwell, is a pyramidal-shaped spire that was the source of many pyroclastic flows during the volcano's development.
- The northern peak, Dalton Dome, is slightly higher than Atwell and was created by the last dacite flows on the mountain.
- Columnar Peak
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Geology
The mountain grew in three phases. Garabldi's first phase resulted in the creation of a broad composite cone made of dacite and breccia that has been potassium-argon dated to 250,000 years old. Parts of this ancestral volcano are exposed on Garibaldi's lower northern and eastern flanks and on the upper 800 feet (240 m) of Brohm Ridge. Around where Columnar Peak and possibly Glacier Pikes are now located, a series of coalescing dacite domes were constructed. During the ensuing long period of dormancy, the Cheekye River cut a deep valley into the cone's western flank that was later filled with a glacier.
After reaching its maximum extent the Cheekye glacier along with part of the area's ice sheet were covered with volcanic ash and fragmented debris from Garibaldi. This period of growth began with the eruption of a dacite plug dome from a ridge surrounded by the several thousand foot ice sheet. As the plug dome rose, massive sheets of broken lava crumbled as talus down its sides. Numerous pyroclastic flows (super-heated mix of gas, ash, and pumice) accompanied these cooler avalanches, forming a fragmental cone 1.5 cubic miles (6.3 km³) in volume and an overall slope of 12 to 15 degrees (erosion has since steepened this slope). Some of the glacial ice was melted by the eruptions, forming a small lake against Brohm Ridge's southern arm. The volcanic sandstones seen today atop Brohm Ridge were created by ash settling in this lake.
Glacial overlap was most significant on the west and somewhat to the south. Subsequent melting of the ice sheet and its component glaciers initiated a series of avalanches and mudflows on Garibaldi's western flank that moved nearly half of the original cone's volume into the Squamish Valley. Gaps left by melting ice caused minor to moderate cone distortion where the ice sheet was thin and major distortion where it was thick (the ice was thickest in and thus cone distortion was greatest over the buried Cheekye valley).
Soon before or after the buried ice had melted away, liquid dacite quietly erupted from a crater north of the Atwell Peak plug dome and flowed down Garibaldi's north and northeastern flanks. About 0.15 cubic miles (0.6 km³) of dacite erupted in Garibaldi's third period of activity. This lava covers the north flank and part of the western flank of the volcano.
Garibaldi Lake Volcanic Field
An unusual volcanic structure called The Table is located 3.5 miles (~5.5 km) north of Garibaldi. This several hundred foot high flat-topped volcano is made of layers of andesitic dacite that are arranged like a stack of more or less equal sized pancakes. The Table was formed in the late Pleistocene at a time when the Cordilleran ice sheet covered the region. As the volcano's lava rose it melted the part of the ice sheet above The Table's vent, creating space for the lava to move into. Repeated eruptions constructed the steep-walled stack of lava seen today.
The Black Tusk is a large spire of extensively eroded dark volcanic rock that is shaped like a Walrus tusk. Its origin is not known but it may have formed in a similar way as The Table.
On the west side of Squamish Valley a series of pinnacles stand near Squamish, British Columbia. The tallest of these is called The Castle and may be a lava spine similar to those near Mount Pelée.
Cinder Cone stands 500 feet (150 m) above a gap between two arms of Helmet Glacier on Garibaldi's flanks. During summer its crater is filled with a snow melt lake.
Gallery
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Reference
- Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, Stephen L. Harris, (Mountain Press Publishing Company, Missoula; 1988) ISBN 0-87842-220-X
External links
- britishcolumbia.com - BC Parks - Garibaldi Provincial Park (http://www.britishcolumbia.com/ParksAndTrails/Parks/details/?ID=49)de:Mount Garibaldi